Biology
Photosynthesis
Photosynthesis converts light energy into chemical energy stored in glucose. The overall reaction: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. It happens in two stages: the light reactions (in the thylakoid membrane) and the Calvin cycle (in the stroma).
How to Approach Photosynthesis
Light reactions
Photosystems II and I absorb photons, splitting water and pumping H⁺ ions. The electron transport chain produces ATP and NADPH. Oxygen is released as a byproduct.
Calvin cycle (carbon fixation)
CO₂ enters the stroma. The enzyme RuBisCO attaches CO₂ to RuBP. The cycle uses ATP and NADPH from the light reactions to convert CO₂ into G3P, the precursor to glucose.
Glucose synthesis
Two G3P molecules combine to form one glucose. The plant uses glucose for energy, cellular building blocks, or stores it as starch.
Frequently Asked Questions
Do plants photosynthesize at night?+
No — the light reactions require photons. But the Calvin cycle can run as long as ATP and NADPH are available, which they aren't at night. Plants rely on stored glucose at night.
What's the role of chlorophyll?+
Chlorophyll absorbs photons (especially red and blue wavelengths). It's the molecule that 'catches' light energy and passes it to the electron transport chain.
How does photosynthesis differ from cellular respiration?+
Photosynthesis builds glucose using CO₂ and water; respiration breaks glucose down to release energy. They're reverse processes — together they cycle carbon through ecosystems.
Related Topics
More step-by-step guides in Biology and adjacent subjects.
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