|How does the level of light affect the rate of
|Question Date: 2014-11-03|
In photosynthesis, the energy from the sun is
used to turn carbon dioxide (CO2) and
water into sugar. Oxygen is a waste product.
More light can mean more photosynthesis.
It doesn’t necessarily mean more though. When we
think of photosynthesis as a process, we can see
that there are at least three things that can
limit the process: light, water, and carbon
dioxide. More light won’t help if we don’t
have enough water and carbon dioxide.
Actually, most places on Earth have the same
amount of carbon dioxide in the atmosphere, but a
plant can only get it by opening holes in its
leaves. These holes are too small for you to see
without a strong microscope, but they are big
enough to let water vapor out of the plant. So
water is an important limit on a plant. More
light is actually a problem if water is scarce,
because even more water will evaporate from the
This is an example of how increasing one factor
(sunlight) can lead to another factor (water)
How can you look at a landscape and tell
whether a lot of photosynthesis usually happens
Thanks for asking,
So by level of light you probably mean light
intensity which is something that can be measured.
Light intensity is usually defined as the
energy hitting an area over some time period.
So in the case of a plant, a higher light
intensity means more packets of light called
“photons” are hitting the leaves. As you rise from
low light intensity to higher light intensity, the
rate of photosynthesis will increase because there
is more light available to drive the reactions of
photosynthesis. However, once the light intensity
gets high enough, the rate won’t increase anymore
because there will other factors that are limiting
the rate of photosynthesis. A limiting factor
could be the amount of chlorophyll molecules that
are absorbing the light. At a very high intensity
of light, the rate of photosynthesis would drop
quickly as the light starts to damage the plant.
This is a very important aspect of photosynthesis.
As you are probably aware, Photosynthesis is a
chemical reaction that captures light energy and
turns it into sugar. These sugars are then
used by the plant as energy for any number of
things. The process of photosynthesis requires
three things: Light, Carbon dioxide and water. If
any one of these things is in short supply, then
photosynthesis cannot happen. When you increase
the level of light, plants will photosynthesize
more. But, if you have too much light, than the
other 2 ingredients become limiting and
photosynthesis can no longer increase with the
level of light. When this occurs, leaves can
experience sunburn damage. If you've ever seen a
leaf with large dry brown sections on a living
leaf, it is because that leaf experienced sunburn.
With too little light, photosynthesis cannot
occur either and the plant suffers without the
production of sugars. There are many complicating
interactions between plants and light. I hope that
you continue to investigate this as the story gets
more interesting and exciting the deeper you go.
Photosynthesis needs light, but it also needs
other things, and too much light can create heat
and dryness that are bad for photosynthesis. For
this reason plants in different environments have
different structures to help them get the right
amount of light. In rain forests, where there
is plenty of water, trees grow very tall to reach
as much light as they can. In deserts, plants use
hairs or scales on their leaves to reduce the
amount of light they receive to keep the light
from driving the temperature up too high or
causing the plants to dry out.
I am not sure what you mean by "level" of
light, but I will answer your question in to ways
- in terms of the intensity of light and
wavelength of light.
Photosynthesis needs water, carbon dioxide,
chlorophyll, light, and the right temperature.
Light is an extremely important factor for the
process. If there is enough water, carbon dioxide,
and the temperature is right, light becomes the
factor which will affect photosynthesis. Most of
the time, when the intensity of light is high,
you will get a a greater rate of
photosynthesis. But, this rate has a limit,
and once that limit is hit you can't increase the
rate past that limit.
Chlorophyll is a green pigment in the
chloroplast of the plant cell which absorbs the
light. This mean it will absorb any wavelength of
light which is not in the green spectrum of light.
If you look at a spectrum from 400nm-700nm. The
amount of light absorbed will increase until it
reaches a peak at about 450nm (blue light). Then
it will start decreasing and be very low (almost
0) through the 500-550nm (green light) and then it
will increase again peaking at about 700nm (red
and yellow light).
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