Photosynthesis Photosynthesis Electron Transport Chain 2

Question 1

What drives the synthesis of ATP by ATP synthase (CF0-CF1) in chloroplasts during the light reactions?

Accepted Answer

A proton (H+) electrochemical gradient across the thylakoid membrane

Answer

Protons accumulate in the thylakoid lumen through water splitting and plastoquinone activity, creating a gradient that drives protons through ATP synthase to phosphorylate ADP to ATP.

Question 2

In cyclic photophosphorylation, electrons cycle around which photosystem?

Accepted Answer

Photosystem I (PSI)

Answer

In cyclic photophosphorylation, electrons from PSI are transferred to ferredoxin, then to the cytochrome b6f complex, and back to PSI via plastocyanin, generating ATP without producing NADPH or O2.

Question 3

What is the primary difference between cyclic and noncyclic photophosphorylation?

Accepted Answer

Cyclic produces only ATP, while noncyclic produces both ATP and NADPH (and releases O2)

Answer

Cyclic photophosphorylation uses only PSI to generate extra ATP without producing NADPH or evolving oxygen, while noncyclic flow through both photosystems produces ATP, NADPH, and O2.

Question 4

The cytochrome b6f complex transfers electrons between which two mobile carriers in the electron transport chain?

Accepted Answer

Plastoquinone (PQ) and plastocyanin (PC)

Answer

The cytochrome b6f complex accepts electrons from reduced plastoquinone (PQH2) and passes them to the copper-containing protein plastocyanin, while pumping protons into the thylakoid lumen.

Question 5

The P700 designation for the Photosystem I reaction center indicates what?

Accepted Answer

The special pair chlorophyll absorbs maximally at 700 nm (far-red light)

Answer

P700 refers to the absorption maximum of the special pair of chlorophyll a molecules at the PSI reaction center, which is 700 nm in the far-red region.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Photosynthesis Electron Transport Chain 2