1)
a) I t is necessary for boiling and then cooling the water before the experiment as it removes the carbon dioxide and other dissolved gasses so that the concentration of carbon dioxide can be controlled.
b) Keeping the water at 25 degrees and brightly illuminated is necessary because the temperature affects the rate of photosynthesis because as the light intensity increases, the consumption of carbon dioxide will also increase.
c) Repeating bubble counts until several consistent counts have been obtained is necessary because this ensures that if there are any anomalies, they would be identified.
2)
Another factor that could be investigated using bubble counts with pondweed is the effect of temperature on the rate of photosynthesis. We could change the temperature instead of changing the concentration of carbon dioxide.
3)
We could measure the rate of oxygen production more accurate by carrying more trials (5 trials) then finding the average of the five bubble counts. Another way is using distilled water from the beginning in order to lessen the trouble in extracting the dissolved gases.
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