Photosynthesis Photorespiration and C4/CAM Pathways

Question 1

Which enzyme is responsible for both carbon fixation in the Calvin cycle and the oxygenase reaction that initiates photorespiration?

Accepted Answer

RuBisCO

Answer

PEP carboxylase

Answer

ATP synthase

Answer

NADP+ reductase

Question 2

During photorespiration, RuBisCO catalyzes the addition of which molecule to RuBP instead of CO2?

Accepted Answer

Oxygen (O2)

Answer

Water (H2O)

Answer

Glucose

Answer

NADPH

Question 3

When RuBisCO catalyzes the oxygenase reaction with RuBP, what two products are formed?

Accepted Answer

One molecule of 3-phosphoglycerate and one molecule of 2-phosphoglycolate

Answer

Two molecules of 3-phosphoglycerate

Answer

One molecule of pyruvate and one molecule of PEP

Answer

One molecule of oxaloacetate and one molecule of malate

Question 4

In C4 plants, what is the first stable product of carbon fixation in mesophyll cells?

Accepted Answer

Oxaloacetate (OAA)

Answer

3-phosphoglycerate (3-PGA)

Answer

Glyceraldehyde-3-phosphate (G3P)

Answer

Ribulose-1,5-bisphosphate (RuBP)

Question 5

Which enzyme fixes CO2 in the mesophyll cells of C4 plants?

Accepted Answer

PEP carboxylase (PEPcase)

Answer

RuBisCO

Answer

ATP synthase

Answer

Malate dehydrogenase

Question 6

In C4 plants, where does the Calvin cycle (carbon reduction) predominantly take place?

Accepted Answer

Bundle sheath cells

Answer

Mesophyll cells

Answer

Guard cells

Answer

Epidermal cells

Question 7

What is the primary advantage of C4 photosynthesis over C3 photosynthesis in hot, sunny conditions?

Accepted Answer

C4 plants concentrate CO2 around RuBisCO, minimizing photorespiration

Answer

C4 plants produce more ATP per glucose molecule synthesized

Answer

C4 plants do not require sunlight for the Calvin cycle

Answer

C4 plants have significantly larger chloroplasts than C3 plants