Photosynthesis Reaction Stages 5

Question 1

What is the fate of the electrons removed from water during the light reactions?

Accepted Answer

They pass through the photosystems and electron transport chain, ultimately reducing NADP+ to NADPH

Answer

Electrons from water oxidation travel through PSII, the electron transport chain, and PSI before reducing NADP+ to NADPH via NADP+ reductase.

Question 2

Which experiment provided direct evidence that oxygen released in photosynthesis comes from water, not CO2?

Accepted Answer

Van Niel's comparison of purple sulfur bacteria using H2S

Answer

Van Niel showed that purple sulfur bacteria using H2S released sulfur instead of oxygen, suggesting by analogy that plant O2 comes from splitting water, not CO2.

Question 3

Which step of the Calvin cycle directly requires NADPH?

Accepted Answer

Reduction of 3-phosphoglycerate to G3P

Answer

NADPH provides the electrons needed to reduce 3-PGA to G3P in the reduction stage of the Calvin cycle.

Question 4

What structural feature allows ATP synthase to harness the proton gradient in the thylakoid membrane?

Accepted Answer

Its CF0 subunit forms a proton channel through the thylakoid membrane while CF1 catalyzes ATP synthesis in the stroma

Answer

The CF0 unit embedded in the thylakoid membrane conducts protons from the lumen, rotating the CF1 catalytic head in the stroma to synthesize ATP.

Question 5

Why does the Calvin cycle stop in the dark even though it does not directly require light?

Accepted Answer

The supply of ATP and NADPH from the light reactions is depleted

Answer

The Calvin cycle depends on ATP and NADPH produced by the light reactions; without light, these substrates run out and the cycle halts.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Reaction Stages 5