The vitamin that acts as a hormone in the body and is synthesized in the skin upon exposure to ultraviolet (UV) sunlight is: MCQ with Answer and Explanation
The vitamin that acts as a hormone in the body and is synthesized in the skin upon exposure to ultraviolet (UV) sunlight is:
A. Vitamin A
B. Vitamin E
C. Vitamin C
D. Vitamin D
Answer: Option D
Solution (By JKExamLibrary)
Vitamin D (specifically cholecalciferol, Vitamin D3) is unique because it can be synthesized endogenously in the human skin. When 7-dehydrocholesterol in the skin is exposed to ultraviolet B (UVB) radiation from sunlight, it is converted to previtamin D3, which then isomerizes to Vitamin D3. It is subsequently hydroxylated in the liver and kidneys to its active hormonal form, calcitriol, which regulates calcium and phosphorus metabolism.
Explanation:
Crassulacean Acid Metabolism (CAM) plants, such as cacti and succulents, adapt to arid environments by opening their stomata at night to fix CO2 into organic acids (like malic acid) and storing them in vacuoles. During the day, the stomata close to prevent water loss, and the stored CO2 is released for the Calvin cycle.
Explanation:
Monotropa (Indian pipe) is a saprophytic angiosperm that obtains nutrition from dead organic matter through mycorrhizal association. Cuscuta is a parasitic plant (dodder), Drosera (sundew) and pitcher plant are insectivorous plants. Saprophytes lack chlorophyll and are heterotrophic. Monotropa belongs to the family Ericaceae. Saprophytism is uncommon in angiosperms.
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