Ch. 10: Photosynthesis (Ps)
• Ps is the process that converts solar energy into chemical energy
– Directly or indirectly, Ps nourishes almost the entire living world – Ps occurs in plants, algae, certain other protists, and some prokaryotes

• Autotrophs sustain themselves without eating anything derived from other organisms
– Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules – Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules

• Heterotrophs obtain their organic material from other organisms
– Heterotrophs are the consumers of the biosphere – Almost all heterotrophs, including humans, depend on photoautotrophs for food (organic molecules) and O2
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Concept 10.1: Photosynthesis converts light energy to the chemical energy of food
Ps stores energy in complex organic molecules, whereas cellular respiration releases it. • Chloroplasts are structurally similar to and likely evolved from photosynthetic bacteria
– Their structural organization allows for the chemical reactions of Ps

• Leaves are the major locations of Ps
– Their green color is from chlorophyll, the green pigment within chloroplasts

• Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf
– Each mesophyll cell contains 30–40 chloroplasts (see next slide’s figure)

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• CO2 enters and O2 exits the leaf through microscopic pores called stomata • Chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana • Chloroplasts also contain stroma, a dense interior fluid
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Tracking Atoms Through Photosynthesis
• Ps is a complex series of reactions that can be summarized as the following