The effect of light on the rate of photosynthesis.
The effect of light on the rate of photosynthesis
I am going to investigate how the change in light intensity can effect the rate of photosynthesis, and I am going to project light onto pondweed at 5 different distances and seeing how the rate of photosynthesis changes as the distance Changes. I will be able measure the rate of photosynthesis by counting the number of oxygen bubbles leaving the pondweed at the end of the stalk.
Prediction
I think my results will show that as I bring the projector closer towards the pondweed the rate of photosynthesis will increase causing oxygen bubbles to leave the pondweed because the product of photosynthesis is oxygen and glucose and the oxygen leaves through the Stomata and because the pondweed is under water the leaving oxygen will form into bubbles.
CO2 + H2O Oxygen (O2) + Glucose
The more I increase the light the faster the reaction will be, and because more light equals faster rate of photosynthesis then this means that light is a limiting factor, CO2 and the temperature are also limiting factors because without one of them the rate of photosynthesis would either stay the same or decrease and so this is why we are going to add Sodium Hydrogen Carbonate which contains CO2 to increase the rate of photosynthesis to make it a better experiment, if we were to increase the temperature as well the rate of photosynthesis would increase, if one of the three were lacking the rate of photosynthesis would either stay the same or decrease.
Graph of Prediction
Why I make this Prediction
If we were to increase the light even more, the rate of photosynthesis would not increase because there is not enough heat or Carbon Dioxide. However at the start of the experiment because there is enough Carbon Dioxide and the temperature is high enough and because the light intensity is increasing the closer the projector gets to the pondweed the more the rate of photosynthesis increases. When we project light onto the pondweed the rate of photosynthesis increases because the chlorophyll absorbs the light and with Carbon Dioxide and H2O photosynthesis occurs producing Glucose and oxygen and so the oxygen leaves the pondweed through the Stomata and because it is under water it forms oxygen bubbles. So the prediction graph levels off at the end because there is not enough Carbon Dioxide and the temperature is not high enough.
Fair test factors
To make it a fair test I will make sure that:
* The light source is the same, because then the light intensity will be the same (except at different distances) otherwise a different light source would make the results incorrect.
* To make sure the temperature stays the same, this way the results will not change drastically, for example if the temperature dropped considerably then the rate of photosynthesis would decrease. To make sure the temperature does not change we will leave a thermometer in the beaker so as if we notice that the temperature is increasing or decreasing we can do something about it.
* To make sure I put in the same amount of Sodium Hydrogen Carbonate. Because more Sodium Hydrogen Carbonate would increase the rate of photosynthesis and too little of it would stop ...
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* To make sure the temperature stays the same, this way the results will not change drastically, for example if the temperature dropped considerably then the rate of photosynthesis would decrease. To make sure the temperature does not change we will leave a thermometer in the beaker so as if we notice that the temperature is increasing or decreasing we can do something about it.
* To make sure I put in the same amount of Sodium Hydrogen Carbonate. Because more Sodium Hydrogen Carbonate would increase the rate of photosynthesis and too little of it would stop the rate of photosynthesis from increasing and if the amount of Sodium Hydrogen Carbonate was different then the rate of Photosynthesis would be dissimilar.
* It will be in a dark room, this way there will be no outside light to stop the light from the projector being properly focused on the pond weed.
* I will use the same piece of pondweed for each different distance otherwise the rate of photosynthesis might be different in another piece of pondweed and in the second piece of pondweed there might be more Carbon Dioxide or it might be warmer than the first piece of pondweed.
Why these factors need controlling
I will need to keep the light source the same because it affects the rate of photosynthesis, this makes it a fair test.
I will need to keep the same amount of Sodium Hydrogen Carbonate because it affects the rate of photosynthesis, this makes it fair.
I will need to keep the temperature the same because it affects the rate of photosynthesis, this will make it fair.
Preliminary work
Equipment
I used a:
Funnel, Beaker, Test tube, Lamp, 100 cm ruler, thermometer, Sodium Hydrogen Carbonate, Spatula, and Water.
Diagram
Method
We first half-filled a beaker with water and then put a funnel in a test tube and I then filled the test tube with water and next I put the test tube in a beaker and then with a piece of pond weed we shaved off the leaves at the cut off end of the pond weed and so I then put the pond weed into the Test tube leading through the funnel and then at 100 cm, 75 cm, 50 cm, 25 cm, 0 cm were the five distances away from the lamp and in the lamp's light we placed the beaker for four minutes at each distance. We measured the temperature with a thermometer (to make it a fair test) , and we measured the amount of oxygen bubbles per minute which came out of the pond weed, more bubbles meant that the rate of photosynthesis was increasing.
Results
Distance (cm)
Number of oxygen bubbles per minute
Light intensity
2
3
4
Average
00
4
8
3
8
3
Low
75
24
2
25
60
30
50
27
37
40
39
36
To
25
1
0
9
9
0
0
30
32
33
34
32
High
Conclusion
My results for my preliminary experiment were very unexpected because the results are going normal until 25 cm because as you can see the results have dropped considerably from 36 to 10 (average) this might have been because there was a bubble stuck in the pondweed and then it got dislodged at 0 or maybe the CO2 levels dropped or possibly it was my fault and I left the beaker to low so the light from the lamp did not reach the beaker. Another unexpected result was that at 4 at the distance 75 cm the rate of photosynthesis suddenly elevated.
In my preliminary experiment I did not take the temperature.
