1. The Necessities of Life Water : your body is approximately 70% water. Most chemical reactions involved in metabolism require water. However, organisms differ greatly in terms of how much water they need and how they get it. A human will survive for about three days without water. Test question: Why do cells require water?

2. The Necessities of Life Air is a mixture of several gases, including oxygen, nitrogen, and carbon dioxide. Most living things use oxygen in the chemical process that releases energy from food. Oxygen may come from the air or may be dissolved in water. Some insects like this spider have unique methods of getting oxygen. Since the spider must breathe air, it traps a thin layer of air around its body using the hairs on its abdomen and legs. It also maintains an air reserve in a "diving bell" constructed from silk, which it anchors to an underwater plant.

3. The Necessities of Life Green plants, algae, and some bacteria need carbon dioxide as well as oxygen. During photosynthesis oxygen and carbon dioxide are used to produce food and oxygen.

4. The Necessities of Life Organisms that can live without oxygen are anaerobic. Botulinus toxin is produced by the anerobic bacillus Clostridium botulinum, which may be found in improperly canned food, and is one of the most potent toxins known. This toxin (the agent responsible for botulism) blocks the release of vesicles. This, of course, leads to muscle paralysis and, if the diaphragm becomes affected, can be fatal.

5. Food All living things need food. The energy from food is used to make cells and build body parts. Making food: Some organisms, like plants are producers Producers: make their own food through photosynthesis. These plants use the energy from the sun to make food. Taking Food: Consumers must eat other organisms, such as plants or animals, to get food.

6. Sunlight is the source of energy for almost all living things Producer: plants use the energy from the sun to make food. Consumer: prairie dogs eat seeds and grass Coyotes and hawks eat prairie dogs Turkey vultures eat what is left by the predators Decomposers eat the waste of consumers.

7. Breaking Down Nutrients All living things need to break down food in order to use the nutrients contained in the food. Nutrients are made of molecules. Molecule: is a substance made when two or more atoms join together. Compounds: molecules made of different kinds of atoms. Molecules found in living things are most often combinations of six elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. These elements join together to form proteins, carbohydrates, lipids, ATP, and nucleic acids. Water Molecules Polymer Compound

8. Proteins Proteins are large molecules that are made up of smaller molecules called amino acids. Living things break down proteins in food to supply their cells with amino acids. The amino acids then combine to form new proteins. Some proteins have more than 10,000 amino acids, some have only a few.

9. In the above comparison of proteins from apples (left) and celery (right) to that from birch pollen, red areas show where surface structure has been conserved across the proteins. Given these two proteins' relative structural similarity to that of birch pollen, people allergic to birch pollen are more likely to also be allergic to apples than to celery. Proteins

10. Test Question: What function do enzymes in cells serve? Proteins have many functions. Some form structures. Spider webs, hair, and feathers are all made from proteins. Other proteins help cells do their job.

11. Proteins Inside red blood cells, the hemoglobin binds oxygen and delivers it throughout the body. Some proteins protect cells. Other proteins, called enzymes, start or speed up chemical reactions in cells.

12. Carbohydrates Carbohydrates: molecules made of sugars. There are two types of carbohydrates: 1.Simple carbohydrates: made up of on e sugar molecule or a few sugar molecules. 2.Complex carbohydrates: are made op of hundreds of sugar molecules linked together. Plants, such as the potato plant store extra sugar as starch. When potato's are consumed your body breaks down this complex carbohydrate to free the energy stored in the food. Complex Carbohydrates

13. Lipids Lipids are molecules that cannot mix with water. Some lipids store energy, while others from the membranes of cells. Phospholipids: are molecules that form much of the cell membrane. The head of the phospholipids molecule is attracted to water. The tail is not.

14. Phospholipids: are molecules that form much of the cell membrane. The head of the phospholipids molecule is attracted to water. The tail is not. Lipids

15. Fats and Oils Fats and oils are lipids that store energy. When an organism has used up most of its carbohydrates, it can get energy from these lipids. At room temperature, most fats are solids, and most oils are liquid. Most lipids stored in plants are oils. Most of the stored lipids in animals are fats.

16. Adenosine Triphosphate This molecule is also known as ATP, and is the major energy carrying molecule of cells. Te energy in carbohydrates and lipids is transferred to APT to provide fuel for cellular activities.

17. Nucleic Acids Nucleic acids serve mostly to store and transmit genetic information. They are found in all living cells and viruses. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). A DNA molecule is like a cookbook called, “How to Make Proteins.” When a cell needs to make a certain protein, the cell gets directions from the sequence of the nucleotides in DNA. The sequence of nucleotides tells the cell the order in which the amino acids must be linked together to make the protein.