Question

Photosynthesis in CAM- plants is minimal because of the limited amount of _______________.
(a) Carbon dioxide fixed at night
(b) Oxygen fixed at night
(c) Carbon dioxide fixed at daylight
(d) Oxygen fixed at daylight

Answer 1

Hint: A plant using CAM has its stomata open during the night, allowing carbon dioxide to enter and be fixed as organic acids by a PEP reaction comparable to the ${ C }_{ 4 }$ pathway. As the Calvin cycle does not work without ATP and NADPH, products of light-dependent reactions that do not take place at night, the resulting organic acids are deposited in vacuoles for later use.

Complete answer:
The metabolism of crassulacean acid, also known as CAM photosynthesis. It is a pathway of carbon fixation that has evolved as an adaptation arid a condition in some plants when the stomata in the leaves remain closed during the day time that uses complete CAM to decrease evapotranspiration, but open at night to absorb carbon dioxide and allow it to diffuse into the mesophyll cells. Carbon dioxide is processed in vacuoles at night as the four-carbon acid malic acid, and then the malate is transferred to chloroplasts during the daytime, where it is turned back to carbon dioxide, which is then used during photosynthesis. The pre-collected carbon dioxide, which increases photosynthetic ability, is localised around the enzyme RuBisCO.

Additional information:
- Some plants are classified as CAM plants, which have Crassulacean Acid Metabolism (CAM) having scotoactive stomata in them. -When stomata are open, carbon dioxide necessary for photosynthesis enters the plant during the night. This carbon dioxide is then fixed overnight, but it only forms sugars during the day while RuBisCO is active.
- Some examples of CAM plants are: Sedum, Kalanchoe, Pineapple, Opuntia. Such plants conduct double fixation of carbon dioxide as well.
- Phosphoenol pyruvic acid (PEP) is the carbon dioxide acceptor in CAM plants during the night, and Ribulose bisphosphate is the acceptor of carbon dioxide during the day.
- In the case of CAM plants, the first stable product is oxalo acetic acid (OAA).
- In plants of the family Crassulaceae, this process of acid metabolism was first discovered.

So, the correct answer is ‘Carbon dioxide fixed at night’.

Note:
- Scotoactive stomata are stomata that remain open during night in the absence of sunlight.
- A plant using CAM has its stomata open during the night, allowing carbon dioxide to enter and be fixed as organic acids by a PEP reaction comparable to the ${ C }_{ 4 }$ pathway.
- The Calvin cycle does not work without ATP and NADPH, the products of light-dependent reactions that do not take place at night, and the resulting organic acids are deposited in vacuoles for later use.