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Question Video: Analyzing Experimental Results to Determine the Impact of Light on Plant Growth and Chlorophyll Synthesis Biology

Two groups of seedlings were grown in different conditions for 4 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?

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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.

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