FAIR TESTING:
It is important to make sure that this experiment is as fair as possible because we need to obtain results as accurate as possible for it to be successful. To keep a fair test we need to keep some of the variables the same, this means making sure that the lamp is the right distance from the boiling tube each time we test and it doesn’t move when we re-test it. We also need to try and make sure that the temperature of the water doesn’t change during the experiment, this is why we are using a thermometer. The last thing we need to do is count the bubbles that the plant will produce accurately so as not to get the wrong results. We are also going to repeat each test three times so that we don’t get any fluke results that will jeopardise our experiment. One thing we have to take into account when doing this experiment is that the bubbles will be different sizes and masses so it is not possible for us to get a completely accurate result. What we are doing is a very rough estimate.
PREDICTION:
I predict that as the light decreases as will the rate of photosynthesis.
EQUIPMENT:
- lamp
- plant
- ruler
- clamp
- test tube
- water
- thermometer
- stopwatch
PLAN:
First we blacked out the room to make sure no other light interfered with our test, then we filled the test tube with water and placed the plant inside it, pushing it to the bottom. Then we decided on the distances that we were going to place the lamp from the plant. We used the clamp to hold the test tube and then set the lamp 5cms away from it and switched it on. As soon as we switched it on we started the stopwatch and we counted the number of bubbles that appeared for one minute, then we stopped the stopwatch and recorded the results in our results table. We did this three times to make sure it was fair. When we finished that length we moved the lamp ten cms away from the test tube and did the experiment again.
SAFETY:
There are a few safety rules that we needed to follow very carefully, to prevent serious injury. The lamp, when switched on, could become hot, which could be dangerous. Also the water may heat up from the intense heat from the lamp, so we must be careful not to spill it as serious injury could occur. Water and electricity do not mix so we had to be careful that our hands weren’t wet when switching the lamp on.
RESULTS:
5 cm 15cm 25 cm 35 cm 45 cm
1st 60 41 20 15 13 (plant 1)
2nd 52 43 32 25 19
3rd 67 39 26 5 1
1st 35 39 24 17 16 (plant 2)
2nd 32 29 21 17 9
3rd 69 61 35 26 13
1st 52 30 22 21 10 (plant 3)
2nd 50 31 20 18 11
3rd 47 29 19 11 2
ANALYSIS:
From my results I can see that my prediction was right, as the light intensity increases the rate of photosynthesis increases. A plant cannot photosynthesise in the dark, the more light it is subjected to, the faster it can photosynthesise , as I explained earlier in my background knowledge. On my graph of all the results, there are a few obviously different results, but none look like they were that weird. But when I put the separate plants results into separate graphs it showed that all the results were completely different, except for the third one because all the lines, although they were decreasing, they were all decreasing from different amounts of bubbles to another test of the same plant. For example, the third test on the second plant: the number of bubbles at five cms away from the light was 69 whereas the other two were 35 and 32. These weird results will uneven our average, and it isn’t a very fair test of accuracy. The only plant that did have the most near results to each other was the third plant, so if we wanted a more fair result we could just average those up but then we wouldn’t have much to compare to. If two out of three sets of results are dodgy then this must mean there is something wrong with the way we were doing our experiment. From our averaged graph there is an obvious pattern, the number of bubbles produced by the plant starts of at a high number usually between fifty and sixty and then decreases steadily until it gets to twenty five cms away from the light where then it still decreases but less steeply than before.
EVALUATION:
Our experiment didn’t go to well because although we managed to keep everything under control as much as possible, and we didn’t get a huge amount of freak results, it still isn’t a very reliable way of testing what we wanted to find out as it is way too basic. If we wanted to use the same method but improve it we could involve more people so that we would be able to check we had counted the bubbles correctly. Also we would need to control the background light as it would interfere with the experiment, but we didn’t have the means for it this time. Because of all these problems the strange results we got are very likely to be accuracy problems when counting the bubbles. It isn’t a fair test to have one person counting them all because they might not count properly, but a way of solving this is to have a few people counting so that the results would be more exact. The background lighting interferes because it adds to the rate of photosynthesis when we want to be testing from a certain light intensity. We managed to keep the temperature pretty much the same for the whole experiment, it dipped between 23c and 25c, so even though we did as best as we could, if there was a way of keeping a constant level temperature it would make the test a lot more fair. An even better way of improving this experiment would be under properly controlled conditions where we wouldn’t need to rely on someone having to count the bubbles, and we could use more reliable tools.
