Video Transcript
Complete the following
statement. In the absence of light, the
production of chlorophyll becomes reduced, and this causes the leaves of the plant
to turn blank. (A) Green, (B) black, (C)
translucent, (D) yellow, or (E) white.
The question asks about the color,
or pigmentation, of plant leaves when chlorophyll is reduced. Chlorophyll is a biological
pigment, which is a molecule that absorbs specific wavelengths of light while
reflecting others. Chlorophyll absorbs blue and red
wavelengths of light more efficiently than green wavelengths. This means more green light is
available to be reflected by the plant, giving it a characteristic green
appearance.
You probably know by now that
chlorophyll is also responsible for converting light energy to chemical energy
during photosynthesis. Due to fluctuations in
environmental factors, such as light intensity, the level of chlorophyll inside the
plant’s chloroplasts is constantly changing. Under conditions of high light
intensity, the plant will have higher levels of chlorophyll and will therefore
appear green. Under conditions of low light or no
light, the plant will have lower levels of chlorophyll. But what does this mean for the
color of the leaves?
To understand how the level of
chlorophyll affects the color of plants, we need to consider a second class of
pigments called carotenoids, which give plants a red, orange, or yellow color. Under conditions of high light,
such as during spring and summer, the amount of chlorophyll in leaves is typically
greater than the amount of carotenoids. However, when light levels decline,
such as occurs during autumn, the amount of chlorophyll in leaves is typically less
than the amount of carotenoids.
Now, let’s return to our answer
choices to see if we can figure out what happens to the color of leaves when
chlorophyll becomes reduced. We know that chlorophyll
preferentially absorbs blue and red wavelengths of light, leaving more green light
to be reflected. Therefore, a reduction in
chlorophyll would make leaves appear less green, not more green, so we can go ahead
and eliminate answer choice (A).
We’ve also learned that even under
low-light conditions, carotenoid pigments are still present in the leaves. So answer choices (C), translucent,
and (E), white, are also incorrect.
Finally, because these remaining
carotenoids will reflect specific wavelengths of light, the leaves will not appear
black. In the absence of light,
chlorophyll declines and the remaining carotenoids become more visible, causing the
leaves to appear less green and more yellow. So the correct statement reads “In
the absence of light, the production of chlorophyll becomes reduced, and this causes
the leaves of the plant to turn yellow.”
