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8th Grade Living Environment Mr. Ardito's Classes Study Guide - Homeostasis Unit 1. Characteristics of Life 2. Homeostasis 3. Cells 4. Photosynthesis/Cellular Respiration 5. Diffusion 1. Characteristics of Life This is the set of processes that a living thing must do in order to be considered alive. M -- Metabolism -- The total of all chemical reactions within the organism R -- Regulation -- Being able to respond to changes in the internal and external environment. L -- Locomotion -- Moving from place to place in search of food, water, shelter, and mates. S -- Synthesis -- Building big things from small things. T -- Transport -- Moving materials within the organism R -- Respiration -- Burning food for energy N -- Nutrition -- Obtaining energy from the environment G -- Growth -- More cells and bigger cells E -- Excretion -- Removing waste R -- Reproduction - The organism makes copies of itself 2. Homeostasis This is the process by which living things maintain the optimal internal environment for themselves. One example we talked about in class was thermoregulation, which is managing body temperature. The chemical reactions within our bodies work best and at all only at certain temperatures. So, our bodies work to keep our core body temperature within certain levels. Feedback Mechanisms These are the processes that living things use to maintain homeostasis. We studied two types: Negative Feedback Loops Positive Feedback Loops Negative Feedback Loops This is a situation where one thing happening causes another thing to stop happening. Here is an example:

Ardito Homeostasis Study Guide


Positive Feedback Mechanisms This is a situation where one thing happening causes another thing to happen more. In class, we used the examples of arguing or putting a microphone to a speaker. One thing happening causes more of that thing to happen. 3. Cells Cells are the smallest living things. They have to perform all of the Characteristics of Life in order to function. The cell organelles are parts of the cell that carry out these life processes.

Ardito Homeostasis Study Guide


Cell Organelles Cell Wall - Surrounds the plant cell and provides structure to the cell Cell Membrane -- Found in both plant and animal cells. Determines what goes in and out of the cell. Nucleus -- Considered the control center of the cell. Houses the chromosomes and the nucleolus. Chromosomes -- Found in the cell nucleus. Contains the genetic information for the cell (the recipes it needs to do everything it needs to do to function). Nucleolus -- Found in the nucleus. Makes the ribosomes. Ribosomes -- Found in the cytoplasm. Makes proteins. Endoplasmic Reticulum -- Found in the cytoplasm, just outside the nucleus. Finishes up the proteins made by the ribosomes. Cytoplasm -- A jelly like fluid that contains all the other organelles. Mitochondria -- The powerhouse of the cell. This is where the cells burn glucose for fuel. The home of cellular respiration. Golgi apparatus -- The post office of the cells. It packages up materials made by the cell. Vacuoles - Storage containers within the cell. In plant cells, they are very big and help provide structure for the cell. Lysosomes -- Little vessels that break down waste produced by the cells. Chloroplasts -- Found in plant cells only. They are the place where photosynthesis takes place.

4. Photosynthesis/Cellular Respiration These are two of the most important chemical reactions performed by living things. If it were not for these two reactions, there would be no life on Earth. Photosynthesis This is performed by plants. Photosynthesis happens in the chloroplasts. In photosynthesis, plants convert some of the Sun's energy into a form that can be used by all living things. In photosynthesis, inorganic molecules (carbon dioxide and water) are converted into an Ardito Homeostasis Study Guide


organic molecule (glucose). The energy that is converted from sunlight is stored in the bonds connecting the carbons in glucose. Formula for Photosynthesis: Carbon Dioxide + Water ---SUNLIGHT-----> Glucose + Oxygen + Water CO2 + H20 ---SUNLIGHT-----> C6H12O6 + O2 + H2O Cellular Respiration This is performed by both plants and animals. Cellular Respiration happens in the mitochondria. In cellular respiration, cells combine glucose and oxygen to release energy. This energy is in the form of another molecule called ATP (which stands for adenosine triphosphate). ATP is the form of energy that cells use to perform all of their life functions. Formula for Cellular Respiration Glucose + Oxygen ------------> Carbon Dioxide + Water + ATP C6H12O6 + O2 ------------> CO2 + H20 + ATP 5. Diffusion Diffusion is the process where stuff moves from where there is more of it to where there is less, unless a balance (or equilibrium) is reached. Diffusion is the process by which substances move across the cell membrane. The cell membrane is called semi-permeable, because it lets some things through and keeps other things out.

Three types of Diffusion Osmosis - the diffusion of water across the cell membrane. This process uses NO ENERGY. Diffusion (passive transport) - the diffusion of substances other than water across the cell membrane. This process uses NO ENERGY. Active Transport -- This is the movement of substances across the cell membrane from where there's less to where there's more (the opposite of what normally happens in

Ardito Homeostasis Study Guide


diffusion). This process uses ENERGY. Active transport is how your nerve and muscle cells work.

Ardito Homeostasis Study Guide


Homestasis Study Guide  

Study guide for a unit on homeostasis for a middle school science class.

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