Investigating effect of changing glucose concentration on respiration in yeast

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Investigating the Effect of a Variable on the Rate of Respiration in Yeast

Method

  1. Make a yeast solution with the yeast concentration of 20% by mixing 4 parts water with 1 part powdered yeast.
  2. 20cm3 of this is added to a conical flask
  3. Now, add 10cm3 of water and the appropriate amount of glucose
  4. Keep the contents of the conical flask at a constant temperature (40c) using a water bath.
  5. Use a glass gas syringe to measure the amount of CO2  produced in two minutes.
  6. Repeat each reaction three times to get an average of carbon dioxide produced.
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To work out the percentage of glucose solution, I divided the mass of glucose added by 30 as the yeast solution added was 20cm3 and the water 10cm3 hence a total volume of 30cm3.

Results

To find the average of the carbon dioxide produced, I added the 3 repeats and divided it by 3.
To work out rate of reaction I divided average CO
2 by the time taken in seconds (120).

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The punctuation, spelling and grammar are all fine, and the reader communicates meanings clearly. Also uses the correct units throughout the experiment for the different substances. Could have been a bit more explicit with how to do each part of the experiment and the meaning behind it.

The analysis is appropriate for this level as it considers the main factors involved in respiration and uses them appropriately to investigate the question e.g. CO2 output. However, the results are not analysed so there is no knowledge as to if the student understands why they are doing the experiment or if they are just collecting data and following a set experiment. They do not explain why the variable was used and why it would affect yeast respiration.

A good essay for explaining how this type of experiment may be carried out, but does not explain the overall scientific reasoning behind the experiment or explain the results with a conclusion. The student provides a basic response to the question and rather than explaining the purpose to the experiment, the science behind it and the prediction they just display a set of results and how they did the experiment, and whilst the overall results are correct and if you had an understanding of the respiration topic you would understand the results, I would like to see a bit more background and scientific explanation in this essay, as well as a prediction and conclusion. Explains how the experiment is done very well.