Photosynthesis Calvin Cycle 3

Question 1

How does photorespiration differ from the Calvin cycle in terms of RuBisCO activity?

Accepted Answer

RuBisCO fixes O₂ instead of CO₂, releasing CO₂ and wasting energy

Answer

During photorespiration, RuBisCO adds O₂ to RuBP instead of CO₂, producing a 2-carbon compound that is metabolized to release CO₂ without making sugar.

Question 2

C4 plants minimize photorespiration primarily by doing what?

Accepted Answer

Concentrating CO₂ around RuBisCO in bundle sheath cells

Answer

C4 plants initially fix CO₂ via PEP carboxylase in mesophyll cells, then release concentrated CO₂ near RuBisCO in bundle sheath cells, suppressing O₂ competition.

Question 3

What is the net output of the Calvin cycle per 3 CO₂ fixed?

Accepted Answer

One G3P, 9 ATP consumed, 6 NADPH consumed

Answer

Per 3 CO₂ fixed, the cycle produces one net G3P while consuming 9 ATP and 6 NADPH.

Question 4

Which of the following best describes the role of ATP in the regeneration phase of the Calvin cycle?

Accepted Answer

It phosphorylates ribulose-5-phosphate to form RuBP

Answer

ATP donates a phosphate group to ribulose-5-phosphate, converting it to RuBP so the cycle can continue.

Question 5

If a plant is exposed to radioactive ¹⁴CO₂ and illuminated for only 2 seconds, which compound would first become labeled?

Accepted Answer

3-PGA

Answer

The first stable product of CO₂ fixation is 3-PGA; Calvin's experiments confirmed this through short-pulse ¹⁴C labeling.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Calvin Cycle 3