Photosynthesis Energy Conversion 3

Question 1

What is the quantum yield of photosynthesis and why is it important?

Accepted Answer

The ratio of photons absorbed to O2 released, measuring efficiency

Answer

Quantum yield (Φ) measures photosynthetic efficiency as the number of O2 molecules released per photon absorbed; the theoretical maximum is ~0.125 (8 photons per O2).

Question 2

In the Z-scheme, electrons ultimately flow from which molecule to which molecule?

Accepted Answer

H2O → NADP+

Answer

The Z-scheme traces electron flow from the oxidation of water (splitting O–H bonds) through PSII and PSI to the reduction of NADP+ into NADPH.

Question 3

Why does the Calvin cycle require more ATP than NADPH on a per-CO2 basis?

Accepted Answer

Because the regeneration of RuBP requires extra ATP beyond what's needed for G3P reduction

Answer

For every 3 CO2 fixed, 9 ATP and 6 NADPH are needed; the extra 3 ATP (vs. 6 NADPH) are consumed specifically in the phosphorylation step that regenerates RuBP.

Question 4

Which pigment extends light absorption into wavelengths that chlorophyll a cannot efficiently capture?

Accepted Answer

Carotenoids (β-carotene and xanthophylls)

Answer

Carotenoids absorb blue-green and blue light (400–500 nm) and transfer that energy to chlorophyll a, broadening the usable spectrum of sunlight.

Question 5

What happens to the energy of a photon that is absorbed by an antenna pigment but NOT transferred to the reaction center?

Accepted Answer

It is re-emitted as fluorescence or dissipated as heat

Answer

Excess excitation energy not funneled to a reaction center is released as fluorescence (longer-wavelength light) or thermal energy, a process exploited in chlorophyll fluorescence assays.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Energy Conversion 3