Video Transcript
Absorption spectra for the visible
light spectrum are provided. Which line shows the correct
absorption for the photosynthetic pigment chlorophyll a?
We know that plants can use light
to make their own food through a process called photosynthesis. You might remember that
photosynthesis is the process of turning carbon dioxide and water into glucose and
oxygen using light energy. The glucose sugar provides energy
for growth, reproduction, and metabolism, so light is absorbed for the process of
photosynthesis. This absorption is performed by
photosynthetic pigments, such as chlorophyll a, which reside in the chloroplasts of
a photosynthetic plant cell.
Let’s take a closer look at one of
these chloroplasts. The chloroplast interestingly has
two membranes, and it contains its own DNA within a fluid-filled space called the
stroma. Within the stroma, there are also
grana or a singular granum. Each granum is made up of disklike
structures called thylakoids, and they are linked by lamellae, which in the singular
form is a lamella. It’s the thylakoids within the
chloroplast that contain the pigments that absorb the light energy to initiate
photosynthesis. They contain chlorophyll a and
chlorophyll b. Chlorophyll a is one of the most
abundant photosynthetic pigments in a plant’s leaf. It absorbs red, orange, yellow, and
blue light but not green. In fact, since green light is not
absorbed, most plant leaves look green to our eyes.
Now, let’s take a look at the
absorption spectra provided by the question. Each of the three black traces on
the graph shows the level of light of different wavelengths that are absorbed by
different molecules. So which one of the three black
traces shows an absorption of red, orange, yellow, and blue but not green
wavelengths of light? The solid line, line one, shows
absorption peaks in all colors except green. Therefore, the line that
illustrates the absorption spectrum for chlorophyll a is line one.
