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Spheres and Layers of Earth
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Think about It
Have you ever cut an apple in half and looked at the layers inside? When you cut something in half, the resulting view is called a cross section. When you look at the cross section of an apple, you see several layers: the skin, the pulp, the core, and the seeds. Much like an apple, Earth is made up of layers too. Unlike an apple, scientists cannot cut Earth in half to see a cross section.
1. How do you think scientists know about Earth’s internal layers?
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The Layers of Earth
When we talk about Earth’s layers, we are referring to the layers of Earth that are part of the geosphere. They can be categorized in two ways—by physical state and by chemical composition. Categorizing the layers by physical state depends on the state of the matter: solid, liquid, or gas. Categorizing the layers by composition depends on what the layers are made up of. The physical state and chemical composition developed over time during the formation of Earth.
Earth formed about 4.6 billion years ago. Early Earth was a very different place than the planet is today. When Earth first formed, it was in a molten state, which means it was in the liquid state of matter. When Earth was still a liquid, the different chemicals began to float or sink in the molten Earth based on their different densities. As Earth cooled and formed into a more solid planet, the less dense elements rose toward the surface, forming layers around the denser inside. The least dense silicates floated to the very top. The heaviest elements, iron and nickel, sank to the center of Earth.
This diagram shows Earth’s layers categorized by composition (top) and state of matter (bottom).
Earth’s layers: the division of the composition of Earth determined by either chemical composition or the physical state of matter
chemical composition: the types, quantities, and arrangement of elements that make up a substance
states of matter: distinct forms of matter known in everyday experience: solid, liquid, and gas; also referred to as phases
density: the amount of matter in a given space or volume
2. What are the two different ways to categorize the layers of Earth?
Layers of Earth by Physical State
If we categorize by physical state moving from the surface to the center, we first see the lithosphere. The lithosphere is the cool, rigid, outermost layer of Earth and is in the solid state of matter. It contains the crust and part of the solid upper mantle. The prefix litho- from the ancient Greek word means “stone.” It got the name because it is made of solid rock. Elements in the lithosphere include oxygen, silicon, aluminum, and many others. It has the lowest density of all of Earth’s layers. Density increases the farther you go inside Earth. The solid rock is broken into large pieces called lithospheric plates, also known as tectonic plates.
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The layer under the lithosphere is the asthenosphere. It includes the upper mantle and is about 180 km thick. This area is also solid; however, it is less rocky and rigid than the lithosphere. It has plasticity, which is the condition of a material in a solid state that gives it the ability to flow. Think of putty, clay, or dough, all of which have plasticity. The prefix astheno- comes from the Greek word asthenes, which means “weak” or “lacking strength.” The asthenosphere gets its name because of its plasticity and because it is soft and weak compared to the strong, rigid rock of the lithosphere above it. The lithospheric plates “float” on top of the asthenosphere. As the material in the asthenosphere slowly flows, it moves the lithospheric plates in different directions.
Beneath the asthenosphere is the mesosphere. The prefix meso- comes from the Greek word mesos, which means middle. The mesosphere is made up of the inner part of the mantle. It is an area of hot solid rock. Even though the mesosphere is hotter than the asthenosphere, the pressure from the upper layers is too high and the rock cannot liquify. The state of matter depends on a balance between pressure and temperature. Pressure causes matter to become solid. But at a high enough temperature, even under pressure, matter can change to a liquid state.
Beneath the mesosphere is the core. The core is divided into two parts, the outer and inner core. They are divided because they are in two different states. At the outer core, the temperature is high enough to overcome the pressure from above and this layer liquifies. Moving further toward the center, the pressure grows again, and the temperature is not high enough to overcome the pressure. The inner core is a solid.
So from the surface to the center, you pass through solid surface rock to a weaker soft rock to a solid, then liquid, and finally a solid again at the center.
pressure: force exerted on matter through contact with other matter; affects melting and boiling points
temperature: average kinetic energy of all the particles in a material
lithosphere: the cool, rigid, outermost layer of Earth that consists of the crust and the uppermost part of the mantle; broken into pieces or segments called plates
tectonic plate: huge piece of crust that slowly moves on the upper, ductile part of the mantle
asthenosphere: the solid layer with plasticity in the upper mantle that is located just below the lithosphere; lithospheric plates “float” and move on
plasticity: a characteristic of the material in the asthenosphere; existing in a solid state yet having the ability to flow
outer core: the outer layer of Earth’s core; surrounds the inner core and is made up of liquid nickel and iron
inner core: the sphere of solid nickel and iron at the center of Earth; surrounded by the liquid outer core
3. Why is the inner core of Earth solid even though it is extremely hot?
Layers of Earth by Composition
Crust
Outer core
EARTH’S STRUCTURE
Earth’s layers are most commonly separated by chemical composition. The outermost layer is the crust. Earth’s crust is the thin, solid, outermost layer of Earth and consists of continental landmasses and oceanic crust. The continental landmasses are made mostly of granite and include an abundance of oxygen and silicon. The oceanic crust is made of very dense basalt and includes minerals and other substances like magnesium. The crust is 50–75 kilometers deep at its deepest point and contains all three types of rocks—igneous, sedimentary, and metamorphic.
Mantle
Inner core
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The mantle is the solid layer of Earth between the crust and the core. It is just below the crust and is made of molten, semi-solid silicate rock. The mantle has the most mass of all the layers by far. It is about 2,900 km thick. Magnesium and iron are the main elements in this layer. The densities in this layer at the top and bottom are very different, and this causes movement called convection to occur in this layer. Because of convection, the tectonic plates that cover Earth move.
crust: the thin, solid, outermost layer of Earth; is either continental (landmasses) or oceanic (ocean floors)
mantle: the solid layer of Earth between the crust and the core; made of dense silicates
convection: heat transfer caused by the rising of hotter, less dense fluids and the falling of cooler, denser fluids
4. Explain how the characteristics of Earth’s mantle allow the continental and oceanic plates to move on the crust.
As we go deeper inside Earth, we arrive at the outer core. The outer core is the outermost layer of Earth’s core. It surrounds the inner core and is made of liquid nickel and iron. This layer is liquid because of the extreme heat inside Earth. Temperatures in this area range between 4,000 and 5,000 degrees Celsius, or about 7,230 to 9,030 degrees Fahrenheit. This is extremely hot, but not quite as hot as the Sun. The outer core is about 2,300 km thick, and the movement in this liquid layer may contribute to Earth having a magnetic field.
Continental plate
Mantle convection currents
Oceanic plate
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The innermost layer of Earth is the inner core. The inner core is a sphere of solid nickel and iron at the center of Earth. This layer reaches temperatures of 5,000 to 7,000 degrees Celsius; the inner core consists of metals like iron. Since it is compressed under the weight of the other three layers, the pressure in this layer is massive—so much that the pressure causes the inner core to be solid even though it is extremely hot. This layer is spherical and has a radius of about 1,220 km.
Interestingly, the inner core spins much more quickly than the rest of Earth. This feature may also be part of the reason Earth has a magnetic field, but scientists are not sure.
outer core: the outer layer of Earth’s core; surrounds the inner core and is made of liquid nickel and iron
inner core: the sphere of solid nickel and iron at the center of Earth; surrounded by the liquid outer core
5. What two reasons are listed for why Earth may have a magneticfield?
Related Earth Features and Events
Recall that the core of Earth reaches very high temperatures. This heat radiates outward through the mantle. Even though the mantle is mostly solid, it is capable of slowly flowing by convection. As heat reaches the lower portion of the mantle, the solid material starts to heat, expand, decrease in density, and rise higher in the mantle. At the same time, material at the top of the mantle, in the asthenosphere, cools, shrinks, increases in density, and sinks.
Remember, the lithosphere is solid and includes the parts of solid rock that are broken into pieces called tectonic plates. Tectonic activity is a result of the interaction of tectonic plates of the lithosphere and typically takes place at the boundaries of these plates. Beneath the lithosphere is the plasticized asthenosphere that enables the movement of the tectonic plates. Tectonic plates can collide, move apart, or slide against one another. These interactions can create mountains and ocean basins or cause earthquakes or volcanic eruptions.
Modeling the Layers of Earth
If you were asked to make a model of the layers of Earth, what would you need to know to do it? First, let’s think about what makes a good model.
Good models are based on facts or observations. They do not try to be exactly like the concept they are explaining, but they are good for representing concepts that are hard to investigate, such as the layers of Earth. Since we cannot go on a field trip inside Earth, we must think of ways to represent the layers and their characteristics.
This model of Earth’s layers can help us understand the order of the layers and how wide they are in comparison to one another.
Then, we can use a good model to create explanations for what we learn about Earth.
For example, a model of Earth can show us where each layer is located. This is helpful when we need to visualize why the inner core is under so much pressure. We can use materials of different densities to help us understand how density changes in each Earth layer.
What are good materials to model Earth’s crust? Knowing that it is brittle and thin allows us to decide on a material that has those same characteristics. Paper is thin, but it is not brittle. Peanut brittle is both thin and brittle. For the mantle, materials that are solid but flexible are needed. Modeling clay or putty would work well to model this layer.
core,
These three-dimensional models of Earth’s layers are accurate models of the order of the layers, but do not show the correct thickness of each layer, so they are not to scale.
Scientists use different kinds of models for different purposes. By using more than one kind of model— for example, an illustration and a 3-D model—we can learn different things about objects that are too big or small to bring into our science class.
6. What materials would you use to make a model of the outer and inner cores of Earth?
Advanced Topics
Describe and differentiate the layers of Earth and the interactions among them. When tectonic plates in the lithosphere interact with each other, they can impact the surface features of Earth. When two oceanic plates move apart, the molten rock from the asthenosphere rises to the surface. Since it is within the ocean, the molten rock cools in the water, and an underwater ridge is created. There are three different types of interactions between tectonic plates: divergent, convergent, and transform.
Divergent boundaries are those where two tectonic plates diverge, or move apart, in opposite directions. These interactions result in the already mentioned underwater ridges as well as oceanic trenches. Convergent boundaries are when plates converge or collide with one another. When two plates converge, one result is a rise that can cause mountain building or volcanoes. These interactions also cause about 80% of the earthquakes on Earth. Another possible result is subduction, where one plate slides under the other. Finally, transform boundaries are where plates slide past one another in opposite directions. This can also result in earthquakes.
Crust, brown rice
Mantle, orange rice
Outer core, yellow rice
Inner
red rice
Scientist in the Spotlight
Jessica Murray USGS Earthquake Science Center
Jessica Murray is a Research Geophysicist in the Earthquake Science Center in Menlo Park, California, studying hazards caused by earthquakes. She studies earthquake impacts by looking at changes in Earth’s crust before and after earthquakes, observing and measuring movements that happen before, during, and even after an earthquake. She strives to develop ways to use real-time data from satellites to help improve early warning systems for people living in earthquake-prone areas.
The image shows damage caused when Earth’s mantle and crust move and cause earthquakes. The United States Geological Survey, or USGS, works to understand the changes in Earth’s crust that might indicate future earthquakes so they can develop warning systems.
The Big Picture
Earth’s interior can be divided into layers. This division can be done by the physical state of matter of the layers or the chemical composition. The most commonly known layers are the crust, mantle, outer core, and inner core. This is the breakdown by chemical composition. The physical state of matter breakdown is the lithosphere, asthenosphere, mesosphere, outer core, and inner core. Heat from the interior of Earth is responsible for convection in the mantle. This convection is responsible for movement of the tectonic plates which can lead to earthquakes, volcanoes, mountains, and ocean basins.
Connect It
How do you think scientists know about Earth’s internal layers?
Because scientists cannot dig down into the layers, they must rely on observation in order to determine more about the layers of Earth. For example, scientists study the way that vibrations from earthquakes, called seismic waves, travel through Earth. These waves change speed and bend as they travel through different densities and different states of matter. By carefully studying the way these waves travel and bend through Earth, scientists can learn about each of Earth’s layers. This allows them to construct a model of Earth’s interior even though they have never actually seen most of it.
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Summarize It
1 Depending on the method of classification, the first layer of Earth on which we live is known as either the–
A crust or the lithosphere.
B crust or the asthenosphere.
C mantle or the lithosphere.
D mantle or the asthenosphere.
2 Which is the solid layer of Earth that has plasticity, allowing rock to flow very slowly and tectonic plates to move on top of it?
A Mesosphere
B Outer core
C Asthenosphere
D Lithosphere
3 Which of the following statements correctly describes the crust and outer core?
A The crust is thick and has convection currents; the outer core is solid and hot.
B The crust is thin and cool; the outer core is the thickest layer and is molten.
C The crust is thick and molten; the outer core is solid and composed of nickel and iron.
D The crust is thin and brittle; the outer core is hot liquid just outside the inner core.
4 Fill in the table with the correct layers described (crust, mantle, outer core, inner core).
Name of Layer
Description
Made of iron, the densest layer of Earth
Most of Earth’s volume; very warm, semi-solid rock
Features
Hottest layer; shaped like a sphere
Convection causes plates to move
Thin and brittle outermost layer Contains all three kinds of rocks
Mostly iron and nickel; liquid Movement in this layer may cause Earth’s magnetic field
5 How does the heat from the core of Earth cause activity in the tectonic plates?
Plate Tectonics
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Think about It
Earthquakes around the world happen in patterns. There are places on Earth that experience much more frequent earthquakes than others. North Dakota has only had two small earthquakes in the last 30 years—and only 13 since 1870. California experiences more than 100 quakes every day! About 90% of the world’s earthquakes happen in a ring surrounding the Pacific Ocean called the Ring of Fire.
Ring of Fire Pacific
1. What could a pattern of frequent earthquakes indicate about what is happening beneath Earth’s happeningsurface?beneath
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You may have heard of the concepts of continental drift and plate tectonics. Continental drift is the idea that the continents were once connected but move and drift apart. The theory of plate tectonics explains why and how this happens.
Plate Tectonics
Plate tectonic theory states that the crust is divided into large pieces called tectonic plates that slowly move on top of Earth’s mantle. Remember that the interior of Earth is divided into layers. The two outer layers are the lithosphere and the mantle. The crustal plates make up the lithosphere and float on an upper layer of the mantle.
Think of the crustal plates, or tectonic plates, like pieces of a huge puzzle. A tectonic plate is a huge piece of crust that slowly moves on the upper part of the mantle. The outer edges of the plates fit together, and they bump into one another as they move. However, the edges of the major tectonic plates do not match the outlines of the continents that are on them, as you can see above.
The plates are drifting very slowly, at about the rate your fingernails grow. They are driven by convection currents in Earth’s mantle.
continental drift: the theory that continents were once connected but have drifted apart
plate tectonic theory: the theory that the crust is divided into large pieces called tectonic plates that slowly move on top of the mantle
tectonic plate: huge piece of crust that slowly moves on the upper, ductile part of the mantle
2. Explain what tectonic plates are and how fast they move.
The red outlines in the image show the edges of the tectonic plates. They do not exactly match the continental outlines.
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Earth’s Mantle
Earth’s mantle is the driver behind continental drift. Put another way, it is the reason the tectonic plates move. Think of a pair of graham crackers with marshmallow fluff in between. You can move each of the graham crackers because the marshmallow fluff is flexible enough to allow that movement. The topmost part of Earth’s mantle is the same way. It has a property called plasticity that allows for the tectonic plates to shift on top of it.
Earth’s core is extremely hot and unevenly heats the molten rock in the mantle. When the heat reaches the mantle, it makes the rock less dense, causing it to rise. As it nears the bottom of the tectonic plates, the molten rock cools and sinks as it becomes more dense. This pattern creates movement like that of a lava lamp. We call these convection currents, and they are the reason the tectonic plates move.
Historical Evidence for Plate Tectonic Theory
You might wonder why this theory is called the theory of plate tectonics rather than the law of plate tectonics. A theory explains a phenomenon without giving scientists a way to precisely calculate when and where the plates move, so it is not a law.
Abraham Ortelius was the first in history to note that there might be movement between the continents. As a mapmaker, Ortelius published a book of maps in the late 1580s. In the book, he noted that the coastlines of the continents were so similar that they looked like they had been torn apart.
However, Ortelius’s ideas were not given any serious attention by scientists until 1912. In that year, Alfred Wegener noted that he thought the continents were once connected. Scientists had located fossils from the same plant and animal species from the same time period on different continents. Wegener thought the way these fossils were distributed meant that the continents were once joined. He called this single supercontinent Pangaea.
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Wegener spent most of his adult life investigating these and other similarities between the continents. The one thing he could not explain was how the continents moved.
For the most part, his ideas were ignored until scientists discovered the mid-ocean ridges, where Earth’s crust seemed to reverse polarity as it expanded from a central point.
In 1962, Harry Hess published a book in which he explained an idea that could explain how the continents moved. It was a new concept called seafloor spreading, and it said that oceans grew from the middle, where molten magma pushed through to Earth’s surface and created large underwater mountains called mid-ocean ridges. The new crust then moved away from the ridge on both sides.
Cynognathus
Mesosaurus Glossopteris Lystrosaurus
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A year later, scientists Frederick Vine and Drummond Matthews, and independently Lawrence Morley, investigated a pattern of magnetism along the sides of the mid-ocean ridges. They noted a pattern of magnetic stripes on the ocean floor. As the new crust was forming and hardening, a magnetic mineral within it aligned with the current polarity of the planet, preserving a record of Earth’s magnetic field. The stripes indicated that the planet’s polarity was reversing over time. The direction of the striping matched on both sides. In addition, the ages of the rocks at these locations showed that younger crust was located near the ridge, and older crust was located farther from the ridges. This supported Wegener’s theory.
Let’s take a closer look at what is happening under Earth’s surface.
3. What evidence do we have that supports plate tectonic theory?
Older rocks
Magma rises to form new rock
Older rocks
N: Normal polarity, north S: Reversed polarity, south
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Dating of Earth Materials
As scientists develop the theory of plate tectonics, it is helpful for them to know the age of Earth’s materials. Two scientific methods of doing this are radioactive dating and superposition.
Radioactive decay is happening in all rocks because they contain radioactive elements. This is part of Earth’s natural system and is one of the main causes of heat within Earth. This convection within Earth causes tectonic plates to move, which in turn causes volcanoes and earthquakes.
Understanding radioactive decay helps us understand the age of Earth. Radioactive dating calculates the age of geologic Earth materials by measuring radioactive elements such as carbon-14. Through the emission of particles, the nucleus of a radioactive atom transforms into an atomic nucleus of a different, stabler isotope. Scientists measure the decay of atoms in terms of half-lives; a half-life is the length of time it takes for half of the atom to decay into a new isotope. Because this happens at a fixed rate of time, scientists can calculate the age of the sample.
The law of superposition states that within the layers of undisturbed sedimentary rock, the oldest layer is at the bottom. Layers are progressively younger as we move upward. In other words, any layer of sedimentary rock is older than the one above it and younger than the one below it. This is important in understanding Earth’s history, because within any layer we can tell the relative age of rock layers and the fossils within them.
Early horses
Land-dwelling dinosaurs Fish and shells
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There are times when subsurface events, such as the movement of tectonic plates and mountain building, or surface events, such as erosion and weathering, change the layers of rock. Notice in the diagram how the layers of rock have shifted. Earth’s surface is shaped by both plate tectonics and the rock cycle. The rock cycle is a group of processes that outlines how rock forms and breaks down over time.
radioactive dating: technique used to determine how old a rock is by analyzing the amounts of a radioactive isotope and its decay products in
superposition: the law that says that younger rock layers sit on top of older rock layers
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Events and Formations Caused by Plate Tectonics
Plate movement causes a variety of events around the globe, both at the edges of tectonic plates and at seemingly random places. There are three main types of boundaries, each of which is associated with certain geologic events.
First, basins are formed at places where tectonic plates move apart from one another. This type of boundary is called a divergent boundary. Recall that Harry Hess had the idea that magma from the mantle rises, seeps through gaps in tectonic plates, cools and solidifies, and creates new layers of crust. These new layers form depressions between continents that are called ocean basins. An ocean basin is a depression of Earth’s surface in which an ocean lies. Basins, rift valleys, and mid-ocean ridges like the Mid-Atlantic Ridge form at divergent boundaries. When tectonic plates diverge under continental crust, rift structures, faults, and valleys form along the boundary.
The image shows an ocean basin forming at a divergent boundary where two tectonic plates are moving apart.
divergent boundary: a place where two tectonic plates move away from each other
ocean basin: a depression of Earth’s surface in which an ocean lies
Magma
Ocean basin
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A second type of boundary is one where two plates slip laterally, or sideways, past each other. This is called a transform boundary. The San Andreas fault system in California is located at a transform boundary. The most common geological event at these types of boundaries is earthquakes, which happen when pressure builds up between the plates and is suddenly released when the plates move. However, earthquakes can happen at any of the three plate boundary types.
transform boundary: a place where two tectonic plates slide past each other
earthquake: major geological event that occurs when plates shift suddenly and release stored energy; a frequent occurrence along all types of plate boundaries
4. How does plate tectonics cause ocean basin formation and earthquakes?
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The third type of plate boundary is a convergent boundary. This is a place where two tectonic plates move toward each other and collide. If one plate is more dense than the other, the more dense one slips below the other, forming a subduction zone. Subduction happens when a more dense plate is pushed downward beneath a less dense plate as they converge. When the edge of the sinking plate is heated and melted by the magma upwelling, it melts and is eventually recycled into magma itself. In the meantime, the subducting plate can also cause a volcano to form when the magma pushes through the plate on the top.
Mountain ranges can also form at convergent boundary zones when both tectonic plates are of equal density. The Himalayan Mountains in Asia formed this way. Mountain building is caused by the edges of the plates pushing against one another and forcing each other to crumple. As the plates buckle and fold, mountains form.
convergent boundary: a place where two tectonic plates move toward each other and collide
subduction: the process in which a denser plate is pushed downward beneath a less dense plate when plates converge
mountain building: a major geological event that occurs when continental plates of equal density converge, resulting in mountain chains
These diagrams show convergent plate boundaries and how this type of boundary causes mountain building when two continental plates collide and a subduction zone when a continental plate converges with an oceanic one.
Volcanic Eruptions
About 85% of Earth’s volcanoes are found in a ring around the Pacific Ocean, where dense oceanic plates meet less dense continental plates. As convection currents in the mantle push the plates around, subduction zones form in these areas, followed by volcanoes.
A volcanic eruption is a geological event in which molten rock spews out from the mantle to the surface of Earth as ash, lava, and gases. The same molten rock that is circulating under the tectonic plates pushes through a volcano and erupts as lava.
Canadian geophysicist J. Tuzo Wilson suggested that Hawaii and other islands formed when a tectonic plate moved over a stationary place called a hot spot in the mantle. A hot spot is an extremely hot area of Earth’s mantle that causes the crust above it to melt and creates volcanoes. Over time, as the tectonic plates move, the volcano that was formed moves away from the hotspot. Volcanic island chains like the Hawaiian Islands were formed in this manner.
