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Introduction Glossary
1. 2. 3. 4. 5.
Levels of organisation Cells: smallest units of life The microscope: viewing cells Alive, non-living or dead? Seven characteristics of living organisms Tissues, organs and organ systems
Introduction
1 Part of something bigger You are made up of all kinds of body parts. A Siberian tiger is also made up of all kinds of body parts. The same goes for an apple tree and a blue whale. Your body parts are part of a something bigger: You! You yourself are also a part of something bigger: you, the Siberian tiger, the apple tree and the blue whale are all part of a living system called the Earth.
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1.1 Levels of organisation Organism Organ
organism
organs tissues cells
Tissue Cell
Species Ecosystem
Planet Earth is rich with all kinds of living things. Any living thing is called an organism. You are an organism! Have you ever wondered what you are made of? You are made up of many different body parts and systems that are organized to work together. These parts are called organs. However, your organs are also made up of something: they are made up of tissues. Tissues in turn are made up of cells. Every part is organized into smaller and even smaller parts.
2. tissue level
1. cellular level
smooth muscle tissue
smooth muscle cell
3. organ level
Human beings are 1 life form out of an estim ated 100 million life forms on Earth!
muscle layers
5. organism level stomach
epithelial tissue
4. organ system level oesophagus liver gallbladder pancreas smal intestine large intestine digestive system
rectum
Fig. 1.1 Levels of organisation in the human body
species
Even though you are made up of many small parts, you are also a part of something bigger. You are a member of a group of organisms called human beings. Human beings are a species. Siberian tigers are also a species, as are apple trees and blue whales. Members of the same species can together produce fertile offspring.
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Table 1.1 shows how the different levels of life are organized. Level
Example
Cell organelle
Nucleus, chloroplast
Cell
Nerve cell, blood cell
Tissue
Muscle
Organ
Brain, heart
Organ system
Blood circulatory system
Organism
You and all other living things
Species/population
Human family, herd of deer
Ecosystem
Forest, ocean
Biosphere
Zone where life is possible
Planet
Earth
Table 1.1 Levels of organisation of life
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ecosystem
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All human beings in turn are part of something bigger still, we are part of an ecosystem that consists of human beings and other species all organised to live together. We share our planet with millions of other species.
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1.2 Cells: smallest units of life Cell membrane Nucleus Chloroplast
Cytoplasm Cell wall Cellulose
Organelle Mitochondrion Permanent vacuole
All living things are made up of cells. A cell is the very smallest living part of an organism. The smallest organism is made up of only one cell, see figure 1.2. It takes trillions of cells to make up a human body.
Scientists are not su re exactly how many cells are in the human body. Som e say the average adult hum an body is made up of “50 tr illion cells”, while others pu t the figure closer to 10 tr illion. The number will va ry from person to person, de pending on their size. The nu mber of cells in your own body is constantly changing , as cells die or are destroyed and new ones are formed.
Fig. 1.2 Paramecium is an organism that is made up of only one cell
Big Numbers
iljoen” in anslated as “b tr is n io ill tr 000. r mbe 1.000.000.000. y el The English nu m na r, be m ry large nu about 31.000 Dutch. It is a ve seconds takes on li il tr a , n For compariso years! owever, word billion. H e th as h so al uage which means The English lang rd” in Dutch, ja il “m as ed at lion (1000 billion is transl ords 1000 mil w r he ot in or 1.000.000.000 miljoen).
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Robert Hooke For centuries, scientists did not know that the human body is made up of trillions of cells. Before the invention of the microscope, nobody even knew cells existed! In 1665, an English scientist named Robert Hooke built a simple microscope and looked at a piece of cork, the dead cells of oak bark. What he saw were small, box-shaped structures. He called them cellulae (the Latin word meaning small rooms) because the boxlike cells of cork reminded him of the cells in which monks live at a monastery. It is from Hooke’s discovery that we have the word cell.
Your red blood cells are the only cells in your bo dy that do not have a nucleu s.
