To investigate the effect of light intensity on the rate of photosynthesis on elodea (pondweed)

Apparatus:

* Boiling tube

* Elodea (Pondweed)

* Lamp

* Clamp Stand

* Ruler

* Stopwatch

* Bicarbonate

Method:

We are going to observe how many bubbles are given off from 6 different distances between the lamp and clamp stand. This will give us a much better perspective of how the light intensity effects the amount and speed of bubbles given of or in other words the rate of photosynthesis. Then for each distance we are going to record it three times so that then we can calculate the mean average of our results and therefore give us much more accurate results.

I chose to time the number of bubbles given off for the first one minute. This is because in the first minute the bubbles were at their most effervescent and this enabled us to calculate how the light intensity effected the rate of photosynthesis.

I also chose to take the reading from an increasing distance by 10cms. This was because I thought that it would not be necessary to do them at 5cm interval because if we did 3 results for each 10cm interval then the average of this would be more accurate.

Try and keep the temperature of the water in the test tube the same throughout the experiment! This is because enzymes are used in the photosynthesis reactions of a plant and as the temperature increase so will the rate of photosynthesis until a point when they will denature.

. Fill the boiling tube with 40mls of water. We fill the test tube with water because if water is lacking then the stomata will close up and the carbon dioxide intake will be flawed

2. Add bicarbonate. We add this to our experiment because if it is lacking then it is a limiting factor to the photosynthesis and therefore are results will have an impeding affect on them.

3. Put the elodea into the boiling tube

4. Attach the boiling tube to a clamp stand

5. Measure a distance of 10cm between the foot of the clamp and the lamp

6. Then wait for one minute (until the bubbles are constant)

7. Then time for one minute with the stopwatch counting and recording the number of bubbles produced.

8. Then immediately time for another a minute counting and recording the number of bubbles produced

9. Repeat the last instruction once again

0. Then move the lamp a further 10cms away from the clamp stand

1. Repeat instructions 6 ,7 and 8

2. Then move the lamp a further 10cms away

3. Repeat instructions 6, 7, 8, and 9 but increasing 10cms to the distance with each time until the distance between the clamp stand and lamp is 60cms

Diagram:

Fair test:

To make sure that this experiment was as accurate as possible we had to make sure that it was a fair test. We did this by keeping all the variables except the light intensity (distance from lamp to clamp) the same. Although I am happy with my experiment I know that it was not as accurate as it could have been. This is because when we were counting the bubbles we were relying on them all being the same size, which they definitely were not. Also as we carried on with the experiment the heat from the lamp was effecting our results as it speeds up the rate of photosynthesis. Another thing that could have made it fairer was that we were not in a completely pitch black room so the light in the room may have effected our results.

Results

Distance

(cm)

st recording at 1 minute(secs)

2nd recording at one minute(secs)

3rd recording at one minute(secs)

Average(secs)

0cm

85secs

62secs

74secs

74secs

20cm

71secs

56secs

68secs

65secs

30cm

52secs

46secs

48secs

49secs

40cm

20secs

00secs

94secs

05secs

50cm

57secs

52secs

30secs

46secs

60cm

25secs

23secs

6secs

21secs

Analysis:

My results showed that as the light intensity increases so does the rate of photosynthesis and vice-versa. This proves that my prediction was correct. My graph was in the form of a best-fit curve. I drew it as a curve rather than a straight line because of the clear pattern of the points. This meant that the rate of photosynthesis increased as the light intensity increased. This was because photosynthesis is a reaction, which needs energy from light to work, so as the amount of energy available from light increased with the rise in light intensity, so did the amount of oxygen produced as a product of photosynthesis.

Overall, both the graph and my results support my predictions fully.

Also in my graph I had no anomalous points, which proves that my results were fairy accurate even though there was hiccups in keeping it a fair test due to the heating of the lamp and the room being light. This may have effected the results we gained however they have not disputed the fact that the closer the lamp was the faster the bubbles were produced.

Evaluation:

I think that the experiment went well and that the average results for each distance were accurate. I think that there could be numerous improvements on this experiment including calculating the distance between the pondweed and the lamp instead of the foot of the clamp and the lamp. Also you could improve the experiment by collecting the oxygen in upside down test tube. You do this by filling the test tube up with water then turning it upside down then having a delivery tube going from the pondweed into it and as the gas goes in it pushes the water out and so you can measure how much gas you have collected.

and we therefore experienced light pollution from other student´s experiments. This would have had a very marginal effect on my results as a whole, but to eliminate this problem completely, it would have been necessary to perform the experiment in a totally dark room. A further inaccuracy was in the heat generated by the lamp.