A chain of volcanoes can form over a stationary hot spot. The Aleutian Islands in Alaska and the Hawaiian Islands formed this way.
Hot spots do not only form over oceanic crust. The hot spot under Yellowstone National Park fuels geysers, hot springs, and other geologic activity in the area.
Volcano 1
Volcano 2
Fixed hot spot
Eruption of Volcano 3
Eruption of Volcano 1
Direction of plate movement
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Supervolcanoes are volcanoes that have erupted a huge amount of material—over 240 cubic miles of lava and ash—at some point in their lifetime. They eject so much material that a circular impression called a caldera forms above the magma. Inside some supervolcanoes, magma in the mantle rises into the crust from a hot spot but is unable to break through the crust. Pressure builds in a growing magma pool until the crust is unable to contain the pressure.
Old Faithful is a geyser in Yellowstone National Park. It erupts boiling groundwater that has been heated by magma under the crust.
hot spot: extremely hot areas of Earth’s mantle that cause the crust above them to melt and create volcanoes away from plate boundaries
supervolcano: a volcano with an eruption rating of 8 on the VEI (Volcano Explosivity Index), meaning it has ejected more than 240 cubic miles of material at some point in its lifetime; all supervolcanoes have been dormant for thousands to millions of years
volcanic eruption: a geological event in which molten rock spews out from the mantle to the surface of Earth as ash, lava, and gases
5. How does tectonic activity influence volcanic eruptions?
Scientist in the Spotlight
Rufus Catchings
United States Geological Survey (USGS)
Rufus Catchings is a research geophysicist at the Earthquake Science Center with the United States Geological Survey, or USGS. He was one of the first Black geophysicists to join the organization. His current work studies the structure of Earth beneath the surface and how faults create earthquake hazards, especially near cities. He also studies earthquake aftershock monitoring.
He got interested in plate tectonics after hearing debate about whether faults were located in certain places, and he thought that scientific methods could be used to find out. Early in his career, he examined the structure of Earth’s crust and mantle, and later, he looked at rocks and faults.
Grand Prismatic Spring, Yellowstone National Park, Wyoming
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The Big Picture
Continental drift is the concept that the continents were once connected but move and drift apart. Plate tectonics is the theory that the crust is divided into large plates that move. Plate tectonics and the interactions at convergent, divergent, and transform boundaries cause formation of ocean basins, mountain chains, earthquakes, and volcanoes.
Mapmaker Abraham Ortelius published a book of maps in the late 1580s. He noted that the coastlines of the continents looked like they had been torn apart. After scientists located fossils from the same plant and animal species on different continents, Wegener used the distribution of these fossils as evidence for his claim that the continents were once joined. Then, additional evidence showed that new crust was forming at mid-ocean ridges, pushing older crust away.
Connect It
What do volcanoes tell us about Earth’s geological activity?
Volcanoes form at a place where one tectonic plate subducts under another. This type of plate movement is seen at convergent boundaries where two plates are pushing toward each other. Most of Earth’s volcanoes are located in a ring around the Pacific Ocean called the Ring of Fire, which is also where much earthquake activity takes place.
Advanced Topics
When we think about all the discoveries that have contributed to the development of the scientific theory of plate tectonics, it reminds us that scientists are always learning. How do you think the ideas of Ortelius or Wegener were received during their lifetimes? How do you think major events such as earthquakes or volcanic eruptions were explained during the time of early scientists? We now know that the movement of large tectonic plates is responsible for these events. This also results in the formation of various features such as mountains, trenches, and rift valleys.
Various processes are happening not only underground, such as with the convection of magma, but also on Earth’s surface. Each of these processes contributes to the ever-changing landscape of Earth. Weathering is the breaking down of rock into smaller pieces. These small pieces of rock are then carried by wind or water in a process known as erosion. Finally, these small pieces of rock are deposited in new areas; this process is called deposition.
Summarize It
1 Which of the following does NOT support the theory of plate tectonics?
A Matching fossils from the same species on different present-day continents
B Magnetic stripes on the ocean floor that cause Earth’s polarity to shift
C Coastlines from different continents that match one another
D Seafloor spreading that results in new crust
2 Plate tectonics causes all of the following EXCEPT–
A mountain building.
B ocean basin formation.
C meteor showers.
D earthquakes and volcanoes.
3 Which choice correctly states the order in which the concepts about plate tectonics evolved?
A Matching coastlines, matching fossils, seafloor spreading, magnetic striping on the ocean floor
B Matching fossils, seafloor spreading, matching coastlines, magnetic striping on the ocean floor
C Magnetic striping on the ocean floor, matching fossils, seafloor spreading, matching coastlines
D Seafloor spreading, matching coastlines, matching fossils, magnetic striping on the ocean floor
4 Fill in the following table with the types of plate boundaries described.
Boundary Type Geological Events Associated with the Boundary
5 Describe how plate tectonics causes volcanic eruptions, supervolcanoes, and hot spots.
Rock Cycle and Classification
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Think about It
Think about a rock at a riverbank, the water cascading over it. Flowing water seems gentle and soft, but over time, it can make rocks undergo changes, such as becoming more rounded in shape. How does water help form and change rock? And is that the only way that rocks change, or are there other ways?
1. How can water help form and change rock? Can rocks change by other means?
Three Types of Rock
Have you ever had a rock collection? Chances are that if you have, you collected rocks that look different from one another. Some may be solid-colored, while others could have stripes or other bits of rocks and minerals cemented within them. Perhaps some are flat and flaky.
Geological processes constantly happening on Earth can cause rocks to change. There are three main types of rock, and each can be identified by the results of the processes that formed it. Rocks are made of different types of mineral grains held together. Various processes change rock structures, which in turn change the way they appear.
The rock cycle is the cycle through which Earth’s rocks change from one type into another over time due to various Earth processes including surface events, such as weather and erosion, and subsurface events, such as the movement of tectonic plates and mountain building. It creates changes in mineral compositions and physical structures. It is called a cycle because rocks are made and destroyed at every part of the cycle—there is no real beginning or end to a rock’s existence.
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The diagram below shows the full rock cycle. We will look at three parts of this cycle separately.
Rock Cycle
and recrystallization
and erosion
and erosion
and erosion
Deposition and cementation
Volcanism, or volcanic eruptions, form and change rocks by heating and cooling massive amounts of material. Erosion and weathering usually happen from wind, water, and ice and can cause sediments and small rock pieces to break off from the main rock. Sedimentation can cause layers of material to form into rocks, sometimes trapping fossils of dead organisms inside. These processes can change any kind of rock into any other type of rock. Material is constantly being recycled through the processes that drive the rock cycle. Through subsurface events, such as mountain building and the movement of tectonic plates, rock layers that are below Earth’s surface become exposed. Once these layers become exposed, they are then able to be affected by weathering, erosion, and deposition.
rock cycle: the cycle through which Earth’s rocks change from one type into another over time due to various Earth processes; creates changes in mineral compositions and physical structures Metamorphic
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Igneous Rock
Let’s look at each of the three types of rock, beginning with the most common type, igneous. The diagram below highlights the part of the rock cycle involved in the formation of magma and igneous rock. You can see that igneous rock forms from magma.
Cooling and recrystallization
Igneous rock
rock
Sedimentary rock
The presence of igneous rock in a landscape indicates volcanic activity, either currently or in the past. Igneous rocks form deep inside Earth. All igneous rocks have crystals that are formed when molten lava or magma cools, but these crystals are different sizes. The speed at which the lava or magma cools determines the crystal size in any given igneous rock. If the rock cools quickly, crystals within the rock do not have as much time to form. When the molten rock cools slowly, it can result in large crystals.
Metamorphic
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These are two samples of obsidian, also known as volcanic glass. Both were formed from magma that cooled. The sample on the left was formed from magma that cooled too quickly for the rock to form crystals. The sample on the right formed from lava that cooled very slowly, so large crystals formed.
Other igneous rocks, like pumice, show remnants of bubbles formed when water and gas from a volcanic eruption become trapped in fast-cooling rock. This results in a lightweight rock that is useful for abrasive products used for scrubbing, such as toothpaste, cleaning stones, and rubber erasers. It is also used to make concrete.
Igneous rocks can be further classified by their mineral compositions. One group consists of lightcolored, less dense minerals like quartz and feldspar. Another group is made of darker, more dense minerals such as olivine. Two additional igneous rock groups have different combinations of minerals than in the previous two groups.
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Granite is a common igneous rock that is abundant, and because of that, frequently used in building materials such as countertops, tiles, and floors. The kitchen in the picture below has granite countertops and floors.
Granite is a strong rock that gets its color variations from different minerals that are in each rock sample. Feldspar can make granite pink, and quartz can make a sample appear white or clear. Biotite and muscovite can make granite appear green, dark brown, or black.
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Basalt is another common igneous rock. It is usually dark and dense, without large crystals. The ocean floor is made of basalt. It forms when lava erupts through underwater volcanoes or cracks or in the oceanic crust and solidifies quickly under the cold ocean water. It is commonly used in home insulation and as a decorative rock.
Basalt samples can look slightly different from one another based on how long it took the rock to cool. The world’s ocean floors are made of basalt.
igneous rock: rock formed when lava or magma cools, forms crystals, and solidifies
lava: molten rock, or magma, that has reached Earth’s surface by volcanic action
magma: melted, or molten, rock material beneath Earth’s surface; cools slowly to form rocks with larger crystals
2. Are you more likely to find an igneous rock in a river or at the base of a mountain? Why?
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Sedimentary Rock
Weathering, erosion, deposition, and cementation are the main ways that sedimentary rocks are created. Sedimentary rocks are made of sand, dirt, rock pieces, and dead organisms. They form when particles of other rocks are deposited in layers and cement together. The diagram below shows part of the rock cycle that focuses on sedimentary rock.
Weathering and erosion
Weathering and erosion
Weathering and erosion
Deposition and cementation
Some sedimentary rocks are made from rock fragments that have been worn down by wind, water, or ice. Others contain organic materials like the remains of organisms that died. Other sedimentary rocks are made of precipitates that are left after water evaporates from a solution, such as in a cave.
Metamorphic rock
Igneous rock
Sediment
Sedimentary rock
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This sedimentary rock consists of sediments, or small bits of rock, containing the remains of a onceliving organism. When scientists conduct fossil digs, they must use tools to gently separate the fossil remains from the surrounding sediments and rock.
Sedimentary rocks are the only ones that are created on top of Earth, instead of inside. The first step in sedimentary rock formation is weathering, where rocks are broken into smaller pieces by wind, water, ice, or gravity. Weathering is a very slow process that usually happens over hundreds or thousands of years. Sediments can range in size from a grain of sand to a boulder. Sediments that form rocks are usually small and can easily be picked up by moving wind or water, which drops sediments in places like riverbeds or swamps.
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Erosion and deposition from wind and water helped create these rock formations.
The next step is compaction, when rock particles or sediments are pressed together or packed down. This can happen by gravity and the pressure of other layers of rock as more and more sediments are deposited in the same area. This extremely slow process takes millions of years, so the sediments that are in the upper layers are being added by the same processes as time passes. The weight of those sediments causes the ones underneath to squeeze together.
After more time passes, the compacted sediments stick together and turn into rock during a process called cementation. During cementation, spaces in between the rock sediments (called pores) fill with groundwater, natural gas, or oil. They can also fill with minerals that act as cement while other minerals crystallize.
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Sediment
Compaction
Cementation
Sedimentary Rock
Common examples of sedimentary rock include limestone and sandstone. Limestone consists mostly of calcite and makes up about 15% of Earth’s crust. Sandstone is made of mostly quartz, which makes it look beige or tan. It can contain feldspar, which makes it look pink. If a sample also contains iron, it may look red.
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This sedimentary rock formation in California’s Death Valley National Park contains various minerals in its layers. Note the effect of erosion on the rock formation as well. Many of the eroded sediments from this formation will be deposited in other places and may reform into new sedimentary rocks.
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Most sedimentary rocks can be identified by their layered appearance. Some types have smaller rocks embedded within them, such as the breccia in the center of the image below
sedimentary rock: rock formed when particles of other rocks are deposited in layers and cemented together
weathering: the mechanical or chemical processes by which gravity, water, wind, and ice break rocks into smaller pieces
sediment: Earth material that is broken down by processes of weathering; can be eroded and deposited by the agents of water, wind, ice, and gravity
compaction: when rock particles or sediments are pressed together or packed down by gravity and the pressure of overlying rock layers
cementation: when compacted sediments stick together and
3. What are three factors that can affect the appearance of sedimentary rocks?
Metamorphic Rock
Some rocks look like sedimentary rocks because they have layers, but they are wavy. These rocks are actually called metamorphic rocks. Metamorphic rocks are rocks that have changed from another rock type. The prefix meta- means “to change” and the root -morphos means “form.” They have formed deep underground and have changed because of the intense heat and pressure inside Earth. Pressure is a force exerted on matter through contact with other matter. The process itself is called metamorphism
This rock formation in Greece shows the curved, wavy layers common in rocks that have undergone metamorphosis.
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Both igneous and sedimentary rocks can become metamorphic rocks if they undergo changes deep within Earth. Metamorphic rocks can also change into other metamorphic rocks.
Igneous rock
Sedimentary rock Magma
Metamorphic rock
The main difference between igneous and metamorphic rocks is that when igneous rock forms, the crystals melt. When the rock changes its texture or composition without the crystals melting, it is classified as a metamorphic rock. Metamorphic rocks do not get as hot as igneous rocks that melt during their transformation. Many metamorphic rocks have their crystals arranged in bands that may look like stripes.
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Common minerals in metamorphic rocks include calcite, mica, and quartz. The mineral grains in metamorphic rocks sometimes align in different ways to create various patterns. They can be found in areas of high tectonic activity, such as near mountain ranges, areas of volcanic activity, and other places where geological processes cause high pressures and temperatures to change rocks.
These samples show the many variations that metamorphic rocks have. Metamorphic rocks undergo intense heat and pressure to change them. They do not get so hot as to melt like igneous rocks do.
melting: when a sample of matter changes from a solid to a liquid metamorphic rock: rock formed deep underground due to heat and pressure pressure: force exerted on matter through contact with other matter; affects melting and boiling points
4. If you found a rock while on a hike, what clues might tell you that it is a metamorphic rock?
Scientist in the Spotlight
Anna Jonas Stose US Geological Survey
Anna Jonas Stose was one of the first geologists to work for the United States Geological Survey. She named many geological formations in the Eastern United States and studied rock formations in that area. Her first published paper discussed the rocks in the Appalachian Mountains, and throughout her life, she traced the origins of many rock formations. She was the first person to discover the rocks and formations that indicate a huge crustal fault extending from Virginia to Alabama. Most of her ideas were not recognized as correct until long after her death since, during her lifetime, most women did not enjoy the same respect as their male peers.
The image shows the side of a rock formation in the Appalachian Mountains in the Eastern United States.
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The Big Picture
Rocks can change through geological processes in the rock cycle such as volcanism, plate tectonics shifting, mountain building, heat and pressure within Earth, and weathering and erosion. Igneous rocks form from melted rock called magma and crystallize. Sedimentary rocks form from deposition and compaction of sediments that cement into new rock, sometimes trapping the remains of dead organisms inside and forming fossils. Metamorphic rocks are rocks of any type (including other metamorphic rocks) that have been heated and undergone pressures that caused them to change but did not get hot enough to melt completely before reforming.
Connect It
What are some of the processes that form and change rocks?
The geologic processes that change rocks are all around us and happen constantly. From active volcanoes to crashing waves, many processes form and change rocks around the world.
Wind and water change rocks by weathering them and eroding small sediments. Volcanism and other tectonic activities involving lava and magma change rocks by heating them near or above their melting point. Rocks are constantly changing into other rock types through the rock cycle and will continue to do so.
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Summarize It
1 Imagine you were digging for rocks and found one you wanted to classify. Which of the following characteristics would help you the most?
A The dark colors of the rock
B The rock’s wavy layers
C The large size of the rock
D The overall density of the rock
2 What event is not likely to cause changes in rocks?
A Heat and pressure deep within Earth
B Magma seeping through a crack in the ocean floor
C A volcano erupting ash and lava
D A tsunami
3 A classroom investigation asks students to crumble bread into a tray, place a few plastic animals on top, crumble more bread, and then apply pressure to make the mixture form a solid mass. Which type of rock formation is this modeling?
A Metamorphic rock
B Igneous rock
C Molten rock
D Sedimentary rock
4 Look at the rock cycle diagram below. Which two rock types are formed by processes involving heat within Earth?
Rock Cycle
A Metamorphic and igneous rock
B Igneous and sedimentary rock
C Sedimentary and metamorphic rock
D Sedimentary and molten rock
Human Impact on Climate Change
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Think about It
If you lived in Florida in January of 2022, you may remember the time when temperatures dropped well below normal levels and snow fell in places that do not usually see snow—such as in the panhandle area. Meteorologists agree that this was unusual for a Florida winter season. But could it also be one result of a changing climate?
An extended freeze can severely damage or kill orange trees, like the one shown.
1. Can unusual freezes be influenced by greenhouse gases?
What Is Climate Change?
You know that in a polar region, regardless of when you visit, it will be cold, with the possibility of snow for most of the year. However, in the tropics, you would experience warm, humid conditions most of the year. These generalizations we make about weather patterns describe climate. Climate is the average pattern of weather for a particular region. The climate of any area describes the long-term conditions in the area related to precipitation, temperature, humidity, and more.
Although it does not seem like the climate changes much from one year to the next, small changes in temperature or precipitation happen over long periods of time, like decades or centuries. These changes are referred to as climate change. Climate change is the long-term change in the prevailing weather patterns in an area. Changes can affect conditions in the atmosphere. The atmosphere is the layer of gas surrounding Earth held in place by gravity. It is where weather happens.
As climate changes, it affects many areas of Earth, including the atmosphere and ice in the polar seas.
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One of the largest influences on climate in recent years has been global warming. This is where the atmosphere traps short-wave radiation from the Sun and reflects some of it back into space as longer-wavelength infrared radiation. Gases in the atmosphere absorb some of this radiation, sending it back out in all directions, including toward Earth’s surface. This contributes additional heat to Earth’s atmosphere, as you can see in the diagram below.
Radiation from the Sun reaches Earth, and some is reflected back into space while some is trapped by the atmosphere and radiated in different directions, including back toward Earth’s surface, increasing overall temperatures.
Global warming is not necessarily a bad thing. This effect has kept Earth’s temperatures about 30 degrees warmer than they normally would be, and this allows humans and other species to survive.
Earth has experienced changes in temperature in its past. Earth’s average temperature has been rising about 0.08°C per decade since 1880, but since 1980, it has risen about 0.18°C per decade, which is a faster rate. Overall, the average global temperature has risen about 1.1°C over pre–Industrial Revolution levels.
Earth’s temperatures have been changing, both warming and cooling, for millions of years. In fact, the most recent cold period, known as an ice age, ended about 20,000 years ago. Earth tends to cycle between cooler temperatures and warmer ones about every 100,000 years. Temperatures during these times have fluctuated between 3 and 8 degrees Celsius.
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However, the present warming trend has been happening during an extremely short period of time when compared to previous periods of warming.
During the time of increasing temperatures since 1880, we have also noticed a pattern of evidence revealing more instances of severe weather, melting sea ice, and changes in ocean currents.
History of Global Surface Temperature
The graph shows the difference from Earth’s global average surface temperature during the 20th century. In 1880, for example, global temperatures were about 0.1 degree below average, but in 2020, they were 1 degree above average.
climate: average weather patterns for a particular region
climate change: long-term change in the prevailing weather patterns
atmosphere: the layer of gas surrounding a planet that is held in place by gravity
2. Have there been times where Earth’s overall temperature has been cooler than normal?
The Carbon Cycle and Human Activity
The carbon cycle is an important process on Earth. The carbon cycle is the continuous movement of carbon in and between the abiotic and biotic environments on Earth. Carbon is an element stored all over Earth, particularly in rocks, the oceans, and living organisms. Carbon is a common element on Earth, existing in fossils, volcanic gases, and plants. It circulates through the biosphere, atmosphere, and geosphere.
It enters the atmosphere as carbon dioxide, which is absorbed by plants during photosynthesis. Carbon dioxide is a gas that is naturally found in the atmosphere and is produced by cells during cellular respiration and used by plants and other organisms during photosynthesis. Animals consume green plants and the carbon dioxide they contain. After organisms die, their decomposing bodies release carbon back into the atmosphere, where the cycle continues, moving the atoms through the cycle again and again.
Not all carbon is constantly cycling through, however. Some carbon is stored in the atmosphere, hydrosphere, and geosphere. The carbon in the geosphere stays underground for a long period of time—millions of years—in rock layers deep below the surface called carbon sinks.
In the past 50 years, human activity has changed the world in unprecedented ways. Human activity includes things that humans do. Hundreds of years ago, the world was dominated by products and professions centered around manual labor and farming that was done without the assistance of engines or automated systems. Beginning in 1751 with the invention of the first steam engine and continuing for about 200 years, the Industrial Revolution brought on an economy driven by manufacturing and industry. At that time, there were about 280 parts per million of carbon in Earth’s atmosphere.
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As more manufacturing processes developed, the amounts of carbon dioxide and other gases began to pour into the atmosphere at greater levels. By 2000, the world had become heavily dependent on fossil fuels: coal, oil, and natural gas. In 2005, there were 380 parts per million of carbon dioxide in Earth’s atmosphere. Human activities had contributed to changes in the amounts and properties of gases in the atmosphere, particularly carbon.
The 2014 National Climate Assessment indicates that human activity has mostly influenced global warming trends in the past half century. Human activity has had a tremendous influence on climate change, as opposed to events like volcanism, meteor impacts, and solar radiation from space. These activities have only contributed to a temperature increase of about 0.1 degree Celsius in Earth’s atmosphere since 1890.
carbon cycle: the continuous movement of carbon in and between the abiotic and biotic environments
carbon dioxide: a gas that is a natural component of the atmosphere; produced by cells during cellular respiration and used by plants and other organisms for photosynthesis
human activity: things that humans do
3. What are two effects of releasing additional carbon into the atmosphere through fossil fuelthroughburning?
Greenhouse Gases and Climate Change
Greenhouse gases are gases in the atmosphere that trap heat within the atmosphere. They absorb infrared radiation, or heat, trapping it in the atmosphere instead of allowing it to escape into space. This influences Earth’s climate. Greenhouse gases naturally occur in the atmosphere, but human activities are adding to it. This effect was discovered in the 1850s by Sir John Tyndall.
One of the ways greenhouse gases enter the atmosphere is through the burning of fossil fuels like coal, oil, and natural gas. Burning releases carbon compounds from the fuels into the atmosphere. This can happen by the direct burning of these resources or by the combustion that takes place in a car or truck. The addition of greenhouse gases to Earth’s atmosphere has contributed to changes in climate.
