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

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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Example Questions

Example Question #1 : Help With Light Reactions

Which molecule transfers electrons from photosystem II to photosystem I?

Possible Answers:

NADP+

Cytochrome c

Ferredoxin

Plastocyanin

Correct answer:

Plastocyanin

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. 

Example Question #2 : Help With Light Reactions

Which product is made in photosystem I?

Possible Answers:

ATP

NADH

NADPH

Glucose

Correct answer:

NADPH

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.

Example Question #3 : Help With Light Reactions

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

Possible Answers:

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

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

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

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 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

Correct answer:

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

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. 

Example Question #4 : Help With Light Reactions

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

Possible Answers:

Correct answer:

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. 

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
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