Help with Light Reactions

Help Questions

GRE Subject Test: Biochemistry, Cell, and Molecular Biology › Help with Light Reactions

Questions 1 - 4
1

Which molecule transfers electrons from photosystem II to photosystem I?

Plastocyanin

Ferredoxin

Cytochrome c

NADP+

Explanation

Photosystems I and II are each capable of conducting electrons, with photosystem II handing off electrons to photosystem I. This is accomplished by the electron carrier molecule plastocyanin.

2

During the photosynthetic light reactions, which of the following molecules acts as the electron acceptor?

Explanation

Electrons excited in photosystem I are accepted by , thus converting to . is the reduced form of and while acts as an electron acceptor in certain reactions, the light reactions utilize which has an extra phosphate. and are not used to accept electrons in this context.

3

Which product is made in photosystem I?

NADPH

NADH

ATP

Glucose

Explanation

Photosystems I and II are responsible for the light-dependent reactions of photosynthesis. These two photosystems work in tandem to create ATP and NADPH products. ATP is created in photosystem II, while NADPH is created in photosystem I.

4

What fuels ATP synthase to make ATP from ADP + Pi in the light reaction of photosynthesis?

Light excites photosystem II to split water into hydrogen and oxygen. Hydrogen ions accumulate in the thylakoid space. Hydrogen moves down its concentration gradient from the thylakoid space to the stroma by passing through ATP synthase, fueling the synthesis of ATP

Light excites photosystem I to generate electrons that pass through the thylakoid membrane to excite ATP synthase to generate ATP

The mechanism by which ATP synthase is fueled is not entirely known

Light excites photosystem II to split water into hydrogen and oxygen. Oxygen accumulates in the thylakoid space. Oxygen then moves down its concentration gradient from the thylakoid space to the stroma by passing through ATP synthase, fueling the synthesis of ATP

NADPH is formed from NADP+ reductase in the thylakoid membrane. NADPH can then donate hydrogen to ATP synthase to fuel the synthesis of ATP

Explanation

Excitation of photosystem II splits water in the thylakoid space into hydrogen and oxygen. The hydrogen then passes through ATP synthase to move down its concentration gradient and into the stroma. Excitation of photosystem I passes electrons to NADP+ reductase to convert NADP+ to NADPH. Regeneration of NADPH is necessary for the Calvin cycle.

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