Greenhouse gases include more than carbon dioxide. Methane, nitrous oxide, and fluorinated gases called hydrocarbons are also considered greenhouse gases. The addition of more greenhouse gases into the atmosphere amplifies the heating effect of greenhouse gases, known as the greenhouse effect Addition of more greenhouse gases amplifies the greenhouse effect and causes the temperature in Earth’s atmosphere, hydrosphere, and geosphere to increase.
greenhouse gases: gases in the atmosphere that trap heat within the atmosphere
4. How does emission of greenhouse gases influence the amount of heat in the atmosphere?
Deforestation, Urbanization, and Desertification
Trees play an important role in the carbon cycle. They help regulate carbon dioxide levels in the atmosphere. Cutting them down releases the carbon dioxide they store and adds even more CO2 into the atmosphere. It also prevents the tree from being able to absorb any more carbon dioxide through photosynthesis. Deforestation is the removal of a forest or a section of trees for human use.
During the deforestation process, some tree waste is burned, and this adds carbon dioxide into the atmosphere too. Deforestation in the world’s rain forests has added more carbon dioxide into the atmosphere than vehicles on the world’s roads.
Trees like these help regulate carbon dioxide levels in the atmosphere.
Livestock farming also influences climate because cows and other animals release methane, a greenhouse gas, during digestion. Land clearing for farming also reduces tree cover in the area, increasing carbon in the atmosphere.
Deforestation is often necessary to make room for new buildings as cities grow. Urbanization is the term for the process by which cities grow and develop. It can create heat islands, which are urbanized areas that have higher temperatures than natural areas. This can occur on an even larger scale when a whole city has a higher temperature than natural areas nearby. This effect is often seen in larger metropolitan areas.
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Urbanized areas like this one in Nerja, Spain, can have higher overall temperatures than surrounding natural landscapes because buildings and sidewalks retain more heat than forests, oceans, and rivers. Buildings, roads, and concrete areas absorb and reflect more of the Sun’s heat than other natural areas such as forests, oceans, and rivers. Temperatures in areas like these can be up to 7 degrees Fahrenheit warmer than other areas. In addition, building heating, cooling, and manufacturing can influence the climate in a particular area if it is heavily urbanized.
Another human impact that is less talked about is desertification. Arid drylands make up a little more than 40% of Earth’s surface. Deterioration of land has always occurred in history, but the rate at which it is happening is increasing due to human activity. This deterioration is driven by urbanization, farming, ranching, and mining. As these things occur, trees and vegetation are cleared away by deforestation. Animals compact the dirt. Crops deplete the soil of nutrients. These processes contribute to further erosion and the inability of land to hold water or grow plants. Currently, two billion people live on dryland areas that are at risk of desertification.
deforestation: removal of a forest or section of trees for human use
urbanization: the process by which cities grow and develop
desertification: the rapid depletion of plant life and the loss of topsoil caused by a combination of drought and the overexploitation of grasses and other vegetation by people
How does urbanization affect climate?
5.
How Can Human Activities Positively Influence Climate?
While humans do contribute to an increase of carbon in the atmosphere and hydrosphere, there are things we can do to limit our impact, such as reducing the use of fossil fuels. Choose to walk or bike whenever it is possible. Conserve energy by reducing usage or replace fossil fuels with renewable energy sources. There are now lots of choices of hybrid and electric cars and choosing a power provider that utilizes renewable sources instead of just fossil fuels.
We can plant trees to help offset trees that are cut down. Green roofs in urban areas are a great idea to help reduce temperatures in these areas.
Be an advocate on social media and support government officials who care about climate change. Support initiatives that work to reduce pollution and use renewable energy. Just by being aware of the problem and looking for solutions, every individual can contribute positively.
Scientist in the Spotlight
Mario J. Molina NASA Jet Propulsion Laboratory
Mario Molina was born in Mexico City and was always fascinated with chemistry. He earned an undergraduate and doctorate degree in chemical engineering, and then worked as a researcher at a university and at NASA’s Jet Propulsion Lab. He began exploring the idea of what was happening to chlorofluorocarbons (CFCs) released into our atmosphere. CFCs are used as refrigerants, in aerosol sprays, and in plastic foams. There was evidence to support his idea that CFCs were destroying the ozone, but it took a long time for people to listen. In 1995, Molina and his partners were awarded the Nobel Prize in Chemistry for the work they did explaining the mysteries and dangers of CFCs.
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The Big Picture
Climate is the average pattern of weather for a region. Climate change occurs over very long periods of time and is a natural occurrence. Humans have contributed to climate change happening faster or more dramatically than before humans industrialized the world. For one, industrialization contributed to the rise of greenhouse gases in the atmosphere and hydrosphere. But humans are also cutting down forests, which contributes to an increase in greenhouse gases. As populations grow, cities grow, and humans are urbanizing. Urban areas have higher temperatures than natural areas. While humans do make negative contributions to climate change, there is much we can do to have a positive impact or slow the addition of greenhouse gas into the atmosphere.
Connect It
Can unusual freezes be influenced by greenhouse gases?
Yes. In 2021, a freeze happened in Texas because of an interaction between an extremely cold air mass near the North Pole, called a polar vortex, and air in the stratosphere that was heated extremely quickly. Usually, the polar vortex stays within the confines of the Arctic Circle, circulating around it. However, it can be displaced if warmer air moves into that area.
High levels of greenhouse gases influenced temperatures in the upper layers of the stratosphere, causing them to warm several degrees over just a few days. When the superheated air in the stratosphere met the polar air over the poles, it made the polar air mass move south, dropping temperatures drastically and creating the unusual freeze Texas saw in 2021. This unusual period of cold weather can happen in typically warm climates anytime there is an unusually warm air mass displacing the polar vortex.
1 What is deforestation?
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Summarize It
A Removing debris from a forest area
B Clearing of forest area on a large scale
C Clearing a small patch of trees
D Planting trees in a forest
2 What is the primary cause of increasing carbon dioxide levels?
A Carbon dioxide has been increasing since the last ice age.
B Carbon dioxide is released from the oceans as they warm.
C Carbon dioxide increases as fossil fuels are burned.
D Carbon dioxide increases as the human population increases.
3 Which of the following is NOT an example of a greenhouse gas?
A Nitrogen
B Nitrous oxide
C Fluorinated gas
D Methane
4 The process by which cities grow and develop is called ________________.
5 Carbon stored in the geosphere is stored in ___________________, which exist in rock layers below the surface.
6 Describe how urbanization and deforestation are related.
Human Impact on Watersheds
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Think about It
Have you ever thought about where streams and rivers get their water? Watersheds channel rain and snow into small bodies of water, such as creeks and streams. Eventually, the water in these areas reaches larger bodies of water, such as oceans and lakes. Human activities influence watersheds every day and have both beneficial and harmful effects.
1. What are some ways that human activities can affect watersheds?
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Water on Earth
Almost all of Earth’s water—97%—is salt water in oceans, seas, and salt lakes. The remaining 3% is fresh water, and of that, 1% is surface water (all of the water on Earth’s surface). One-third of this amount is groundwater that has seeped under Earth’s surface. The rest is frozen in glaciers and polar ice caps.
The water cycle is responsible for the circulation of water on Earth. As it circulates, water collects and drains into a body of water. A watershed is an area of land where the surface water and groundwater drain into a particular body of water. A watershed is separated from other watersheds by drainage divides.
Water Vapor 8
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This is a diagram of a watershed showing tributaries or smaller sections of a river that join together at a confluence to flow into a single main river channel. Finally, the confluence then flows further downstream into a larger body of water—in this case, an ocean.
The health of any watershed depends on the choices of humans in the area. Currently, almost half of the watersheds in the US are not able to support drinking, swimming, or eating fish from that area.
Watersheds are important because they provide drinking water supplies and food to towns and cities. They are popular sites for swimming, boating, and many other watersports. They also provide habitats for numerous species of plants and animals.
Human activities impact watersheds. Human activities are things that humans do. Our choices to conserve water may benefit watersheds, while putting excess nutrients in the water from factories can upset the balance of life in these areas. Runoff of chemicals and other waste products can contaminate local watersheds. Runoff is rain and surface water that drains or flows from the land into streams, rivers, lakes, or the ocean.
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watershed: an area of land where the surface water and groundwater drain into a particular body of water; separated from other watersheds by drainage divides human activity: things that humans do runoff: rainfall and surface water that drains or flows from the land into streams, rivers, lakes, or the ocean
2. Explain what could happen if a factory was built near one of the tributaries of a river and dumped industrial waste into the water.
Human Activity and Surface Water
Surface water is probably what you think of when you think of bodies of water outdoors. Surface water is all the water above the surface of the ground and includes lakes, rivers, and streams. Surface water can be found all over Earth. It is fed by precipitation and water that runs off of surfaces upstream, such as mountain ranges. Water in a watershed always flows downstream toward a larger water body such as an ocean or a river. So, any activity or building we construct has the potential to affect the water next to and downstream from it.
Human activities can be beneficial or harmful to surface water in watersheds. For example, dam building is one way humans change the surface water. A human-made dam can trap sediments upstream, changing the chemistry of the water further downstream in the watershed. In some cases, human-made dams can change the amount and temperature of the water that flows past them, and this can change the ecosystems downstream as well.
Construction of buildings and roads has a large impact on watersheds because the materials used do not allow for water to seep or flow through rock layers. One way builders and engineers compensate for this is by designating a nearby area as an area off limits to more construction. When the ground near surface water is left to be a natural area without pavement or metal building material, it allows precipitation and runoff to seep down through the ground, replenishing the watershed.
Humans can minimize these harmful effects on watersheds in several ways. One is to install buffer strips along stream beds that help filter nutrients, stabilize areas of erosion, and allow animal movement. Planting submerged grasses into watersheds can also improve the populations and biodiversity of organisms in the watershed. Finally, communities can take action to prevent pollution from ever making its way into the local waterways.
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Hydroelectric dams like this one harness the power of moving water in order to create renewable electricity for communities. Human activity like this can have both beneficial and harmful effects on the surface water in a watershed.
Dams or other construction built by humans can also reroute rivers or change the way water flows and drains into and out of communities. In addition, waste discharge from factories can change the temperature or chemistry of surface water, affecting the amount of dissolved oxygen available to aquatic organisms. Or, if heated water is dumped into nearby waters, it can cause thermal pollution. Pollution is the presence of harmful or unwanted levels of material in the environment. In this case, heated water can cause damage to plants and animals that need colder temperatures to live.
Excess nutrients from fertilizers can enter watersheds and cause uncontrolled algae growth. This also affects the health of the organisms that compete with the algae for sunlight and other nutrients, such as dissolved oxygen in the water.
Water treatment can prevent harmful pollutants from entering watersheds. After humans use water, it flows back into watersheds. From there, it can be treated for later human use or allowed to flow back into a larger collection area.
surface water: all the water above the surface of the ground; includes lakes, rivers, and streams
pollution: the presence of harmful or unwanted levels of material in the environment
3. What is one beneficial effect and one harmful effect of human activity on the surface water in a watershed?
Human Activity and Groundwater
Layers of rock underground are not completely solid; they have small cracks and pores where water can accumulate. This is called groundwater. Groundwater is water that collects in cracks and pores in underground soil and rock layers.
Groundwater is constantly being replenished when rainwater soaks into the ground. It is able to flow because the holes and spaces between rocks are big enough to allow movement. Groundwater is usually located in an aquifer. An aquifer is an area of permeable rock underground that holds or transmits groundwater. Aquifers have two areas, or zones, that hold water. The first is the saturated zone. Water flows through the water table into the soil zone, permeates through that layer, and accumulates in the saturated zone, which is filled with water. The unsaturated zone is the layer immediately below the land surface, where the holes and pores between rocks are not filled with water. The unsaturated zone is on top of the saturated zone. These two layers are separated by the water table, which is the top of the saturation zone, where water fills all open spaces within the rock.
The Upper Floridan aquifer, located beneath parts of Florida, Alabama, Georgia, and South Carolina, is the major water supplier for west central Florida. Water from this aquifer is used for drinking, irrigation for agriculture, livestock, and other industrial uses. It also is an important part of wetland ecosystems. Humans gain access to water in aquifers by drilling wells into the rock and pumping the water from the aquifer to the surface.
Human activity has a major influence on the health of the groundwater under our feet. As humans withdraw groundwater, they remove water that can be used to feed ecosystems. In addition, paved roads serve as runoff areas for rainwater, so it does not soak into the ground and replenish groundwater supplies. Paved surfaces can also cause runoff to sweep chemicals or pollution into groundwater supplies.
Groundwater in a cave
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Groundwater withdrawal can also alter the rock layers surrounding it. Water has mass and takes up space underneath layers of rock on Earth’s surface. If a large amount of groundwater is not carefully removed, it can result in the formation of air pockets in underground rock layers, and eventually a sinkhole, where rock layers at Earth’s surface collapse. Sinkholes can change the landscape for large areas.
Sinkholes are not the only hazard humans can introduce when pumping groundwater. Pumping water into the ground for fossil fuel extraction can cause the watershed to hold too much water. If that groundwater runs off, it can gather in other areas, causing stream erosion and affecting ecosystem balance in the area.
One way we can ensure the health of groundwater is to manage agricultural waste. This means being sure that the runoff from pesticides or fertilizers is kept safely away from groundwater supplies nearby. This will prevent pollution of the groundwater.
Chemical spills can also cause damage to groundwater supplies. Deforestation, or cutting down trees to make room for buildings, can contaminate nearby groundwater. It also increases erosion, which can send sediment into areas where the water was cleaner.
How can humans protect the health of groundwater? First, we can monitor the amount of water we draw from watersheds. If we minimize our consumption of water, then it will make the process of accessing groundwater more sustainable and less disruptive to the nearby ecosystems.
Humans can also choose native garden plants and use the minimum amounts of fertilizer on gardens and lawns. Another option for lawns is using organic fertilizers, which are less dangerous to the groundwater supply. Humans can choose to plant trees. Tree roots hold soil rather than allowing it to run off, so planting trees is one way to prevent erosion that could end up contaminating groundwater.
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Planting trees, using only organic fertilizer, and being mindful of our water use will help protect the groundwater supply near our communities.
Keeping pet waste picked up and using proper disposal techniques will prevent our pets from contaminating groundwater near our homes.
In the garage, we can recycle motor oil instead of dumping it on the ground. Many auto parts stores will collect motor oil for this purpose. And on a larger scale, we can help prevent industrial pollution by choosing to build factories as far downstream as we can.
The government can declare land near water bodies as protected natural areas. This would reduce human activity such as construction, further protecting areas of delicate groundwater.
Finally, cities can be planned with consideration for watersheds. Designs that include green spaces allow precipitation to run off and replenish watersheds. Minimizing paved areas and buildings also helps impact watersheds in positive ways.
groundwater: water that collects in cracks and pores in underground soil and rock layers
aquifer: an area of permeable rock underground that holds or transmits groundwater; pumps are used to retrieve water from these areas
water table: the top of a saturation zone, below which water fills all open spaces within the rock
4. What is one beneficial and one harmful effect of human activity on groundwater in a groundwaterwatershed?
Scientist in the Spotlight
Nam Jeong Choi
United States Geological Survey
Nam Jeong Choi is a hydrologist who specializes in urban drainage and infiltration. She works with the US Geological Survey office in San Antonio, Texas, researching and reporting on how water flows in various situations, including storm sewer systems. She has studied the effects of flooding rains in Bandera, Texas, and created flood maps for areas of the Medina River. These help homeowners and engineers plan for the effects of flooding rains in the area.
The office she works with studies water flow in an area covering 50,000 square miles of Texas, including 165 streams and 6 lakes. The office also monitors water quality for the watersheds in those areas.
The Medina River near Castroville, Texas
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The Big Picture
Human activity can either have beneficial or harmful effects on groundwater and surface water in a watershed. Watersheds are important because they provide water supply and recreational activities to residents. They also provide habitats for many species of aquatic organisms. Human activity damages watersheds by introducing chemicals into the water, changing the temperature of the water, or allowing pollution into these delicate areas. We can choose activities that benefit watersheds by monitoring our use of pesticides and chemicals, regulating industrial waste, and carefully extracting water, oil, and gas from underground.
Connect It
How do human activities affect rivers and other watersheds?
Human activities can have both beneficial and harmful effects on rivers and other watersheds. Perhaps the most obvious harmful effect is polluting watersheds with plastic trash and chemicals. We also pollute watersheds with runoff from chemicals such as pesticides and pet waste. Watersheds can benefit from human activities as we choose sustainable methods of groundwater extraction, carefully monitor our use of water, and drill carefully to extract water from aquifers.
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Summarize It
1 All of the following are uses of watersheds EXCEPT–
A recreation, including swimming and boating.
B reservoirs for industrial waste.
C sources of food.
D habitats for plants and animals.
2 Rain and surface water that drains or flows from the land into streams, rivers, or oceans is–
A correctly treated.
B runoff.
C flowing upstream.
D contaminated.
3 Which of the following statements about factories is correct?
A Some factories dump chemicals into watersheds that help increase fish growth.
B Factories must always be located near a human-made dam.
C Factories are allowed to dump small amounts of industrial waste into watersheds.
D Factories can influence the health of ecosystems located downstream from them.
4 Why are buffer strips helpful when planted along stream beds?
5 Describe how human activities can result in sinkholes.
Temperature and Kinetic Energy
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Think about It
Lava on the surface of an erupting volcano is extremely hot—about 2,000 degrees Fahrenheit (700–1250 degrees Celsius). Heat flows in a predictable way: it is always moving from warmer to cooler sites until the sites reach the same temperature. Thus, the lava cools as it oozes down the side of the mountain, solidifying and forming rocks. What is responsible for the changes in state of matter, and what does it look like on a molecular level?
1. How does the temperature of lava affect the kinetic energy of the particles that make it up?
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Kinetic Energy
You already know that matter is composed of atoms and molecules. But did you know that they are always moving, even within a solid? In solids, molecules are vibrating in place. This energy of motion is called kinetic energy. All substances, regardless of their state of matter, have some amount of kinetic energy in their molecules.
Of the three states of matter, molecules that make up solids have the least amount of kinetic energy. The molecules are tightly bonded to one another, and the molecules are packed very tightly together. This does not give them much room to move. This property of low kinetic energy is also what allows solids to hold their shape.
Liquids have molecules as well, but these have slightly more kinetic energy than molecules in solids. The molecules in liquids have enough energy to be able to move, so these substances are able to flow. This includes honey, milk, gasoline, and water.
Molecules in a gas, like air or water vapor, have the most kinetic energy of all three states of matter. The molecules have so much kinetic energy that they are free to move around within their container.
2. Explain the difference in the amounts of kinetic energy in molecules making up a solid, liquid, and gas.
Solid
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Temperature
We can measure kinetic energy. Temperature is the average kinetic energy of all the particles in a material. It is usually measured in degrees Celsius or in degrees Fahrenheit.
Just like kinetic energy, the temperature of a substance can vary. In addition, the state of matter or phase of a substance is largely determined by its temperature. Most kinds of pure matter have a given melting point, a temperature at which the matter will change from a solid to a liquid. They also have a certain boiling point at which a substance in a liquid form will turn into a gas. For instance, the melting point of pure water is 32°F or 0°C. The boiling point of pure water is 212°F or 100°C.
All matter is made of atoms or molecules that are affected by heat. Heat is the energy transferred between two objects of different temperatures. Energy will always continue to move in a predictable pattern from warmer to cooler sites until all sites have reached the same temperature. If you leave ice cream out on a table, it will melt. Why? The ice cream is being heated by the air around it. This is an addition of thermal energy, making the atoms and molecules move faster. When they move faster, the average kinetic energy of the ice cream increases, causing its temperature to rise. The ice cream moves from a somewhat solid state to a liquid state.
The melting point of all substances is not the same. Here is a table of the melting and boiling points of various substances:
temperature: average kinetic energy of all the particles in a material; measured by a thermometer in degrees (usually degrees Celsius or degrees Fahrenheit)
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Kinetic Energy, States of Matter, and Temperature
Remember that temperature is a measurement of kinetic energy. It makes sense, then, that there is a direct relationship between temperature and kinetic energy of the molecules within a substance.
Molecules in all three states are always in motion. In solids, the kinetic energy is not enough for the molecules to break their bonds with one another. The molecules in a solid are very close together but still in motion, rapidly vibrating in place. However, as heat is added, the molecules move more. This increase in kinetic energy can be measured as an increase in temperature.
Eventually, enough heat is added for the molecules to break their bonds with each other. As this happens, the molecules in the matter begin to flow and move. The butter in the image below has reached its melting point and is beginning to melt. At this point, there is enough kinetic energy in the molecules for them to begin to move and flow around one another. As heat is added to matter, the kinetic energy of the molecules increases, and the temperature increases as well.
If heat continues to be added, the molecules will continue to gain energy. This will cause the temperature to rise, and eventually, the matter will reach its boiling point and turn into a gas. The state of matter is directly determined by its temperature.
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When the particles in matter begin to move more rapidly, the object feels warmer, and the temperature is higher. When the particles move more slowly, the object feels cooler, and the temperature is lower as well. There is a positive relationship between kinetic energy and temperature, meaning that as one increases, the other does as well. When one decreases, so does the other.
Boilingpoint
Meltingpoint
3. Describe what happens to the kinetic energy of a liquid when it reaches its boiling point.
Can Kinetic Energy Cause Substances to Expand?
When heat is added to some substances, such as to gases in a helium balloon, it will cause the expansion of a substance. Tiny spaces exist between the molecules in matter.
We know that as molecules gain kinetic energy, they begin to move more. As they do so, the space between them increases as well. This may increase the volume of the substance, as it does in a gas. The number of particles in the matter does not change, so the mass of the object is the same; however, the volume increases. This makes the substance less dense overall. We can find density by dividing an object’s mass by its volume. What happens to an object’s density if volume increases and mass stays the same?
Remember, molecules move faster as thermal energy is added, which causes them to move faster. As they do so, they also begin to move so much that they put pressure on their container. In the case of a helium balloon, as long as the balloon can hold up to the additional pressure, it will not pop as the kinetic energy increases and the temperature increases inside the balloon. However, if too much thermal energy is added, such as if the balloon is in the hot summer sunlight, it may cause the thin balloon to pop, releasing the hot molecules in the helium.
4. What is the difference in the density of a balloon with a mass of 50 g and a volume of 100 cm3 and the density of the same balloon when the temperature increases and its volume increases to 150 cm3? Show both equations.
Scientist in the Spotlight
Laurence Kemball-Cook Pavegen Corp.
Laurence Kemball-Cook is the leader of a company in England called Pavegen that has pioneered a flooring system that converts kinetic energy from footsteps into electricity.
The idea began when Kemball-Cook was in college, and after spending three years perfecting the technology, he launched a company to bring it to life. The company now boasts over 1,500 investors. One of the first projects using this technology is a football pitch in South America that uses player footfalls to power the stadium lights.
A company called Pavegen wants to help fight climate change by installing technology in buildings that converts the kinetic energy from people walking to electricity.
