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.
