Nutrition of the cell
By way of nutrition cells are autotrophic (making organic matter from inorganic substances) or heterotrophic (needing ready-made organic matter). The main autotrophs are green plants, which use chlorophyll to turn light energy into chemical energy: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in light, with chlorophyll). The light stage of photosynthesis takes place on the thylakoid membranes of the chloroplast: a photon excites chlorophyll, water undergoes photolysis releasing O₂ (the oxygen of photosynthesis comes from water), and ATP and the hydrogen carrier NADPH are formed. The dark stage (the Calvin cycle, in the chloroplast stroma) does not require light directly: CO₂ is reduced to glucose with the help of ATP and NADPH. Photosynthesis is the source of organic matter and oxygen and the main way of turning solar energy into chemical energy on Earth; plants also respire, but over the day they release much more oxygen than they use.
“Photosynthesis factory”. A factory model: “raw material” (CO₂, water), “energy” (light), “products” (glucose, O₂). Groups show the light and dark stages as “workshops” and explain where each raw material is used.