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Chapter 10 Photosynthesis Lecture Outline Overview: The Process That Feeds the Biosphere Life on Earth is solar powered. The chloroplasts of plants use a process called photosynthesis to capture light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules. Photosynthesis nourishes almost all the living world directly or indirectly. All organisms use organic compounds for energy and for carbon skeletons. Organisms obtain organic compounds by one of two major modes: autotrophic nutrition or heterotrophic nutrition. Autotrophs produce organic molecules from CO2 and other inorganic raw materials obtained from the environment. Autotrophs are the ultimate sources of organic compounds for all heterotrophic organisms. Autotrophs are the producers of the biosphere. Almost all plants are autotrophs; the only nutrients they require are water and minerals from the soil and carbon dioxide from the air. Plants are photoautotrophs, using light as a source of energy to synthesize organic compounds. Photosynthesis also occurs in algae, some other protists, and some prokaryotes. Heterotrophs live on organic compounds produced by other organisms. Heterotrophs are the consumers of the biosphere. The most obvious type of heterotrophs feeds on other organisms. Animals feed this way. Other heterotrophs decompose and feed on dead organisms or on organic litter, like feces and fallen leaves. These are decomposers. Most fungi and many prokaryotes get their nourishment this way. Almost all heterotrophs are completely dependent on photoautotrophs for food and for oxygen, a by-product of photosynthesis. Concept 10.1 Photosynthesis converts light energy to the chemical energy of food. Photosynthetic enzymes and other molecules of photoautotrophs are grouped together in a biological membrane, allowing the necessary series of chemical reactions to be carried out efficiently. The process of photosynthesis likely originated in a group of bacteria with i