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.
