Good vision depends on adequate intake of carotene rich food. Select the best option from the follow

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Question

Good vision depends on adequate intake of carotene rich food. Select the best option from the following statements(a) Vitamin A derivatives are formed from carotene(b) The photopigments are embedded in the membrane discs of the inner segment(c) Retinal is a derivative of vitamin A(d) Retinal is a light absorbing part of all the visual photopigments

Accepted Answer

Correct Answer: CStep-by-step Solution:Evaluating each statement:(a) Vitamin A derivatives are formed from carotene: Correct. Beta-carotene (a carotenoid) is a provitamin A that is enzymatically cleaved in the intestinal wall to yield two molecules of retinal (vitamin A aldehyde), a derivative of vitamin A.(b) The photopigments are embedded in the membrane discs of the inner segment: Incorrect. Visual photopigments (rhodopsin, iodopsin) are embedded in the membrane discs of the outer segment of rods and cones, not the inner segment. The outer segment contains stacked membrane discs rich in photopigment molecules. The inner segment contains the cell nucleus and metabolic organelles.(c) Retinal is a derivative of vitamin A: Correct. Retinal (retinaldehyde) is the aldehyde form of vitamin A (retinol). It is the chromophore component of all visual pigments.(d) Retinal is a light absorbing part of all the visual photopigments: Correct. Retinal is the light-sensitive component (chromophore) in both rod photopigment (rhodopsin = retinal + opsin) and cone photopigments (iodopsins = retinal + different opsins for different color ranges).Therefore, statements (a), (c), and (d) are correct.Why other options are incorrect:Option A includes statement (b) which is factually wrong. Option B includes only (a) and (b), missing (c) and (d). Option D only includes (a) and (c), missing (d).Key Concept:Visual cycle: Carotene (diet) &#8594; cleaved to Retinal (vitamin A derivative) &#8594; combines with opsin &#8594; Rhodopsin (in rods, for dim light) or Iodopsin (in cones, for color vision). Photopigments are in outer segment discs of photoreceptors. Deficiency of vitamin A &#8594; night blindness (nyctalopia).

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