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The Big Picture
Kinetic energy is the energy of motion. As kinetic energy increases in molecules that make up matter, the molecules begin to move. If enough kinetic energy is added, the molecules break their bonds and begin to flow. We can see this change in kinetic energy by using a thermometer to measure temperature. As kinetic energy in molecules increases, temperature increases as well.
Connect It
How does the kinetic energy in lava affect the temperature of the particles that make it up?
As Earth heats the particles in molten magma, which is a liquid, the kinetic energy of the particles increases. As the volcano erupts, it spews liquid magma out as lava and ejects gaseous steam. As the lava cools off, the temperature drops, reflecting the slowing kinetic energy in the molecules.
Earth’s thermal energy increases the kinetic energy of molecules of rock, melting it. Then, as it cools, the kinetic energy slows and the temperature drops.
The molecules in the molten lava above have a large amount of kinetic energy. As temperature drops, kinetic energy of these molecules decreases, causing the substance to solidify as igneous rock.
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Advanced Topics
Temperature is related to the kinetic energy of atoms. The faster the atoms move, the higher the temperature. As the kinetic energy of atoms decreases, the atoms move more slowly and the temperature decreases. These changes in temperature can also mean changes in a substance’s state of matter. States of matter include solid, liquid, gas, and plasma.
States of Matter
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Summarize It
1 The molecules of a substance placed in a refrigerator–
A gain kinetic energy as they cool and the temperature increases.
B lose kinetic energy as they cool and the temperature increases.
C gain kinetic energy as they cool and the temperature decreases.
D lose kinetic energy as they cool and the temperature decreases.
2 Which of the following statements correctly explains the relationship between temperature and the kinetic energy of the molecules within a substance?
A As the kinetic energy of the molecules increases, the temperature doubles.
B As the kinetic energy of the molecules increases, the temperature decreases.
C As the kinetic energy of the molecules increases, the temperature increases.
D As the kinetic energy of the molecules decreases, the temperature increases.
3 Which of the following situations correctly describes the change in kinetic energy of the molecules within a substance as the temperature changes?
A Water molecules move faster when an ice cube is put in the sunlight.
B Ice molecules break their bonds to evaporate as an ice cube is put in the sunlight.
C Molecules in water vapor experience a temperature increase as they condense.
D Molecules in solid chocolate increase kinetic energy as they cool.
4 Analyze the models below and fill in the blanks to label the diagram with the state of matter or the process by which the state of matter is changing. Use the words gas, solid, liquid, increasing kinetic energy, melting, increasing temperature, and decreasing temperature.
Kinetic energy and temperature in matter
5 Describe an investigation that would model part of the relationship between temperature and kinetic energy of molecules within a substance. How would you change the temperature and what would happen in the molecules of your substance?
Energy Conservation and Transformations
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Think about It
Millions of watts of electrical energy are used and transferred in cities around the world every day. We see light energy in traffic lights, office buildings, car headlights on the freeways, and even in our own neighborhoods. Once this energy is used, where does it go? Can it just go away? And where does new energy come from?
1. Where does a city’s extra energy go once it is used?
How Does Energy Help a System Function?
Our world is full of individual parts that come together and act as one unit. For example, our solar system consists of planets, moons, and the Sun. Your school system consists of students, teachers, and other staff members who work together to educate students. An ecosystem consists of living and nonliving elements that function together. A system is any group of interacting, interrelated, or interdependent elements forming a complex whole.
system: a group of interacting, interrelated or interdependent elements forming a complex whole
energy: the ability of a system to do work; required for changes to happen within a system
energy transformation: the change of energy from one form to another
Any system where work is being done or something is being transformed runs on energy. Energy is the ability of a system to do work. It is required for any changes to happen within the system. For example, the human body needs nutrients in order to function. A plant system needs sunlight and carbon dioxide for photosynthesis.
Within a system, energy can change from one form to another (for example, from electrical energy to light and thermal energy in an electrical lamp). This is called an energy transformation. However, the same forms of energy cannot always sustain a system. For instance, the electrical energy in a kitchen cannot by itself heat food, but the electrical energy can be changed into another form, thermal energy, as a microwave heats food.
2. Name one example of a system in your life. What are the individual parts of your system, and how do they function as a whole?
What Types and Forms of Energy Can Be Transferred and Conserved within Systems?
There are two main types of energy: kinetic and potential. Kinetic energy is the energy of motion. Potential energy is the energy of position and has the potential to cause a change within a system.
Within these main energy types are six main forms of energy: mechanical, radiant (or light), thermal, electrical, chemical, and sound.
Energy can be transferred within a system, or from one system to another. Energy transfer is the movement of energy from one system to another. For example, let’s look at the human body. Chemical energy from the food we eat is transferred through various organs. As usable energy is pulled out from our food, the nutrients in our food are changed to other forms of energy, such as electrical signals that help our brains and hearts function. Some of that chemical energy is changed into kinetic energy that helps our muscles move, and some is given off as thermal energy when we sweat.
We fill our cars with gasoline, and then the chemical energy in the gasoline is converted to mechanical energy when the car moves. The engine gives off thermal energy that can be felt as heat.
The law of conservation of energy is a scientific law stating that energy can be neither created nor destroyed but just changes form. This means that used energy does not just go away—it is either transferred to another part of a system, transformed to another form of energy, or transferred to another system altogether.
energy transfer: movement of energy from one system to another
law of conservation of energy: scientific law stating that energy can be neither created nor destroyed but just changes form
3. What are the three things energy in a system can do? What is one thingcannotenergy do?
Electricity and Amusement Park Rides
Energy can be transferred, transformed, and conserved within electrical systems. Chemical energy is stored in batteries. When batteries are inserted into a toy, the chemical energy is transferred from the battery to the wires and other components of the electrical system as it moves through the electrical wires, switches, and connections in the toy. It can be transformed to other forms, such as sound or light.
During this process, the same amount of energy is present in the electrical system. Since it cannot be created or destroyed, all of the energy that was originally present in the battery is still present somewhere within or around the system. In the case of a remote-controlled toy, the chemical energy transformed into electrical energy, and then some of the electrical energy was transformed into kinetic, light, and sound energy. An amount of chemical energy remains in the battery for another use.
Electrical energy behaves in this manner in a mobile phone system as well. When the mobile phone is plugged into a charger, electrical energy from the home enters the mobile phone system and is converted to chemical energy as the battery is charged. When the phone is used, the light or sound energy and the kinetic energy from vibrations are energy that has been transferred from the house and converted from chemical energy into another form.
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Energy can be transformed within our homes and bodies. For example, when we use a microwave to heat food, the electrical and radiant energy in the microwave is transformed into thermal energy to make our food hot. And when we eat a meal, the chemical energy stored in the food is transferred to our body systems and used in the form of mechanical energy for movement and much more.
In amusement park rides, energy of position or potential energy is used, transferred, and converted to kinetic energy. For example, the track of a roller coaster takes the roller-coaster car to its highest point at the top of the first hill. Through the duration of the ride, potential energy is converted to kinetic energy and back again as the car changes heights along the track. The total amount of potential and kinetic energy together does not change throughout the ride, only the balance of each. The car does, however, slow down as it progresses through the ride. It loses energy that is given off as thermal energy in the form of heat.
Energy Transformations in a Roller Coaster
Amusement park rides use electrical energy to power their illumination and sound effects. In this transformation, electrical energy is transformed into light and sound energy.
4. Think of your favorite amusement park ride (not a roller coaster). Describe at least one way energy is transferred or transformed in your ride.
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Energy in Food Webs and Photosynthesis
Energy transfer and transformations take place in the natural world as well. In photosynthesis, plants collect and store light energy in their chloroplasts, which are organelles in green plants that give them their color. They convert light energy from the Sun, along with carbon dioxide and water, into chemical energy stored in the form of glucose. Energy is conserved in this kind of transformation because no energy is destroyed; the energy is used for plant functions such as growth and reproduction. Glucose is used during cellular respiration. Oxygen is given off through holes on the underside of the plant.
The chemical energy in any single plant can be transferred to other organisms when it is eaten. When a cow eats grass, some of the chemical energy stored in the grass is transferred to the cow, who uses it for bodily functions such as movement and digesting food.
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Producers like grass and other green plants are one part of a food web. Food webs can be found in any ecosystem, and they can help scientists trace the flow of energy through them. In the diagram of an ocean food web below, you can trace the flow of energy through the various levels of the food web, and see how, at each level, chemical energy is converted to thermal energy and given off as organisms carry on life processes. Only about 10% of the energy at any level of a food web is made available to the organisms at the level above it. Energy is continually recycled and conserved in all food webs. Without this energy, life would not exist on Earth.
5. What forms of energy are involved in the transformationenergythat happens in plants duringhappensphotosynthesis?
Scientist in the Spotlight
Lewis Latimer Edison Electric Light Co.
Lewis Latimer was an inventor and draft writer who improved the process for manufacturing filaments in light bulbs. Before working for Thomas Edison, he worked for one of Edison’s competitors. During this time, Latimer modified the process for manufacturing carbon filaments in light bulbs. Latimer’s new method involved placing the blanks for the filaments into carbon envelopes during manufacturing to protect them. These are known as threaded sockets.
He received patents for his manufacturing process in 1882. Two years later, he went to work for Thomas Edison’s Electric Light Company, where he wrote the first book on electric lighting in 1890 and helped oversee the installation of electric lights in cities like New York and Montreal, Quebec, Canada. He was inducted into the National Inventors Hall of Fame for his modifications to the carbon filament manufacturing process.
He also worked for Alexander Graham Bell, the inventor of the telephone.
Inventor Lewis Latimer was inducted into the National Inventors Hall of Fame for his incandescent light bulb filament manufacturing techniques.
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The Big Picture
Our world is full of individual parts that come together and act as one unit. Any system where work is being done or something is being transformed runs on energy. Energy is the ability of a system to do work. It is required for any changes to happen within the system. The law of conservation of energy states that energy can be neither created nor destroyed but changes form. This means that used energy does not just go away; it is either transferred to another part of a system, transformed to another form of energy, or transferred to another system altogether. Energy transformations occur in electrically powered devices, in amusement park rides, in photosynthesis, and in food webs.
Connect It
Where does a city’s extra energy go once we use it?
You now know that according to the law of conservation of energy, a city’s extra energy cannot be created or destroyed. It can, however, change form. Electrical energy is converted to other forms of energy that are used by people. Energy does not just disappear within any system, but it can be reused in other ways.
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Summarize It
1 How is energy conserved through transformations in a food web?
A When producers eat consumers, the energy is transformed from chemical to mechanical energy.
B Energy leaves the system and is destroyed after it reaches the top-level consumers.
C Energy is transformed from chemical energy to radiant energy in photosynthesis and does not leave the system.
D The same overall amount of energy is always in the system, but it is converted to other forms such as chemical energy during photosynthesis.
2 What is the main kind of energy transformation in a roller coaster at an amusement park?
A Chemical to sound and back again
B Light to chemical and back again
C Potential to kinetic and back again
D Kinetic to potential and then to chemical
3 How is energy conserved through transformations in home electrical systems?
A Electrical energy is transformed into light or sound energy in radios and lamps but is never created or destroyed.
B Light or sound energy is transformed into electrical energy and is created in the walls of the home.
C Energy is transformed from electrical to light or sound and then is destroyed after it is used.
D Energy is conserved when the user turns off the light or radio.
4 How is energy conserved through transformations in systems such as plants during photosynthesis?
A Chemical energy from the Sun is converted to light energy inside of green plants and used for life processes.
B Mechanical energy from cows walking on plants during grazing is converted to chemical energy and given off when the plant blooms.
C Light energy from the Sun is stored as chemical energy in the plant’s roots.
D Light energy from the Sun combines with water and carbon dioxide to form chemical energy in the form of glucose.
5 Describe what a system is and how energy is conserved through transformations in a system you choose.
Transverse and Longitudinal Waves
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Think about It
Water waves crash onto beaches, earthquakes shake buildings, the Sun’s light travels to Earth on the electromagnetic spectrum as radiation, and sound waves boom from speakers. Have you ever thought about how these things happen? We know that waves carry energy; however, let’s think about how that happens.
1. Water itself does not move toward the beach through ocean waves, but energy is transferred from deeper to shallower water. How is this possible?
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What Are Waves?
Waves transfer energy but not mass from one particle or molecule to another. In a spring toy, the coils move back and forth as energy is transferred through each coil, but the toy as a whole stays in the same place.
Most waves move through a medium, although some kinds do not require a medium and can move without matter. Waves—whether light, sound, or other types—travel at different speeds depending on the material they are traveling through. Water molecules vibrate in a water wave, air molecules vibrate in a sound wave, and electrical and magnetic fields vibrate in an electromagnetic wave. Energy in any system is conserved, so energy is not put into waves or taken out of them. It is changed from potential to kinetic as the particles move and return to their resting state as energy passes through them. This energy causes particles to bump into one another, allowing an energy transfer to take place.
energy: the ability of a system to do work; required for changes to happen within a system
energy transfer: movement of energy from one system to another
medium: the material through which a wave travels
2. Explain to your friend why there is no sound in the vacuum of space.
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Transverse Waves
Energy in surface water waves, earthquakes, and electromagnetic energy (light energy) move in transverse waves. The energy in transverse waves vibrates particles in an up-and-down motion, causing a disturbance that moves through the medium. The wave itself moves horizontally. The motion of the particles is perpendicular to the wave.
During an earthquake, some of the energy that travels through Earth moves rock up and down, or perpendicular to the direction the wave is moving.
From the side, it looks like a wavy line with peaks and valleys. The peaks and valleys, or the highs and lows, are crests and troughs. The crest is the highest point on the wave. The trough is the lowest point of a wave.
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You can see the up-and-down motion of a spring toy when you shake it. The spring toy is moving up and down, but the direction of the wave is forward. Similarly, you can see the vibrations on a guitar string as you pluck it. The vibrations are left to right, but the movement of the energy is forward.
Transverse waves can be mechanical waves or electromagnetic waves. Mechanical waves have particles that oscillate, or move side to side, while energy travels through the medium. Certain types of waves from earthquakes can only go through solid matter. The earthquake shakes the ground by moving soil and rock particles as the energy moves through them. Electromagnetic waves do not require a medium to travel through. Radiant waves from the Sun travel through space without a medium.
transverse wave: a wave that moves in a direction perpendicular to the displacement of the transmitting medium
crest: the highest part of a wave
trough: the lowest part of a wave
3. Draw and label a transverse wave. Include a direction arrow showing the movement of energy, as well as the following labels: Transverse wave, Crest, and Trough.
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Longitudinal Waves
Sound energy moves in longitudinal waves. The energy in longitudinal waves vibrates particles in a back-and-forth motion in the same direction as the wave itself. It looks like a spring toy being pushed and pulled back and forth.
While you can’t see the sound waves traveling to your ear, you sometimes can see a music speaker moving back and forth as the sound waves are pushed forward.
Longitudinal waves transfer energy through solids, liquids, and gases. They are mechanical waves and need a medium to move through. For example, sound requires a medium such as air in order for its energy to be transferred. If a medium is not present, such as in a vacuum or space, then the sound energy will not be transferred.
Longitudinal waves are characterized by compressions and rarefactions. A compression is the result of compressing particles into a smaller space, increasing their density. A compression is the denser, tightly compressed region of a longitudinal wave. A rarefaction is where particles move and expand into a larger space, decreasing their density. Rarefaction is the less dense, more spread-out region of longitudinal waves.
Another way to visualize energy from sound is to put some rice on a speaker. It will bounce to the music because of compressions and rarefactions. During earthquakes, some of the waves formed stretch and push Earth’s crust together. These longitudinal waves are responsible for the loud sounds one might hear during the beginning of an earthquake.
longitudinal wave: a wave that moves in the same direction as the displacement of the transmitting medium
compression: a denser, tightly compressed region of a longitudinal wave
rarefaction: a less dense, more spread-out region of longitudinal waves
4. Draw and label a longitudinal wave. Include a direction arrow showing the movement of energy, as well as the following labels: Longitudinal Compression,wave, and Rarefaction.
Electromagnetic Spectrum
Electromagnetic waves do not require matter and can travel through air, water, and solid material; they can also travel through space, which has no matter in it. The Sun’s energy arrives on Earth as radiation from the electromagnetic spectrum. When we talk about light or electromagnetic energy, we are using two names for the same idea. The electromagnetic spectrum arranges these waves according to frequency and wavelength, beginning with radio waves and progressing to gamma radiation.
The visible spectrum is a small part of the complete electromagnetic spectrum, with wavelengths ranging from 380 to 740 nm. Humans perceive differences in wavelength as different colors. White light is made up of a spectrum of many different colors. In addition, the amplitude of light in the visible area of the spectrum can be perceived by human eyes. Higher-amplitude waves come from brighter, more intense light.
electromagnetic spectrum: a continuum of all electromagnetic waves arranged according to frequency and wavelength, from radio waves to gamma radiation
Scientist in the Spotlight
Lucy Jones, “The Earthquake Lady” California Institute of Technology
Lucy Jones is a seismologist whose research is known around the world; seismologists study earthquakes and other disturbances within Earth’s inner layers. She has a strong desire to keep people informed about when and where possible earthquakes might happen. One of her first memories of an earthquake happened when she was two years old; an earthquake struck her home in California. Her mother felt the ground tremble and quickly moved Lucy and her siblings into a hallway, shielding them with her body. This event had a great impact on the young Lucy, which has fueled her desire to research earthquakes and how to keep people safe from their powerful energy.
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The Big Picture
Waves carry energy, not mass. There are two forms of waves: transverse and longitudinal. Transverse waves include earthquakes, surface water waves, and electromagnetic energy (light energy). The energy in transverse waves vibrates particles up and down while the waves move horizontally. These waves do not need a medium for energy to be transferred. Sound waves are longitudinal waves and need a medium (such as air molecules) for energy to be transferred. The energy in longitudinal waves vibrates particles in a back-and-forth motion in the same direction as the wave itself.
Connect It
Water itself does not move toward the beach through ocean waves, but energy is transferred from deeper to shallower water. How is this possible?
The surface water wave is a transverse wave; the energy travels across the water molecules. Surface water waves transfer energy by moving water molecules and other particles in an up-and-down motion and moving the wave horizontally.
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Summarize It
1 Which wave example does not need a medium for energy to be transferred?
A Ocean wave
B Light
C Sound
D Earthquake
2 What is the lowest part of a transverse wave called?
A Crest
B Rarefaction
C Trough
D Compression
3 Which definition best describes compression in a longitudinal wave?
A A denser, tightly compressed region of a wave
B A less dense, more spread-out region of a wave
C The highest part of a wave
D The lowest part of a wave
4 Fill in the blank.
Waves transfer energy but not ______________ from one particle or molecule to another.
5 Fill in the blank.
The energy in ____________________ vibrates particles in an up-and-down motion, causing a disturbance.
6 Describe how sound waves travel and be sure to include the medium used.
Observing the Behavior of Light
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Think about It
Suppose you were looking at the reflected image of a mountain on the surface of a lake. Can you trace the path of the light that makes it possible for you to see the reflected image?
1. How are we able to see the image of the mountain in the water?
How Does Light Energy Travel?
Light is a form of energy that can travel from one place to another. Light always travels in a straight line unless it bounces off an object or passes into a different material. Materials that light can pass through are transparent. Materials that transmit, or give off, light are called mediums. (Sometimes, media is used as the plural of medium.) Some everyday transparent mediums are air, water, glass, and nothing (like we find in space). That is right—we said “nothing”! Unlike sound, which needs particles, light can pass through empty space.
light: a form of energy that exhibits wavelike behavior as it travels through space; part of the electromagnetic spectrum
transparent: allowing light to pass through so that objects can be distinctly seen
transmit: to pass something from one place to another
medium: the material through which a wave travels
2. What are some materials that are transparent?
How Can the Path of Light Be Changed?
Remember, light travels in a straight line until it comes to an object or enters a different medium. If light cannot pass through an object, it will be reflected, absorbed, or both. Reflection happens when light bounces off the surface of an object. Absorption happens when light enters an object but does not pass through.
Shiny surfaces such as mirrors reflect almost all light, while black surfaces absorb almost all light. Absorption occurs when all or some of the light energy from light waves is transferred from one medium to another. Colored surfaces absorb all wavelengths except for the color reflected (the color we see). That is, certain pigments reflect or transmit the wavelengths they cannot absorb, making them appear in the corresponding color. Visible light is made up of all the colors of the rainbow; this range of colors is called the visible light spectrum.
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When light passes from one transparent medium to another, it changes speed. When light changes speed, it changes direction. This change of direction, or bending, is called refraction. The image shows a ray of light bending as it passes from air (above the line) into water (below the line). The light ray bends down because light travels more slowly in water than in air. If a light ray sped up as it changed mediums, it would bend in the other direction.
This image demonstrates refraction, or bending.
Some species of birds, such as pelicans and cormorants, can dive into the water and catch fish. If you tried to throw a spear at a fish, you would almost certainly miss because the fish would not be where it appeared to be. This is because the light reflected from the fish changes direction as it leaves the water and enters the air. Remember, this bending is called refraction. It is interesting that fishing birds have adapted, learning to adjust their aim to account for refraction.
Here is an easy way to see how refraction can fool you. Find a thumbtack; a long nail or pencil; and a large, wide bowl with a flat bottom. Place the tack, point up, in the bowl, near one side; then, fill the bowl with water. Bend your head down so you are looking across the bowl at the tack from a low angle. Now, slowly lower the nail, point first, into the water, and try to touch the point of the tack with the point of the nail. How did you do?
visible light: electromagnetic waves with wavelengths longer than ultraviolet waves but shorter than infrared waves and within the range that can be detected by the eye absorption: the transfer of energy into a medium
reflection: energy waves bouncing off the surface of an object
refraction: energy waves bending (changing direction and speed) as they pass from one type of object
3. Which characteristic of light causes your seat to heat up in the car on a hot day?
How Do Mirrors Change the Path of Light?
Have you ever noticed anything strange about images in a mirror? What you may have seen is that right and left are reversed. Look at the image of your right hand in a mirror, and compare it to your real right hand. Odd, isn’t it? This reversal is due to the way light is reflected off the mirror.
Are you familiar with the books Alice’s Adventures in Wonderland and Through the Looking-Glass by Lewis Carroll? In the second book, Alice imagines that the world she sees in a large mirror is a real world where everything is slightly different. When she looks at an image of written words in the mirror world, she sees that the people there seem to write from right to left and that some of the letters in their alphabet are different from our letters. If you hold the page of a book up to a mirror, you will see what puzzled Alice.
You may also have noticed that some letters and some words are the same in the mirror and some are not. Write the words MOM and DAD on a piece of paper, and hold the paper up to a mirror. What do you see? Make a list of all the capital letters that are the same as their mirror images. Use this list to see how many words you can write that look just like their mirror images. Can you find any words that become different words in the mirror?
