Photosynthesis Basic Concepts 3 — Questions and Answers
Question 1: What is the approximate ATP yield from one full turn of the Calvin cycle per CO₂ fixed?
- 1 ATP
- 2 ATP
- 3 ATP (Correct answer)
- 6 ATP
Correct answer: 3 ATP
Three ATP molecules are consumed per CO₂ fixed during one turn of the Calvin cycle.
Question 2: Which enzyme catalyzes carbon fixation in the Calvin cycle?
- ATP synthase
- RuBisCO (Correct answer)
- Phosphofructokinase
- Photosystem II
Correct answer: RuBisCO
RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) is the enzyme that combines CO₂ with RuBP.
Question 3: In which direction do electrons flow in the photosynthetic electron transport chain?
- From NADPH to water
- From water to NADP+ (Correct answer)
- From glucose to CO₂
- From ATP to ADP
Correct answer: From water to NADP+
Electrons flow from water (via splitting) through the electron transport chain to ultimately reduce NADP+ to NADPH.
Question 4: How many molecules of CO₂ must be fixed to produce one molecule of glucose?
- 2
- 3
- 6 (Correct answer)
- 12
Correct answer: 6
Six CO₂ molecules are required because glucose (C₆H₁₂O₆) contains six carbon atoms.
Question 5: What is the function of the antenna complex in a photosystem?
- Split water molecules
- Synthesize ATP
- Absorb and transfer light energy to the reaction center (Correct answer)
- Reduce NADP+ to NADPH
Correct answer: Absorb and transfer light energy to the reaction center
Antenna pigments harvest light energy and funnel it to the reaction center chlorophyll for photochemistry.
Question 6: Which statement correctly describes the relationship between photosynthesis and cellular respiration?
- Both processes produce CO₂
- Photosynthesis stores energy; respiration releases it (Correct answer)
- Both occur only in plant cells
- Photosynthesis produces ATP directly for cell use
Correct answer: Photosynthesis stores energy; respiration releases it
Photosynthesis captures and stores light energy in glucose, while cellular respiration breaks down glucose to release usable energy as ATP.
Question 7: What happens to the oxygen produced during photosynthesis?
- It is used in the Calvin cycle
- It is stored in the vacuole
- It is released into the atmosphere as a byproduct (Correct answer)
- It combines with NADPH
Correct answer: It is released into the atmosphere as a byproduct
Oxygen is a byproduct of water splitting during the light reactions and is released through stomata into the atmosphere.
Photosynthesis Basic Concepts 3
What is the approximate ATP yield from one full turn of the Calvin cycle per CO₂ fixed?