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Plants and other autotrophs are producers • Autotrophs (producers) produce organic molecules from CO2 and other inorganic raw materials obtained from the environment. • Can be categorized by source of energy that drives their metabolism. • Photoautotrophs use light. • Photosynthesis occurs in plants, algae & some other protists, and some prokaryotes. • Chemoautotrophs (occurs in some bacteria) get energy from oxidizing inorganic substances, including sulfur and ammonia. • Heterotrophs (consumers) live on organic compounds produced by other organisms. • Herbivores plants only • Carnivores animals only • Omnivores plants & animals • Detritivores feed on dead organisms and organic litter, like feces and fallen leaves • Decomposers break down dead organisms / absorb nutrients • Almost all heterotrophs are completely dependent on photoautotrophs for food and oxygen. Chloroplasts = sites of photosynthesis in plants • Any green part of a plant has chloroplasts. • Leaves = major site of photosynthesis for most plants. • About half a million chloroplasts per square mm of leaf. • Color of a leaf comes from chlorophyll, the green pigment in the chloroplasts. • Chlorophyll absorbs light energy (usually sunlight) during photosynthesis. O2 exits and CO2 enters the leaf through microscopic pores, stomata, in the leaf. • Veins (xylem) deliver water from the roots and carry off sugar from mesophyll cells to other plant areas (phloem). • A typical mesophyll cell (where photosynthesis takes place) has 30-40 chloroplasts. Each chloroplast has two membranes around a central watery space, the stroma. • In the stroma are membranous sacs, the thylakoids that may be stacked into columns called grana. Fig. 10.2 Photosynthesis Equation • Using glucose as our target product, the equation describing the net (overall) process of photosynthesis is: • 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings The light reactions and the Calvin cycle cooperate in converting light energy to chemical energy of food: an overview • Photosynthesis is two processes, each with multiple stages. • Light reactions: solar energy chemical energy. • Occur in thylakoids • Calvin cycle: incorporates CO2 from the atmosphere into an organic molecule; uses energy from the light reaction to reduce the new carbon piece to sugar. • Occurs in stroma