Scientist in the Spotlight
C. V. Raman (1888–1970)
BioNTech
C. V. Raman discovered that when light contacts a molecule, it transfers energy to it. When this occurs, light changes its color. This change in color is like a fingerprint for the molecule and can be used to identify molecules, analyze cells without harming them, and detect some diseases.
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The Big Picture
Light is a form of energy that travels in a straight line through space. Once it hits a medium such as water, glass, or air, it can reflect (bounce off the object), be absorbed by the object, or refract. Shiny surfaces reflect light and allow us to see images. Some colors absorb light, which can cause the surface to heat up. Darker colors absorb more light than lighter surfaces. We see the color of an object when that color of light wave is reflected and the other colors are absorbed. Refraction causes light to bend. When light waves come into contact with a medium, their speed changes, causing the refraction.
Connect It
Think about how light travels in straight lines. Do you see why Earth, the Moon, and the Sun must be in a straight line to cause a solar eclipse?
During a solar eclipse, it can become very dark in the middle of a sunny day. This may seem amazing to us, but it was terrifying to ancient peoples who did not understand why it was happening. Today, we know that a solar eclipse happens when the Moon moves between Earth and the Sun so that the three are in a straight line. Therefore, when you are experiencing a solar eclipse, you are standing in the shadow of the Moon. The Moon is blocking the Sun’s light, which cannot bend around the Moon. If sunlight cannot reach your eyes, then you cannot see the Sun.
We see things only when light enters our eyes, right? This may seem obvious, but some people incorrectly think that our eyes produce the light to see. They think that light (or something like light) travels from our eyes to the objects we see. For example, some early Greek philosophers believed that the eye contained a kind of fire that beamed out to the things they were looking at.
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Summarize It
1 The path of light can be bent through–
A refraction.
B absorption.
C reflection.
D all of the above ways.
2 Which statement describes reflection?
A Light passes through an object.
B Light bends when it hits an object.
C Light is absorbed by an object.
D Light bounces off an object.
3 Which of these objects would absorb light?
A A black hat
B A mirror
C A glass of water
D A shiny metal
4 Which statement describes refraction?
A Light bounces off water, allowing us to see images.
B Light interacts with water, bending the light and causing objects to appear distorted.
C Light is absorbed by water.
D Light passes through the water in a straight line.
5 A frog appears to be green. Which of the following explains why we see green?
A Green light is absorbed, and all the other colors are reflected.
B Green light is absorbed, and yellow and blue are reflected.
C Green light is reflected, and all the other colors are absorbed.
D Green light is reflected and absorbed.
6 ___________________ energy waves bounce off surfaces, while __________________ energy waves are taken in or soaked up.
Evidence for Evolution
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Think about It
Have you ever wondered what life was like before we had constant access to smartphones? What were some of the features of the first cell phones? How have cell phones changed over time?
Evolution is defined as the change in a population over time. In technology, this is represented by advancements such as 5G LTE and Face ID, but it is also represented by the changes to the physical features of technology. Think about the very first cell phones invented. They were giant bricks that required long antennae and had big physical buttons to push. Now our phones are small, mostly touchscreen, and we can easily access the internet in a matter of seconds, but they all descended from that original giant brick. Evolution doesn’t just happen in the technological world; it happens everywhere, especially in the biological world.
1. What is another example of technological evolution that you are familiar with?
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Evolution
In biology, the genetic makeup of a population evolves over time. Evolution does not happen to individual organisms; instead, it happens to an entire species or population of species. These changes don’t just happen from one generation to the next. Rather, evolution is a slow process occurring over several generations. Charles Darwin formulated the theory of evolution in 1859. This theory proposed that, through natural selection, species change over time as a result of changes in physical or behavioral traits. These changes help them better adapt to their environments and survive to reproduce.
For example, animals today are smaller than ancient animals were because of changes in the amount of food and habitats available. The megalodon, estimated to have lived 20 million years ago, is the largest known marine creature in the history of Earth. By comparing the megalodon’s tooth size to the great white, the largest shark of today, scientists contend that the megalodon was 55 to 60 ft. long and weighed as much as 100 tons. In comparison, the great white can reach 21 ft. long and weigh over 7,000 pounds. Today, sharks are very similar to the way they were millions of years ago, only smaller.
When did these changes start? The theory of evolution describes a concept called common ancestry, which states that all biological organisms descend from a common ancestor. We can take two different biological organisms and, using various forms of evidence, can trace the changes in the genetic makeup of the organisms back to until we find a common ancestor. There are several different pieces of evidence we can use to support the theory of evolution and common ancestry of organisms.
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evolve: to change the frequencies of alleles in a population over time
species: a group of organisms with similar characteristics that are able to interbreed or exchange genetic material
theory of evolution: an explanation for how living things change over time
natural selection: process by which organisms with favorable traits produce more successful offspring than organisms with less-favorable traits, causing the favorable traits to become more common in the population
The Fossil Record
2. What evidence do you think scientists use to support the theory of evolution?
Fossils are preserved remains or traces of animals and plants that lived in the past. We call this fossil evidence. We can use the fossil record as evidence of evolutionary change in populations. Earth’s crust is made up of layers. The layers form over time, so that the most recent layers are at the top and older layers are underneath. We can distinguish older fossils from more recent fossils based on which layer they are found in.
Fossils are mostly found in sedimentary rock. Sometimes when fossils are removed, they leave imprints in the rock. These molds might be filled in by other material, but the shape of the original fossil is still there.
Youngest
Oldest
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Scientists can use comparative anatomy to compare the early fossils of species to more current fossils to determine how organism’s physical structures have changed over time. The fossil record also provides evidence of where and how organisms lived. By comparing fossils from different time periods, we can see not only the changes to the physical structures of plants and animals, but the changes happening to Earth. This allows us to provide some reasoning for why evolutionary changes occurred and the rates at which the changes happened.
fossil evidence: any remains, impression, or trace of a living thing of a former geologic age
sedimentary rock: rock formed when particles of other rocks are deposited in layers and cemented together
comparative anatomy: the study of the similarities and differences of body structures of different species
3. What do you think is happening when a new species suddenly appears in the rock layers?
Scientists in the Spotlight
Charles Darwin
Charles Darwin is often referred to as the Father of Evolution. Darwin travelled around the world on the HMS Beagle studying different organisms, identifying fossils, and observing Earth’s geological features. One of the most important studies conducted by Darwin was the Galapagos finches. During his time on the HMS Beagle, Darwin identified several different species of finches all over the Galapagos Islands. All across the islands, there were different food sources for the finches to eat, and Darwin observed that finches in different areas of the islands had different beak shapes. After his trip on the HMS Beagle, Darwin presented his theory of natural selection using the finches as evidence. He stated that the finches with the beak shape best fit to eat the food in their area survived, while finches with other beak shapes died off, until there were completely different and separate species of finch populations. Darwin’s theory of natural selection and his observations became the basis of modern evolutionary theory, and we still study Darwin’s finches today.
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The Big Picture
Evolution is the change in the genetic makeup of a population over time. All biological organisms descended from a common ancestor and there are several pieces of evidence to support this conclusion. The fossil record provides evidence of the evolution of physical traits in organisms and can be used with the geographic location of organisms living in the past and present to show how organisms have adapted based on their environment.
Connect It
How has technology evolved?
Evolution is all around us, even in the world of technology. The first cell phones were big and bulky. They needed an antenna to be used, and they could only make phone calls. The next cell phones were slightly smaller with smaller buttons and smaller antenna. Then came flip phones, and text messaging, and then phones with full keyboards. Then we had smaller and thinner phones that were able to access the internet. Now we have touch screen smartphones which are like small computers in our pockets. Each new version of the cell phone was adapted from the version before it with changes to their physical appearance and their technology capabilities.
4. How is the evolution of technology like the evolution of biology?
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Summarize It
1 Which of the following terms is used to describe two species that share fossil history and genetic evidence of a shared past?
A Fossil evidence
B Theory of evolution
C Common ancestor
D Evolution
2 The theory of evolution predicts that related organisms will share similarities that are derived from common ancestors. Which of the following is not a conclusion from fossil evidence?
A The chronological sequence in which different organisms first appeared
B Evidence of every species that has ever existed
C Links between groups leading to various modern species
D Relation through common descent from older organisms
3 José is learning about the fossil record. He knows the fossil record is the total number of fossils and their locations and that they provide information about an organism that once lived. Which of the following can José gather from studying the fossil record and its evidence?
A Similarities between past and present species
B How organisms will evolve in the future
C Every plant and animal species that has ever lived
D Origin of species and life on the planet
4 Whales, which live in the water, have hips. These structures are important for carrying the weight of animals that walk on land. Finding this body part in animals that don’t walk on land would lead us to predict what finding in the fossil record?
A Hips in ancient animals that always lived in water
B Land dwelling animals that don’t have hips
C A form of whale that lacked this structure
D An ancestor of whales that walked on land
5 What can Earth’s fossil record reveal about past organisms compared with organisms of today?
Natural and Artificial Selection
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Think about It
Have you ever wondered how there came to be so many species of plants and animals on Earth? Over time, organisms have changed and evolved from a common ancestor into millions of species with distinct features. This is called the theory of evolution (a term shortened from the original term “theory of evolution by natural selection” first proposed by Charles Darwin). Why do traits in organisms change over time? Let’s explore how natural selection enables organisms to produce offspring that are better able to survive.
1. What causes traits in plants and animals to change?
Why Do Plants and Animals Change?
There are two main reasons why plants and animals change over time. The first is to cope with changing environmental conditions.
The second is to ensure a population’s ability to survive and reproduce. A population is a group of interacting individuals of the same species located in the same area.
This population of jellyfish live together in the ocean. Since they need to capture and stun prey with venom in their tentacles, the individuals with characteristics that allow them to do so most efficiently are more likely to survive.
theory of evolution: an explanation for how living things change over time
population: a group of interacting individuals of the same species located in the same area
2. What traits in a population of pond fish do you think will change over time? Why?
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Natural Selection
British naturalist Charles Darwin developed the idea of natural selection, which builds on another concept called “survival of the fittest.” This is the idea that when two organisms compete, the organism best suited for the environment will survive. The “most fit” organism survives to pass on its features and characteristics.
Darwin spent his lifetime trying to understand why and how organisms change. After obtaining a college education, Darwin traveled the southern hemisphere aboard HMS Beagle, where he explored several continents and species. He noted that the land showed evidence of change, such as rising above seabeds, and developed a theory explaining how and why coral reefs formed. He hypothesized that reefs grew as the underlying land sank, and that they did so in order for organisms to reach the light and temperatures they needed. This would have taken hundreds of years and many generations to happen. This idea, along with others stemming from fossil collecting and ecosystem observation, led him to think that organisms compensated for changing environmental conditions by developing different traits over successive generations.
A trait is a characteristic of an organism. It can be genetic or acquired. Genetic traits are passed down from parents to children. The traits that make organisms the biggest, strongest, or smartest are not necessarily the ones that benefit an organism’s survival. Rather, the traits that allow the organism to adjust to its environment are the ones that favor survival and are passed down.
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Natural selection causes changes in the genetic traits in a population. In this example, the trait for white fur in mice allows these individuals to be spotted by the fox and eaten. Over time, the trait for dark fur increases in the population because it helps the mice survive.
We can look at giraffes for an example of how this works. Millions of years ago, giraffes had short necks. Individuals with longer necks had a survival advantage; they could reach leaves in high trees more easily, so more of them survived. Over time and several generations, this trait became more common in the population and was passed down. Now, all giraffes have this trait.
TIME
If a trait is genetic, it is inherited from the previous generation. A generation consists of organisms of the same species that are at the same level of descent from a common ancestor. A parent is a member of one generation, and its offspring are members of the next generation. Offspring are products of reproduction.
Darwin also began to wonder what caused large animals to die out, and whether variations in species happened quickly or slowly over time. He realized that population growth would lead to competition, and that organisms who were not able to fulfill their needs would die. He called this idea natural selection. Natural selection is the process by which organisms with favorable traits produce more successful offspring than organisms with less favorable traits.
Natural selection is the idea of survival of the fittest but on a larger scale. It includes whole populations of organisms.
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These two tortoises on the Galápagos Islands compete over resources. Natural selection is the idea that the traits in the population that favor survival will be passed from generation to generation.
Genes are the basic physical and functional units of heredity. They are made up of DNA.
trait: a characteristic of an organism; can be genetic or acquired
generation: organisms of the same species that are at the same level of descent from a common ancestor; a parent is a member of one generation, and its offspring are members of the next generation
offspring: product of reproduction; a new organism produced by one or more parents
3. In a population of desert lizards, what genetic traits do you think will change over thinkgenerations? What factors determine this?
natural selection: process by which organisms with favorable traits produce more successful offspring than organisms with less favorable traits, causing the favorable traits to become more common in the population
gene: the basic physical and functional unit of heredity made up of DNA
Conditions for Natural Selection
In order for natural selection to occur, three things must take place—reproduction, heredity, and variation in the fitness of organisms. Let’s look at each one of these.
First, there must be variations in the population. This means that there must be differences in organisms that allow some to survive better than others. For example, birds with longer wing feathers are able to fly more effectively and for longer distances, and since these traits will aid survival, they will be more likely to be passed down. In an ecosystem where food sources are scarce, organisms that can eat a variety of foods are more likely to survive.
Second, organisms must reproduce. In reproduction, more organisms are produced than can survive. Not all organisms can successfully reproduce because of limiting factors in the environment.
Finally, the traits that lead to the survival advantage must be inherited by the offspring. This means that the trait that leads to an organism’s survival must actually be inherited by the next generation.
This jackal lives in a desert in Namibia. Traits for long ears have been passed down through several generations of jackal since they allow this organism to maintain a cooler body temperature in spite of scorching temperatures.
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There are many factors that influence natural selection. The environment is perhaps the most important one. If the environment changes, it will affect the traits that will be passed down. For example, if the amount of water in a pond decreases, the traits allowing fish to tolerate less space will become more likely to be passed down within the population. If a fire destroys a forest ecosystem, traits allowing animals to survive this change are going to influence their fitness and thus will be more likely to be passed down to another generation. An increase in predators can cause organisms that can better camouflage in that environment to survive over those who are less suited to camouflage in that ecosystem.
Natural selection changes the traits of a population of organisms over time. For example, moths have developed eyespots as a form of mimicry because organisms with this variation were better able to elude predators. They survived to pass along their genes, and the trait then became more common in successive generations.
Another example can be found in the corpse flower, which smells like rotten flesh. The individual plants with the strongest odors attract the most pollinators, so the individuals with genes for strong odor are more likely to be pollinated and thus reproduce.
4. Explain how natural selection influences the development of traits in a population over several generations.
Artificial Selection
Sometimes, humans manipulate the traits of a species in order to produce the traits they want. This is called artificial selection. Artificial selection is the process by which humans breed other animals and plants for particular traits.
Another term for artificial selection is selective breeding. Selective breeding is a form of artificial selection where humans deliberately breed plants and animals for desired traits. We see this in genetic engineering used to modify foods and in other processes. Foods like corn and plums and animals like dogs have been selectively bred over several generations to produce more desirable traits. These can range from producing more seeds to disease resistance in plants, and structural features and fur colors in animals. This can be achieved by choosing two organisms to breed that each have the desirable trait.
Cauliflower and broccoli are examples of foods that have been selectively bred. Both of these vegetables have been modified from the naturally occurring mustard plant.
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Artificial selection works when humans intervene with the breeding process in a lab or greenhouse. It is beneficial because the effects can be seen over fewer generations. Changes can include domestication of animals or even the development of a new species.
Cloning is the process that scientists use to produce exact genetic copies of living things. Cloning can produce exact copies of genes, cells, tissues, or complete animals. In nature, single-celled organisms make copies of themselves when reproducing. Human twins share almost the exact same genes. Scientists in labs often clone genes to study and understand genes better
artificial selection: the process by which humans breed other animals and plants for particular traits
selective breeding: a form of artificial selection where humans deliberately breed plants and animals for desired traits
cloning: producing a copy or imitation of an object or living thing
5. Imagine you could selectively breed an organism for a desired trait. What species would you choose, and for what trait would you artificially select?
Scientist in the Spotlight
Evangelina Villegas International Maize and Wheat Improvement Center
Evangelina Villegas was a cereal biochemist who worked to improve the protein in maize, also known as corn. Her work led to the development of corn varieties with increased amounts of amino acids that humans need. She achieved this through natural breeding methods as opposed to genetic modification. It is thought that this technique will help people in areas without access to nutritious foods. Her process allows access to those nutrients more easily since the changes are made while the plants are growing instead of when the food is processed.
In 2000, she became the first woman to receive a World Food Prize.
The Big Picture
There are two main reasons why plants and animals change over time. The first is to cope with changing environmental conditions. The second is to ensure a population’s ability to survive and reproduce. There are two main ways that populations of organisms change their traits: natural and artificial selection. Natural selection is the process by which organisms with favorable traits produce more successful offspring than do organisms with less favorable traits. Artificial selection is the process by which humans breed other animals and plants for particular traits.
Connect It
What processes cause the traits in organisms to change?
Natural and artificial selection are the two processes by which genetic traits change in populations over time. Natural selection can result from genetic traits that allow organisms to cope with their environment, escape predators, and be more successful in reproduction. Artificial selection is a process where humans change the genetic traits in organisms to produce desired traits.
Advanced Topics
Natural selection is all about survival. Some species live long enough to reproduce and pass on traits, while others are eaten or die before being able to reproduce and add more of their species to the ecosystem. In some organisms, it is of great advantage to be able to produce great numbers of offspring. This means that hopefully more of their offspring can survive past the juvenile stage and live long enough to reproduce and add more of their kind to the population. The fewer offspring an organism can produce, the less likely that its traits will be passed on to future generations.
For example, the manatee is able to produce only one offspring at a time. Their gestation period is 11 to 12 months, making it hard for the population to increase dramatically in a short time. In contrast, the American alligator usually lays anywhere from 35 to 90 eggs, with an incubation period of about 65 days. Though the hatchlings are very vulnerable early in their lives, the mother is very protective of the young, offering a chance for survival.
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Summarize It
1 Beavers build dams by knocking over trees and stopping the water flow of a river, creating a dam, under which they live and reproduce. Which of the following choices explains why this behavior has been naturally selected in a population of beavers?
A Building a pond keeps young beavers entertained.
B The pond allows beavers to protect themselves more effectively from predators.
C Dam-building skills are more often observed in beavers that are fully grown.
D Areas with beaver dams attract anglers because they provide shade for game fish.
2 Genes are DNA fragments that produce traits. The traits that help an organism adapt to changes in its environment–
A are less likely to appear in the organism’s offspring.
B are rarely inherited from the generation above.
C are usually related to the animal’s ability to hunt effectively.
D are more likely to be passed down to the next generation.
3 What is the difference between natural selection and artificial selection?
A Human intervention happens with artificial selection.
B Human intervention happens with natural selection.
C Natural selection enables organisms to attract more suitable mates.
D Artificial selection is only used to genetically modify food.
4 Millions of years ago, woolly mammoths roamed Earth. Traits that helped woolly mammoths cope with cold environments included a layer of thick, coarse hair on their bodies. Today’s Asian elephants, which evolved from woolly mammoths, live in hotter environments. The gene producing the trait of thick, coarse hair was not naturally selected because–
A it was scraped off on nearby trees during migration.
B other species of elephants had the gene for thick, coarse hair.
C it did not give elephants living in hot environments a survival advantage.
D Asian elephants did not choose mates with coarse, thick hair.
5 Describe how natural and artificial selection change genetic traits in a population over generations.
Environmental Change and Populations
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Think about It
Some animals, such as chameleons and octopuses, have the ability to change colors in response to stimuli in their environments. For example, chameleons can change their skin color to regulate temperatures, becoming darker to absorb heat or lighter to reflect it. They can also use color changes to signal other chameleons. Some octopuses can completely change colors to blend in with environments, helping them stalk prey. When animals like these change color, do they always change to the same hues as other members of their populations? Or are there variations within individual organisms of the same species?
1. When animals change color, do they always turn the same colors as others in their species?
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Variations in a Species
Every kind of plant or animal species has variation between individual members. In humans, we see variations in eye color, skin color, personality, and height, among other things. A variation is the occurrence of an organism, trait, or gene in more than one form. For example, human eye color is directed by a gene that occurs in several forms. Depending on which form is expressed, individual people can have green, blue, or brown eyes. These are eye color variations.
All of the features we see that make individuals different—eye shape, eye color, length of eyelashes, etc.—are the results of variations within the human population.
variation: the occurrence of an organism, trait, or gene in more than one form
2. What are at least three examples of variations in the groups of plants or animals around you?
Examples of Variation in Populations
A group of interacting individuals of the same species located in the same area is called a population. For example, a pack of coyotes or a flock of birds of the same species is a population. A grove of maple trees or a group of daisies in a meadow is a population.
What are some examples of variations that can be seen in a population? There are so many! In animals, traits such as feather or fur color, length of neck or tail, or ear floppiness can vary between individuals. In plants, the thickness of bark or stems can vary. Some plants may be better able to photosynthesize than others. The texture of leaves can vary within a population. Some individual plants may more easily float in streams or oceans than others.
In the picture above, we see many pink daisies. All of the daisies together form a single population. There are variations between the individuals. Some have darker colors on their petals or leaves than others. Some have more petals than others. Some are taller or shorter. All of these are variations.
population: a group of interacting individuals of the same species located in the same area
Advantages and Disadvantages for Survival
As environments change, variations can change the odds of survival for individuals. You know that a plant with colors appealing to pollinators is more likely to get pollinated. This is an example of how a variation can create a survival advantage.
In a snowy environment, animals with thicker, whiter fur are warmer and better hidden from predators.
In the image above, the rabbit in the front of the group has whiter ears than the others. This variation could create a survival advantage for it in a snowy environment. However, when the environment changes and the snow melts, the advantage may shift to the rabbit in the back with the darkest ears, as it will be the least visible to flying predators against the dark ground.
In most plant and animal species, some trait variations will provide a survival advantage. For example, let’s look at a population of minnows in a murky pond. Some minnows will be less likely to be targeted by predators. Are those more likely to be the ones that have lighter scales or darker ones?
If you said darker scales, you are right! The minnows with darker scales are more likely to avoid death because their darker scales make them harder to be spotted by predators. Their survival is more likely because they are harder to see. Survival is the avoidance of death or extinction. We say that the minnows with the darker scales have a survival advantage in this environment.
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Which ladybugs have a survival advantage in this image because of their color? Which have a survival disadvantage? Why?
Color is not the only trait that can result in a survival advantage. Stronger, bolder, or more unusual features might attract more potential mates. For instance, some birds with longer tail feathers more easily attract mates. Structural variations that affect abilities like swimming or hunting can be useful in some environments.
survival: the avoidance of death or extinction
3. Which ladybugs in the image have a survival advantage because of their color? Which ones have a survival disadvantage? Why?
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For example, let’s look at a group of ducks in a pond near a park. In this environment, there are plenty of bugs to eat, both in the water and on the ground near the pond. Which ducks would have the survival advantage in this scenario?
