Photosynthesis Reaction Stages 2

Question 1

Which protein complex in the thylakoid membrane splits water molecules to release oxygen?

Accepted Answer

Photosystem II

Answer

Photosystem II contains the oxygen-evolving complex that oxidizes water, releasing O2, protons, and electrons.

Question 2

What is the primary electron donor that reduces NADP+ at the end of the light reactions?

Accepted Answer

Ferredoxin

Answer

Ferredoxin passes electrons from Photosystem I to NADP+ reductase, which reduces NADP+ to NADPH.

Question 3

During the Calvin cycle, how many carbon dioxide molecules must be fixed to produce one molecule of G3P that exits the cycle?

Accepted Answer

3

Answer

Three CO2 molecules are fixed per turn of the Calvin cycle to net one G3P molecule for export.

Question 4

Which enzyme catalyzes the regeneration of RuBP from G3P in the Calvin cycle?

Accepted Answer

Phosphoribulokinase

Answer

Phosphoribulokinase uses ATP to phosphorylate ribulose-5-phosphate, regenerating RuBP.

Question 5

In cyclic photophosphorylation, electrons cycle back to which component after leaving Photosystem I?

Accepted Answer

Plastoquinone

Answer

In cyclic flow, electrons from PSI return to plastoquinone, driving proton pumping and ATP synthesis without producing NADPH.

Photosynthesis Practice Test