These factors must all be kept constant otherwise each time the experiment is carried out the results will change, then the experiment would be biased.
The pond weed must stay the same.
The results would be more accurate if the factors were replaced (the same) each time.
Prediction: I predict that increasing the light intensity will increase the rate of photosynthesis because the light intensity is much greater when the light is closer to the plant I think this because in the summer when the light intensity is greater, plants and flowers grow larger and have many different fruits and colours. This I know is due to more photosynthesis taking place, therefore more chlorophyll and more oxygen produced.
Evidence: To make the results accurate I will repeat the counting of bubbles five times at each distance away from the light.
Method
1. Set up the lamp at a fixed distance away from the test tube but leaving out the pond weed, funnel, test tube, water, and the sodium hydrogen carbonate.
2. Fill the beaker with water the same each time and 1 spectacular of Sodium bicarbonate.
3. Select 1 piece of pond weed roughly 5-7cm long and cut off the stems.
4. Place the pond weed in the test tube and secure the funnel upside down over (on top of) the pond weed using the plasticine.
5. Place the pond weed in the test tube.
6. Place the ruler so that the "0" measurement is aligned with the side of the beaker. (distance measured from side of beaker to edge of light bulb)
7.) Place the lamp 5 cm away from the beaker.
8.) With the light shining on the plant, record the number of bubbles emitted in a 5 minute duration. Switch off the lamp and wait for another minute before taking another reading.(so bubbles stop/slow down)
9.) Take 5 readings at the current distance and move the lamp 5 cm further away from the plant.
10.) Repeat steps until 5 readings from at intervals of 10 cm have been taken.
11.) For better accuracy I will use two sets of results, my own and student A's.
Results:
The temperature of the water stayed a constant at about 20C throughout the experiment.
(Bubbles per 5 min)
Distance from light
Conclusion:
From the results and graphs that I have gathered I now know that an increase in light intensity certainly does increase the rate of photosynthesis. also, the relationship between light intensity and the rate of photosynthesis was non-linear. From one of the graphs there is a best-fit curved line. This means that the rate of photosynthesis increases at an exponential rate.
The greater the light intensity the more intense photosynthesis was, the greater the distance, the slower the rate of photosynthesis. Photosynthetic rate is being limited by certain factors such as carbon dioxide and temperature. As light intensity increases further, these factors limit the rate of photosynthesis even more until photosynthesis is completely limited and the graphed line become horizontal. This is when photosynthesis is being carried out at a constant rate.
The lamp that I used had a cover that directed the light energy somewhat. The light energy did not spread out as much as a plain light bulb with no cover. The distribution of the light energy was more concentrated, changing the gradient of the graph.
Evaluation:
Overall, I would state the experiment as a success since my predictions were supported by my results. My prediction needed to be brief, sensible and logical.
While performing the experiment, the piece of pond weed did not photosynthesize at a steady rate, even when the distance from the plant to the light source was kept a constant. This is evident because my graphs were not all exactly the same this was why it is better to carry out the experiment more than once, if this was not done the results may not go down at a steady rate.
While the number of oxygen bubbles was being recorded, the rate at which the plant was photosynthesizing had increased several times. This may be due to the poor circulation of sodium hydrogen carbonate at the beginning of the experiment. Carbon dioxide may have initially limited the rate of photosynthesis. Almost all readings were in correlation with each other. A large factor in determining data accuracy is the amount of human error during experiments. To improve the accuracy of the results, the readings would have to be taken several more times.
The classroom that we worked in was a poor site for carrying out this experiment, we were working very close to a large window and on a hot summers day, the lights were switched on, and also there were other experiments (the same) going
On in the same room this would change the concentration of oxygen and carbon-
dioxide in the air.