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The Affects of Light Intensity on the Rate of Photosynthesis

Free essay example:

The Affects of Light Intensity on the Rate of Photosynthesis


  1. Independent: light intensity
  2. Dependent: the rate of photosynthesis, and the number of oxygen bubbles produced.
  3. Controlled:
  • The same type of plant must be used.
  • The time in which the oxygen bubbles are counted must be the same (five minutes, measured using a stopwatch).
  • The time taken for the plant to adapt in its new environment must be kept the same (two minutes measured with a stopwatch).


  • A Green plant
  • A Test tube
  • Some Water
  • Stop-watch
  •  A pair Scissors
  • Table of results
  • Two lamps


  1. Gather the apparatus listed above.
  2. Cut the plant from both ends using the pair of scissors.
  3. Fill the test tube with water, and put the plant in the tube.
  4. Make sure that the plant, which was put in the test tube fully, sinks in the water.
  5. You need to wait two minutes before you can start counting the oxygen bubbles.
  6. Make sure that you use the same plant for every experiment.
  7. Make sure that the temperature is the same, for accurate readings.
  8. As soon as the two minutes is over, you start the oxygen bubbles.
  9. After the second five minutes are over, turn on of the lamps on, and wait for wait another two minutes. And when the two minutes are over start the count again.
  10. Redo the whole experiment again with tow lamps. And make sure you keep the temperature and plant the same.

Data Collection:

Table showing the number of oxygen bubbles produced when certain numbers of lamps are turned on

Bubbles counted when no lamps were on

Bubbles counted when one lamp was on

Bubbles counted when two lamps were on

In the First five minutes




In the second five minutes




In the third five minutes




In the fourth five minutes




In the fifth five minutes












Data Processing and Presentation:



With a greater light intensity the rate of photosynthesis increases, because with more light there are more photons which are taken in by the plant leaves. This will increase the rate at which light dependent phase takes place. In the light dependent phase, the photosynthetic organism converts the light energy (photon) into energy carried by electrons. In photosynthesis the electrons are picked up by electron carrier which uses the energy in the electrons to make energy carrying compounds called ATP (Adenosine Tri Phosphate). It also makes another compound called NADPH. And the main product of this phase is to create oxygen. Because this phase depends on light, the more light we have the more oxygen is produced. My graph proves this theory.  By looking at my graph, one can see that when no lamps were turned on the total oxygen production was 259. And when one lamp was turned on the production of oxygen bubbles increased to equal 307. Finally when two lamps were turned on the production of oxygen increased even more to equal 320.


Measuring the rate of photosynthesis is very tricky, because the controlled factors are hard to control. In this experiment the light intensity was changed and the oxygen bubbles were counted. A more efficient count would be to capture the oxygen produced in the experiment and measure it volume. We could also more than one plant to see if we can find a pattern. So that we can make sure that our results are accurate. We can also try the experiment with more than two light bulbs so we can have a bigger range of results. We can do the experiment more than once to get more results, and by doing that we get even more accurate results. the temperature had to be measured for accurate results, however the temperature was not measured. So it the experiment is to be carried out again, then I would need to measure the temperature and keep it constant. For better results we would need to control the limiting factors.

Bashar Abu Al-Soof 10C Vienna International School 10/31/2008

This student written piece of work is one of many that can be found in our GCSE Green Plants as Organisms section.


Here's what a star student thought of this essay

3 star(s)

Response to the question

The response could have been more explicit for example, a hypothesis could have been stated at the beginning as this would had given the student more to talk about when it came to the conclusions and evaluation sections. The question ...

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Response to the question

The response could have been more explicit for example, a hypothesis could have been stated at the beginning as this would had given the student more to talk about when it came to the conclusions and evaluation sections. The question set has been answered and the appropriate evidence e.g. method has been given to support the answer

Level of analysis

The student should had started with a hypothesis as this would have helped them later on in the essay, this only need to be a sentence max about what you think is going to happen in the experiment. The student has identified which are the independent and dependant variables in this experiment and which are the other variables that need to be controlled; this is a good skill to have as throughout scientific education you are expected to do this. To make this section better the student could have said why the other variables needed to be controlled and how they were going to be controlled. The apparatus list is basic, stating what is needed and not why it is needed, this is a skill that will prove to examiners that you have a higher level of understanding about the experiment you are carrying out; phrases such as ‘Some Water’ should not be used instead say water or state a volume of water that you will be using as ‘some water’ is not scientifically correct. The conclusion is good explaining the concepts behind the results. The evaluation is also basic using words such as ‘tricky’ instead use words such as difficult as tricky as it does not show the examiner that you have good understanding of what is required for a experiment write up. All of the advice I have given I would not have known at GCSE it is only from doing about one write up a week for As Biology that I have gained all of the skills so do not worry about not doing them this time just remember them for next time!

Quality of writing

There are a few grammatical and spelling errors that should have been picked up during the reviewing process as, reviewing what you have written before you hand it in is essential for any piece of coursework. The technical terms used are basic in places and good in others, proving that the student has the potential to fulfil the expectations at this level.

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Reviewed by cheekymokeyxxx 24/03/2012

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