Fig. 1.3 Robert Hooke’s microscope
A basic cell Each of your organs consists of specific types of cells. You have blood cells, bone cells, skin cells, muscle cells and so on. This means that there must be many different types of cells in your body. However, all cells have two things in common. First, they all have a cell membrane. This is a soft outer covering that controls what goes into and out of the cell. Second, they all have cytoplasm, which is a gel-like liquid inside every cell. Here, all kinds of chemical reactions take place. The cytoplasm of most, but not all, cells contains a nucleus, which controls what the cell does. The nucleus contains hereditary material in the form of DNA.
cell membrane cytoplasm nucleus hereditary
Different cell types in different types of organisms When biologists study cells, they like to put them into different groups, depending on the type of organism the cells belong to. The cells of plants and animals are different. The same goes for bacteria and fungi. Besides a cell membrane, cytoplasm and often a nucleus, cells sometimes have a cell wall. This is a second outer covering that is made of hard, tough material called cellulose. Some cells also have cell organelles. These are little cell organs that do different jobs for the cell. A chloroplast is a cell organelle that makes food inside a plant cell. A mitochondrion (plural: mitochondria) is a cell organelle that turns food into energy. A plant cell has a permanent vacuole in which it stores food, waste products and water. Table 1.2 shows the differences between a bacterial cell, a fungus cell, a plant cell and an animal cell.
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cell wall cellulose organelles chloroplast mitochondrion permanent vacuole
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Bacterial cell Cell wall Cell membrane Cytoplasm -
Fungus cell Cell wall Cell membrane Cytoplasm Nucleus -
Animal cell Cell membrane Cytoplasm Nucleus Mitochondria -
Plant cell Cell wall Cell membrane Cytoplasm Nucleus Chloroplasts Mitochondria Permanent vacuole
The biggest (longe st) cells in the human body ar e nerve cells. They can grow up to one metre long! How ever, they are also very th in!
Table 1.2 Differences between cells of different organisms
Different types of cells within one organism Cells come in many shapes and many sizes. A human egg cell is about the size of the dot at the end of this sentence. This is actually still pretty big when you’re a cell! A red blood cell is ten times smaller than that. The
Fig. 1.4 Human egg cell
shape of a cell depends upon the job it has to do. A nerve cell is long and thin and it has many extensions with which it reaches out to other nerve cells to transmit messages. A red blood cell has a small and round disc-like shape that fits inside even the smallest blood vessels.
Fig. 1.5 Red blood cells
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Fig. 1.6 Nerve cells
Fig. 1.7 Smooth muscle cells
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A white blood cell and a muscle cell can change shape. A muscle cell, for instance, can get shorter when the whole muscle contracts and longer when the muscle relaxes again. Some plant cells on the other hand, have shapes like hollow tubes to transport water and food to different parts of the plant.
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1.3 The microscope: viewing cells Ocular Objective Eyepiece Body tube Revolving nosepiece
Arm Base Inclination joint Coarse focus adjustment Fine focus adjustment Slide
Cover slip Stage Stage clips Mirror Light source Diaphragm
When Robert Hooke first built his microscope, he could only see very few details of the cells he was studying. Nowadays, our microscopes are much more powerful, making even the smallest cell organelles clearly visible.
Parts of the microscope ocular objective
eyepiece body tube
arm base revolving nosepiece coarse focus adjustment fine focus adjustment slide stage stage clips mirror light source diaphragm
A microscope consists of several glass lenses and uses light to produce a magnified image. The lens that is closest to your eye when you look through a microscope is called the ocular. The lens that is closest to the object you want to magnify is called the objective. Each lens magnifies the image of the previous lens. For instance, when the ocular magnifies 4 times and the objective magnifies 10 times, the total magnification would be 40 times (40x). The ocular in located inside the eyepiece, which in turn fits inside the body tube. Below the body tube you find the revolving nosepiece, which holds several objectives that differ in their magnification power. On the microscope’s arm, which attaches the eyepiece and body tube to the base, there are usually two knobs. These knobs help you adjust the focus of the image: the coarse focus adjustment knob makes large adjustments to the focus; the fine focus adjustment knob makes small adjustments to the focus. The object, or slide, you want to magnify is placed on the stage and is held in place by a pair of stage clips. Below the stage there is a mirror or a small light source (a lamp) to illuminate the slide. The amount of light illuminating the slide can be adjusted using the diaphragm. Figure 1.8 on the next page shows a typical school microscope with its various parts labelled.
In the word “micro scope” you recognize the w ords “micro” meaning sm all and “scope” meaning to view. A microscope helps yo u view small things. A tele scope helps you view thin gs that are far away, such as ga laxies and stars. You gues sed it: “tele” means far aw ay! 16
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eyepiece, contains the ocular lens
revolving nosepiece
objective lenses
arm
stage clips
coarse adjustment knob
stage
diaphragm fine adjustment knob light source
base Fig. 1.8 Parts of a microscope
Electron Microscope Things that are too small to be seen with regular microscopes can be made visible with an electron microscope. Instead of using lenses to direct beams of light, an electron microscope uses a magnetic field in a vacuum to direct beams of electrical particles. Some electron microscopes can magnify images up to one million times.
