WATER:
Water is reacted in the photosynthesis reaction, and when it is lacking, the plants stomata close to prevent further water loss. This closing of the stomata cells also leads to little carbon dioxide being able to diffuse through, however, in a water plant, like the elodea, as long as the plant is fully under the water at all times, this will not be a problem.
TEMPERATURE:
Temperature will increase the rate of photosynthesis, until enzymes denature.
Prediction:
I predict that as the light intensity increases, the rate of photosynthesis increases up until a certain level is reached and then eventually it will go down.
INPUT VARIABLES: The thing that will vary is the light intensity, it will be varied by increasing and decreasing the distance from the light source to the plant.
OUTPUT VARIABLES:
Volume of oxygen produced will be measured by counting the amount of oxygen bubbles produced in a minute.
APPARATUS:
- Pond weed
- Thermometer
- Measuring cylinder
- Water
- Stop Watch
- Ruler
- Scalpel
- Sodium Hydrogen Carbonate
- Scissors
- Desk Lamp
METHOD:
Cut a stem of elodea at the end. Fill a test tube with water and place the elodea in the test tube; making sure the elodea is completely immersed in the water. Insert a thermometer into the beaker, and record the temperature. Set up the lamp at a set distance from the plant. Insert one spatula of sodium hydrogen carbonate. When bubbles are being produced at a steady rate. Start the stopwatch wait for five minutes for the elodea to get used to the light at the first distance then time for two minutes and count the amount of bubbles for another two minutes and repeat this until you have five different distances that the light is at, waiting five minutes each time at each distance for the elodea to get settled to the light intensity and then count the amount of bubbles that come off the elodea over the period of two minutes.
Place the weed into the cylinder first quite near to the lamp to encourage the weed to start photosynthesising.
Fair test
In order to make this experiment a fair test I will use the same elodea because if I used different elodeas the rate that one plant photosynthesises may not be the same as the other elodea.
I will use the same amount of time for the elodea to settle with the light when changing the intensity of light.
I will also keep the temperature the same and the amount of carbon dioxide will also be the same.
Evaluation
I think my experiment went well but there were a few problems. We all did this experiment alone, this way it took more longer, but working alone I find my results more accurate then if I had worked in a group as I understand fully what I had set out to do and would have to concentrate more as there is just one person doing it.
One of the things I did not find suitable, in my opinion was my results as I had to round them up to an integer they became less accurate and reliable, however if I had rounded them to two decimal places I believe my results would have become more accurate and more reliable.
Another problem that I found was that it is very difficult for the human eye to judge when the dot disappears completely. While I was doing my experiment I asked another student to watch the reaction with me and decide when the dot disappears we both saw the dot disappear at different times so the time could be misjudge which is why I did the experiment again to get more accurate results.
One reason I think my results were accurate was because I took multiple readings and then an average time from these results as you can see from the graph of the average time, however I still think my results are quite accurate as I only had one anomalous results.
Conclusion
I conclude that the higher the temperature the lower the rate of the reaction, so the temperature does affect the rate of reaction. So my predication was correct.
Overall I think my investigation went well, there were a few problems but I managed to over come them. In my graphs there was one anomalous result, but that is to be expected. One other thing that I think was a problem was when I poured the solutions in to the conical flasks I was not able to start the stopwatch at the exact time that I poured it in. Also while I was timing the reaction I found that the human eye is not always accurate enough to tell when the experiment had taken place.
Analysis
My graph was in the form of a line of best fit. I found that as light intensity increased, photosynthesis increased, this is because photosynthesis is a reaction, which needs energy from light to work.
From these results I can say my hypothesis does appear to be accurate and that an increase in light intensity does in fact increase the rate of photosynthesis. As light intensity increases eventually the rate of photosynthesis does gradually decrease by enzymes being denatured.
Results
Bubble count
Average
Investigating The Light Intensity And The Effect It Has On Photosynthesis