Experiment to Show the Rate of Photosynthesis
Length: 648 words (1.9 double-spaced pages)
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Aim: Experiment to show the rate of photosynthesis when pondweed is
under different life intensities.
Prediction: I predict that the closer the light is to the pondweed the
(or the higher the light intensity) the more oxygen will be produced
until a certain point where the temperature or carbon dioxide levels
will be the limiting factor. The further away the light, the slower
the oxygen bubbles will be produced so the less light the less
photosynthesis will occur which is needed for the plant to make food.
The rate increases (A) but only to a certain extent. Then they
don't increase any more because of the other limiting factors of the
carbon dioxide levels and temperature.
v Sodium Hydrogen Carbonate
v 1 Meter Ruler
v Measuring Cylinder
* Set up apparatus like above with the light source 5 cm from the
beaker and cut the end of the pondweed.
* Some potassium hydrogen carbonate might have to be added which
provides carbon dioxide for the plant which is needed for
photosynthesis. Then wait for the plant to 'acclimatise'.
* Count the number of bubbles seen in 1 minute which is a way of
measuring the rate of photosynthesis.
* A row of dots on paper while counting can represent each bubble
* Move the light 10cm away. Wait 2 minutes and then count the bubbles
* Repeat this at 15cm, 20cm then 5cm intervals until the bubbling
stops and repeat each measurement twice to get a more accurate result
and find the average.
Changing variable: Light intensity
Variables kept the same:
* Amount of pondweed-
Why: More pondweed, the higher the rate of photosynthesis
How: Weigh pondweed with scales
* Water to absorb heat distance
Why: Closer or further means temperature differs around the pondweed
How: Keep water 2cm away from beaker at all times
* Amount of KHCO3 added
Why: The CO2 provided can affect the rate of photosynthesis
How: One scapula full put in to the water with the pondweed every time
* Dark room or same light around the pondweed other than the lamp
Why: If more light is focused on the pondweed the rate of
photosynthesis will be increased and it will not be a fair test.
How: Investigation to take place in dark room
Conclusion: The most bubbles were produced when the light intensity
was 5cm away from the pondweed which means more oxygen is produced
which suggests that the more light focused on the pondweed the more
photosynthesis will occur and the photosynthesis occurred very fast on
that measurement which also prooves my prediction was correct. When 10
cm away from the lamp photosynthesis was till occuring as quite a few
oxygen bubbles were being produced but not as much as when the
pondweed was closer to the light source. Less bubbles were produced in
the 15cm test due to the fact that there was less light and therefore
less photosynthesis so less oxygen is produced. This patter continued
as the light involved in the photosynthesis process decreased less
bubbles were produced 20cm, and 25cm away.
Evaluation: The results from the 5cm tests were equal which shows that
the results were right with an average of 14 bubbles per minute. The
results for the 10 cm test were close with an average of 8
bubbles/minute. The 15cm one was very close too, in the first test 6
bubbles were counted and then 7 bubbles in the next test which makes
them about right with an average of 6.5 bubbles/minute. The oxygen
produced for both tests for the 20cm distance were the same which
shows that the results were correct. The 25cm distance was also close
and had an average of 3.5 bubbles per minutes which shows that all of
my results were pretty much correct and less oxygen is produced when
the light source goes further away. There were also no major anomilies
but a couple of problems were faced during the investigation. The
initianal pondweed used for some of the experiments did not produce
any oxygen so the experiment had to be redun. To improvw this I should
be using fresh autotrophic pondweed to produce oxygen first time
around. Another problem faced was that the distance between the light
and the beaker wasn’t exactly spot on so to make this a better test
the measurements should be taken accuretly and marks should be made
where appuratus should be placed.