BioInteractive Photorespiration and Alternative Carbon Fixation 2

Question 1

What is CAM photosynthesis?

Accepted Answer

A strategy where CO2 is fixed at night and stored as organic acids, then released for the Calvin cycle during the day

Answer

CAM (Crassulacean Acid Metabolism) plants open stomata at night to fix CO2 into malate, then close stomata during the day and release CO2 for the Calvin cycle.

Question 2

Which plants use CAM photosynthesis?

Accepted Answer

Cacti and succulents

Answer

CAM photosynthesis is common in succulent plants like cacti, agaves, and pineapples that live in arid environments.

Question 3

What is the key advantage of CAM over C3 photosynthesis in desert environments?

Accepted Answer

Stomata open only at night, dramatically reducing water loss

Answer

By opening stomata at night when temperatures are cooler and humidity is higher, CAM plants lose far less water through transpiration than C3 plants.

Question 4

In C3 plants, what is the first stable product of carbon fixation?

Accepted Answer

3-phosphoglycerate (3-PGA)

Answer

In C3 plants, RuBisCO fixes CO2 onto RuBP to produce two molecules of 3-phosphoglycerate, a 3-carbon compound.

Question 5

Why is RuBisCO considered an inefficient enzyme?

Accepted Answer

It has a slow catalytic rate, a dual affinity for both CO2 and O2, and is easily inhibited

Answer

RuBisCO is slow (3–10 reactions/second), can react with O2 (causing photorespiration), and requires large amounts of protein to compensate, making it metabolically expensive.

BioInteractive - Photosynthesis BioInteractive Test Practice Test

BioInteractive - Photosynthesis BioInteractive Test Practice Test

BioInteractive Photorespiration and Alternative Carbon Fixation 2