Fig. 1.9 An image of an ant’s head, magnified 40.000x, from a scanning electron microscope
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How do you use a microscope? Preparing the slide cover slip
The object you want to magnify is prepared by placing it in a drop of water on a slide. The wet object is then covered by a cover slip, which is a very thin, square piece of glass. The slide is then placed on the stage and held in place with the stage clips. Be careful to hold the slide and the cover slip by the edges to prevent smudges from your fingerprints!
Looking at the object through the microscope When you first start focusing the image, you always use the low power objective lens and adjust the focus using the coarse focus adjustment knob. When the image is focused, you then change to a higher power objective by turning the revolver. If you need to focus the image again, you may only use the fine focus adjustment knob. If you still use the coarse focus adjustment at this point, you might very well push the objective lens right through the slide! Always let your teacher or your teacher’s assistant check you for the correct use of the microscope.
Making a biological drawing biological drawing
When you observe an object such as a group of plant cells, you may want to keep a record of the things you saw. In order to do this, biologists usually make a special kind of drawing of the object, called a biological drawing. In a biological drawing you leave out the small details so that only the important parts remain. In the box below you see which rules you have to follow to make a biological drawing.
Rules for making a biological drawing Use a drawing pencil, not a pen. Make large drawings, using the entire surface of your paper. Draw straight lines and smooth curves: no sketching. Draw only what you see, not what the book says you should see. Write down the name of the object and the magnification at the top of your paper. • Label the parts, using lines drawn with a ruler, on the right-hand side of your drawing. • • • • •
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1.4 Alive, non-living or dead? Seven characteristics of living organisms
Dead
Non-living
Alive
You probably never wonder if something is alive or dead: you just know. However, do you know the difference between “dead” and “non-living”? They seem to mean the same thing, but this is not so! • We say that something is dead when it was once alive. • We call something non-living when it has never been alive. • When biologists say that something is alive, they mean that it has certain characteristics, see table 1.3. A living thing, or organism, has all of these 7 characteristics.
Characteristic of Life
Example
Description
Movement
Going from one place to another, opposite of standing still. Some types of movement, like a cheetah running, are very obvious. Other types of movement, like plants growing towards the light, are very subtle.
Feeding
Taking in food and fluids. Animals must take in food and fluids. They get their food from other organisms. You can go for a week without food. However, you can go without water from only a few days. Plants make their own food during the day, which they can use during the night.
Respiration
Getting energy out of food. All living things need energy to survive. Their cells turn food into energy. Living things need energy to move, feed, sense, excrete, reproduce, grow and yes… even some of it to respire!
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dead non-living alive
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Excretion
Removing waste. When cells make energy, they also make waste, just like a factory does. When a dog pees, he removes waste by way of his urine.
Sensitivity
Reacting to changes in the environment. These changes are called stimuli. The reaction is called a response. The leafs of Mimosa pudica quickly fold into a closed position when you touch them. Your touch is the stimulus, the leafs folding is the response.
Reproduction
Making new living things. Living things reproduce and pass along characteristics from one generation to the next. Pandas can only continue to exist as long as they reproduce.
Growth
Getting bigger. The result of growth is getting more mass, usually it means getting more cells. Most organisms stop growing after a while. Others keep on growing for a very long time. The tallest tree in the world is the giant sequoia tree.
Table 1.3 The 7 characteristics of life
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1.5 Tissues, organs and organ systems Epithelial tissue Muscle tissue
Connective tissue Nerve tissue
Organ Organ system
In paragraph 1.1 you learned that you are made up of many different parts that are organised to work together. These parts are called cells, tissues and organs. You have already seen a few types of cells under a microscope and you have learned what cells are made of. In this paragraph you will learn about the organisation of cells into tissues, organs and organ systems.
