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CAM plants open their stomata during night only because they tend to
A. Promote the rate of light reaction
B. Promote the rate of dark reaction
C. Minimize the rate of transpiration
D. Maximize the rate of transpiration

Last updated date: 01st Mar 2024
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IVSAT 2024
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Hint: Most plants unlock their stomata during the day because that is when energy is received from the Sun. The energy from the Sun is harvested by the chloroplasts and used to make ATP and NADPH. These short term energy storage molecules are then used to power the obsession of carbon into sugar.

Complete Answer:
- CAM is the short term used for Crassulacean Acid Metabolism, a technique of carbon fixation evolved by some plants in dry circumstances. In most plants the stomata which are like minute mouths that receive in oxygen all along the surfaces of their leaves that open during the day take in carbon dioxide and to release oxygen.
- Plants must obtain carbon dioxide since they use it as a source for carbon atoms to build sugars, proteins, nucleotides and the other building blocks of life. They must also discharge waste oxygen, which is the byproduct that is left over after the carbon atom has been integrated into sugar.
- CAM plants are usually xerophytes which are growing in deserts. They open their stomata during night and fix atmospheric carbon into organic acids, like oxaloacetic acid and malic acid. These organic acids are normally four carbon atoms containing compounds.
- During daytime the organic acids are decarboxylated to let go carbon dioxide, which is fixed through RuBisCo and normal Calvin cycle. The opening of stomata through night time is a physiological alteration to prevent loss of water through transpiration.
- Sedum, Kalanchoe, Pineapple, Opuntia are some examples of CAM plants. These plants also carry out double carbon dioxide fixation.

Hence the correct answer is option C.

Note: The term “Crassulacean Acid Metabolism” comes from the Crassula plant, which was the first place that CAM metabolism was exposed and studied.
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