Video Transcript
Two groups of seedlings were grown
in different conditions for four weeks. One group was grown in constant
light, and the other was grown with very limited access to light. The diagram provided shows the
results. What can be assumed about
chlorophyll synthesis from these results? (A) Synthesis of chlorophyll is not
affected by the presence of light. (B) Plants grown in limited light
synthesize more chlorophyll and, therefore, appear yellower. Or (C) plants grown in constant
light synthesize more chlorophyll and, therefore, appear greener.
The question asks about the
relationships between chlorophyll and light. But what is chlorophyll? How does it respond to
environmental factors such as availability of light? Well, chlorophyll is a pigment that
is thought to be responsible for the green color in plants. It absorbs energy from sunlight for
use in photosynthesis. The amount of chlorophyll
synthesized by the plant depends upon the amount of light present. More light prompts more chlorophyll
to be produced so that more energy can be harnessed for the plant.
First, let’s take a look at answer
(B). We know that in photosynthesizing
plants with abundant chlorophyll, the leaves have a green color. So a plant that synthesizes more
chlorophyll should appear greener. In addition, plants exposed to
limited light will actually synthesize less chlorophyll. So answer (B) is in direct
opposition to what we see in the diagram provided. And it incorrectly states what we
know about the environmental effects of gene expression in plants. Therefore, we can eliminate
(B).
Now, let’s look at answer (A). We can see clearly in the diagram
provided that chlorophyll production is not the same in these two plants. We can see the limited-light plant
is smaller, more wilted, and yellower. This is a result of less
chlorophyll and lower rates of photosynthesis due to the limited light. So we know that answer (A) is also
incorrect.
Let’s look at (C). Exposure to light in the
environment stimulates production of chlorophyll in plants. With constant exposure to light,
more chlorophyll will be synthesized and therefore the plant will appear
greener. In addition, the plant is receiving
more energy because it is absorbing more light. This explains why the plant is
larger and more robust than the limited-light plant.
Therefore, (C) must be the correct
answer. These results indicate to us that
plants grown in constant light synthesize more chlorophyll and, therefore, appear
greener.
