Photosynthesis Photorespiration and C4/CAM Pathways 2

Question 1

In C4 plants, which molecule(s) serve as the CO2 carrier transporting fixed carbon from mesophyll cells to bundle sheath cells?

Accepted Answer

Malate or aspartate

Answer

Oxaloacetate is quickly converted to malate or aspartate in mesophyll cells; these 4-carbon acids are transported to bundle sheath cells where they are decarboxylated to release CO2 for RuBisCO.

Question 2

CAM plants open their stomata primarily during which part of the day to minimize water loss?

Accepted Answer

Night

Answer

CAM plants open stomata at night when temperatures are cooler and humidity is higher, allowing CO2 uptake with far less water loss than if stomata were open during the hot daytime.

Question 3

In CAM plants, CO2 collected at night is stored in vacuoles as which organic acid?

Accepted Answer

Malic acid (malate)

Answer

CO2 fixed by PEP carboxylase at night forms oxaloacetate, which is rapidly reduced to malate; malate accumulates in vacuoles overnight and is released during the day for the Calvin cycle.

Question 4

Which of the following plants is a classic example of CAM photosynthesis?

Accepted Answer

Prickly pear cactus (Opuntia)

Answer

Cacti like Opuntia are classic CAM plants adapted to desert environments; they fix CO2 at night and keep stomata closed during hot days to conserve water.

Question 5

What is the immediate substrate for PEP carboxylase in C4 and CAM plants?

Accepted Answer

PEP (phosphoenolpyruvate)

Answer

PEP carboxylase catalyzes the carboxylation of phosphoenolpyruvate (PEP) using CO2 (as HCO3−) to produce the 4-carbon compound oxaloacetate.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Photorespiration and C4/CAM Pathways 2