Size of elodea: The rate of photosynthesis can vary depending on the size of the elodea the rate of photosynthesis will increase. The bigger the surface area of the plant the more palisade cells. The palisade cells is where the chloroplasts are and furthermore where photosynthesis takes place. So if there is a big Elodea plant the speed that photosynthesis happens will increase as there are more palisade cells that can be photosynthesising
I have decided to explore into how light intensity affects the rate of photosynthesis in the elodea. To do this I will carry out my experiment counting the air bubbles coming off from the Elodea and recording them into a table. I will repeat this experiment several times over short periods of time changing the variable and recording the results each time.
I will record my data in a table like this:
Whilst the experiment is taking place I will be recording my results in a tally chart because it is quick easy and simple to use, I have no idea yet how any bubbles or how fast the bubbles will be coming but I expect that a tally chart will be okay to measure fast coming bubbles as well as slow coming ones.
Preliminary experiment:
A preliminary experiment is one or two experiments where you test your method and see if there is anything that needs improving. You then use the results from these tests to alter or even completely
For our preliminary experiment we used this method first:
However this experiment turned out to be very poor and difficult to set up. It was hard to measure how much gas was coming off the elodea because they all kept getting stuck to the side if the funnel. Also the elodea blocked the funnel so it was hard to count bubbles.
Because of all these difficulties we decided to try out a much simpler method like this one below:
We found this experiment a lot easier to take out and the measurement of gas was a lot easier to do. So we chose to do this experiment
After making this choice, we then needed to decide the range of the input variable (distance from lamp to elodea). We wanted to start as close to the elodea as possible; zero centimetres, we put the lamp there, but as we started to measure the bubbles we could feel the boiling tube heating up. Because we need the experiment to be a fair one and we know from our research that temperature can affect the rate of photosynthesis we needed to cut down the heat transferring from the light to our experiment as much as we can. We came up with the idea of putting a beaker of water around the test tube to absorb any excess heat energy but still let the light energy pass through (because water is transparent.) Although the beaker solves the problem of having excess heat energy being transferred it made it hard for us to get close measurements to the test tube. The closest we could get was 10cm, so this would be our lowest point range. Also whilst we were experimenting we found that the furthest away from the elodea that the light could be for the elodea to carry on releasing bubbles was 45cm, so this would be our highest point range.
Final Method:
To set up my experiment on how light intensity affects the rate of photosynthesis in the elodea I will need the following equipment:
- Piece of elodea plant
- Boiling tube
- Beaker
Meter ruler
- Pair of scissors
- Paper clip
I will set up the experiment as shown in the diagram below by attaching the boiling tube filled with 50ml water onto a clamp that ensures it stays upright during the experiment and then placing that boiling tube into a beaker filled with 100ml of water. The ruler needs to be straight from the boiling tube to the lamp. I will attach a paper clip firmly to the end of my elodea and place my piece of elodea into the boiling tube I will carefully cut the end of my elodea using a pair of scissors, making sure that it is kept under the water at all times. To make sure that the light intensity is entirely controlled by me I will turn off all the room lights and cut off any other major light sources. When my experiment is set up correctly I will make sure my lamp is lined up at 10 cm and turn it and the stop watch on at exactly the same time. I will then time the 2 minutes whilst counting the bubbles carefully and recording the measurements and the number of bubbles per 2 minutes. I will repeat this experiment 6 times changing nothing but the distance the light is away from the Elodea. The distances will be 10cm 20cm 30cm 40cm 50cm 60cm 70cm and 80cm. To get more accurate results I will repeat the experiment 3 times if possible
Predictions:
Using my scientific knowledge and the research that I have been doing I would predict that light intensity will affect the rate of photosynthesis in this way: The closer the lamp is to the elodea the stronger the light intensity will be, I know this because we have being doing tests to measure the light intensity using specialist equipment. Our findings from this are that the brighter the light or the closer the light, the stronger the light intensity. I can also predict that the stronger the light intensity (i.e. the closer the light to the elodea) the more oxygen bubbles will be produced, showing evidence that more photosynthesis has taken place. I think this because I already know that a plant needs sunlight to be able to perform photosynthesis as shown in the formula below:
Water + Carbon dioxide >> Sunlight >> chlorophyll >> Glucose + oxygen
Also I know that if you increase anything on the left-hand side of this formula (the part I have boxed on the diagram above), everything on the right hand side will increase (Increase of input = increase of output.) This means that if the concentration of light were to be increased, the levels of glucose and oxygen (The rate of photosynthesis) will increase.
