1. Investigation Photosynthesis
Introduction:
Photosynthesis is the process a plant uses to combine sunlight, water, and carbon dioxide to
produce oxygen and sugar (energy).
Research Question:
What kinds of variables can influence a plant's process of photosynthesis, and what kind of an
influence do they have?
Hypothesis:
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.
Hypothesis Explanation:
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.

2. Compounds
 125 mL distilled water
 125 mL tap water
 a couple pieces of Elodea canadensis
 1 desk lamp (light source)
Variables
Dependent:
 the rate of photosynthesis
Independent:
 the light intensity
Controlled:
 amount of water
 water temperature
Apparatus
 1 lab apron
 1 pair of scissors
 2 beakers
 1 stopwatch
 1 ruler
 1 pencil and paper to record data

3. Method
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.

4. Raw Data
Table 1: showing the number of oxygen bubbles produced by Elodea plants in distilled water,
tap water and NaHCO3 solution in a distance of 10 cm between the breaker and the light
Trials H2O ( tap water) H2O (distilled water) NaHCO3 solution
1 19 2 132
2 24 2 120
mean 21.5 2 126
Graph 1: showing the number of oxygen bubbles produced by Elodea plants in distilled water,
tap water and NaHCO3 solution in a distance of 10 cm between the breaker and the light
Oxygen bubbles produced by Elodea
140
120
100
oxygen bubbles
80 distilled water
tap water
60
NaHCO3 solution
40
20
0

5. Table 2: showing the number of oxygen bubbles produced by Elodea plants in distilled water,
tap water and NaHCO3 solution in a distance of 30 cm between the breaker and the light
Trials H2O ( tap water) H2O (distilled water) NaHCO3 solution
1 11 1 84
2 12 1 97
mean 11.5 1 90.5
Graph 2: showing the number of oxygen bubbles produced by Elodea plants in distilled water,
tap water and NaHCO3 solution in a distance of 30 cm between the breaker and the light
Oxygen bubbles produced by Elodea
100
80
oxygen bubbles
60 distilled water
tap water
40
NaHCO3 solution
20
0

6. Evaluation and Conclusion
By undergoing this investigation the hypothesis proves to be correct. This is clearly seen in the
results of the experiment, such as in Table 1. While in the distilled water no bubbles whatsoever
appeared, in the tap water the bubbles were so abundant that it became hard to count them. This
is because minerals present in tap water such as magnesium act as catalysts when a plant
undergoes photosynthesis. Also, when the distance between the light and the plant source was
halved into 10cm, the bubbles almost doubled in amount. The intensity of light also proves to be
an influencing factor in maximizing a plant's photosynthesis.
This experiment of course could be improved, by using a greater amount of water (the laboratory
just happened to be running out of distilled water the day of the experiment), and using natural
light as the light source and not a lamp. Also, more variables could be tested when it comes to
water; carbon dioxide could be added to see what happens, and other kinds of ideas like this
could be investigated. Lastly, more trials could be held to check the accuracy of the results. For
the most part though, the aim of this investigation was accomplished.
Felix Dyrek