Photosynthesis is the process a plant uses to combine sunlight, water, and carbon dioxide to produce oxygen and sugar (energy).
What kinds of variables can influence a plant's process of photosynthesis, and what kind of an influence do they have?
If samples of Elodea canadensis (Canadian pond weed) are placed in distilled water and tap water, and have light from various distances come into contact with them, then the samples in the tap water will produce more bubbles than the ones in the distilled water, and also more bubbles will be produced when the distance between the light and the pond weed is reduced.
The bubbles that appear to come out from the pond weed are proof that oxygen is being produced, which is a product of photosynthesis. This way it is known that the process is taking place. If the source of light is closer to the plant, the more intense the light is and the rate of photosynthesis should quicken. Also, distilled water is essentially just hydrogen and oxygen molecules, because the other compounds have evaporated when the water was distilled. Tap water, however, is hard water, meaning it is rich in dissolved minerals, especially calcium and magnesium. Tap water in Poland is especially hard and it is recommended not to drink it. A couple of minerals are actually required for healthy plant growth and for maximizing the rates of photosynthesis, so this is why more bubbles would appear in the tap water.
- 125 mL distilled water
- 125 mL tap water
- a couple pieces of Elodea canadensis
- 1 desk lamp (light source)
- the rate of photosynthesis
- the light intensity
- amount of water
- water temperature
- 1 lab apron
- 1 pair of scissors
- 2 beakers
- 1 stopwatch
- 1 ruler
- 1 pencil and paper to record data
1. Put on apron.
2. Pour the 125mL of distilled water into one beaker and the 125mL of tap water into the other beaker.
3. Using the scissors, cut the Elodea canadensis into two pieces, so that they each fit into the beakers.
4. Place one piece of Elodea canadensis each the beaker with distilled water.
5. Using your stopwatch, let the plant assimilate to the water for three minutes.
6. While these three minutes are passing, set up the lamp by plugging it in and turning it on.
7. Once the three minutes are up, stop the stopwatch, reset it and take the beaker with the distilled water and place it by the lamp.
8. With the ruler, measure out a 20cm distance between both objects and adjust the lamp so that the light is directed towards the beaker .
9. Start your stopwatch. For the first minute, let the pond weed again assimilate, this time to the light. Then, when the stopwatch reaches the one-minute mark, start counting the bubbles that the Elodea canadensis emits. After the remaining two minutes are up, stop counting and record your results.
10. Repeat steps 4 through 9, but this time using tap water.
11. Repeat steps 4 through 10, but this time the distance between the lamp and the beaker should be 10cm instead of 20cm.
12. Clean up after your experiment.
13. Design your method of presentation of data, and then record your final results.