Wednesday, 15 May 2013

5.6 describe a simple experiment to investigate carbon dioxide production by yeast, in different conditions

Have a test tube of yeast in glucose solution. Put a layer of oil on top if you want the yeast to respire anaerobically (as it will prevent oxygen entering the solution.)

Put the test tube in a water bath, heat the water to vary the temperature.

Collect gas coming off in a tube then: count the bubbles; use downwards displacement.


18 comments:

  1. If the O2 can't get through the oil, the CO2 wont either

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    2. Thats why you use downwards displacement- the tube is under the water so the gas can move into it without having to go past the oil :)

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  2. You can put the collected gas in limewater, if carbon dioxide is present then it will turn the limewater milky white for people still unsure about it. Thanks for the blog by the way, has helped me so much.

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  4. i would suggest you to use a lid to prevent oxygen entering instead of oil because sometimes things can react or change with oil added (making the test unreliable)

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    1. incorrect, you don't need to worry about that in IGCSE

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  6. Add glucose solution to a conical flask
    Add dried (killed) yeast to the test tube and stir
    Add 1/2 drops of oil to ensure that oxygen can't interfere with the reaction (making it anaerobic)
    Seal the conical flask with one end of the delivery tube
    simultaneously, invert a test tube filled with water with your thumb sealing the test tube into a beaker of water, stick the other end of the delivery tube up the test tube (Do this underwater).
    The carbon dioxide produced will eventually displace most of the water, you can then take out the test tube from the water and seal it with a bung the moment its out of the water.
    add lime water to the test tube as soon as the bung has been removed, whatever water is left in the test tube will turn milky proving that CO2 is release during fermentation.

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    1. forgot to mention to heat the test tube with the mixture :P by placing the test tube in a water bath.

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  7. Hannah, what did you get for your igcse biology exams?
    Well done on your page, it inspires me to revise better :)

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  8. The Biology Syllabus has changed…

    Here is a New blog for the 2017 Syllabus:

    http://igcse-biology-2017.blogspot.hk

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  9. more at

    http://igcse-biology-notes.blogspot.hk/2017/06/56-describe-simple-experiment-to.html

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