The Effect of Light on Photosynthesis
Length: 969 words (2.8 double-spaced pages)
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Plants need and use the same light of foods as animals but while
animals have to eat other things to get their food, plants make it
themselves. The way they do this is called photosynthesis. The other
ways that plants are different from animals, such as having leaves and
root or being green, they are all linked with photosynthesis. In
photosynthesis, plants take carbon dioxide from the air and water from
the soil, and use the energy from the sunlight to convert them into
food. The first food they make is glucose but that can later be
changed into other food types. The sunlight is absorbed by the green
Carbon hydrates contain the elements carbon, hydrogen, and oxygen as
in glucose. The carbon and oxygen could be supplied by carbon dioxide
from the air. In addition, the hydrogen could come from the water in
the soil. The nitrogen and sulphur needed for making protein could
come from nitrates and sulphates in the soil.
This builds up of complex food molecules from simpler substances this
is called synthesis. It needs enzymes and energy to make it happen.
Enzymes are presented in the plants cells and the energy for the first
stages in the synthesis comes from sunlight, this is called
photosynthesis. And that there is a green substance and chlorophyll.
Chlorophyll is in the chloroplasts of the plant cells. Chlorophyll
absorbs sunlight and makes the energy from sunlight.
[IMAGE]Carbon Dioxide + Water Glucose + Oxygen
Where does photosynthesis occur?
Photosynthesis takes place mainly in the leaves, although it can occur
in any cells that contain green chlorophyll. Leaves are adapted to
make them very efficient at photosynthesis.
Leaves are broad, so as much light as possible can be absorbed. A
leave is thin, so it is easy carbon dioxide to diffuse in to each of
the cells in the centre of the leaf. It also contains green
chlorophyll, in the chloroplasts, which absorbs the light energy.
Leaves have veins to bring up water from the roots and carry food to
other parts of the plant; a leaf as well has a stalk, or petiole, that
holds the leaf up so it can absorb as much sunlight as possible.
Factors that affect photosynthesis
If a plant gets more light, carbon dioxide, water or a higher
temperature, then it might be able to photosynthesise at a faster
rate. However, the rate of photosynthesis will eventually reach a
maximum because there is not enough of one of the factors needed, one
of them becomes a limiting factors.
If a factor pumps extra carbon dioxide into a greenhouse, the rate of
photosynthesis might increase so the crop will grow faster. However,
if the light is not bright enough to allow the plants to use the
carbon dioxide as quickly as it supplied, the light intensity would be
the limiting factor.
Temperature is also a limiting factor; temperature affects the enzymes
that control the chemical reactions of photosynthesis.
I predicted that the smaller the distance between the plant and the
sauce of light, the greater would be the rate of photosynthesis. As
out lined in the introduction, light is essential for the process of
photosynthesis. Therefore the closer the light source is to the plant,
the greater will be the intensity of the light and so the chlorophyll
within the plant will be able to photosynthesise at a faster rate.
As discussed in the introduction light is one of the limiting factors
in the process of photosynthesis. The existence of light is esational
for this process, as the following equation shows:
[IMAGE]Carbon Dioxide + Water Glucose + Oxygen
The role of light within photosynthesis is too absorbed by
chlorophyll. Chlorophyll is a green pigment present in the leafs of
plants, once chlorophyll has absorbed light it is able to convert
carbon dioxide and water into glucose and oxygen. Therefore, the more
the light that is available to the green plant, the greater will be
the rate of photosynthesis and so more glucose and oxygen will be
Breaker Test tube Lamp (light)
Test tube holder Elodea (pondweed) 6 cm Water 30ml
Goggles Stopwatch Thermometer
* Tie your scarf back
* Wear goggles
* Button up your sleeves
* Don't spill water everywhere (just in case it their might be any
* Don't touch the lamp when heated
* Use the same amount of water
* Apply the same amount of time
* Same amount of plant type
* Same placement of sunlight
* Same length of plant
* Same temperature of water
* Use the same bulb in the lamp
Temperature of water (0C)
Number of bubbles (min) time
[IMAGE][IMAGE] 2 4 6
150 120 156
106 110 99
54 50 48
2 14 11
2 2 3
The purpose of the experiment was to find out if light affects the
rate of photosynthesis, after carrying out this experiment; I have
learnt that light does affect the rate of photosynthesis. The closer
the light to the plant the more bubbles were produced which means that
the rate of photosynthesis increased.
I predicted that the further the light to the plant the less bubbles
will be produced this is because as the intensity of light is
increased more light can be trapped by chlorophyll to produced glucose
and oxygen. In this experiment the oxygen produced forms bubbles were
counted to determine the rate of photosynthesis. The results that I
got what I expected as they agreed with my prediction.
I think overall I obtained a good set of results. My process was well
planned and it was repeated so that I could take an average of the
results. This made sure that I do not end up with any anonymous
For my experiment, I had to find out whether light affects the rate of
photosynthesis. From my results I obtained, I found that light does
affect photosynthesis. The results that I got where the ones that I
predicted. The results that I obtained were good as they were as I
excepted. However, there are ways in which I could have improved my
results and made them more accurate. I could have improved my
experiment by counting the bubbles more accurately buy letting two
people counting instead of just one person counting.
The apparatus that I used was accurate, so I did not get any anonymous
results. My range was good because I had measured every 10 cm but if
had measured it every 5cm I would have get more accurate. I had enough
results to figure out if light does affect the rate of photosynthesis.
If I had wanted to, I could have obtained more results by getting
closer distances e.g. every 5 cm, but I do not think it would make
much of a difference to my conclusion.