Survival depends on whether the duck can get a meal more quickly than other members of the population. The ducks that are the fastest swimmers are more likely to survive in this environment because they will reach the bugs more quickly.
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Extreme weather can cause environments to change. For example, the desert plains experience sudden high winds and fierce downpours during summer thunderstorms. What variations in plants would provide a survival advantage?
The image above is from Joshua Tree National Park in the western United States. What variations in roots would help the plants stay anchored and get water during the infrequent desert rains? Individuals with longer roots might stay anchored better than others. Individuals with strong yet flexible stems can avoid damage while bending with the wind. These plants with thick leaves and flexible stems are wellsuited for this environment and have an advantage here.
Sometimes, variations in individuals can cause a survival disadvantage. Think back to the image of the ladybugs on the wood. The red ladybugs have a survival disadvantage in this environment because they are more easily spotted by predators against the light-colored wood.
Any variation of a young animal that makes it more easily seen or heard by a predator, such as a shrill call, can be a disadvantage. Variations that make animals more sensitive to environmental changes can also be disadvantages, such as plants that cannot withstand brief cold spells in the spring.
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Variations in shape can also be disadvantages. Look at the fish below.
These are Japanese koi, a type of carp that eats insects, algae, and plants. Mouth shape is extremely important for each koi’s survival. Which koi would have a survival disadvantage compared to others in this population?
Any koi with a smaller or deformed mouth would be at a disadvantage because it would be harder for them to eat.
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In a similar manner, individual plants with deformations that affect the ability to photosynthesize would be at a disadvantage in an environment where sunlight is limited. In an environment with abundant flowering plants, those with less showy colors are at a disadvantage.
This apple tree is covered in aphids, small bugs that suck the fluids out of the leaves. This individual tree is at a survival disadvantage over its neighbors with healthier leaves.
Environmental Change
Any environment will change over time. An environment is all of the living and nonliving things in a given area. Changes in environments could include a change in the availability of sunlight, space, or water. Pollution can change an environment. Increased competition can alter the resources available to individuals of a population. For example, if a new neighborhood is built in an area that previously contained a forest, it might displace a pack of coyotes. The coyotes that have longer legs might have an easier time moving to a new place. If water is not as easily accessible in the old area, the individual coyotes that can tolerate drier conditions have a survival advantage over ones that cannot.
A change in the amount of ice in an arctic area is an example of an environmental change. Animals that are better swimmers would have a survival advantage in this environment. Can you think of other variations that would result in a survival advantage here?
Variations occur through natural selection and evolution, but this does not always mean that species are born with the traits they need to survive environmental changes caused by natural processes or by human impact. Some species have traits that help them thrive during an environmental change, but others may not and therefore risk extinction. If a species or population does not have the right variation of traits, it will not evolve in response to an environmental change. The inability of a species to adapt to a changing environment can contribute to the extinction of that species.
environment: all the living and nonliving factors in an area
4. What individual plants and animals enjoy a survival advantage in an environment that is very hot and humid, such as the Florida coast?
Scientist in the Spotlight
Tanisha Marie Williams Bucknell University
Tanisha Williams is a plant ecologist and botanist who studies plants and how they respond to the world around them, especially in light of changes in climate. She is a Burpee Postdoctoral Fellow in Botany at Bucknell University.
One of her recent experiments studied how certain plant species responded to changes in their environments and which trait variations helped create survival advantages in the new environments. She has been featured in the Washington Post and on National Public Radio (NPR) to explain the effects of climate change on tree species and leaf color and why leaves change color each autumn.
In 2020, she founded #BlackBotanistsWeek, an annual online campaign to promote and create a safe place for Black people who love plants.
Plant ecologist and botanist Tanisha Williams studies plants and the variations that can create survival advantages, especially in light of climate change.
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The Big Picture
A variation is the occurrence of an organism, trait, or gene in more than one form. As environments change because of natural or human-made events, variations can change the odds of survival for individuals. The organisms with advantages tend to survive and pass along the variations to their offspring. Over time, these variations can cause the overall characteristics of a population to change as well. Many situations can cause environments to change, such as extreme weather or an influx of new organisms. Variations in traits can either then become advantages or disadvantages for the survival of the population in the new environment.
Connect It
Do organisms always have the same colors as others in their population?
No, they may have similar colors, but individual animals can have color variations that are different from other individuals. Depending on the environment, these variations can aid, hinder, or have no effect on the survival of the population as a whole.
The flowers on this passionflower vine show color variations in their structures. This variation in color can provide an advantage or a disadvantage to the survival of the population as its environment changes.
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Summarize It
1 A population of horses lives on a farm where bugs are abundant. Horses swish their tails to swat flies. Which variation within the fly population is an advantage for survival in this environment?
A Shorter wings
B Slow reaction time
C Quick reaction time
D Longer legs
2 Many plants have drip tips on the edges of their leaves. A drip tip is a point on the end of the leaf that helps concentrate rainwater into a channel, where it flows off of the leaf’s edge quickly. Some rain forests get more than 60 inches of rain per year. Look at these leaves collected from two different fig trees. Which of these two individual plants has a survival advantage in a rain forest environment, and why?
Plant A Plant B
A Plant A, because it can collect more water on its leaves
B Plant B, because it can channel water off its surface easily
C Plant B, because it has a thicker stem
D Plant A, because it can collect more sunlight
3 Two scorpions in the same population burrow into the dirt under rocks in the same area in Florida. Soil and rocks provide shelter from winds and rain by blocking both. Which scorpion would be at a survival disadvantage during a winter snowstorm?
A The scorpion that is able to dig a deep hole for shelter
B The scorpion that is less active in the early morning hours
C The scorpion that moves its home to a tree
D The scorpion that cannot dig well due to a missing leg
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4 A group of flowering plants in a garden develops color variations in its flowers. These color variations result from the traits of individual plants, along with other environmental factors. Over several years, the population grows, and plants with brighter flowers are more numerous within the population than the ones with more faded flower colors. Write an explanation for why this might happen.
5 The table below lists a change to an environment and organisms from a population in that environment. In the third column, write an example of a variation within the population that would create a survival advantage for that population as the environment changes. Then, in the last column, write an example of a variation that would create a survival disadvantage in this environment. The first one has been done for you. Environment
A forest that has experienced a recent fire
A river where the temperature is dropping due to melting snow upstream
A prairie that has recently had several weeks of rain
Red-shouldered hawks
Salmon living in the river
Prairie grasses
An urban environment with increasing air pollution levels due to a new factory Humans
Variation Creating an Advantage Variation Creating a Disadvantage
Ability to migrate to a safer location with more resources
A hawk that only eats one kind of rodent in the area
Genes and Traits
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Think about It
Have you ever noticed how family members look alike? This is because certain characteristics are passed from the parents to their kids. These include physical traits such as eye color and body shape that are easy to observe.
1. What are some characteristics that parents can pass on to their kids?
Genes and Chromosomes
Inherited traits are determined by information stored in an organism’s genes. Genes are sequences of DNA that are part of the structure of the organism’s chromosomes. Chromosomes are located in the nucleus of every cell in that organism. An organism has two copies of each chromosome. During sexual reproduction, one copy comes from the organism’s female parent. The other copy comes from the organism’s male parent.
gene: the basic physical and functional unit of heredity made up of DNA
DNA (deoxyribonucleic acid): a molecule containing information that forms the hereditary material of all cells
chromosome: a single, highly organized and structured piece of DNA
2. Do siblings inherit the exact characteristics of their parents?
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Traits
Heredity is the transmission of traits from one generation to the next. How are these traits passed on? Genetic instructions are a set of directions, and traits are like the results of following the directions. Cells follow genetic instructions provided by deoxyribonucleic acid, or DNA, that determines their form and function. For example, one cell may be directed to be a red blood cell, another to be brown eye pigment, and a third to form bone cells. DNA forms strands that are made up of smaller pieces, or segments, called genes. It is these genes that govern the many traits of an organism. Traits are inherited qualities of an organism and can be divided into three types: physical traits such as height, eye color, or hair color; behavioral traits such as protective instincts; and predisposition to a medical condition such as cancer, heart disease, sickle cell anemia, or diabetes. The same trait can be shared by many organisms, yet it is the combination of traits that makes every individual unique.
When the process of heredity occurs asexually from a single parent, the offspring receive an exact duplicate of the parent’s genetic material. When the process of heredity occurs from the sexual reproduction of two parents, the offspring receives half of the genetic material from the mother and half from the father.
heredity: the transfer of genetic information from parent to offspring
trait: A characteristic of an organism; can be genetic or acquired
3. What is the function of genes and traits?
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Alleles
Because each chromosome is present in two copies, each gene is present in two copies. However, the DNA sequences of the two copies may not be the same. These variations of a gene are called alleles. As an example, suppose that a scientist inspected the chromosomes present in a flowering plant. The scientist might observe something similar to the situation diagrammed.
Alleles for the same gene have been identified on two chromosomes. One allele is coded for purple flower color. The other allele is coded for white flower color. One allele came from the plant’s female parent. The other allele came from the plant’s male parent. The pair of alleles an organism inherits for each gene determines the genotype of that individual. Suppose the purple color allele is given the abbreviation P and the white color allele is given the abbreviation p. This plant’s genotype for flower color is Pp.
An individual’s phenotype refers to the traits that are expressed and observed. Suppose that the plant with a genotype of Pp has purple flowers. We say the plant’s phenotype for flower color is purple. The table summarizes the possible genotypes and phenotypes resulting from the allele combinations for flower color (purple or white). Remember, in sexual reproduction, an offspring inherits one allele from each parent.
Allele Combinations for Purple and White Flowers
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allele: a version of a gene
genotype: the exact genetic information carried by an individual phenotype: the physical expression of a gene or set of genes; the appearance of an organism
4. Suppose a plant has two alleles for purple flowers. What is the plant’s genotype for flower color? What is the genotype and phenotype for flower color if a plant has two alleles for white flowers?
Dominant and Recessive Alleles
You may have noticed an interesting phenomenon in the table about the flower alleles. Three different genotypes (PP, Pp, and pp) produced only two phenotypes (purple color or white color). This is because the allele for purple color, P, is dominant and the allele for white color, p, is recessive. Dominant alleles are expressed if they are present. Recessive alleles are expressed only when the dominant allele is absent. Therefore, PP and Pp genotypes have the same purple phenotype. Only the pp genotype has the white phenotype.
There are different ways to describe and predict the genetic makeup and appearance of offspring. One common method of describing how a trait is inherited across generations is a pedigree. In a pedigree, different generations are shown on separate lines (rows labeled I, II, and III), with males typically represented by squares and females by circles. Pedigrees show not only the gender of offspring throughout multiple generations but also the way a particular trait is inherited. Individuals who exhibit a particular trait are shaded, while those who do not exhibit that trait are left unfilled. In the example, the father in the first generation and his grandson in the third generation both exhibited a particular trait, while none of their other family members did. By examining the shaded and unshaded shapes in the pedigree, it is easy to trace from where a certain trait was inherited.
Another way to predict the probabilities of genetic outcomes is through a Punnett square. In a Punnett square, the genotypes of both parents are listed around the diagram. One parent’s genotype is listed in the top row with one allele per column, while the other parent’s genotype is listed in the far-left column with one allele per row. The remainder of the diagram is filled out by combining the parent alleles that are closest to that square.
For example, imagine you wanted to predict the fur color of the offspring of a black rabbit and a white rabbit. The alleles for fur color are R for black, which is dominant, and r for white, which is recessive. Suppose the female parent is a black rabbit with the genotype Rr and the male parent is a white rabbit with the genotype rr. In creating the Punnett square for this scenario, the female parent’s alleles would
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go along the top row, and the male parent’s alleles would go down the left column. Because there are two alleles for these genotypes, the Punnett square has four possible outcomes. In the top-left square, the dominant black allele R from the female parent would combine with the recessive white allele r from the male parent for an Rr genotype. Similarly, in the top-right square, the recessive white allele r from the female parent would combine with the recessive white allele r from the male parent for an rr genotype. This same pattern leads to the bottom two squares showing Rr and rr genotypes. Female parent (black rabbit)
= Black fur r =
Possible Offspring
The Punnett square for this rabbit fur-color scenario reveals that, of the four possible genotype outcomes, two have Rr genotypes and two have rr genotypes. This means there is a 50% (two out of four) chance that the offspring will have black fur (Rr genotype) and a 50% (two out of four) chance that the offspring will have white fur (rr genotype). Punnett square diagrams are very useful tools in predicting the probability of an offspring inheriting a certain trait.
It is important to note that just because the probability of an outcome is 50%, it does not mean that 50% of the actual offspring of a population will have that trait. The size of the population affects the proportions. For instance, in a large population of humans, about half of all babies born will be boys and half will be girls. However, in a small population, such as one particular family, a generation of offspring could be all boys or all girls.
dominant: the inherited characteristic that is always expressed when present
recessive: the inherited characteristic that is expressed only when no dominant allele is present
5. Could the shaded squares on the pedigree be dominant, or are they recessive? How do you know?
What Is Biotechnology?
Biotechnology is the use of living things as tools to create new products that are beneficial to individuals, society, and the environment. Genetic engineering, artificial selection, and cloning are types of biotechnology.
Genetic engineering is the term used when scientists take genes from organisms in which they naturally occur and insert them into organisms that do not normally contain those pieces of genetic information. In this form of biotechnology, the genetic makeup of an organism is changed to create a useful characteristic. The work being done with genetic engineering today is based on a discovery made in 1952 that showed DNA contains the genetic code that makes each organism unique. Experiments have been taking place since 1972, when the first successful combining of DNA from different organisms took place.
Artificial selection is the intentional reproduction of individuals in a population that exhibit the most desirable traits. Naturally, this process can take thousands of years. But using this type of biotechnology, the targeted traits are produced in just one generation. Continued reproduction from this generation allows a population with the new trait to grow quickly. Experimentation with artificial selection has been taking place since the 18th century and has evolved throughout history with improvements in technology. Today, scientists working on the International Space Station are using this form of biotechnology to investigate multigenerational plants.
In cloning, the DNA of one organism is used to create a duplicate of itself. The offspring that are produced have the same DNA as the parent. The process of cloning involves removing the DNA in the nucleus of a host cell and replacing it with the DNA of the organism that is being cloned. The host cell containing the new DNA will grow and divide, creating copies of the cells found in the parent. Cloning experiments have been taking place for over 50 years, with the most well-known breakthrough being the 1996 cloning of the first mammal, a sheep named Dolly.
biotechnology: the use of living systems and organisms to develop or create useful products or processes
genetic engineering: the direct manipulation of genetic material to alter the hereditary traits of a cell, organism, or population
artificial selection: the process by which humans breed other animals and plants for particular traits
cloning: producing a copy or imitation of an object or living thing
Example of Biotechnology
A good example of all three biotechnologies has to do with ordinary potatoes. Scientists use genetic engineering, artificial selection, and cloning to make them pest resistant, more nutritional, and even less greasy. The potato plant typically requires many pesticides to keep diseases and bugs from ruining the crop. Using genetic engineering, scientists have developed a way to insert a gene into the plant that creates a protein that is toxic to the Colorado potato beetle. The beetle dies from eating any part of the plants, which has greatly reduced the need for using pesticides and has increased potato plant productivity.
Scientists are also using artificial selection to create potato plants that produce a higher yield and are disease resistant. To do this, the scientists select only the plants with the most desirable traits to cross-pollinate. The resulting potato plants feature the best qualities of the parent plants. When these offspring are mature, they will be used to continue the improved potato plant population through further cross-pollination. In one species of potato plants created through artificial selection, the crop that is produced has a higher vitamin content than typical potatoes and does not absorb oil. As a result, potato chips made from these potatoes are healthier and more nutritious.
Once scientists have created what they believe to be the perfect potato, they can use cloning to continue to produce the new species. Cloning potato plants allows scientists to continue to produce a specific potato plant without the risk of accidental pollination with a different potato species. With the United States exporting over a billion dollars of potatoes each year, biotechnology is tremendously important to potato farmers in our country.
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Impacts of Biotechnology
Genetic engineering has been useful in crops, medicines, and conservation efforts. It has helped plants survive with less water and in extreme temperatures. The nutritional value of several types of plants has been improved with genetic engineering. Some plants, such as bananas, have even been engineered to contain medicines important to helping people. In addition to food modification, medicine can be mass produced for things like penicillin, cortisone, and human proteins. In fact, more than 125 approved drugs are being produced through genetic engineering. Using microorganisms, genetic engineering has improved how we handle water treatment as well as testing of soil, air, and water contamination. Because plants are being modified to be pest resistant, farmers need less pesticides. This keeps our water supplies freer of chemicals. Erosion is also reduced by eliminating weeds without needing to plow fields.
Artificial selection allows scientists to choose which individual organisms in a population should reproduce based on having the most beneficial traits. Most of the food we eat comes from species that have been produced in this way. Plants are chosen to increase nutritional value, amount of harvest, and resistance to pests. Fish that have more tolerance to cold and cows that can produce more milk are some other examples of animals being altered through artificial selection.
Cloning has been used to grow new organs for people who need transplants, to generate new skin for burn victims, and to create nerve cells for patients that have nerve disease. Cloning helps reduce the risk of rejection to outside transplants by using a patient’s own cells. Human cells have also been cloned for stem cell research, which has led to important changes in the way that doctors treat genetic diseases.
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While biotechnology has many benefits, some people are concerned with the widespread use of genetic engineering, artificial selection, and cloning. Studies show that plants that have been genetically engineered to contain better nutritional content are also removing nutrients from the soil. This leaves farmers with areas of land that are not usable. Using genetic engineering with animals that roam free, especially fish and insects, is hard to monitor. This could lead to more modifications that scientists did not expect.
The use of biotechnology by humans has led to ethical and religious debates. It is also worrisome to scientists who are concerned about problems that might arise from creating a larger population of humans who can live longer because of medical advancements.
6. Give one example of how each type of biotechnology impacts the biotechnologyenvironment.impacts
Advanced Topics
In reality, genetics is much more complicated than single gene traits and not all patterns follow the basic laws. In fact, many traits are much more complex and follow more than one gene. These are called polygenic traits. Many human traits are controlled by polygenic traits. Some examples include adult height, skin color, eye color, blood type, and hair color. Polygenic traits are also found in animals and plants.
Codominance is an interaction between alleles where both alleles are dominant and are expressed equally in the phenotype. This may result in a spotted appearance such as in speckled chickens.
Sex-linked inheritance occurs when a trait is related to or found on the sex chromosomes, X or Y, such as color blindness, hemophilia, night blindness, or high blood pressure.
Multiple alleles inheritance occurs when more than one version of a single gene exists. This is seen for humans who have blood type O and in the coats of rabbits.
Scientist in the Spotlight
Jaclyn Haven Lead Genetic Counselor at Shodair Children’s Hospital
Jaclyn Haven received her Master of Science degree in genetic counseling from the University of Colorado and earned undergraduate degrees in both human biology and psychology from the University of Montana. Jaclyn sees both adult and pediatric patients for a variety of genetic and metabolic conditions at Shodair’s outreach clinics statewide. Additionally, Jaclyn has a special interest in cancer genomics and sees patients at the Helena Cancer Genetics specialty clinic. She is currently enrolled in the renowned City of Hope Intensive Course in Cancer Genetics Risk Assessment. Jaclyn has been certified by the American Board of Genetic Counseling since 2014. She is a member of the National Society of Genetic Counselors.
Genetic counselors advise patients who have been diagnosed with hereditary diseases such as hemophilia.
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The Big Picture
It is important to remember the differences between traits, genes, and alleles. A trait is one particular characteristic, such as eye color. The gene is the segment of DNA that codes for that trait. Alleles are the different possibilities for the trait (brown, blue, green). Genotypes are the different possibilities for a trait and phenotype is the trait that is actually observed in the individual.
Humans have 46 chromosomes. This leads to many different possible combinations of chromosomes that each child can inherit. Recall that each parent contributes a set of chromosomes to a child. This is why children look similar but not identical to their parents. However, the set of chromosomes that a child inherits from each parent is random. This is why siblings, other than identical twins, look similar to one another but not identical. Identical twins actually do inherit the same sets of chromosomes.
Biotechnology is useful to humans, allowing the use of living things to create new products through genetic engineering, artificial selection, and cloning. There are benefits to individuals, society, and the environment, as well as concerns that are being raised about the use of biotechnology.
Connect It
How common are some physical traits in your family?
Select different physical traits—such as dimples, widow’s peak, earlobes detached, etc.—and survey your family to see who shares these characteristics. You can create a chart or a graph and try to figure out from which parent you inherited these characteristics.
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1 What do genetic instructions do?
Summarize It
A Determine your decisions on a healthy diet
B Create a code to decipher the amount of energy you will use while moving
C Control how traits are passed from one generation to the next
D Direct transportation of nutrients throughout your body
2 What are alleles?
A Variations of a gene
B A set of directions; and traits are like the results of following the directions.
C Genetic material inherited from the mother
D Instructions provided by deoxyribonucleic acid
3 _____________ alleles are expressed if they are present.
4 _____________ alleles are only expressed when the dominant allele is absent.
5 Eye color for fruit flies is represented with R for the dominant color red and r for the recessive color white. What are the combinations for genotype and how does that express itself as phenotype?
6 Which of the following is not a form of biotechnology humans are using today?
A Cloning
B Genetic engineering
C Natural selection
D Artificial selection
7 What determines your physical traits?
Reproduction
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Think about It
Plants, animals, and humans all grow. Looking at pictures taken when you were younger, it’s easy to see how much you have grown and matured over the years. You can measure your increasing height, and you can weigh yourself to see how your weight increases with your height. What biological process allows an organism to grow?
1. Do cells multiply when you grow or do they just get larger?
What Is Reproduction?
Reproduction is the process that allows a parent organism, or organisms, to produce new organisms known as offspring. Plants, animals, humans, microorganisms, and even individual cells can be considered “parents” in the reproductive process. Reproduction is a characteristic that helps define what is living and what is not. The process of reproduction ensures that the genetic information from a parent, or parents, is passed on. Reproduction is responsible for the continuation of the tremendous variety found on Earth.
reproduction: the process by which organisms produce more of their own kind
2. Is the ability to reproduce more important for the species or for the individual organism, and why?
Types of Reproduction in Organisms
There are two basic types of reproduction: asexual reproduction and sexual reproduction. One type of reproduction isn’t considered better than the other. They both have advantages and disadvantages to the individual and species.
Asexual reproduction is the process that involves just one parent. In this process, a large number of offspring can be produced in a very short amount of time. It also produces offspring that are genetically identical to the parent. In other words, asexual reproduction produces clones of the original parent. Asexual reproduction is the main form of reproduction for single-celled organisms like bacteria and archaea. Other asexually reproducing organisms that might be more familiar to you are sea stars and stick insects. Although many organisms reproduce asexually, most organisms reproduce sexually.
