19. which molecule is the final electron acceptor in the electron transport chain of aerobic respiration?
a) nad⁺
b) fad
c) oxygen
d) carbon dioxide
20. photorespiration is most likely to occur when:
a) stomata are open and co₂ levels are high
b) stomata are closed and o₂ levels are high inside the leaf
c) light intensity is very low
d) temperatures are very cold
21. which of the following is a product of the calvin cycle?
a) o₂
b) atp
c) g3p (glyceraldehyde-3-phosphate)
d) nadph
22. cam plants open their stomata primarily at:
a) midday when temperatures are highest
b) night
c) early morning only
d) never—they are non-photosynthetic
23. which stage of cellular respiration produces exactly 2 atp by substrate-level phosphorylation per glucose in both aerobic and anaerobic pathways?
a) krebs cycle
b) electron transport chain
c) glycolysis
d) link reaction
24. when chlorophyll absorbs a photon, an electron becomes:
a) excited and jumps to a higher energy level
b) immediately lost from the molecule
c) converted into atp
d) transferred directly to co₂
25. the h⁺ gradient used for atp production in photosynthesis is established across the:
a) inner mitochondrial membrane
b) thylakoid membrane
c) plasma membrane
d) outer chloroplast membrane
26. which of the following processes can occur in the dark as long as atp and nadph are available?
a) light reactions
b) calvin cycle
c) glycolysis
d) electron transport chain
27. a total of how many nadh are produced per glucose from glycolysis, link reaction, and krebs cycle com
a) 4
b) 6
c) 8
d) 10

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Accepted Answer

### Question 19
# Brief Explanations:
In aerobic respiration's electron transport chain, oxygen is the final electron acceptor. It accepts electrons and protons to form water. NAD⁺ and FAD are electron carriers, and CO₂ is a product of respiration, not an electron acceptor.
# Answer:
c) Oxygen

### Question 20
# Brief Explanations:
Photorespiration occurs when stomata are closed (limiting CO₂ intake) and O₂ levels are high inside the leaf. High CO₂ (option a) favors photosynthesis, low light (c) and cold temps (d) reduce photorespiration.
# Answer:
b) Stomata are closed and O₂ levels are high inside the leaf

### Question 21
# Brief Explanations:
The Calvin cycle produces G3P (a 3 - carbon sugar). O₂ is from light reactions, ATP and NADPH are inputs (not products) of the Calvin cycle.
# Answer:
c) G3P (glyceraldehyde - 3 - phosphate)

### Question 22
# Brief Explanations:
CAM plants open stomata at night to take in CO₂ (storing it as malate) and close them during the day to reduce water loss. Midday (a), early morning (c) are incorrect, and they are photosynthetic (d is wrong).
# Answer:
b) Night

### Question 23
# Brief Explanations:
Glycolysis produces 2 ATP by substrate - level phosphorylation in both aerobic and anaerobic pathways. Krebs cycle produces more, electron transport chain uses oxidative phosphorylation, and link reaction produces no ATP by substrate - level phosphorylation.
# Answer:
c) Glycolysis

### Question 24
# Brief Explanations:
When chlorophyll absorbs a photon, an electron becomes excited and jumps to a higher energy level. It's not immediately lost (b), not converted to ATP directly (c), and not transferred to CO₂ (d).
# Answer:
a) Excited and jumps to a higher energy level

### Question 25
# Brief Explanations:
In photosynthesis, the H⁺ gradient for ATP production is across the thylakoid membrane (during the light - dependent reactions). Inner mitochondrial membrane (a) is for cellular respiration, plasma membrane (c) and outer chloroplast membrane (d) are not involved in this gradient for photosynthesis.
# Answer:
b) Thylakoid membrane

### Question 26
# Brief Explanations:
The Calvin cycle (dark reactions) can occur in the dark as long as ATP and NADPH (from light reactions) are available. Light reactions (a) need light, glycolysis (c) and electron transport chain (d) are part of respiration, not directly dependent on light - derived ATP/NADPH for dark operation.
# Answer:
b) Calvin cycle

### Question 27
# Brief Explanations:
- Glycolysis: 2 NADH per glucose.
- Link reaction: 2 NADH (1 per pyruvate, 2 pyruvates).
- Krebs cycle: 6 NADH (3 per acetyl - CoA, 2 acetyl - CoA).
- Total: 2+2 + 6=10? Wait, no, correction: Glycolysis: 2 NADH, Link reaction: 2 NADH (2 pyruvates→2 acetyl - CoA, 1 NADH each), Krebs cycle: 6 NADH (2 acetyl - CoA, 3 NADH each). Wait, 2 (glycolysis)+2 (link)+6 (Krebs)=10? But let's recheck: Glycolysis: 2 NADH. Link reaction: 2 pyruvates→2 acetyl - CoA, producing 2 NADH. Krebs cycle: for 2 acetyl - CoA, 3 NADH each, so 6. Total 2 + 2+6 = 10? But the options: a)4, b)6, c)8, d)10. Wait, maybe I made a mistake. Wait, glycolysis: 2 NADH. Link reaction: 2 NADH (2 pyruvates). Krebs cycle: 6 NADH? Wait, no, per glucose, glycolysis: 2 NADH, link reaction: 2 NADH (2 pyruvates), Krebs cycle: 6 NADH? Wait, no, let's calculate again. Glycolysis: 2 NADH. Link reaction: 2 pyruvates→2 acetyl - CoA, each produces 1 NADH, so 2. Krebs cycle: for each acetyl - CoA, 3 NADH, so 2 acetyl - CoA→6 NADH. Total: 2+2 + 6 = 10. So the answer is d)10.
# Answer:
d) 10

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