Chapter 8: Photosynthesis Flashcards
What is the overall equation for photosynthesis?
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
Where does photosynthesis occur in plant cells?
In chloroplasts, specifically in the thylakoid membranes (light reactions) and stroma (Calvin cycle).
What are the two main stages of photosynthesis?
Light-dependent reactions (convert light energy to ATP/NADPH) and Calvin cycle (uses ATP/NADPH to fix CO₂ into glucose).
What is the role of chlorophyll in photosynthesis?
Chlorophyll absorbs light energy (mainly red/blue wavelengths) and transfers it to reaction centers in photosystems.
What are photosystems?
Protein complexes in thylakoid membranes containing chlorophyll and other pigments.
Photosystem II (PSII): Absorbs light at 680 nm (P680). Photosystem I (PSI): Absorbs light at 700 nm (P700).
Describe the steps of the light-dependent reactions.
PSII: Light splits water → O₂, H⁺, and electrons (photolysis). Electron Transport Chain (ETC): Electrons move from PSII → PSI, pumping H⁺ into thylakoid lumen. PSI: Re-energized electrons reduce NADP⁺ → NADPH. ATP Synthase: H⁺ gradient drives ATP production (chemiosmosis).
What is photolysis?
The splitting of water into O₂, H⁺, and electrons (occurs in PSII).
What are the outputs of the light-dependent reactions?
ATP, NADPH, and O₂ (released as waste).
What is the Z-scheme?
The flow of electrons through PSII → ETC → PSI, visualized as a zigzag diagram due to energy changes.
What is the Calvin cycle also called?
The light-independent reactions or dark reactions (though it requires ATP/NADPH from light reactions).
Describe the three phases of the Calvin cycle.
Carbon Fixation: CO₂ + RuBP (5C) → 2 molecules of 3-PGA (3C), catalyzed by RuBisCO. Reduction: 3-PGA → G3P using ATP and NADPH. Regeneration: G3P → RuBP (requires ATP).
What is RuBisCO, and why is it important?
Ribulose bisphosphate carboxylase/oxygenase: Fixes CO₂ into organic molecules. Most abundant enzyme on Earth.
How many turns of the Calvin cycle are needed to produce 1 glucose?
6 turns (fixes 6 CO₂ molecules).
What are the inputs and outputs of the Calvin cycle?
Inputs per glucose: 6 CO₂, 18 ATP, 12 NADPH. Outputs: 1 glucose, 18 ADP, 12 NADP⁺.
What is photorespiration?
RuBisCO binds O₂ instead of CO₂, wasting energy (common in hot/dry conditions when stomata close).
How do C₄ plants minimize photorespiration?
Spatial separation: Fix CO₂ into 4C compounds (e.g., malate) in mesophyll cells → transport to bundle sheath cells for Calvin cycle.
Example: Corn, sugarcane.
How do CAM plants minimize photorespiration?
Temporal separation: Open stomata at night to fix CO₂ into malate → Calvin cycle during the day.
Example: Cacti, pineapples.
Compare C₃, C₄, and CAM plants.
C₃: Standard Calvin cycle (e.g., rice, wheat). C₄: Spatial CO₂ fixation (efficient in high light/heat). CAM: Nighttime CO₂ fixation (adapted to arid climates).
How is photosynthesis linked to cellular respiration?
Photosynthesis produces O₂ and glucose, which are used in respiration. Respiration releases CO₂ and H₂O for photosynthesis.
Why are leaves green?
Chlorophyll reflects green light (500–600 nm) while absorbing red/blue.
What is the action spectrum of photosynthesis?
Shows efficiency of different light wavelengths. Peaks at red (650 nm) and blue (450 nm).
How do environmental factors (light, CO₂, temperature) affect photosynthesis?
Light intensity: Increases rate until saturation. CO₂ concentration: Limits rate at low levels. Temperature: Optimal around 25–35°C (denatures enzymes at extremes).
What is the role of carotenoids in photosynthesis?
Accessory pigments absorb blue-green light and dissipate excess energy to protect chlorophyll.
What is cyclic electron flow?
Electrons cycle back to the ETC (PSI → cytochrome complex → PSI) to produce ATP without NADPH.
