1. Sunlight 7

2. Objectives Compare and contrast how autotrophs and heterotrophs obtain food. Explain how cellular respiration harvests the energy in food.

3. Key Terms autotroph photosynthesis producer heterotroph consumer cellular respiration

4. All organisms need food for energy and building materials. Biologists classify organisms according to how they obtain food. Autotrophs An organism such as a plant that makes its own food is called an autotroph, which means "self-feeder". Starting with inorganic molecules, autotrophs make organic molecules.autotroph For example, plants use the sun's energy to convert water and carbon dioxide into sugars. This process is called photosynthesisphotosynthesis

5. Autotrophs are also called producers because they produce the organic molecules that serve as food for the organisms in their ecosystem. On land, plants are the major producers.producers

6. Heterotrophs Organisms that cannot make their own food, such as humans, are called heterotrophs, meaning "other eaters." Heterotrophs, also called consumers, must obtain food by eating producers or other consumers. Heterotrophs depend on producers to supply energy and materials for life and growth. Since most producers depend on sunlight as their energy source, you could say that life on Earth is solar-powered. heterotrophsconsumers

7. Many organisms, including both producers and consumers harvest the energy stored in foods through cellular respiration. Cellular respiration is a chemical process that uses oxygen to convert the chemical energy stored in organic molecules into another form of chemical energy—a molecule called adenosine triphosphate (ATP). Cells in plants and animals then use ATP as their main energy supply. Cellular respiration

8. The processes of photosynthesis and cellular respiration recycle a common set of chemicals: water, carbon dioxide, oxygen, and organic compounds such as glucose.

10. Water and carbon dioxide are the raw ingredients for photosynthesis. Plants use energy from sunlight to rearrange the atoms of water and carbon dioxide, producing glucose and oxygen. Oxygen is used by both plant and animal cells during cellular respiration to release the energy stored in glucose. The released energy enables cells to produce ATP. Cellular respiration also produces carbon dioxide and water. The result is a continual cycling of these chemical ingredients.