Video Transcript
Why are carrots orange in
color? (A) Because they are not fully
developed and still immature. (B) Because they have carotene
pigments. (C) Because they always grow past
the point of ripeness and begin to decay. (D) Because xanthophyll is the most
dominant pigment in carrot roots.
Did you know that carrots have not
always been orange? In fact, originally, carrots were
white. Through mutations, some carrots
then got a yellow or purple coloring. Another mutation then led the
carrot to become orange. This seems to have been a pleasing
and delicious color so that they were highly in demand and farmers started to
specifically grow the orange variety to please their customers.
But the question remains, why are
they orange? Does it have something to do with
its age as answer choices (A) and (C) suggest? If we are having a look at the
development of a carrot from its seed to the adult plant, we can observe that the
carrot is orange already when it is still very young and remains this way until its
leaves have wilted and longer. With this knowledge, we can exclude
answer options (A) and (C).
Answer options (B) and (D) suggest
that the orange coloring has something to do with photosynthetic pigmentation, which
is indeed the case. So let’s review what we know about
photosynthetic pigments.
The most abundant photosynthetic
pigment in most plants is chlorophyll. Here you can see a diagram that
shows the different wavelengths of the visible spectrum of light and the color
belonging to the wavelengths. Different pigments absorb different
spectra of light. For example, chlorophyll A absorbs
much of the visible light spectrum with the exception of green light. As chlorophyll is the most abundant
photosynthetic pigment in plant leaves and green light is the least absorbed light
spectrum of this pigment, the leaves of plants appear green.
However, plants also contain other
photosynthetic pigments, such as xanthophyll and 𝛽-carotene. These two pigments fall into the
category of the carotenoids. As you can see in the graph,
carotenoids mainly absorb blue and green light. They are therefore responsible for
giving plant structures a yellow, orange, or reddish color. We can nicely see these pigments at
work in the fall, when chlorophyll that is responsible for the green color drains
from tree leaves and only the carotenoids remain.
Xanthophylls are a class of
oxygen-containing carotenoid pigments, and carotenes are carotenoid pigments which
do not contain oxygen. The major pigments responsible for
the orange of the roots is 𝛽-carotene. And 𝛽-carotene often represents 50
percent or more of the total carotenoids content in a carrot root. Xanthophylls are often referred to
as the molecule responsible for yellow coloring.
Now we have enough information to
answer the question. The orange carrots are orange
because they have carotene pigments.
