Photosynthesis Calvin Cycle 4

Question 1

Which carbon-containing molecule exits the chloroplast stroma to be used for sucrose synthesis?

Accepted Answer

G3P

Answer

G3P (glyceraldehyde-3-phosphate) leaves the chloroplast stroma and is used in the cytosol for sucrose and other carbohydrate synthesis.

Question 2

How many molecules of CO₂ must be fixed to produce enough G3P to synthesize one molecule of glyceraldehyde-3-phosphate (net)?

Accepted Answer

3

Answer

Three CO₂ molecules are fixed per cycle to yield one net G3P, since the other G3P molecules are recycled to regenerate RuBP.

Question 3

What happens to the Calvin cycle when light intensity drops to zero in a leaf?

Accepted Answer

It slows and stops as ATP and NADPH from the light reactions are depleted

Answer

The Calvin cycle depends on ATP and NADPH supplied by the light-dependent reactions; without light, these substrates are exhausted and the cycle halts.

Question 4

Which enzyme phosphorylates 3-PGA to form 1,3-bisphosphoglycerate in the Calvin cycle?

Accepted Answer

Phosphoglycerate kinase

Answer

Phosphoglycerate kinase uses ATP to phosphorylate 3-PGA, forming the high-energy intermediate 1,3-bisphosphoglycerate.

Question 5

In terms of carbon bookkeeping, what happens to the 18 carbon atoms from 6 RuBP when 6 CO₂ are fixed?

Accepted Answer

All 24 carbons become 12 G3P molecules, of which 10 regenerate RuBP and 2 are exported

Answer

18 carbons from RuBP plus 6 CO₂ carbons = 24 carbons forming 12 G3P; 10 G3P (30 carbons rearranged) regenerate 6 RuBP and 2 G3P exit as net product.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Calvin Cycle 4