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

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

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Three groups of plants belonging to the same species are exposed to different intensities of light. Group 1 was exposed to the light intensity shown for 12 hours, group 2 for 24 hours, and group 3 for 36 hours. The graph provided shows the amount of chlorophyll synthesized by these groups of plants at different light intensities. What can be concluded from this graph? [A] For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 12 hours than when it is exposed to the light for 36 or 24 hours. [B] For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 24 hours than when it is exposed to the light for 36 or 12 hours. [C] The intensities of light does not have an effect on how much chlorophyll is synthesized by a plant, but the duration of exposure does. [D] For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 36 hours than when it is exposed to the light for 24 or 12 hours.

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### Video Transcript

Three groups of plants belonging to the same species are exposed to different intensities of light. Group one was exposed to the light intensity shown for 12 hours, group two for 24 hours, and group three for 36 hours. The graph provided shows the amount of chlorophyll synthesized by these groups of plants at different light intensities. What can be concluded from this graph? (A) For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 12 hours than when it is exposed to the light for 36 or 24 hours. (B) For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 24 hours than when it is exposed to the light for 36 or 12 hours. (C) The intensity of light does not have an effect on how much chlorophyll is synthesized by a plant, but the duration of exposure does. (D) For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 36 hours than when it is exposed to the light for 24 or 12 hours.

The graph shows light intensity in lx on the 𝑥-axis and the amount of chlorophyll being synthesized by the plant in milligrams per gram on the 𝑦-axis. The three curves represent the three groups of plants that were exposed to different light intensities: group one for 12 hours, group two for 24 hours, and group three for 36 hours. We can see that all three groups had an increase in chlorophyll synthesis as light intensity increased from zero to 5000 lx. And from this we can make a conclusion that an initial increase in light intensity also increases chlorophyll synthesis.

We can also see that at zero lx, group three, the 36-hour group, synthesized more chlorophyll than groups one or two. And this pattern holds true for every light intensity. So a second conclusion we can make is that group three synthesize the most chlorophyll at every light intensity. We now have enough information to answer the question. So let’s bring back the answer options one at a time to determine the correct one. “For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 12 hours than when it is exposed to the light for 36 or 24 hours.” We concluded that group three, the 36-hour group, synthesized the most chlorophyll at all light intensities. So we can rule this answer choice out.

“For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 24 hours than when it is exposed to the light for 36 or 12 hours.” As with the previous answer, we can rule this one out because we know that group three, the 36-hour group, synthesized the most chlorophyll at all light intensities. “The intensity of light does not have an effect on how much chlorophyll is synthesized by a plant, but the duration of exposure does.” Well, our first conclusion was that an increase in light intensity initially increases chlorophyll synthesis. So we can rule this answer choice out.

“For all light intensities, more chlorophyll is synthesized when the plant is exposed to the light for 36 hours than when it is exposed to the light for 24 or 12 hours.” This answer choice is correct because it restates our second conclusion about group three.

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