Throughout my experiment, I'm going to study the speed of photosynthesis, whilst altering the water to five separate temperatures and observing the speed of the reaction. In order for my experiment to be more reliable, I will carry out three repeats for each temperature.
From these factors, I decided upon changing the temperature. I did so due to the fact I thought it'd be an interesting - yet challenging experiment, and I'd never conducted an experiment with the variable as temperature before. I would personally like to investigate how temperature affects the amount of oxygen produced throughout the process of photosynthesis. Finally, I will be counting the number of bubbles released from the stem of the plant I will be using.
Prediction:
I predict that as the temperature's increased, the number of oxygen bubbles produced within the given 30 seconds will also increase, until the plant reaches its optimum temperature - when the rate of photosynthesis will decrease sufficiently. I have predicted this due to my general knowledge on photosynthesis and collision theory.
Equipment:
-
Water bath (I chose this piece of apparatus as it is incredibly accurate and is able to keep the water at a constant temperature)
Elodea (I chose to use this as it's a plant which you can very easily monitor all the elements required for photosynthesis)
- Sodium Hydrogen Carbonate
Test tube
Test tube holder
Paper clip
Spatula
Kettle
Lamp
Thermometer
Stopwatch
Water
Universal Indicator
Method:
My independent variable in my experiment was temperature, whereas the dependent variable was air. I researched the seven other factors which affect photosynthesis and kept these the same. Firstly, as elodea is an aquatic plant, it's underwater, as long as the whole of the plant is underwater, the water level is controlled automatically. I placed a lamp 5cm away from the test tube throughout the entirety of my experiment, and replaced the water between every testing, adding quarter of a spatula of Sodium Hydrogen Carbonate, which helps to produce carbon dioxide – thus keeping the CO2 levels constant. The light colour during the experiment was the same, and I used the same plant to ensure the amount of chlorophyll was constant. On top of this, I used universal indicator to make sure the pH is the same throughout the experiment. As I changed the temperature, I kept it under close control and checked it regularly.
In order for this to be a fair test, I counted the bubbles myself, there was no change of person counting.
- I filled the water bath with water from the kettle, turned off before the water met boiling point. I then set the water bath to 50ºc, and checked when the water had met 50ºc.
- I cut roughly 6cm of elodea underwater, cutting the stem diagonally. I anchored a paper clip to the end which had not been cut. The piece of elodea was then placed into the water-filled test tube, ensuring the diagonally cut end was pointing upwards.
I used the test tube holders to put the test tube into the water bath and fill the test tube with water from the bath.
- After checking the temperature in the test tube, I added a quarter of a lab spatula of Sodium Hydrogen Carbonate to the test tube and stirred gently.
- Immediately after doing so, I timed for 30 seconds on my stopwatch whilst counting the number of bubbles produced from the cut stem of the elodea.
I repeated this test a further two times to give me three results for this temperature.
- I turned the temperature control on the water bath to 40ºc in order to prepare for the next temperature test.
- I repeated these steps for each temperature, lowering the temperature of the water bath to the temperature required.
My Preliminary Experiment:
My preliminary experiment allowed me to identify faults in my plan and alter them for the real experiment. I needed to work out which temperatures I could count the gas bubbles at, and found that at the temperature of 60ºc, none were produced. Therefore, I made the maximum temperature 50ºc. Following this, I tested the lowest temperature I could make the water, and decided 10ºc was the lowest yet most practical temperature. I then chose to record the number of gas bubbles within 30 seconds at 10ºc, 20ºc, 30ºc, 40ºc and 50ºc. After testing these temperatures, I was left with these prelimary results:
I decided upon conducting five separate temperature readings, and three repeats per temperature. Therefore, there is a sufficient number of readings which enable me to see the trend and correlation – from the time given. I chose to have three repeats as it wouldn't take a lot of time and there are other results to compare with.
Final Results:
On seeing my results, I am proud to say they are very reliable, I conducted my experiment with care and only had one outlier, which was roughly 50% higher than the previous results, which I quickly identified and re-tested. Given that elodea is a living thing, and does not produce uniform results, I'm not worried about it. Enzymes can stop working and denature when they get too hot, but my results show that they still function at 50ºc. There is a positive correlation between temperature and the number of bubbles produced, and each temperature had repeated results which ranged no more than 5 bubbles.
Evidence:
Enzymes are fundamentally catalysts which speed up chemical reactions, like said earlier when introducing photosynthesis. But for the reaction to occur, enzymes in the plant must work, or the rate of reaction would be too slow. From my graph and my results, it is evident that as the temperature increases, the enzymes can absorb more heat energy, therefore they're able to move faster and react quicker during these temperatures. Green pigment called chlorophyll traps the light energy from the sun, and the light energy is used to make a sugar called glucose. The chloroplasts which contain the chlorophyll are located in the plant leaves, which are able to catch and absorb the sun's light. In the stems, no photosynthesis occurs. Stomates, which are located in the lower epidermis are used for air exchanged, letting CO2 in and O2 out. Again, there are seven variables which control photosynthesis, these seven things can change the rate of the enzymes reacting.
My Graph:
I am happy with the results on my graph. In my prediction, I predicted that the number of bubbles produced would increase, as the temperature increased. Therefore, my prediction was correct. I have identified one outlier, this could've been due to the length of time the cutting of elodea was left in the water before timing and counting – it's best to begin testing the reaction as soon as possible. Cloud cover could have altered the amount of light allowed to the plant, as the day passed. If so, this could not be helped.
Conclusion:
How does changing the temperature affect the rate of photosynthesis? To answer my original question, as the temperature increases, the rate of photosynthesis increases – more oxygen bubbles are produced. The higher temperatures allow more heat energy to be absorbed by enzymes, and collide with the carbon dioxide and hydrogen which they can only accept, they consequently work more quickly, and collide more frequently.
Evaluation:
I managed to conduct this experiment with as little help as possible, only allowing another person to help time with the stopwatch. I am happy and confident that my results are of a good quality and reliable. If I were to conduct this experiment again, I should like to repeat my readings more than three times to ensure I have the most reliable results possible, along with a more accurate average. My error bars are of a reasonable span. My technique throughout the experiment was good, though occassionally due to the complexity of this investigation, the elodea was left in the water longer than other times, therefore it could've become more familiar with the temperature, slowing down its reaction.
