Video Transcript
Which of the following would not be
classified as a photosynthetic pigment in plants? (A) Chlorophyll a, (B) chlorophyll
b, (C) xanthophylls, (D) melanin, or (E) carotenoids.
Photosynthetic pigments are what
allow the plant to absorb light and use its energy for photosynthesis. As we’ll see, they also are what
give plants their color. To understand how this works, let’s
discuss what the photosynthetic pigments found in plants are.
As you probably know, plants
usually have green leaves. This is because of the large number
of chlorophyll pigments present in a plant’s leaves. Chlorophyll is commonly found in
plants in the forms of chlorophyll a and chlorophyll b. Chlorophylls absorb most of the
light of the visible light spectrum, as you can see in the graph. But they do not absorb green
light. As the green light is the light
spectrum that is not used by chlorophyll for photosynthesis, the leaves appear
green. Because chlorophyll a and b are
both photosynthetic pigments, answers (A) and (B) can be eliminated.
Although chlorophylls are the main
pigmentation in the leaves, other photosynthetic pigments are present in the
chloroplasts as well. These pigments include
carotenoids. Carotenoids are a class of pigments
which do not absorb yellow and red light. These pigments are responsible for
the foliage that appears in autumn, when chlorophyll production is reduced in
response to limited sunlight. As carotenoids are photosynthetic
pigments and because xanthophylls are included in the class of carotenoids, answers
(C) and (E) can be eliminated as well.
Melanin is a pigment that can be
found in plants. However, it does not play a role in
photosynthesis. It is a dark pigment found in human
skin and browning fruits, such as bananas. Melanin is therefore the only
pigment in our list of answer choices that would not be classified as
photosynthetic. The correct answer is therefore
melanin.