Fair test:
It is important that the experiment is fair to ensure accurate results and a 100% accurate conclusion. To make sure that the experiment I am going to do is fair I will make sure that I keep a number of things the same throughout the test. I will use the same piece of elodea because the size and surface area of the leaves on the plant changes from plant to plant and even if the plant was the same size and weight there still could be slight differences in palisade cells that would alter our results and therefore make out results unfair. I will also make sure that every time I carry out the experiment it is for the same period of time, if I don’t do this correctly the test would be unfair for obvious reasons. Another thing that I have to make sure is the same throughout the experiment is the water temperature, I will do this by putting the boiling tube with the elodea in it into a beaker also filled with water, the outer layer of water would soak up and excess heat energy coming from out light source, as mentioned above. To make sure there isn’t any excess bubbles being carried over from the last experiment every time I repeat the experiment I will make sure that I turn off the lamp and make sure that the plant has fully stopped photosynthesising before I start the repeat experiment. We need to spend a lot of time making the test a fair one, as it is vital that no other variable except light intensity changes.
Safety precautions:
In this experiments there aren’t any harmful or dangerous chemicals so there aren’t many important precautions that we have to remember. However, we are working with water and electricity and we need to make sure that we don’t touch any electrical equipment with wet hands or spill any water near sockets or equipment. We also have to be careful about spilling water on the floor and if we do we need to clean it up immediately in case people slip up.
Observation
I have calculated an average amount to bubbles for each measurement; I would use this average if I were to need to do any further calculations in my analysis or conclusion as an overall result for that distance.
I think that the results for this test are clear and there are very few anomalies. I think that repeating the experiment a fourth time is not necessary because the results that we have already are similar enough to each other that I can happily say that all 3 experiments were a success.
Analysis
The most obvious observation from my investigation out that the elodea releases oxygen bubbles i.e. photosynthesises faster, if the light is very close to it. Also the results show that at around about 45cm the rate of photosynthesis starts to rise again. This seems unlikely so will need to be investigated further.
Above is a simple bar graph of my average results showing how as I increase the amount light intensity by moving the lamp closer to the plant the number of bubbles coming off the plant increases. The shape of my graph is a curve, starting at 10cm and having a high amount of bubbles released and the sloping down to when the lamp is 40cm away from the elodea, it is at this point that the number of bubbles coming off the plant starts to increase again and the shape of the graph starts to slowly slope up again. The upturn at the end of the graph shows that after the light gets past 45cm (part with the arrow pointing to it) the rate of photosynthesis starts to rise again. This was unexpected and it is very unlikely that this is the pattern that the experiment should follow. After further research we realised that all results that we have taken after 45cm must be invalid because we know that the rate of photosynthesis should not rise again after 45cm and should only carry on falling.
Below is a line graph of my average results:
This line graph also shows how the rate of photosynthesis rises after 45cm, If we had not done further research into this we would have found it very unlikely that these results are anomalies because each time we did the 3 experiments the same pattern has occurred, this could be down to coincidence but the same pattern occurring 3 times would be very unlikely. It is more likely that the similar anomalies results are due to faults the equipment that was used because we used exactly the same equipment each time. It could also be due to light coming from other sources to our experiment causing the rate of photosynthesis to rise with the light coming in though I do not know however how this could have happened in all 3 experiments.
My prediction was fairly similar to the results that I got from my investigation.
Conclusion
Although there is a clear pattern in my experiment, as I have mentioned before, the evidence I obtained hasn’t corresponded with research and other sources of information that has been found. This makes me uncertain of how accurate my results are and therefore causes me to think that the results that I have obtained are not exact enough to prove my hypothesis. The experiment was simply not carried out with enough attention to detail.
This experiment could most defiantly be improved. More elodea in a larger water holder would have been better and produce many more bubbles and getting better results. The light could have been a lot brighter so, again, we would get more bubbles, and also the range of distance of which we measured could be increased.
For further results, we could have tested how temperature affected the plants along with testing how carbon dioxide levels affected photosynthesis. We would achieve temperature with usage of electric heaters and thermometers and carbon dioxide by putting bottles over the plant.
In summary, this whole experiment could and should have been redone, we more care, thought and better equipment.