Sexual reproduction is the process involving two parents whose genetic material is combined to produce a new organism different from either parent. Sexual reproduction leads to a tremendous amount of genetic variation in offspring because the two parents are genetically diverse. This has the advantage of better survival of a species. The offspring is born with a mix of traits from both parents. However, it takes a longer amount of time for the offspring to be produced and usually results in a smaller number of offspring in comparison to asexual reproduction.
asexual reproduction: the reproductive process that involves one parent and produces offspring identical to the parent
sexual reproduction: the reproductive process involving two parents whose genetic material is combined to produce a new organism different from themselves
3. Why is reproductionasexual asexual necessary?
Asexual Reproduction
Let’s think about asexual reproduction as an analogy. Paige has several hobbies, but baking is by far her favorite thing to do in her free time. She is such a great baker that people have started asking her to make her special cupcakes for their parties. A few times, people have placed large orders, and Paige has had to double the recipe. To do this, she multiplies the measurement of each ingredient by two and puts that amount in the mixing bowl. The end result is twice as many cupcakes, all exactly the same as those that are made when she uses the original recipe.
Inside your body, your cells are undergoing the same kind of “recipe.” They are doubling all the time. Most of your cells use the process of mitosis to create more cells. Mitosis results in two identical daughter cells that have the same genetic material as the parent cell. This process allows for growth as well as repair of damaged tissues. Mitosis begins when a cell doubles its genetic material, or DNA, in the nucleus. The doubled chromosomes line up in the center of the cell; then, they separate and move to opposite sides of the cell. The cell splits in half, forming two new daughter cells. The daughter cells are identical to the parent cell. In this way, mitosis is similar to Paige’s cupcakes from the doubled recipe.
Since asexual reproduction produces a clone of the parent, very little genetic variation occurs in offspring. Offspring look like the parent because the gene pool (all the genes in a population) contains more copies of the same genes. For example, in skin cells undergoing mitosis, this is a good thing because each “offspring” cell is just a clone of the “parent” cell.
Genetic variety in a species can make some members better suited to tolerate changes in their environment. Because of the lack of genetic variation, it is more difficult for organisms that reproduce asexually to tolerate changes in their environment. Traits, or characteristics, that might help some individuals cope with environmental changes may not be present in offspring that are identical to the parent.
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There are other forms of asexual reproduction. Some of these include budding used by hydra and a few other organisms. In this process, the growth of an offspring occurs on the surface of the parent. Bacteria and some single-celled organisms use binary fission to reproduce. They double their genetic material and then simply divide in half. Fungi are among organisms that reproduce by producing spores. Some plants reproduce asexually by the process of vegetative propagation. Here, a new plant emerges from a part of the parent plant. It is important to remember that any “parent” organism or cell that reproduces asexually produces a copy of itself. This does not result in genetic variation.
mitosis: a type of asexual reproduction in which a cell splits, forming two identical daughter cells, which each have the same number of chromosomes as the parent cell
4. How is Paige doubling her cupcake recipe similar to the process of mitosis?
Sexual Reproduction
In organisms that use sexual reproduction to produce offspring, the process of meiosis occurs to allow for genetic variation in offspring. Meiosis occurs in cells that are destined to become gametes (eggs or sperm). During meiosis, each parent cell makes a copy of its chromosomes but donates only half to the offspring. This method is commonly seen in multicellular eukaryotes such as flowering plants, humans, and birds. The offspring resulting from sexual reproduction will not look exactly like either parent but will resemble both in different ways. We say that offspring created by sexual reproduction are genetically diverse.
When the process of meiosis occurs in a cell, four daughter cells are produced. The number of chromosomes in the four daughter cells is equal to half the number of chromosomes in the parent cell. Meiosis consists of two divisions known as Meiosis I and Meiosis II. Meiosis I results in the creation of two daughter cells with the same number of chromosomes as the parent cell. Meiosis II occurs when the daughter cells divide to create four cells with half the chromosomes (genetic material) as the parent cell.
Meiosis I
Meiosis II
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Because each parent donates half of the offspring’s genetic material in sexual reproduction, the result is a wide variation in the genes of the offspring. Although sexual reproduction provides this wide genetic variation, it is costly to the organism reproducing. Energy and time must be spent finding mates and nurturing the offspring during pregnancy and often after birth. Sexually reproducing plants must use energy to produce flowers, attract pollinators, and find ways to disperse seeds, among other things.
meiosis: a type of sexual reproduction in which a cell divides to form gametes (sex cells) with half the number of chromosomes as the parent cell
5. Based on this reading, what is one way that cells in the reproductive system are different from cells in other body systems?
The Purpose of Mitosis and Meiosis
Why do most cells reproduce with mitosis but some cells reproduce with meiosis? The reason behind this is the function of each type of cell that is being reproduced. Most of an organism’s cells are somatic cells, which reproduce by mitosis. These cells make up every part of the body except for the germ cells. Germ cells are responsible for producing the gametes (eggs or sperm) of an organism; they reproduce by meiosis.
The purpose of mitosis is to produce more cells that allow an organism to grow or repair itself. It is essential that the cells produced during mitosis are the same as the parent cell so that they can function independently. Meiosis has a much different purpose. The gametes that are produced during meiosis can combine with gametes from another organism to create varied offspring. Meiosis allows for genetic diversity because the offspring’s cells are a mix of gametes from two different parents. This is why you don’t look exactly like either of your parents. Remember that the four cells produced at the end of meiosis have only half the number of chromosomes as the parent cell. The combination of two gametes produced through meiosis yields a full set of chromosomes.
Scientist in the Spotlight
Dr. Sepideh Abbasi PhD, Institut de recherches cliniques de Montréal
Dr. Abbasi studied hair follicle and skin regeneration and the potential use of skin stem cells to generate new dermal tissue in order to benefit burn patients among others. Cells must use the asexual reproduction process of mitosis during skin regeneration.
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The Big Picture
Reproduction is the process that allows offspring to be produced. Plants, animals, humans, microorganisms, and even cells produce offspring. Asexual and sexual reproduction are the two types of reproduction. Asexual reproduction is used by most single-celled organisms and a few others such as sea stars and stick insects, but most organisms reproduce sexually
Most cells in your body use asexual reproduction to make copies of themselves so you can grow. The process is called mitosis. Mitosis is a type of asexual reproduction. During mitosis, a cell’s genetic material is doubled, and the cell divides into two identical daughter cells—clones of the parent cell. There are other forms of asexual reproduction. These forms include budding in hydra, binary fission in bacteria, and vegetative propagation in some plants.
Most organisms on Earth use sexual reproduction to produce offspring. Sexual reproduction requires that the cells destined to become gametes (eggs and sperm) undergo meiosis. During meiosis, the parent cell doubles its genetic material but donates only half to the offspring. The process results in the parent cell giving rise to four cells, each with half the chromosomes (genetic material) of the parent cell.
Connect It
How do organisms grow?
In order to grow, the organism must make more cells. Body cells (somatic cells) reproduce through the process of mitosis. So, your body cells use a form of asexual reproduction for you to grow. The same process, mitosis, allowed you to grow in the womb. To be clear, you were not produced by asexual reproduction, but you grow through the process of asexual reproduction known as mitosis.
Advanced Topics
Cells can divide in one of two ways: mitosis or meiosis. Meiosis is used only to produce the gametes needed for sexual reproduction. Meiosis has several different mechanisms that help ensure that offspring are genetically different from either of their parents. The first mechanism is known as independent assortment. When the cell’s chromosomes line up in the middle, the order in which they arrange themselves is random. This means that the mixture of genes in the resulting gametes is random as well. If things go normally, every gamete has one copy of each chromosome. We call this a haploid. A human gamete, for example, has only 23 chromosomes in it. Other species have different numbers of chromosomes in their gametes.
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Paternal Maternal
Crossing-over
Another mechanism that occurs during meiosis is crossing-over. In crossing-over, two chromosomes of the same type line up with their arms (called chromatids) touching. The chromosomes then swap arms. As a result, some of the genetic material from the first chromosome ends up on the second, and vice versa. For example, the first chromosome in the parent might carry a copy of the gene that codes for blonde hair, while the second chromosome carries a copy of the gene that codes for brown hair. But if crossing over occurs, the locations of those two copies are swapped! Now, the first chromosome has the copy that codes for brown hair, and the second chromosome has the copy that codes for blonde hair.
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Summarize It
1 Which statement is true about how the processes of mitosis and meiosis are similar?
A Genetic material is halved in both; both result in four daughter cells.
B Both are used for growth; both result in two daughter cells.
C In both, the genetic material is doubled; both involve cells dividing.
D Both involve two divisions; genetic material is tripled in both processes.
2 Sexual reproduction results in genetic diversity because–
A the genetic material is doubled in sexual reproduction.
B the process of meiosis results in two identical daughter cells.
C the offspring is genetically identical to the parent.
D each parent donates half of the offspring’s genetic material.
3 Somatic cells (body cells) reproduce by–
A mitosis.
B sexual reproduction
C meiosis.
D vegetative propagation.
4 Which of the following is produced by germ cells undergoing meiosis?
A Budding
B Gametes
C Binary fissure
D Asexual reproduction
5 Which phrase best describes offspring produced by sexual reproduction?
A Genetically identical
B Vegetative
C Genetically diverse
D Always mature at birth
6 Complete the chart below to show the similarities and differences between mitosis and meiosis.
Characteristic
Genetic material duplicated? (yes or no)
Number of cell divisions (1, 2, 3, or 4)
Number of daughter cells produced
Amount of genetic material in each daughter cell compared to parent cell (double, half, or same)
Purpose of the process (growth or genetic diversity)
Daughter cells identical to parent cell (yes or no)
Energy and Trophic Levels
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Think about It
Consider your favorite ecosystem. Try to envision all of the producers and consumers in it. Are there large animals? Small ones? Plants? Are they producers or consumers? Now, think about the numbers of producers and consumers. If you were an ecologist and could count them all, would you find fewer producers or consumers? Is that the case for all ecosystems?
1. Are there more consumers or producers in any given ecosystem?
Organizing Organisms in Ecosystems
There are several levels of organization in any ecosystem. Each organism in any ecosystem occupies a certain level. A trophic level is the position an organism occupies in a food web.
At the bottom of any ecosystem is the first and most basic trophic level, that of a producer. A producer is an organism that transforms energy from the Sun and uses carbon dioxide and water to make food. These are the plants in any ecosystem. Grasses, trees, and flowering shrubs are all producers.
Producers are eaten by primary consumers. A primary consumer is an organism that gets its energy by feeding on producers in the food chain. These are the herbivores in any ecosystem—the horses, insects, and small mammals.
Secondary consumers get their energy by eating primary consumers. Insect-eating birds, spiders, seals, and snakes are examples of secondary consumers. They are the middle level of consumers in a food chain.
Tertiary consumers are the predators or hunters in a food chain. They get their energy from eating secondary consumers. These animals are sharks, wolves, bears, and other large carnivorous animals.
2. Make a list of two producers, two primary consumers, two primarysecondaryconsumers, consumers, and two tertiary consumers in an ecosystem of your choice.
trophic level: the position an organism occupies on the food web
producer: an organism that transforms energy from the Sun and uses carbon dioxide and water to make food
primary consumer: an organism that gets its energy by feeding on producers in the food chain
secondary consumer: an animal that eats primary consumers (i.e., other animals that eat plants)
tertiary consumer: an organism that gets its energy by eating secondary consumers
Energy Flow through Organisms in Ecosystems
Energy is needed in an ecosystem to support the life functions of every organism, from producers to consumers. Energy is the ability of a system to do work and is required for changes to happen within a system. For example, energy is needed for growth, reproduction, migration, and more. Energy flows through a food chain. A food chain is a single, linear path showing the flow of energy from the Sun to a producer and through different levels of consumers. It is a basic representation of what organisms eat.
Look at the simple food chain below. Arrows in the chain between organisms help us understand how the energy flows from one organism to another. Since energy cannot be created or destroyed, the energy within an ecosystem is transferred from one organism to another as they are eaten. Energy only flows in one direction within a food chain.
For example, when the grasshopper (primary consumer) eats the flowers (producer), the energy within the flowers is transferred from that plant to the grasshopper. Then, it transfers to the bird, a secondary consumer, when the bird eats the grasshopper. Energy flows in the direction of the arrows in a food chain.
The same amount of energy is present at each level of the food chain, but the amount of available energy decreases at each trophic level. Some of the energy is given off as heat or other products, and only some is transferred to other organisms.
Energy always flows from the simpler organism, like the producer, to the more complex one, such as the consumer. Food chains can only support about four levels before the available energy is used up.
For tracing energy flow, a food web is more accurate than a food chain. A food web is a diagram of overlapping food chains with different pathways to show the flow of energy in an ecosystem. Food webs are more accurate than chains because they show how one organism can eat or be eaten by multiple organisms.
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As you look at this sample food web, remember that the arrows point in the direction of the energy flow, from the simpler organism to the more complex one. Note that the tertiary consumers are not necessarily placed at the top of the food web.
The plankton provide energy to both the penguin and the krill in this food web. The whale, seagull, and seal are at the top of this food web in the sense that they do not give energy to another organism in the web; they only receive it.
energy: the ability of a system to do work; required for changes to happen within a system
food chain: a single, linear path showing the flow of energy from the Sun to a producer and through different levels of consumers
food web: overlapping food chains with different pathways to show the flow of energy in an ecosystem
3. Create a food chainshowingdiagram how organisms in an ecosystem get energy.
What Is an Energy Pyramid?
An energy pyramid is useful to help us determine the distribution of the energy within a single ecosystem. It is a diagram that shows the total amount of energy contained within each trophic level and illustrates the decrease of biomass as you move up the pyramid.
Energy pyramids are arranged by trophic level and show us how energy flows up through each trophic level, with lower organisms providing energy to those organisms at higher levels. Producers are at the base of the pyramid, or at the lowest level. The next level is primary consumers, and all of the organisms that are primary consumers go on that level. The pyramid also shows secondary, tertiary, and finally quaternary consumers at the highest level.
energy pyramid: a diagram that shows the total amount of energy contained within each trophic level
4. What does an energy pyramid show that a food web or food chain does not? Give an example.
Availability of Energy in Successive Trophic Levels
So, what happens to the amount of available energy in successive trophic levels? It decreases because each organism uses most of the energy it receives when it breathes, digests food, grows, reproduces, and moves. Some energy is also released as heat during these processes, so it is not available to organisms at the trophic level above. Only 10% of the energy moves from one trophic level to the next.
The shape of the pyramid also indicates the amount of available energy at each level. Let’s look at an example.
In this aquatic energy pyramid, the seaweed is the producer, converting sunlight to food through photosynthesis. Energy is transferred to the parrotfish, which are the primary consumers when they consume the seaweed. Not all of the seaweed’s energy is available to the parrotfish—some has been used by the seaweed to grow, metabolize food, and perform other processes. At the primary consumer level, more energy is made unavailable as the fish use it for cell processes. When the shark consumes the parrotfish, the parrotfish’s energy is transferred to the shark. The shark must eat quite a few parrotfish in order to get enough energy to meet its needs. At this level, some more of the available energy is given off as the shark goes about its activities. When the killer whale consumes the shark, it has only a fraction of the energy that was originally available at the bottom of the pyramid.
What ecosystems have the most energy available to their top-level predators? The ones with the largest populations of producers and the most available energy at the producer level will have the most available energy.
5. Explain how the availabledecreasesenergy in successive trophic levels in pyramids.energy
Recycling of Matter and Nutrients
Organisms that are at the top of the energy pyramid are referred to as apex predators. They don’t always have a predator in the wild and are usually where the last bit of energy is used within the trophic levels. Once an organism dies, their bodies are broken down by decomposers, and the matter and nutrients in their bodies are returned to the soil. Decomposers are organisms such as mushrooms, bacteria, and worms that break down dead organic material and put the nutrients and matter back into the soil. Plants then take the recycled nutrients and matter from the soil and put it back into the biosphere to be passed from producers to consumers. The matter and nutrients are passed like energy through the trophic levels.
Look at the example of a food chain that shows the passing of nutrients and matter through the trophic levels below.
decomposers: organisms such as bacteria and fungi that break down the remains of dead plants and animals without need for internal digestion
biosphere: the sum of all living matter on Earth
6. Explain how nutrients and matter are passed from producer to consumer and how they are recycled in the biosphere.
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Advanced Topics
You’ve learned that organisms can be classified as producers, consumers, or decomposers. But organisms can also be classified using the taxonomic system. Aristotle attempted to do this by classifying organisms as either plants or animals. He classified organisms by characteristics such as whether or not they had blood, their parts, and where they could generally be found, such as in the air, in water, or on land. Later scientists came to question this system when they realized that organisms could fit into more than one category and that unrelated organisms were grouped together.
Almost 2,000 years later, Swedish botanist, zoologist, and doctor Carl Linnaeus designed a different system. His system began with two kingdoms: plants and animals. Within the kingdoms, he, like Aristotle, classified living things into two kingdoms—plants and animals. Within the kingdoms, he further classified organisms by their similarities. He distinguished animals by things like whether or not an animal was born alive or came from an egg, had lungs or gills, had warm or cold blood, and other characteristics. This system, which has led to modern taxonomy, is still used today. Taxonomy is the branch of science that formally names and classifies organisms by their structures, functions, and relationships. This means that organisms with similar structures, such as wings or legs, are grouped together and organisms that get their food in similar ways are also grouped together.
Today, all organisms are classified into one of three broad categories called domains. One of the main differences between these categories is the cellular structure of the organisms. There are two types of cells in organisms. Simpler organisms have cells that do not have nuclei or other small parts, called organelles. These are called prokaryotic cells. Very tiny organisms are prokaryotic, such as archaeans and bacteria. The other group of organisms, which are classified into a single domain, have eukaryotic cells. Eukaryotic cells are those with nuclei and membrane-bound organelles. If we were to review a tree map of the three domains, it might look like this:
Eukarya
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Kingdoms are subcategories of domains. Every organism is placed into one of the three domains based mostly on its cell type, and then it is placed into one of the kingdoms that belong to that domain. Domains Bacteria and Archaea have one kingdom each; domain Eukarya has four kingdoms.
Your caregivers might tell you that there were five kingdoms when they were in school. Bacteria and Archaea were classified together in a kingdom called Monera until the 1990s, when scientists decided to split them due to the differences in the organisms’ environments.
The Six Kingdoms
Organisms within the six kingdoms are grouped by similarities in three major ways: their number of cells, how they reproduce, and their mode of nutrition. First, let’s examine the differences between organisms with one cell and those with more than one. Simple organisms can have one cell, or they can have many. Unicellular organisms consist of only one cell. As for multicellular organisms, not only do they have more than one cell but the ones that they do have are differentiated, so these cells look different and are able to perform different functions. Multicellular organisms are larger and more complex. Organisms can also be grouped by how they reproduce. Those with a single parent are called asexual reproducers, and those with two parents reproduce sexually. The third feature that is used to classify organisms is how they obtain nutrients or eat. Some organisms can synthesize their own food, in most cases using energy from the Sun. These are autotrophs. On the other hand, organisms such as humans that cannot make their own food and must consume it are called heterotrophs.
There are four kingdoms in the Eukarya domain. Members of domain Eukarya have cells that contain membrane-enclosed nuclei, so they are eukaryotic. Most organisms in this domain are more complex and tend to be larger than those in the other domains (like Bacteria and Archaea).
Kingdom Protista consists of both single-celled and multicellular organisms that have eukaryotic cells. Organisms in kingdom Protista do not have much in common in terms of structure or function, but they are grouped together because they do not fit elsewhere. Protists live in a variety of environments, from ponds to the insides of other organisms. Some have cells with walls, like plants do, and others have cells that are more like animal cells. This kingdom contains both autotrophs and heterotrophs. Some examples are amoebae, giant kelp, and slime molds.
Kingdom Plantae contains the familiar organisms that we know as plants. They are autotrophic, making their own food, mostly through photosynthesis. They are eukaryotic, so their cells have nuclei and membrane-bound organelles. All plants are multicellular. Some examples are mosses, ferns, flowering plants, and conifers.
Kingdom Fungi includes yeasts, molds, and mushrooms. The main difference between fungi and plants is how they get their food. Fungi are heterotrophic, so they must consume other organisms for food. They reproduce through sexual spores and, like plants, have cell walls.
Finally, there is the animal kingdom—kingdom Animalia. These organisms consume nutrients. However, they differ from fungi because fungi absorb nutrients instead of “eating” other organisms. Animals are multicellular. One important function of this kingdom comes from the millipedes, beetles, and earthworms that help to decompose matter such as fallen plants and dead animals. These organisms play a large part in circulating energy through ecosystems.
Animalia Fungi
Plantae Protista Archaea Bacteria
Scientist in the Spotlight
Chelsea Bennice, PhD Florida Atlantic University
Dr. Chelsea Bennice is a marine biologist who has spent more than 1,000 hours underwater studying octopus behavior and how potential predators impact the behavior of these creatures.
Dr. Bennice studies octopuses because of their adaptations and abilities of camouflage, mimicry, and jets of water to escape from predators. She has also identified beneficial bacteria species living in the octopus’s skin that help improve their health.
She works at the Florida Atlantic University Brain Institute’s ASCEND program, where she helps address the shortage of students interested in science-related careers. She is also a research scientist and science writer for OctoNation, an organization involved in octopus community education.
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The Big Picture
A trophic level is the position an organism occupies in a food web. At the bottom of any ecosystem is the first and most basic trophic level, that of a producer. Producers are eaten by primary consumers. Secondary consumers get their energy by eating primary consumers. Tertiary consumers are the predators or hunters in a food chain.
Energy is needed in an ecosystem to support the life functions of every organism, from producers to consumers. The same amount of energy is present at each level of the food chain, but the amount of available energy decreases at each trophic level.
Connect It
Are there more producers or consumers in an ecosystem?
In a healthy ecosystem, there are more producers present to make enough energy available to organisms at higher levels. Since consumers at every level need a large amount of energy to sustain life, they must consume a large number of organisms at the trophic level below them. To support this, there must be many more producers than consumers.
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Summarize It
1 Which food chain correctly shows how energy flows through organisms?
A Oat grass ← Sun ← Human ← Cattle
B Human ← Oat grass ← Cattle ← Sun
C Sun ← Oat grass ← Cattle ← Human
D Sun → Oat grass → Cattle → Human
Use the food web diagram to answer questions 2–4.
2 Which organism has the most available energy in the ecosystem?
A Lion
B Grass
C Eagle
D Antelope
3 What do the arrows in a food chain or food web indicate?
A The direction of energy flow from least complex to most complex
B Which organism consumes which in the food web
C The order of available energy in the food web
D The order of energy flow from most complex to least complex
Lion
Gira e Rhino
Tree
GrasshopperMouse Antelope
Fox Bird
Snake Jaguar
Grass
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4 Fill in the table with the correct organisms from the food web. Role in ecosystem Organism example
Tertiary consumer
Secondary consumer
Primary consumer Producer
5 Describe how you would create an energy pyramid of organisms in a pond. Which organisms would go on each level? Which level has the most amount of energy available? The least?
