An Experiment Investigating the Factors Affecting Photosynthesis in Canadian Pondweed

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Louise Batty 11V

An Experiment Investigating the Factors Affecting Photosynthesis in Canadian Pondweed

The experiment I am going to investigate involves exploring the effect certain limiting factors have on the rate of photosynthesis in Canadian pondweed. The formula for photosynthesis is as follows:

6CO2 + 6H2O = 6O2 + C6H12O6

Photosynthesis is the process in which green plants make use of the energy in sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. Water is absorbed by the roots and carried to the leaves by xylem tubes, and carbon dioxide is obtained from the air through the stomata and diffuses into the cells containing chlorophyll. Chlorophyll is a green pigment that is capable of converting sunlight energy into a latent form, stored in the plants food.

Preliminary Work

I am going to do this preliminary work so that I can find the boundaries for my experiment by finding the conditions needed for my experiment to work. There are three main limiting factors that could affect the rate of photosynthesis in my pondweed. These are:

  • CO2 levels – to adjust the amount of CO2 in the water I am using for my experiment I can add bicarbonate of soda. This will dissolve in the water and increase the amount of CO2 available for the plant to use during photosynthesis.
  • Light levels – these can be changed by the distance or strength of the light used during this experiment. This experiment should be conducted in the dark so that any other lights (other than the light I am using) will not affect my experiment.
  • Temperature – the heat of the water I am using during my experiment can have an affect on the rate of photosynthesis. The water must not be too cold, as the pondweed will not be able to photosynthesise at a measurable rate. It must also not be too hot, as this will kill the plant.
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A Table of my Preliminary Work Results

Fair Testing

I have decided to investigate light as my limiting factor affecting photosynthesis and therefore I must keep the other variables constant. I will do this by:

  • CO2 levels – adding ½ gram of bicarbonate of soda to each experiment before I begin so that each experiment has an equal amount of CO2 in it. However, the same water cannot be used for each experiment because if the pondweed has not used up the entire ½ gram of bicarbonate of soda during the first experiment, and I add ...

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A fair GCSE account of an investigation into the effect of light intensity on the rate of photosynthesis. The writer includes most of the key components of a valid scientific investigation and collects some useful data. A number of small improvements to the report would have increased its overall grade significantly. They include: [1] A more detailed introduction focusing on the effect of increasing light intensity on the rate of photosynthesis; [2] A clear hypothesis stating the relationship of the IV and DV over a wide range of light intensities (including the point at which light intensity is no longer a limiting factor); [3] A more coherent treatment of controlled variables which includes both why and how they are controlled; [4] A detailed analysis of the results which explores the reasons behind the discrepancy in values obtained for each of the three replicates. Overall, a 3 star account.