The Effect of Wavelength on Photosynthesis Rate

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The Effect of Wavelength on Photosynthesis Rate


To investigate how different wavelength (colors) of light affect the
photosynthetic rate. I will use a pant that is a pond weed called
elodea. I will measure the rate of photosynthesis by measuring the
amount of o2 given off in bubbles per minuet from the elodea. I will
do this by placing the Elodea in a test tube with sodium hydrogen
carbonate then I will vary the light wavelength (color) using colored
filters and count the number of oxygen bubbles given off using a
pencil dot technique.


I predict that with a blue filter the photosynthetic rate will be the
highest as blue is a highly absorbent color it also has a short
wavelength so carries the most energy. The color to have the least
photosynthetic rate will be green as although it has quiet a short
wavelength so a lot of energy it will be reflected by the plant and
not absorbed. Yellow and orange will have average photosynthetic rates
although orange will be slightly more as it is more absorbent than
yellow even low it has a longer wavelength and dose not carry as much
energy as yellow would. Red will have a very high photosynthetic rate
as even though it has the longest wavelength and therefore carries the
least energy it will be greatly absorbed so a lot of the light energy
will be used rater than reflected.

Prediction graph.


Photosynthetic equation

[IMAGE][IMAGE]6CO2 + 6h20 light energy and chlorophyll C6H1206 + 6O2

Carbon dioxide + water converted into glucose and oxygen

Theory of photosynthesis

Photosynthesis is a chemical reaction, which uses the energy from
sunlight to convert carbon dioxide and water to oxygen (The bi
product) and glucose. Plants trap the energy in sunlight using
chlorophyll a light trapping pigment found in leaf plant cells. It
then uses carbon dioxide which enters the plant by small holes found
on the underside of the leaf called stoma and water which enters the

How to Cite this Page

MLA Citation:
"The Effect of Wavelength on Photosynthesis Rate." 29 Mar 2017

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plant thought the roots hair cells and travels up dead xylem cells to
the leaves which all combine to form oxygen the bi product and glucose
which can either be used for growth and repair or stored as starch The
greater light intensity and sunlight there is the greater the amount
of photosynthesis providing there is a constant supply of co2 and

Independent Variable

Light wavelength (color). Different colors of light changed to see how
each color effects the photosynthetic rate. Light Filters are used and
light intensity stays the same The colors used in order of wavelength
blue being the smallest and red the largest so the order will go
white, blue, green, yellow, orange, red.

Dependent variable

The number of o2 bubbles per minuet given off by the elodea.






There are some factors that I must keep the same to ensure accurate
results these are:

* Temperature and PH (preferably at 7) - because if either are
changed or altered they will effect the rate of enzymes which
control the reaction and will make it faster or slower therefore
making the rate of reaction not down to wavelength along but
dependent of several factors and we want to look at wave length.

* Concentration of NaHCO3- because if it is increased/decreased it
will effect the rate of photosynthesis as all plants requires
carbon dioxide in one form or another to photosynthesize and the
more or less they have the more or less photosynthesizing they can
do up to a maximum point.

* Light intensity - as if change it will effect the amount of light
being absorbed by the plant and therefore the amount of
photosynthesis the plant it able to do.

* The elodea - must be keep the same as every different plant of
elodea had different amounts of chlorophyll and surface area so
each plant will have a different rate of photosynthesis depending
on this.

* The technique- the technique for measuring the amount of
photosynthesis must be keep constant in this case using pencil dot

* Equilibrating time

* Time for o2 count

* Apparatus

What I am going to do is set up the apparatus and shown above. I will
then flood the elodea wit light as in the preliminary experiment to
get it photosynthesizing for about ten minuets, after I will set the
light intensity to 80mv using a comparator as light intensity must be
keep constant to ensure accurate result. I will then use different
colored filters in front of the light to change the wavelength of the
light each time I change the filter I have to use the comparator to
set the light intensity back to 80mv as different filters let
different amounts of light though. I am going to use a range of
filters who's wavelength range from blue (shortest) to red (longest).
Looking at my preliminary experiment I have decided on the range of
best colors they are white, blue, green, yellow, orange, and red. Once
I have set the light intensity to 80mv I will leave the elodea to
equilibrate for about 2mins before I take the first reading. To
measure the light intensity I will be counting o2 bubbles per minute
given off buy the elodea and I will count them using a pencil dot
technique. I will do 3 readings for each wavelength and then take an
average to insure more accurate results.


I am going to produce a table of results that will display the 3
readings for the independent variable wavelength and then an average.
I will have separate columns for each colored filter. I will also
produce a results \graph that will display the independent variable on
the x-axis and the dependent variable along the y-axis. It will be
displayed in a bar graph and each will have the value shown at the top
so it is clear.


I will write a conclusion in this I will state the patterns and trends
from my results. I will explain what the result are showing and refer
to my results table and graph.


I will explain what my results show in scientific knowledge looking at
fact form textbooks and the Internet. I will also compare my results
with my prediction to see weather they match and why. I will also look
at the accuracy and validity of my results and weather they are
accurate valid or not and why.

I will also look into extra work and how I could carry my experiment
on or look at other similar experiments I could look at. I would look
into changing the constants around to see how these effect the results
and how I could carry each experiment further and obtain more
evidence. I would also state improvements I could make for the
experiment and what I would change if I did it again


1. Pond weed (elodea)

2. Lamp

3. Different colored filters (white, blue, green, yellow, orange,

4. Beaker

5. Boiling tube

6. Sodium hydrogen carbonate

7. Plasticine

8. Thermometer

Write up

The effect of wavelength (color) on photosynthesis rate

Aim- see plan

Prediction - see plan

Apparatus - see plan

Method - I fallowed my method exactly.


Independent variable


Dependent variable (o2 bubbles per min)

Average dep. Variable

Reading 1

Reading 2

Reading 3































Graphs - see next page


I can see from my results that white light produced the highest
photosynthetic rate at an average of 382 02 bubbles per min and green
the lowest at an average of 21.3 o2 bubbles per min. These aggress
with my prediction. From my results I can conclude that the level of
photosynthesis depends on the level of energy the light carries and
its absorbency. The energy of the light is inversely proportional to
the wavelength so a long wavelength like red carries little energy but
a short wavelength like blue carries a lot if this is true then why
does red have such a high P.V when it carries the least energy, this
is because it is highly absorbed so a lot of the light is taken in
unlike green for example which is highly reflected but carries a lot
of energy.


The results I got matches the scientific information in textbooks and
the internet. My support does support my prediction. There are two
main factors to look at when looking at my results to do with
wavelength. That is that the photosynthetic rate depends on how much
energy the wavelength is carrying and the level it is absorbed at.
Blue carries a lot of energy and is highly absorbed so the level of
photosynthetic rate is high, were as green carries quite a bit of
energy but isn't absorbed at all so the level of photosynthetic rate
is low and red carries little energy but I highly absorbed all these
facts match with my prediction and my results.


My results I believe are fairly accurate but there are some main
factors that could be changed to ensure even more accurate results. my
results did match with scientific knowledge and my prediction so they
must be at least along the lines of valid results. my three readings
for each color filter were also close together giving the impression
that my results are valid. The one main thing I would change if I did
the experiment again would be the way of calculating the
photosynthetic rate. Instead of counting o2 bubbles per min which to
me is inaccurate as every o2 bubble has a different volume and the
accuracy is down to your observation so the likelihood of human error
is very high instead I would measure the volume of o2 given off this
would be far more accurate. I would also repeat the experiment or take
more readings maybe 6 per color filter then find the average to make
it more statistically accurate.

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