This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Chloroplast Function – CO2 Fixation and Carbohydrate Synthesis in CAM Plants”.
1. Which of the following plants undergo CAM photosynthesis?
Explanation: CAM is known as crassulacean acid metabolism. These CAM plants fix CO2 in the arid and hot climate regions.
2. The CAM pathway starts at daytime.
Explanation: The CAM pathway starts at night when there is lower temperature. This is due to the mechanism that reduces water loss by evatranspiration.
3. Where is the malate stored in CAM plants?
d) Endoplasmic reticulum
Explanation: The CO2 is converted to malate, a four carbon organic compound. This is stored in the vacuoles where it is later transported to the chloroplast for conversion of malate to CO2 for photosynthesis.
4. How many aquatic plant genera can undergo CAM photosynthesis?
Explanation: The aquatic plants can also undergo CAM photosynthesis. There are about 4 genera of plants. They also follow the same pathway as the terrestrial CAM plants.
5. The CAM plants undergo daytime acidification and nighttime deacidification.
Explanation: During the nighttime, the plants take up CO2 and convert it into organic acids called as acidification. While in daytime, they utilize the organic acids to form CO2 back known as deacidification.
6. Which enzyme is used in converting bicarbonate ion to oxaloacetate?
a) Phosphoenolpyruvate reductase
b) Phosphoenolpyruvate hydrogenase
c) Phosphoenolpyruvate carboxylase
d) Phosphoenolpyruvate dehydrogenase
Explanation: The phosphoenolpyruvate carboxylase enzyme is used to catalyze bicarbonate to oxaloacetate and phosphate. This is one of the important mechanism in the carbon fixation in CAM plants.
7. Which enzyme is used to convert oxaloacetate to malate?
a) Malate dehydrogenase
b) Malate hydrolase
c) Malate carboxylase
d) Malate dehydratase
Explanation: Oxaloacetate is converted to malate by the enzyme malate dehydrogenase. The oxaloacetate obtains an electron from NAD+ and converts it to a four carbon compound malate.
8. Which of the following is a facultative CAM plant?
a) Century plant
d) Common ice plant
Explanation: Common ice plant is an facultative CAM plant. It usually does not undergo CAM photosynthesis but it undergoes CAM photosynthesis when it is under stress condition, like shortage of water, CO2, etc.
9. How many molecules of ATP and NADPH2 are used in synthesis of one glucose molecule?
a) 30 ATP and 10 NADPH2
b) 10 ATP and 30 NADPH2
c) 30 ATP and 12 NADPH2
d) 12 ATP and 30 NADPH2
Explanation: The CAM pathway uses 30 ATP and 12 NADPH2 for synthesis of one glucose molecule. This is higher than the energy requirements of C4 and C3 cycles.
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