To find out how temperature affects the rate of anaerobic respiration by yeast

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Yeast Investigation

Aim: To find out how temperature affects the rate of anaerobic respiration by yeast.

Method: Yeast is an organism which anaerobically respires. The formula for this type of respiration, called fermentaion, is:

Glucose          Alcohol + Carbon dioxide + A little energy                  

                    enzymes

C6H12O6            2CO2 + 2 C2H5OH + energy

As CO2  is a product I should be able to measure the rate of respiration by collecting CO2 and measuring it. This is the apparatus I plan to use:

As CO2 is produced it will travel along the tubing and into the measuring cylinder (I wanted to use a gas syringe but this wasn’t available to me) where I will be able to measure the amount of water displaced by it.

To keep the experiment fair and produce reliable results, I will need to keep the following variables constant:

  • Glucose concentration – this is a limiting factor to anaerobic respiration and will therefore need to be kept constant otherwise it will affect the results. I will do this by always using the same solution (10mls yeast solution and 10mls glucose solution-glucose concentration ____)
  • Temperature – as I am testing this variable I will need to vary it but I will have to keep it constant throughout each individual test. I will do this by placing a thermometer in the water around the yeast solution and keeping it at a constant temperature by adding hot water when necessary.
  • Time yeast is given to respire – this will need to be kept constant as the longer the yeast is left, the more CO2 it will produce. I will collect CO2 for 10 mins from each temperature.

I will do the experiment in duplicate and then make averages so as to gain more accurate results. This will also allow me to identify anomalies more easily.

 

Fermentation is the breakdown of sugars to produce ethanol and carbon dioxide by bacteria and yeast with the aid of the enzymes. From previous knowledge I know that enzymes work best at a temperature around 40oC. Therefore I predict that the yeast will respire anaerobically the most and produce the most CO2 at this temperature. I also know that after a certain temperature, enzymes become unable to function as the heat causes their sites of action to be distorted. Therefore, I think that for temperatures higher than the optimum temperature, the amount of CO2 collected will decrease as the yeast begin to become unable to work. This decrease will continue until a certain temperature, at which no yeast are able to work and therefore no CO2 is being produced. After this, the rate of AR will remain 0. Similarly for temperatures less than the optimum, the rate of AR will be 0 until there is enough heat energy for AR to begin. The amount of CO2 being collected will then rise until the optimum temperature is reached. A graph of CO2 collected against temperature would be a bell curve.

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As I predict that the optimum temperature for the yeast to respire will be around 40oC, I will need to test temperatures above and below this figure. Therefore I will collect CO2 produced at the following temperatures: 20oC, 30oC, 40oC, 50oC, 60oC. This gives me a good range of temperatures from which I should be able to draw a fair conclusion.

Throughout the experiment I will take care when dealing with hot water, clear up any broken glass and not inhale or consume any substances that I am using.

In my preliminary experiment I tested the rate ...

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