Equipment list
We used the following equipment:
- Pondweed
- Funnel
- Sodium hydrogen carbonate solution
- Clamp
- Boss
- Stand
- Barrette
- Table lamp
Apparatus
The equipment was put up in the following way:
Method
- Set up the experiment as shown in diagram.
- Leave the experiment for 48 hours in cool room (good if away from window).
- Come back after 24 hours and take results from the bottom of mucus.
- Come back after 48 hours and take results from the bottom of mucus.
- Repeat the experiment again with different piece of pondweed.
Preliminary experiment
The concentrations of sodium hydrogen carbonate solution we used in the experiment are 0%, 0.25%, 0.5%, 1% and 5%. We kept the pondweed to 5cm to ensure a fair test so we always have the same amount of surface area for photosynthesis. The light is placed 15cm away from the beaker to ensure that light doesn’t become a limited factor to ensure an accuracy test. There has to be sodium hydrogen carbonate solution in the burette for the experiment to work. We kept all variables the same in the experiment.
Prediction
From my knowledge of this experiment and my knowledge of this subject, I can make a justified prediction. I predict that when the concentration of CO2 increases, the amount of O2 produced will increase but level out, as too much CO2 will result in the other factors being limited. I can make this prediction because I feel that the more chemicals (reactants) that are present, the more chemicals can be used to produce O2.
As I already know from my background knowledge, there are many limited factors for photosynthesis. Therefore I can tell what effects in changing the factors will occur.
I however predict from my background knowledge that there will be an optimum point, as the enzymes will denature at an optimum point before levelling off the graph.
Look at the Carbon Dioxide on page 2.
Results
Conclusion
The lower concentrations show a rapid increase in the rate of photosynthesis but according to the graph there is a steady decrease after 1%. My possible photosynthesis shows a rapid increase then when at around about 2.5% it starts to fall until it reaches 1.65ml3, that is the average oxygen produced over 24 hours under a 5% concentration of CO2. The shape of the graph is that way on the previous page because all the other factors needed to help photosynthesis became limited so the plant couldn’t photosynthesis at an optimum rate so the graph began to fall. The conclusions are that the rate of photosynthesis will not keep on rising and it will stop rising at a certain point. On our graph it was 2.5%. The graph may not have been totally accurate as there was a problem with the 5% experiment. My prediction was right as it says the graph will rise to a certain point were it will, after that, start to fall.
Evaluation
The quality of my results is not that accurate, due to the people growing the plant in 5% sodium hydrogen carbonate. They noticed the plant dead after 48 hours. It may be because the sodium hydrogen carbonate is an alkali and it is used in baking soda, pharmaceutical products like indigestion tablets and fire extinguishers so that may have killed the plant. If you increase the concentration of sodium hydrogen carbonate it will make the pH of the plant rise. The effect this will have on the plants enzymes is that they will be killed because they will work more rapidly killing themselves more quickly. To get round this problem we should of used a percentage of 2.5% and 4% to work out were the graph falls and to see if it won’t of died. I don’t think it was ok to average the results for the first 24 hours and the second 24 hours. This is because there weren’t another results to average it properly. The method could be improved by doing the results again on own instead of relying on other people to take results. I could do further work in order to give more evidence for my conclusions by doing more research in the books and asking the teacher more.
By
Leigh Clements
10a/Sc1
