Review of Photosynthesis: Videos & Practice Problems

Dig Deeper into Review of Photosynthesis

Photosynthesis is the process by which plants convert light energy into chemical energy stored in sugars.

Key Terminology

• Stomata: Openings or pores on the leaf surface that regulate gas exchange, allowing carbon dioxide in and oxygen out.
• Light reactions: The first stage of photosynthesis occurring in the thylakoids, where light energy is converted into ATP and NADPH.
• Thylakoids: Membrane-bound compartments inside chloroplasts that contain pigments and are the site of the light reactions.
• Photosystem II: The first photosystem in the light reactions that absorbs photons and initiates electron transport by splitting water molecules.
• Photosystem I: The second photosystem that absorbs light to boost electrons for NADPH production.
• Electron transport chain: A series of protein complexes that transfer electrons and help generate a proton gradient for ATP synthesis.
• ATP synthase: An enzyme that uses the proton gradient created by the electron transport chain to produce ATP via chemiosmosis.
• NADPH: An electron carrier produced in the light reactions that provides reducing power for the Calvin cycle.
• Calvin cycle: The second stage of photosynthesis occurring in the stroma, where carbon dioxide is fixed into sugar molecules.
• Rubisco: The enzyme that catalyzes carbon fixation by attaching CO₂ to RuBP in the Calvin cycle.
• RuBP (ribulose bisphosphate): The 5-carbon molecule that accepts CO₂ during carbon fixation.
• PGA (3-phosphoglycerate): The first stable 3-carbon molecule formed after carbon fixation.
• G3P (glyceraldehyde-3-phosphate): A 3-carbon sugar produced in the Calvin cycle that serves as a precursor for glucose synthesis.
• Photorespiration: A wasteful process occurring mainly in C3 plants when oxygen is fixed instead of carbon dioxide, reducing photosynthetic efficiency.
• C3 plants: Plants that fix carbon directly through the Calvin cycle but are prone to photorespiration under hot conditions.
• C4 plants: Plants that minimize photorespiration by spatially separating carbon fixation and the Calvin cycle between mesophyll and bundle sheath cells.
• CAM plants: Plants adapted to arid environments that temporally separate carbon fixation and the Calvin cycle by fixing CO₂ at night.
• Mesophyll cells: Photosynthetic cells in C4 plants where initial carbon fixation occurs.
• Bundle sheath cells: Cells in C4 plants where the Calvin cycle takes place, isolated from oxygen to reduce photorespiration.
• Photons: Particles of light energy absorbed by pigments to drive the light reactions.
• Chemiosmosis: The process of ATP generation using the proton gradient across the thylakoid membrane.

Real-World Applications

• Understanding photosynthesis helps improve agricultural productivity by breeding or engineering crops with enhanced photosynthetic efficiency, such as C4 or CAM traits to reduce water loss and photorespiration.
• Research on photosynthesis informs biofuel development by optimizing algae and plant systems to convert solar energy into biomass more efficiently.
• Knowledge of stomatal regulation and photosynthetic pathways aids in managing plant responses to climate change, especially in drought-prone or high-temperature environments.

Common Misconceptions

• Photosynthesis does not produce oxygen from carbon dioxide; instead, oxygen is released when water molecules are split during the light reactions.
• ATP and NADPH are not the final products of photosynthesis but are energy carriers used in the Calvin cycle to synthesize sugars.
• Photorespiration is not a beneficial process; it actually wastes energy and reduces the efficiency of photosynthesis, especially in C3 plants under hot conditions.
• C4 and CAM plants do not perform photosynthesis differently in terms of the Calvin cycle chemistry; they just separate the steps spatially or temporally to avoid photorespiration.
• The Calvin cycle does not directly produce glucose; it produces G3P, which is then used to form glucose and other carbohydrates.