Photosynthesis Calvin Cycle 5

Question 1

What would be the immediate effect on the Calvin cycle if the stroma suddenly became more acidic (lower pH)?

Accepted Answer

Calvin cycle enzymes would denature or lose optimal activity

Answer

Calvin cycle enzymes would become more active

Answer

CO₂ fixation would accelerate

Answer

RuBP regeneration would increase

Question 2

Which of the following correctly describes the stoichiometry of the full Calvin cycle for producing one G3P net?

Accepted Answer

3 CO₂ + 9 ATP + 6 NADPH → 1 G3P + 3 H₂O

Answer

3 CO₂ + 6 ATP + 6 NADPH → 1 G3P

Answer

6 CO₂ + 18 ATP + 12 NADPH → 2 G3P

Answer

3 CO₂ + 6 ATP + 3 NADPH → 1 G3P

Question 3

Thioredoxin activates several Calvin cycle enzymes in the light by:

Accepted Answer

Donating electrons to reduce disulfide bonds in the enzymes

Answer

Providing ATP from the electron transport chain

Answer

Directly fixing CO₂ alongside RuBisCO

Answer

Inhibiting photorespiration enzymes

Question 4

If a mutant plant lacked phosphoribulokinase, which outcome would result?

Accepted Answer

RuBP could not be regenerated and the cycle would stop after one turn

Answer

CO₂ fixation would accelerate due to excess ribulose-5-phosphate

Answer

G3P would accumulate and be exported at higher rates

Answer

3-PGA would be converted directly back to CO₂

Question 5

How does an increase in the CO₂:O₂ ratio in the chloroplast affect carbon fixation?

Accepted Answer

It favors RuBisCO's carboxylase activity and increases Calvin cycle output

Answer

It favors RuBisCO's oxygenase activity and increases photorespiration

Answer

It inhibits RuBisCO completely

Answer

It has no effect because RuBisCO selects only CO₂

Question 6

Which of these statements about the Calvin cycle location is correct?

Accepted Answer

It occurs in the stroma of the chloroplast

Answer

It occurs on the thylakoid membranes

Answer

It occurs in the intermembrane space of the chloroplast

Answer

It occurs in the cytosol of leaf mesophyll cells

Question 7

Which observation best supports the conclusion that the Calvin cycle is cyclic rather than linear?

Accepted Answer

The CO₂ acceptor RuBP is regenerated at the end of each set of reactions

Answer

CO₂ and water are both consumed

Answer

ATP and NADPH are consumed in equal amounts

Answer

G3P can be converted to glucose