Turn it on and count how many oxygen bubbles are made during a minute
Move the lamp 10cms further away (now 20cm from beaker)
Do this until the lamp is 60cms away
Sodium hydrogen carbonate test
Set up the equipment as shown above
Put in 1g of baking powder
Count how many oxygen bubbles are seen in 1minute
Change the water and set up the experiment again
Put in 0.75g of baking powder
Count how many oxygen bubbles are seen in a minute
Repeat with 0.5, 0.25 and 0
Equipment
Fair Test
This will be made a fair test by the fact that when doing the sodium hydrogen carbonate test the lamp will always be 5cm away, so that this won’t be affecting the rate of photosynthesis as well. We will repeat the light test 2 times so that we make sure it is being done properly. We will use different people within our group to do different tasks so that it is timed and carried out accurately.
Prediction
I predict that as the lamp is moved away from the beaker less oxygen bubbles will be produced. I think this because photosynthesis needs light to take place and if the bulb is closer the intensity of the light is greater so the plant will have more energy to photosynthesise. The light is needed because it turns carbon dioxide into glucose. I also think that as the lamp is moved away the gap between the number of bubbles produced will grow larger because when the lamp is close the amount the plant is respiring is limited by the amount of carbon dioxide in the air, therefore when closer it won’t increase by much. I think that as more sodium hydrogen carbonate is added more oxygen will be produced. I think this because hydrogen is used for photosynthesis and so the plant extracts the hydrogen and uses it to produce more oxygen bubbles.
Results
Graphs
See attached sheets
Conclusion
My results show that as more sodium hydrogen carbonate is added the Elodea gives off more oxygen bubbles because carbon dioxide is needed for photosynthesis. As the lamp is moved farther away less oxygen bubbles are given off because intense amounts of light are needed for the plant to photosynthesise, though at a certain point I don’t think the plant would photosynthesise any more even if it was given more light because there wouldn’t be enough carbon dioxide around to let it photosynthesise.
Evaluation
If I was going to do the experiment again then I would have done the sodium hydrogen carbonate test more than once to get more accurate results. I may also use a different method to obtain the results, for example I might do it using the apparatus and set up shown below. I may also have some way of putting carbon dioxide in the air because the amount the plant is photosynthesising may be limited by not enough carbon dioxide even though there is plenty of light.