Grouping similar cells together to build tissues A tissue is a group of similar cells that perform a common, or related, task. There are four basic types of tissues: epithelial tissue, muscle tissue, connective tissue and nerve tissue. Epithelial tissue consists of cells that work together to provide a covering, such as skin or the surfaces of parts inside your body. Muscle tissue is made up of muscle cells that contract. All of these tiny contractions performed by all muscle cells together at the same time make your whole muscle contract. Muscle tissue is not only found in your muscles, but also on the outside of your stomach and intestinal tract and in your heart. Connective tissue supports other tissues and binds them together. It can be found in your bones and in your blood. Finally, nerve tissue is made from nerve cells that work together to send and receive messages to and from other body parts. Your brain, spinal cord and nerves are composed of this. In figure 10 you see examples of these four basic tissue types.
epithelial tissue
muscle tissue
connective tissue Fig. 1.10 The four basic tissue types
nerve tissue
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epithelial tissue muscle tissue connective tissue nerve tissue
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Grouping tissues to build organs An organ is a grouping of two or more tissue types into a recognizable structure that has a specific job. Your stomach is an organ. It is made of different types of tissues that work together to digest part of your food. Your heart is another organ. In your heart, different tissues work together to pump blood around your body. Your kidneys, intestines, lungs and brain are also organs.
After a kidney tran splant, most patients have three kidneys because thei r own kidneys are usually left in place!
Organ transplants When an organ stops working, it can sometimes be replaced by an organ from another person (a donor). So far, organs and other body parts that have been successfully transplanted include the heart, kidneys, lungs, skin, eye lenses and even human hair for cosmetic purposes. The body usually rejects organs that do not belong to it. Because of this, patients with donor organs have to use special medicines for the rest of their lives to prevent rejection.
Fig. 1.11
In figure 1.12 you see a model of a human torso and the location of several major organs. front heart lungs liver stomach small intestine large intestine
Sometimes an orga n is part of more than one or gan system. The pancre as is both part of the endocrin e system and the digestive sy stem!
bladder back heart lungs liver pancreas gallbladder kidneys
Fig 1.12 Model of a human torso with major organs
bladder
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An organ system is a group of related organs that work together to perform a common job. Your stomach digests only part of your food. Other organs have to take care of the rest of the digestion process. Your digestive system consists of your oesophagus, stomach, intestines, pancreas and various other organs. Your circulatory system consists of your heart and your blood vessels. There are a total of eleven organ systems at work inside your body: 1. The integumentary system includes your hair, nails and your skin and its parts. It protects your body from injury, infection and dehydration. It also provides for the removal of dead cells and sweat, which contains waste products. With it, your brain can find out what’s going on in the outside world, for instance whether it is cold or warm. 2. The nervous system includes your brain, spinal cord and nerves. It picks up signals from inside and outside your body. Its organs work together to send and receive messages to and from other body parts and to and from your brain. This way, your brain always knows what is going on inside and outside your body and it can react by controlling and coordinating your body’s many activities. 3. The muscular system includes all of the different muscles inside your body which have to work together to make different movements possible.
digestive system circulatory system
integumentary system
nervous system
muscular system
Hair, fingernails an d toenails are actually accum ulations of dead epidermal cells. As more cells die and ne ed to be removed, the hair an d nails grow.
integumentary system
nervous system
muscular system
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Grouping related organs together to build organ systems
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skeletal system
respiratory system digestive system
4. The skeletal system consists of your skull and bones. Together, they support and protect your organs. Muscles are attached to them in order to make movement possible. Some of your bones also make red blood cells. 5. The respiratory system is formed by your lungs and your windpipe. It helps to give oxygen to your cells and to remove carbon dioxide waste. 6. The digestive system includes your oesophagus, stomach, intestines, pancreas and various other organs that work together to break down and absorb food and to get rid of waste.
skeletal system
urinary system
circulatory system
lymphatic system
respiratory system
digestive system
7. The urinary system includes the kidneys, urethers, bladder and urethra. Its job is to control the fluids inside your body. It filters your blood and gets rid of waste. 8. The circulatory system consists of your heart and blood vessels. Besides pumping blood around your body and keeping you warm, it also transports the things your cells need, such as oxygen and food. When cells need to get rid of waste, this system helps transport the waste for removal. 9. The lymphatic system consists of vessels and organs that help filter blood and protect you from disease.
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urinary system
circulatory system
lymphatic system
10. The endocrine system’s job is to produce hormones, which it makes in many different types of glands. One such gland is the pancreas. 11. The reproductive system is different in females and in males. It consists of organs that produce egg cells and sperm cells. In females, and organ called the uterus gives the developing baby a safe, healthy place to live and grow for nine months.
endocrine system
reproductive system
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endocrine system reproductive system