Question Video: Describing the Relationship between Light Intensity and Synthesis of Chlorophyll | Nagwa Question Video: Describing the Relationship between Light Intensity and Synthesis of Chlorophyll | Nagwa

Question Video: Describing the Relationship between Light Intensity and Synthesis of Chlorophyll Biology • First Year of Secondary School

Which of the following correctly describes the relationship between light intensity and the synthesis of chlorophyll in a plant? [A] The more light a plant is exposed to, the less chlorophyll will be synthesized. [B] Prolonged exposure to low light levels or no light prevents a plant from synthesizing enough chlorophyll. [C] Exposure to light intensity has no effect on the synthesis of chlorophyll, only on how much photosynthesis can be carried out.

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Video Transcript

Which of the following correctly describes the relationship between light intensity and the synthesis of chlorophyll in a plant? The more light a plant is exposed to, the less chlorophyll will be synthesized. Prolonged exposure to low light levels or no light prevents a plant from synthesizing enough chlorophyll. Exposure to light intensity has no effect on the synthesis of chlorophyll, only on how much photosynthesis can be carried out.

The question is asking us about a relationship or link between light intensity and the synthesis of a molecule called chlorophyll. Let’s rephrase the question to be a bit more specific. What we really need to determine is how chlorophyll synthesis in plants is affected by changes in light intensity. Let’s clear our answer choices for now and do a brief review on the amazing molecule chlorophyll.

You probably know that the green parts of plants, such as stems and leaves, perform photosynthesis, a process that uses light energy to convert carbon dioxide and water to glucose and oxygen. Photosynthesis is how plants produce their own food to survive and grow. Inside the plant cells of the photosynthetic parts of a plant are organelles called chloroplasts. And if we zoom in on a chloroplast, we find chlorophyll embedded in the membranes within.

Chlorophyll is the pigment responsible for converting light to energy during photosynthesis. It absorbs wavelengths of red and blue light and reflects green wavelengths. This is why the photosynthetic parts of a plant appear green to our eyes. Inside the chloroplasts, chlorophyll is constantly being broken down, so plants have to continually synthesize new chlorophyll to maintain photosynthesis.

Environmental factors such as CO2 concentration, temperature, and light intensity regulate the expression of many plant genes, including genes involved in chlorophyll synthesis. Under conditions of high light intensity, the expression of genes involved in chlorophyll synthesis is upregulated. This means that lots of chlorophyll can be produced and the plant will be green and healthy.

Under partial light conditions, the expression of genes involved in chlorophyll synthesis will be lower than under high light conditions. But it’s likely the plant will be able to produce enough chlorophyll to survive and grow, although it may not be quite as green and healthy as it would have been under a high light intensity. Under conditions of low or no light, the expression of genes associated with chlorophyll synthesis will be downregulated. So, not enough chlorophyll will be synthesized to maintain photosynthesis. The plant is likely to become yellow, unhealthy and may even die.

We can now see the relationship between light intensity and chlorophyll synthesis. As light intensity increases, chlorophyll synthesis also increases. Now, let’s bring back our answer choices one at a time to find the correct one. The more light a plant is exposed to, the less chlorophyll will be synthesized. Well, we can see in both our diagram and our relationship statement that this is false. More light means more chlorophyll synthesis, not less. So, this is incorrect. Prolonged exposure to low light levels or no light prevents a plant from synthesizing enough chlorophyll. As shown in our diagram of the yellow, unhealthy plant, this choice seems to be correct. But let’s check the last answer choice, just to be sure.

Exposure to light intensity has no effect on the synthesis of chlorophyll, only on how much photosynthesis can be carried out. We clearly established a relationship between light intensity and chlorophyll synthesis. So, this answer choice is incorrect. The statement that correctly describes the relationship between light intensity and chlorophyll synthesis is prolonged exposure to low light levels or no light prevents a plant from synthesizing enough chlorophyll.

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