Photosynthesis Photorespiration and C4/CAM Pathways 3

Question 1

C3 plants are named because the first stable product of carbon fixation is a compound with how many carbons?

Accepted Answer

3 carbons

Answer

In C3 plants, CO2 is fixed directly by RuBisCO onto RuBP, producing two molecules of 3-phosphoglycerate (3-PGA), a 3-carbon compound — hence the name C3.

Question 2

Which type of photosynthesis is generally most efficient in cool, moist environments with moderate light intensity?

Accepted Answer

C3 photosynthesis

Answer

In cool, moist conditions, photorespiration is already low in C3 plants, eliminating the need for the extra energy investment of the C4 CO2-concentrating mechanism, making C3 photosynthesis more energy-efficient.

Question 3

Photorespiration is considered energetically wasteful primarily because it:

Accepted Answer

Consumes ATP and O2 while releasing CO2 without net sugar production

Answer

Photorespiration uses O2, releases previously fixed CO2, and consumes ATP and reducing power to process 2-phosphoglycolate — resulting in a net loss of fixed carbon and energy with no sugar gain.

Question 4

Which of the following crop plants is a well-known example of C4 photosynthesis?

Accepted Answer

Corn/Maize (Zea mays)

Answer

Corn (Zea mays) is a classic C4 plant with Kranz anatomy; this contributes to its high productivity in warm, sunny climates compared to C3 crops like wheat and rice.

Question 5

The spatial separation of initial CO2 fixation and the Calvin cycle in C4 plants occurs between which two cell types?

Accepted Answer

Mesophyll cells and bundle sheath cells

Answer

In C4 Kranz anatomy, PEP carboxylase fixes CO2 in mesophyll cells and the resulting 4-carbon acids are transferred to surrounding bundle sheath cells where RuBisCO runs the Calvin cycle.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Photorespiration and C4/CAM Pathways 3