Question

In higher plants, the light harvesting molecules are:

• A. Vitamin D and cytochrome C
• B. Cytochrome C and chlorophyll
• C. Anthocyanin and carotenoid
• D. Chlorophyll and carotenoid

Hint:

Chlorophyll absorbs light for photosynthesis, while carotenoids protect plants from light-induced damage and expand the range of light absorbed.

Answer 1

The Correct Option is D

A light-harvesting molecule must be a pigment that sits in the photosynthetic membrane and absorbs visible light to pass energy toward the reaction centre.

Vitamin D and cytochrome C have no such role -- vitamin D is an animal steroid precursor, and cytochrome C is an electron-transfer protein in respiration. Anthocyanins are vacuolar pigments that colour flowers and fruits but do not feed energy into photosynthesis.

Chlorophyll and carotenoids are the two pigment classes that genuinely sit in the thylakoid membrane and harvest light for photosynthesis, so this pairing fits the definition.

Answer 2

A useful way to confirm this is to think in terms of the visible-light spectrum and which pigments plug the gaps in each other's absorption.

1. Vitamin D and cytochrome C: Neither molecule has an absorption spectrum tuned to sunlight for photosynthesis, so this pair cannot be responsible for light harvesting.
2. Cytochrome C and chlorophyll: Chlorophyll absorbs strongly in the blue and red regions, but cytochrome C's role is redox chemistry using heme iron, not photon capture, so it cannot complement chlorophyll's absorption gaps.
3. Anthocyanin and carotenoid: Carotenoids absorb in the blue-green region, exactly where chlorophyll absorbs weakly, making them a natural photosynthetic partner; but anthocyanins are not part of this energy-transfer chain, so this pairing is only half right.
4. Chlorophyll and carotenoid: Chlorophyll covers the blue and red ends of the spectrum, and carotenoids fill in the blue-green region chlorophyll misses, together capturing a broader slice of sunlight and channelling it to the reaction centre.

Because chlorophyll and carotenoids together cover complementary parts of the visible spectrum used in photosynthesis, this is the pairing that functions as the light-harvesting system.

So, the correct answer is Chlorophyll and carotenoid.