Method
I put a piece of Elodea Canadensis (pond weed) in a test tube and covered it with water.
The test tube was then placed in a beaker with a thermometer so that the water stayed the same temperature, this was then placed in a cardboard box with a bulb attached to a voltmeter by the electrical wires so that I could concentrate how much light the plant got.
I varied the voltage (intensity) of the bulb and counted how many bubbles of oxygen were created at each voltage in one minute.
I tested each voltage three times for accuracy for a minute each time.
Results
Evaluation
The table shows us that more oxygen was created at a higher light intensity. I think that this experiment was not very reliable as the way of counting the amount of oxygen was not reliable at all. If I was to improve the experiment I would change the apparatus I used so that I could measure the amount of oxygen given off accurately.
I would also test more voltages of light to widen the results of the experiment, thus creating a clearer picture of how the light intensity is affecting the plant. The preliminary experiment is unreliable due to the simplicity of it.
Improved Experiment
Prediction
I predict that the rate of photosynthesis will increase until other limiting factors run out.
Limiting factors are:
- Carbon Dioxide
- Temperature
- Amount of water
- Light Intensity
If we run out of Carbon dioxide, water or light photosynthesis cannot take place. Also if the temperature is too high or too low photosynthesis cannot take place either.
I believe my prediction to be correct as plants need sunlight to photosynthesise. So if the light intensity increases so should the rate of photosynthesis. If you look at a plants leaves surface area and position on the stem you see that it is trying to get more light. This shows us that the more light a plant gets the more it will photosynthesise this all depends on the limiting factors. I will vary the light intensity in the experiment. But I will control the amount of water and temperature so that they are always the same.
Apparatus
- Beaker
- Test tube
- Piece of Elodea Canadensis
- Water
- Voltmeter
- Capillary tube
- Bulb
- Syringe
- Two electrical wires
- Box
- Clamp stand
I will, for safety reasons, keep all water away from the electrical equipment and the bulb.
Method
I will place the piece of Elodea Canadensis and place it in the syringe. Attach the capillary tube to the end of the syringe and fill with water.
Place the syringe in a clamp stand and place the end of the capillary tube in an empty beaker, this will then be placed in the cardboard box. I will draw up some oxygen, using the syringe plunger, into the capillary tube to about half way up, I will then mark where this comes to with a pen on the capillary tube.
I will turn the bulb on by attaching it to the voltmeter by the electrical wires.
I will vary the voltage of the bulb timing each volt for one minute. I will mark the new position of the oxygen in the capillary tube and measure how far it has moved down the tube. I will use this measurement to calculate the amount of oxygen in mm2.
Results
Evaluation
I think that this experiment is much more accurate than the preliminary experiment, due to the fact that the preliminary experiment was very simple.
It shows that the higher the light intensity is the more oxygen is produced. I do have a couple of anomalies which I believe to have occurred because the experiment was run over two separate lessons, so the pond weed/equipment was different in each lesson. Some examples of these anomalies are volts 4, 5 and 8.
Otherwise I think that this experiment is more reliable and gives us a clearer picture than the preliminary experiment.
Conclusion
I have realised in this experiment that without the products of photosynthesis all living organisms would die, including plants as eventually the limiting factors would run out such as carbon dioxide. Both these experiments tell us how much oxygen is produced during photosynthesis by using similar but different methods. Both experiments came up with valuable results even though neither where completely accurate. The improved experiment results showed a wider range of volts and accuracy therefore being the more reliable source of results.
I think that there must be a more reliable way of doing these experiments but with the equipment and time we had I believe that this was the most accurate and reliable way of doing these experiments.
If I was to perform a third experiment which was yet again improved I would test a larger range of volts and find a more reliable way of doing the experiment on a whole.
We have proved that oxygen is a product of photosynthesis and recorded reasonable results showing the amount of oxygen produced. I have also included graphs using the information in the tables. These show the rate that oxygen was produced (rate of photosynthesis).
I think that this experiment was a good investigation into photosynthesis and shows us about production rate of oxygen.