Comparing rate of photosynthesis Natalie Loo 12A

Looking at the results, method 2 seemed to be a better method for measuring photosynthesis, since the average rate in method 2 is higher than the ones being measured in method 1. However, we have to bear in mind that two different types of plants have been used. In method 1 a dry or in other words a land plant was used and in method 2 a water plant was used. The plant type has an effect on the rate of photosynthesis.

Considering the inaccuracy of the techniques, the meniscus might be misread in both methods; the timing for both methods might also be inaccurate. In method 1, the transfer of the discs into the beaker containing 3% sodium bicarbonate solution might not be quick enough. Also, when a number of discs were rising at once, the time recorded for those discs might be slightly inaccurate since I didn’t record the results quick enough. To solve these problems, replication of the experiment is needed to increase the accuracy and the reliability of the results. In addition, when the beaker was placed in a well-lit place, the light intensity wasn’t constant due to the changing intensity of sunlight. Light intensity is a limiting factor to photosynthesis therefore this might have an effect on the rate. A lamp can be used in replacement because it provides a constant amount of light. Though some of my procedures were inaccurate, this method is quite easy to replicate.

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In method 2, I had to ensure that no air bubbles can be present in the microburette and the clip on the rubber tubing also has to be screwed completely tight. This can guarantee the gas column being measured is the volume of gas given off only by the aquatic plant but nothing else. The mouth of the filter funnel can’t touch the bottom of the beaker too, or else water can’t be circulated around the set up. Moreover, when the gas is drawn into the capillary, sometimes the meniscus can’t be observed therefore results might be inaccurate. In order to overcome this difficulty, the clip needs to be entirely unscrewed with caution for the meniscus to travel along the capillary steadily.

Respiration might have some effects on my results of both methods; however, the rate of photosynthesis should have exceeded respiration. In conclusion, there were inaccuracies in both methods but method 2 seemed to be a better method for measuring the rate of photosynthesis.


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