Because of the problems in my preliminary experiment it helped me to not make the same mistakes again in my second experiment like using a lamp instead of a projector for example.
Changes to Method
In my second method I recorded each distance for 2 minutes instead of 4 because 4 minutes took up too much time Andover that longer period of time towards the end of the experiment the rate of photosynthesis would have started to decrease. Also In my second experiment we used a projector instead of a lamp because the light source of the lamp was not strong enough. This time we also increased the amount of Sodium Hydrogen Carbonate to increase the CO2 levels which in turn would increase the rate of photosynthesis. Again this time we did not use a funnel in this experiment because judging from the last experiment it did not make a difference and it was just awkward.
My second experiment
Equipment
I will use:
* Projector: To project the light onto the pondweed.
* Beaker: To hold the water and the test tube and the Sodium Hydrogen Carbonate.
* Test tube: To hold the Test tube and the pondweed.
* 100 cm Ruler: To measure the distances.
* Sodium Hydrogen Carbonate: To add the Carbon Dioxide to the Experiment.
* Thermometer: to measure the temperature in the experiment.
Method
The first thing that we did was to cut off a piece of pondweed and put it under water, where we then half-filled a beaker with water and then we filled a test tube with water and we put the test tube in the beaker, we then shaved off the top leaves of the pondweed and then we carefully placed the pondweed in the test tube with the shaved end at the top of the test tube so next we placed the beaker at the 100 cm away from the projector with the light beaming down on the beaker for 2 minutes where as in my preliminary experiment I used a funnel and I left the beaker at each distance for 4 minutes, I changed this in my second experiment because the preliminary experiment took up too much time. Next in the experiment we placed the beaker at 100 cm, 75 cm, 50 cm, 25 cm and 0 cm away from the projector, and for 2 minutes at each distance we measured how many oxygen bubbles left the pondweed to measure the rate of photosynthesis, we will take two measurements for accuracy.
Diagram
Results
Distance (cm)
Number of oxygen bubbles per minute
Light intensity
2
Average
00
1
5
3
Low
75
3
26
9.5
50
22
46
34
To
25
39
58
48.5
0
56
61
58.5
High
The temperature stayed at 20 degrees Celsius.
Analysing
The only calculations we had to make were the calculating the averages of our results, all we did was add up our results for each distance and then divide them by two which was how many results we had (if we were to have 5 results then we would divide by 5, but we did not have 5 we had 2).
Analysis
a) I have found out that the more light which is projected onto plant then the rate of photosynthesis in the plant will raise causing oxygen bubbles to leave the plant faster. I have noticed in my graph that the closer the beaker is to the projector then he rate of photosynthesis rises or increases.
b) My results turned out the way they did because each distance ids closer than the other (100 cm - 75 cm - 50 cm - 25 cm - 0 cm). so the closer the beaker is to the projector the more light is received and so because more light equals increase in the rate of photosynthesis so at 0cm the rate of photosynthesis would be higher than at 100 cm, that is why at 0cm I counted 58.5 oxygen bubbles (for my average) and at 100 cm I counted 13 oxygen bubbles.
c) I have gathered that my results do match my prediction made in my plan, except at 75 cm because the rate of photosynthesis went unexpectedly low.
d1)In my prediction I stated that as I move the beaker towards the projector causing the rate of photosynthesis to increase and thus causing more oxygen bubbles to be released from the pondweed, this prediction matches my analysis because they are both the same.
d2) On my prediction graph the end levels off because I thought that the CO2 or the heat would run out, but in my actual experiment the end did not level off and so the CO2 or the heat did not run out and so it was not a limiting factor.
Evaluating the results
Overall my method did work well, the only thing which I can see went wrong from my graph is that at 75 cm the rate of photosynthesis dropped, I can tell that because few oxygen bubbles left the pondweed.
Not including my preliminary experiment we actually did two experiments, this was because the results were weak, there were very few oxygen bubbles so the rate of photosynthesis was low, we think that this happened because there might have been a oxygen bubble trapped in the pondweed or because the beaker was not high enough for the light projector so the light did not shine on the pondweed.
Seeing as my results told me that from 100 cm to 0 cm the rate of oxygen bubbles leaving the pondweed increased as well.
One of the problems I had in my experiment was that the pondweed was unpredictable (living thing) and there was an outside light source, and there was not enough Carbon Dioxide dissolved (Sodium Hydrogen Carbonate) into the water.
If I could change anything about the experiment I would do it in a dark room and I would measure the amount of oxygen with an oxygen probe, and I would measure it with a computer to be sure that the results are right and not incorrect, and to get the most out of the light from the projector to measure the real amount of oxygen.
Overall I think my evidence was of a reasonably good standard because they matched my prediction. I had to repeat my experiment because the first pondweed was not very good were as the second experiments results were good and gave good evidence. The only odd results I had were at 75 cm the rate of photosynthesis was a bit slow because there might have been a bubble trapped in there or there might have been fewer bubbles but the bubbles might have been bigger and so in fact there might have been more oxygen released and only fewer bubbles.
I think that my evidence is very reliable because I counted the amount of oxygen bubbles myself and I performed the method accurately. I think my evidence is sufficient to support my conclusion because they match each other almost exactly.
To provide additional evidence I think I could do the same experiment except instead of counting the amount of oxygen bubbles leaving the pondweed I could measure the exact amount of oxygen with an oxygen probe. In my experiment the temperature stayed the same so it did not affect the results.