BioInteractive Photosystems I and II 3

Question 1

In cyclic electron flow, which photosystem is primarily involved?

Accepted Answer

Photosystem I

Answer

Cyclic electron flow involves only PSI, where electrons from ferredoxin cycle back through the cytochrome b6f complex and plastocyanin to return to PSI rather than reducing NADP+.

Question 2

Compared to non-cyclic electron flow, what does cyclic electron flow produce?

Accepted Answer

ATP without NADPH or O2

Answer

Cyclic electron flow generates a proton gradient for ATP synthesis but does not produce NADPH (electrons return to PSI) and does not split water, so no O2 is released.

Question 3

Under what condition would a plant preferentially shift to cyclic electron flow?

Accepted Answer

When NADPH levels are high relative to ATP needs

Answer

When NADPH accumulates but ATP is limiting, cyclic electron flow supplements ATP production without adding more NADPH, helping balance the ratio of these two energy currencies.

Question 4

What is the ratio of ATP to NADPH consumed per three CO2 molecules fixed in the Calvin cycle?

Accepted Answer

3 ATP : 2 NADPH

Answer

Fixing 3 CO2 in the Calvin cycle consumes 9 ATP and 6 NADPH, a ratio of 3:2, which partly explains why cyclic flow is needed to supplement ATP beyond what non-cyclic flow alone produces.

Question 5

What does the Z-scheme diagram in photosynthesis illustrate?

Accepted Answer

The changes in redox potential of electrons as they travel from water through PSII and PSI to NADPH

Answer

The Z-scheme shows electron redox potential on the vertical axis; electrons drop in energy at PSII and PSI as light boosts them, tracing a zigzag (Z) shape from water to NADPH.

BioInteractive - Photosynthesis BioInteractive Test Practice Test

BioInteractive - Photosynthesis BioInteractive Test Practice Test

BioInteractive Photosystems I and II 3