Question

Autumnal leaf colour is due to
A) Chlorophyll A
B) Carotenoids
C) Anthocyanin
D) Betacyanin

Answer 1

Leaves appear green to the presence of chlorophyll, the pigments responsible for photosynthesis. Plants produce several pigments at the same time, and these are present in the leaves.

Complete answer:
Chlorophyll A absorbs most of the violet-blue and orange-red wavelengths of light. It therefore appears green in colour, and starts to break down during autumn. Option A is not the correct answer. with the change in temperatures and day lengths, these green pigments start breaking down.

Carotenoids are present in leaves throughout the year. Because they are the prominent pigment of carrots, that’s why the name. Carotenes are orange and xanthophylls are yellow. When the chlorophyll pigments break down with the shorter days, the carotenoids are more visible. These pigments are present in maximum concentration in the leaves. Option B is the correct answer.

Anthocyanin pigments start getting produced in the leaves when it is cold. Trapped sugar promotes the formation of these anthocyanins which turn the leaves red, but they are in smaller quantities than the carotenoids. Option C is not the correct answer.

Betacyanin pigments are also produced in plants. They give the typical red-violet and yellow colours to fruits and vegetables. These are not present much in leaves and do not contribute to autumn foliage. So option D is incorrect.

Hence the correct answer is option ‘B’.

Note: While carotenoid are the prominent pigments, the wide range of colours present in autumn leaves from violets and purples to reds and oranges are due to the different concentrations of these and other pigments.