6 Explain the role of decomposers in the biosphere of Earth.
Organism Relationships
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Think about It
Have you ever seen birds perched on another animal in a field? Animals perform actions if doing so provides a benefit of some sort to them. The birds on the back of this buffalo in North America must be getting some kind of benefit from staying close to the buffalo. Even though the buffalo has a long tail to use for shooing away annoyances, it chooses not to. Does the buffalo benefit from having the birds near it? If so, what could that benefit be?
1. Why do prairie birds follow buffalo throughout the day? And does the buffalo benefit?
Basic Needs and Limiting Factors
Every living thing, or organism, needs air, water, and food in order to live. Animals need shelter, and plants need light. These basic needs must be met in order for an organism to thrive.
The ecosystem in which an organism lives provides all of these things. An ecosystem is a system comprising all the biotic and abiotic factors in an area and all the interactions among them.
If we listed all of the things in an ecosystem, including the rocks, soil, air, and water, we would be able to separate them into two groups. Biotic factors are those elements that are living. This includes all of the plants, animals, fungi, and microorganisms. They cannot survive without abiotic factors like water, air, and soil. Abiotic factors are the nonliving things that affect the ecosystem. These factors can include such things as buildings, living spaces, nesting sites, and shelters for organisms.
organism: a self-contained living thing
ecosystem: a system comprising all the biotic and abiotic factors in an area and all the interactions among them
abiotic factor: a nonliving thing that affects the ecosystem
biotic factor: a living thing that affects the ecosystem
2. List the biotic and abiotic factors in a park ecosystem.
Can you identify the biotic and abiotic factors in this park ecosystem?
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Any group of organisms of the same species is called a population. A population is a group of interacting individuals of the same species located in the same area. Oak trees, people, dogs, boxwood shrubs, and grasses are all examples of populations. Each population has specific needs it must fulfill in order to thrive. For instance, the grass, the shrubs, and the trees all depend on sunlight. They also need enough water and the correct temperature and soil composition to live.
If all of these things are provided in sufficient amounts, the population will thrive. However, these abiotic resources are in demand by several individuals in several populations. Competition happens when more than one individual or population in an ecosystem relies on the same limited resources. For example, there is a certain amount of sunlight available that must be shared between the trees, shrubs, and grass. If the trees shade the shrubs and grasses too much and the grass cannot get enough sunlight, it will perish.
If far too many organisms depend on the same factors and the growth of the population is limited, the resource becomes a limiting factor. A limiting factor is a biotic or abiotic environmental factor, such as availability of water, space, or food, that restricts the growth of a population.
Light is an abiotic factor that plants and animals need. It can become a limiting factor if there is too much or too little available sunlight. The availability of shelter or nesting sites is also a factor that can limit the growth of a population. Habitat loss, disease, competition, or natural disasters can limit the amount of suitable shelter for plants or animals. Plants and animals depend on consistent temperatures in order to multiply. Sudden cold or warm spells that affect food supply or increasing temperatures that limit available oxygen in aquatic environments are examples of abiotic factors that can become limiting factors.
Biotic factors can turn into limiting factors as well. For example, when a population of consumers faces shortages of food or food sources, such as plants or seeds, it limits the growth of the population. If too many organisms are in a certain ecosystem and compete for resources, the competition can limit the growth of the populations.
Natural disasters such as wildfires, hurricanes, droughts, and floods can become limiting factors if they restrict populations of organisms from growing.
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What are other examples of limiting factors? We have listed several in the table below.
Factor Abiotic or Biotic?
Water Abiotic
Prey animals Biotic
Sunlight Abiotic
Space, shelter, nesting sites Abiotic
Mates Biotic
Soil Abiotic
Disease Abiotic
How This Could Become a Limiting Factor
Drought can cause a lack of water, which will limit the population growth of fish, plants, and microorganisms in a pond.
There must be enough prey animals to sustain a population of predators, such as hawks. If there are not enough, the hawk population is limited.
One plant shades another, and the second cannot get enough sunlight to grow and reproduce.
Urbanization (development of natural areas) can reduce the amount of space available to organisms. If a population cannot grow because of a lack of space, shelter, or nesting sites, it is a limiting factor.
If there are not enough mates for a population of an animal, the population cannot increase.
If soil becomes polluted, plants and animals cannot tolerate the conditions, and the population will be limited.
If a population encounters a disease, that population may decrease. The population of animals that eat the diseased population may also decrease.
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The same limiting factors can affect different populations of organisms. For example, lack of space in an urban ecosystem can affect populations of coyotes and hawks. If an arctic tundra experiences unusually cold temperatures one winter, it can affect reindeer and pine trees, as well as other populations in the area.
population: a group of interacting individuals of the same species located in the same area
competition: when more than one individual or population in an ecosystem relies on the same limited resources
limiting factor: biotic or abiotic environmental factor that restricts the growth of a population
3. Choose an ecosystem and describe a biotic and an abiotic factor that can cause competition.
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Organism Relationships
Organisms live together
Competition: No organism lives in isolation. Every living thing lives in dependence upon other elements in the environment, and this includes those that are biotic. However, resources are scarce and must be shared. This can create competition among organisms. We mentioned earlier that competition results when more than one organism relies on the same resource. Strangler figs compete with other trees in a rain forest for light and nutrients. Two wetland birds that eat the same food will compete for it. Male hummingbirds compete for territory and mates.
Predation: Another type of relationship is a hunting relationship, or predation. Predation is the interaction between two animals in which one animal eats the other. We see predatory relationships in sharks and fish, lions and zebras, snakes and mice, and shrews and worms.
predation: the interaction between two animals in which one animal eats the other
4. Describe the difference between competition and predation.
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Symbiosis: A symbiotic relationship, or symbiosis, occurs any time two different kinds of organisms interact and one or both receive a benefit. There are three types of symbiotic relationships. The following chart shows examples of these interactions, including which organisms benefit and which ones may suffer harm.
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Mutualism: A symbiotic relationship where both organisms enjoy a benefit is known as mutualism The prairie bird–buffalo relationship discussed at the beginning of this scope is an example of mutualism. The prairie birds get a benefit because they eat the insects they find in the buffalo’s fur. The buffalo benefits because the birds free its fur from parasites. Termites have mutualistic relationships with the bacteria in their intestines. The termite mechanically breaks down and chews wood in order to digest it, and the bacteria chemically break it down further into a form that the termite can use for nourishment. Both types of organisms benefit (rather than compete) in this kind of long-term relationship.
In another fascinating relationship, burrowing tarantulas have been observed living in close quarters with dotted humming frogs, which they are quite capable of eating. The frogs eat ants that prey on the spiders’ eggs. In turn, the spiders protect the frogs from predators and give the frogs access to the spiders’ meal remains. Both organisms benefit in this mutualistic relationship.
Sea anemones and clownfish are in a mutualistic relationship. The sea anemone provides shelter and protection to the clownfish, while the clownfish nourishes the anemone with its waste. Both organisms benefit from this relationship.
The sea anemone and clownfish have a mutualistic relationship where both organisms benefit.
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Commensalism: Another type of symbiotic relationship is commensalism. Commensalism is an interaction between organisms or species that is helpful to one but neither helpful nor harmful to the other. Barnacles attach to marine animals that provide transportation and food. The whale is not harmed by this attachment, but also does not receive a benefit from the presence of the barnacles.
Commensal relationships can be short-term or long-term, lasting for an organism’s lifetime. Shark and remora have a commensal relationship, as do bacteria that live on human skin. The bacteria benefit but humans are not affected. Orchids grow on trees and enjoy a commensal relationship—the orchid gets better access to water and sunlight, but the tree is not helped or harmed.
Whales and barnacles are in a commensal relationship. The barnacles attach to the whales and receive transportation and better access to food, and the whale does not benefit or suffer from the barnacles’ presence.
Parasitism: The third kind of symbiotic relationship is parasitism. In this kind of interaction, one kind of organism benefits at the expense of the other. One organism lives off another, and the host is harmed or killed in this relationship. For example, dogs are hosts for fleas, which harm the dogs. Leeches are organisms that harm hosts by attaching to them and nourishing themselves with the host’s blood. Hookworms and roundworms interfere with the digestive processes of their hosts in other examples of parasitic relationships.
In addition, parasites are often much smaller than their hosts. Lice, fleas, and worms usually interact with a host that is much bigger than they are.
symbiosis: a long-term relationship between two different kinds of organisms where one or both receive benefit
mutualism: a relationship between organisms or species that is helpful to both
commensalism: an interaction between organisms or species that is helpful to one but neither helpful nor harmful to the other
parasitism: a relationship between two organisms of different species where one organism benefits at the expense of the other
5. Give one example of a relationshipsymbiotic in which an organism is harmed.
Scientist in the Spotlight
Jeff Corwin Biologist and Conservationist
Jeff Corwin is a biologist, naturalist, and conservationist who works in the TV industry bringing awareness to issues involving a variety of animals. Although he has a special interest in rain forest ecosystems, he has advocated for endangered species in many different ecosystems. He is a lecturer on wildlife, ecology, and conservation and has opened an environmental education center called EcoZone in Massachusetts.
He also starred in a 2008 documentary about a fungus that kills certain species of frogs and salamanders by clogging up their pores, which they use for respiration. He has hosted many TV series on ABC, NBC, Disney, Discovery, and Animal Planet. His newest series, Wildlife Nation, focuses on efforts to save endangered species in North America. It came together in part because of the COVID-19 pandemic, which prevented international travel for Corwin and allowed him to focus on inspiring North American students to pursue careers in wildlife conservation.
Corwin has bachelor’s degrees in biology and anthropology and a master’s degree in wildlife and fisheries conservation. He also has an honorary doctorate degree in public education from Bridgewater State College.
Conservationist and TV personality Jeff Corwin has studied relationships between animals in many ecosystems and educates the public on threats to their survival.
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The Big Picture
Organisms and populations in an ecosystem depend on and may compete for biotic factors such as food and mates. They may also compete over abiotic factors such as quantity of light, water, range of temperatures, or soil composition.
Organisms interact with other organisms in a variety of ways in an ecosystem. The three main types of relationships are predatory, where one organism eats another, competitive, where two organisms or populations compete for resources, and symbiosis, a long-term relationship between two different kinds of organisms where one or both receive benefit. There are three kinds of symbiotic relationships: mutualism, where both organisms benefit; parasitism, where one benefits and the second suffers; and commensalism, where one organism benefits and the other is not affected.
Connect It
Do prairie birds and buffalo mutually benefit from their relationship?
Yes, they do. This interaction is an example of mutualism, where both animals benefit from the presence of the other. The prairie birds get access to an abundant supply of food in the form of insects that live in the buffalo’s fur. The buffalo benefits from having the prairie birds because they clean its fur of the pests. This is not the only mutualistic relationship in nature; there are many. Another one is the relationship between honeybees and flowering plants, where nectar for the bee is exchanged for pollination of the flowering plants.
STEMscopedia
Summarize It
1 Which of the following descriptions demonstrates two organisms competing for an abiotic factor in their environment?
A An arctic fox and a wolverine stalk a snowshoe hare.
B An antelope and a giraffe eat the same kinds of leaves and grasses.
C Two scorpions fight over a hole under a rock that they need for shelter.
D An oak tree and a maple tree grow best in locations that receive plenty of rain.
2 The female indigobird lays eggs into nests of other birds. Which of the following statements explains how this affects the birds of the other species?
A The parents of the other species compete with their young for food.
B The parents of the other bird species benefit from this commensal relationship.
C The young of the other bird species is in a predatory relationship with the indigobird young.
D The indigobird babies compete with the other birds’ young for biotic and abiotic resources.
3 All of the following are factors on which honey badgers depend. Which of the following choices is a biotic factor on which the honey badger depends?
A Honeybees that they might eat
B Unpolluted air to breathe
C Shelter from predators
D A temperature range of 30° to 90° Fahrenheit
4 The graph below shows the change in populations of two organisms in the same terrarium over time. Which type of relationship is represented in this ecosystem?
STEMscopedia
5 Read the descriptions in the chart below and fill in the type of relationship each represents.
Type of Relationship
Description
Lynx hunt and kill snowshoe hares.
Birds follow army ants to eat the insects that the ants scare away.
Ticks cover an African rhinoceros in a grassland ecosystem.
A trumpet honeysuckle plant is visited and pollinated by a hummingbird, who enjoys a meal of sweet nectar.
6 Describe two abiotic resources that plants in a temperate forest might compete over.
abiotic factor
GLOSSARY OF TERMS
abiotic factor: a nonliving thing that affects the ecosystem absorption: the transfer of energy into a medium allele: a version of a gene
aquifer: an area of permeable rock underground that holds or transmits groundwater; pumps are used to retrieve water from these areas
artificial selection: the process by which humans breed other animals and plants for particular traits
asexual reproduction: the reproductive process that involves one parent and produces offspring identical to the parent
carbon cycle
asthenosphere: the solid layer with plasticity in the upper mantle that is located just below the lithosphere; lithospheric plates “float” and move on this layer
atmosphere: the layer of gas surrounding a planet that is held in place by gravity
biosphere: the sum of all living matter on Earth
biotechnology: the use of living systems and organisms to develop or create useful products or processes
biotic factor: a living thing that affects the ecosystem carbon cycle: the continuous movement of carbon in and between the abiotic and biotic environments
GLOSSARY OF TERMS
carbon dioxide continental drift
carbon dioxide: a gas that is a natural component of the atmosphere; produced by cells during cellular respiration and used by plants and other organisms for photosynthesis
cementation: when compacted sediments stick together and turn into rock
chemical composition: the types, quantities, and arrangement of elements that make up a substance
chromosome: a single, highly organized and structured piece of DNA
climate: average weather patterns for a particular region
climate change: long-term change in the prevailing weather patterns
cloning: producing a copy or imitation of an object or living thing
commensalism: an interaction between organisms or species that is helpful to one but neither helpful nor harmful to the other
compaction: when rock particles or sediments are pressed together or packed down by gravity and the pressure of overlying rock layers
comparative anatomy: the study of the similarities and differences of body structures of different species
competition: when more than one individual or population in an ecosystem relies on the same limited resources
compression: a denser, tightly compressed region of a longitudinal wave
continental drift: the theory that continents were once connected but have drifted apart
GLOSSARY OF TERMS
convection: heat transfer caused by the rising of hotter, less dense fluids and the falling of cooler, denser fluids
convergent boundary: a place where two tectonic plates move toward each other and collide
crest: the highest part of a wave
crust: the thin, solid, outermost layer of Earth; is either continental (landmasses) or oceanic (ocean floors)
decomposers: organisms such as bacteria and fungi that break down the remains of dead plants and animals without need for internal digestion
deforestation: removal of a forest or section of trees for human use
density: the amount of matter in a given space or volume
desertification: the rapid depletion of plant life and the loss of topsoil caused by a combination of drought and the overexploitation of grasses and other vegetation by people
divergent boundary: a place where two tectonic plates move away from each other
DNA: a molecule containing information that forms the hereditary material of all cells
dominant: the inherited characteristic that is always expressed when present
earthquake: major geological event that occurs when plates shift suddenly and release stored energy; a frequent occurrence along all types of plate boundaries
GLOSSARY OF TERMS
Earth’s layers gene
Earth’s layers: the division of the composition of Earth determined by either chemical composition or the physical state of matter
ecosystem: a system comprising all the biotic and abiotic factors in an area and all the interactions among them
electromagnetic spectrum: a continuum of all electromagnetic waves arranged according to frequency and wavelength, from radio waves to gamma radiation
energy: the ability of a system to do work; required for changes to happen within a system
energy pyramid: a diagram that shows the total amount of energy contained within each trophic level
energy transfer: movement of energy from one system to another
energy transformation: the change of energy from one form to another
environment: all the living and nonliving factors in an area
evolve: to change the frequencies of alleles in a population over time
food chain: a single, linear path showing the flow of energy from the Sun to a producer and through different levels of consumers
food web: overlapping food chains with different pathways to show the flow of energy in an ecosystem
fossil evidence: any remains, impression, or trace of a living thing of a former geologic age
gene: the basic physical and functional unit of heredity made up of DNA
GLOSSARY OF TERMS
generation law of conservation of energy
generation: organisms of the same species that are at the same level of descent from a common ancestor; a parent is a member of one generation, and its offspring are members of the next generation
genetic engineering: the direct manipulation of genetic material to alter the hereditary traits of a cell, organism, or population
genotype: the exact genetic information carried by an individual
greenhouse gases: gases in the atmosphere that trap heat within the atmosphere groundwater: water that collects in cracks and pores in underground soil and rock layers
heredity: the transfer of genetic information from parent to offspring
hot spot: an extremely hot area of Earth’s mantle that causes the crust above it to melt and creates volcanoes away from plate boundaries human activity: things that humans do
igneous rock: rock formed when lava or magma cools, forms crystals, and solidifies
inner core: the sphere of solid nickel and iron at the center of Earth; surrounded by the liquid outer core
kinetic energy: energy of motion
lava: molten rock, or magma, that has reached Earth’s surface by volcanic action
law of conservation of energy: scientific law stating that energy can be neither created nor destroyed but just changes form
GLOSSARY OF TERMS
light mountain building
light: a form of energy that exhibits wavelike behavior as it travels through space; part of the electromagnetic spectrum
limiting factor: biotic or abiotic environmental factor that restricts the growth of a population
lithosphere: the cool, rigid, outermost layer of Earth that consists of the crust and the uppermost part of the mantle; broken into pieces or segments called plates
longitudinal wave: a wave that moves in the same direction as the displacement of the transmitting medium magma: melted, or molten, rock material beneath Earth’s surface; cools slowly to form rocks with larger crystals
mantle: the solid layer of Earth between the crust and the core; made of dense silicates
medium: the material through which a wave travels
meiosis: a type of sexual reproduction in which a cell divides to form gametes (sex cells) with half the number of chromosomes as the parent cell
melting: when a sample of matter changes from a solid to a liquid
metamorphic rock: rock formed deep underground due to heat and pressure
mitosis: a type of asexual reproduction in which a cell splits, forming two identical daughter cells, which each have the same number of chromosomes as the parent cell
mountain building: a major geological event that occurs when continental plates of equal density converge, resulting in mountain chains
GLOSSARY OF TERMS
mutualism predation
mutualism: a relationship between organisms or species that is helpful to both
natural selection: process by which organisms with favorable traits produce more successful offspring than organisms with less-favorable traits, causing the favorable traits to become more common in the population
ocean basin: a depression of Earth’s surface in which an ocean lies
offspring: product of reproduction; a new organism produced by one or more parents
organism: a self-contained living thing
outer core: the outer layer of Earth’s core; surrounds the inner core and is made up of liquid nickel and iron
parasitism: a relationship between organisms of different species where one organism benefits at the expense of the other
phenotype: the physical expression of a gene or set of genes; the appearance of an organism
plasticity: a characteristic of the material in the asthenosphere; existing in a solid state yet having the ability to flow
plate tectonics: the theory that the crust is divided into large pieces called tectonic plates that slowly move on top of the mantle pollution: the presence of harmful or unwanted levels of material in the environment population: a group of interacting individuals of the same species located in the same area
predation: the interaction between two animals in which one animal eats the other
GLOSSARY OF TERMS
pressure secondary consumer
pressure: force exerted on matter through contact with other matter; affects melting and boiling points
primary consumer: an organism that gets its energy by feeding on producers in the food chain
producer: an organism that transforms energy from the Sun and uses carbon dioxide and water to make food
radioactive dating: technique used to determine how old a rock is by analyzing the amounts of a radioactive isotope and its decay products in the rock
rarefaction: a less dense, more spread-out region of longitudinal waves
recessive: the inherited characteristic that is expressed only when no dominant allele is present
reflection: energy waves bouncing off the surface of an object
refraction: energy waves bending (changing direction and speed) as they pass from one type of object to another
reproduction: the process by which organisms produce more of their own kind
rock cycle: the cycle through which Earth’s rocks change from one type into another over time due to various Earth processes; creates changes in mineral compositions and physical structures
runoff: rainfall and surface water that drains or flows from the land into streams, rivers, lakes, or the ocean
secondary consumer: an animal that eats primary consumers (i.e., other animals that eat plants)
GLOSSARY OF TERMS
sediment symbiosis
sediment: Earth material that is broken down by processes of weathering; can be eroded and deposited by the agents of water, wind, ice, and gravity
sedimentary rock: rock formed when particles of other rocks are deposited in layers and cemented together
selective breeding: a form of artificial selection where humans deliberately breed plants and animals for desired traits
sexual reproduction: the reproductive process involving two parents whose genetic material is combined to produce a new organism different from themselves
species: a group of organisms with similar characteristics that are able to interbreed or exchange genetic material state of matter: distinct forms of matter known in everyday experience: solid, liquid, and gas; also referred to as phases
subduction: the process in which a denser plate is pushed downward beneath a less dense plate when plates converge
superposition: the law that says that younger rock layers sit on top of older rock layers
supervolcano: a volcano with an eruption rating of 8 on the VEI (Volcano Explosivity Index), meaning it has ejected more than 240 cubic miles of material at some point in its lifetime; all supervolcanoes have been dormant for thousands to millions of years
surface water: all the water above the surface of the ground; includes lakes, rivers, and streams
survival: the avoidance of death or extinction
symbiosis: a long-term relationship between two different kinds of organisms where one or both receive benefit
GLOSSARY OF TERMS
system visible light
system: a group of interacting, interrelated or interdependent elements forming a complex whole
tectonic plate: huge piece of crust that slowly moves on the upper, ductile part of the mantle
temperature: average kinetic energy of all the particles in a material; measured by a thermometer in degrees (usually degrees Celsius or degrees Fahrenheit)
tertiary consumer: an organism that gets its energy by eating secondary consumers
theory of evolution: an explanation for how living things change over time
trait: a characteristic of an organism; can be genetic or acquired
transform boundary: a place where two tectonic plates slide past each other
transmit: to pass something from one place to another transparent: allowing light to pass through so that objects can be distinctly seen
transverse wave: a wave that moves in a direction perpendicular to the displacement of the transmitting medium
trophic level: the position an organism occupies on the food web
trough: the lowest part of a wave
urbanization: the process by which cities grow and develop
variation: the occurrence of an organism, trait, or gene in more than one form
visible light: electromagnetic waves with wavelengths longer than ultraviolet waves but shorter than infrared waves and within the range that can be detected by the eye
GLOSSARY OF TERMS
volcanic eruption weathering
volcanic eruption: a geological event in which molten rock spews out from the mantle to the surface of Earth as ash, lava, and gases.
water table: the top of a saturation zone, below which water fills all open spaces within the rock
watershed: an area of land where the surface water and groundwater drain into a particular body of water; separated from other watersheds by drainage divides
weathering: the mechanical or chemical processes by which gravity, water, wind, and ice break rocks into smaller pieces
