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Photosynthesis Investigation

to find effects of distance of a light source from pond weed has on the amount of oxygen
produced


 Photosynthesis

All green plants need to be able to make their own food.They do this by a
process called photosynthesis.For photosynthesis to occur they need sunlight
energy.This energy is absorbed by a green pigment called chlorophyll,which
is mainly found in the leaves.This energy then combinEs with water molecules
(from the soil) and carbon dioxide (from the air).Then as a result of this,a
type of sugar is produced .This is called glucose.Also oxygen is made.

For my experiment I have chosen to use light distance as my variable.This
means that to carry out a fair test everything else must be kept the same
during the experiment.

Hypothesis

I think that as the light source (desk lamp) is moved closer to the
pondweed,the rate that oxygen is produced will increase therefore more
oxygen willbe produced and also more glucose. I believe this will happen
because when the the light source is nearer to the plant more of the plants
surface area is coming in to contact with the light from the desklamp
therefore more photosynthesis will occur which will  mean more oxygen and
glucose will be produced.

Apparatus

· Funnel.
· Measuring cylinder.
· Stop watch.
· Card board and foil(used to fillter the light).
· Beaker.
· Desklamp.
· one metre ruler stick.
· Balance.
· Pondweed.
· Carbon dioxide Powder.
· Water.
· Scapular.


Fair Test

To ensure that a fair test is carried out the following things must be done
· The same pondweed must be used every time we change the  light distance.
· Do th e experiment three times for each distance to get an accurate
average.
· There must only be one variable and that is the distance of the light
source  from the plant.
· Chose a value for carbon dioxide mixture and keep at the same value allthe
way through the experiment(3 grams).
· Keep the experiment at a constant 20degres (this is because more oxygen is
produced at this temperature).
· Take results after three minutes for each induvidual experiment.

Safety

· Follow lab safety rules (eg no running bags at back etc).
· keep the desklamp away from contact with water.
· Be careful when using scapuar.

Method

· Collect apparatus.
· Set up apParatus as in diagram.
· Fill measuring cylinder and beaker with water.
· Add carbon dioxide mixture to water.
· Set up desklamp in correct position(eg 10cm).
· Turn on desklamp and start stopwatch.
· Count the bubbles for the next three minutes and also make a note of the
change in volume.
· Record your results.
· Repeat experiment twice more for distance 10cm and then do the same with
distance 20,30,40,50,60,70,80,90, and 100cm.




Results

These are my results


Because my results did not go entirely to plan(because my pondweed was not
photosynthesising quick enough) I have been given a past years results which
I will now usS as my results instead.They are as follows-





Analysis

Looking at my results a can see a significant increase in the rate of
photosynthesis as the distanse decreases.All of the results I was given show
this pattern.In the experiment when the distance was 50cm there was not much
photosythesis taken place only about 13 bubbles of oxygen were produced,but
when the desklamp was 0cm away alot of photosythesis was occuring on average
184 bubles in three minutes a quite substanchal difference from 50cm,overall
it was a quite significant increase.I belive This is because when the
desklamp is close tho the pondweed more of the pondweeds surface area has
light energy shining upon it which means more photosythesis will occur in a
shorter time. The average no. of bubbles for different distances
arebasnfollows-



Looking at my results it is quite evident that the number of bubbles
produced is much greater when the distanse of the pondweed from the desklamp
is less.This proves that my original hypothesis was correct that "as the
distance decreases of the desklamp from the pondweed therefore more oxygen
bubbles are produced".As i mentioned before this is because there is more
light energy shining on a greater surface area when the desklamp is closer
so therefore greater surface area equals more photosynthesis.

Evaluation

        I think that on the whole my experiment was ok.The results
i gathered were very odd i belive this is because of the poor quality of the
pondwed we used.But with the set of resuts we were  given we were able to
calculate acurate averages which followed my prediction.
       I belive our measurments were about as accurate as we could get usill
oung the apparatus that we did.
       We experienced quite a few problems throughout our experiment.These
were first of all in our first experiment our pondweed was not of a high
standard and was photosynthesizing very slowly the only way we could have
got around this problem without using new pondweed would be to leave the
experiment for longer.Another problem we encountered was the change in
temperature when the desklamp was close to the pondweed because we could not
do anything to ammend this we had to accept any slight change in our
results.another problem we faced was counting the bubbles when the plant was
photosythesising the bubbles were different sizes,but as talked about in my
pelimenary data we overcame this problem by counting every individual bubble
as one.

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