In this experiment, I am going to investigate the effect of heat on the respiration of yeast.

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Alisha Meertins        10PB        Mr Beckley

Biology Coursework

Planning

Title

  In this experiment, I am going to investigate the effect of heat on the respiration of yeast.

Safety

  When doing the experiment there will only be one main hazard and that will be the hot water.  One way of controlling this hazard is for the teacher to bring us the hot water instead of all walking to the front of the classroom to get the hot water.  To always have green paper towel so that if the beaker needs picking up the green paper towel can be wrapped around the beaker and used as a handle and instead of pouring the hot water from the beaker into the other beaker, use a dropper to transfer the water.  Another way of controlling the hazard of hot water is to keep all electrical sockets and electrical equipment off when someone is not keeping an eye on them; this is because water near electricity can cause someone to have an electric shock.  It is also important to make sure that if any water is spilt on the floor it is wiped up immediately so as not to cause someone to slip and hurt themselves.  These points would all help in preventing a hazard.

Prediction

  I think that as the temperature rises by 10ºC each time the rate of Carbon Dioxide bubbles produced will double.  I think that his will happen until the temperature of the water reaches 40ºC, when I think that the rate of carbon dioxide bubbles produced will fall quite dramatically.

Scientific Explanation

  I think that every time the temperature goes up by 10ºC the rate of Carbon Dioxide bubbles produced will double because the higher the temperature of the water, the more energy the molecules involved in the reaction has.  This makes them move around faster, increasing the chance of them colliding with one another, with enough energy to cause a reaction.  When an enzyme is heated at high temperatures, around 40ºC - 50ºC, the enzyme stops working and therefore its reaction stops or slows down.  This is because the heat energy causes the enzyme molecules to change shape so they longer cause the reaction to happen.  When this happens, it is said that the enzyme has been denatured (Complete GCSE Biology).  It is said that all “enzymes denature at 40ºC” and this is a rule, and this is why I think that rate of Carbon Dioxide bubbles produced will fall quite dramatically when the temperature of the limewater is 40ºC.  

The Denaturing of an Enzyme

 

Preliminary Experiment and Calculations

 In my preliminary experiment, I am going to use the temperatures of 22ºC, 30ºC and 40ºC.  I have decided to use these temperatures, as 22ºC is the temperature of the room in which I am going to do the experiment and 30ºC and 40ºC are very round numbers.  They increase by 10ºC, which is what I want so that I can see whether it is accurate that if the temperature is increased by 10ºC the rate of carbon dioxide produced will double as well.  I am going to start the experiment with 30ºC then go onto 22ºC and then finally do 40ºC.  This is because 30ºC is a good temperature to get the yeast “started up”.  I then will decrease the temperature instead of increasing it because if I were to do the 40ºC temperature I would denature the yeast and have to use new yeast to do 22ºC, which would not be a fair test.

   I am going to set up the apparatus as shown above and firstly set the limewater to 30ºC.  When I get the water to 30 º C, I will leave the yeast in it for five minutes in order for the yeast to equilibrate, which means become an equal temperature to the water.  I will then count the number of bubbles that come out of the delivery tube per minute and I will do this for three minutes in total therefore collecting three results for each temperature.  Once I collect all the results for 30ºC, I will repeat exactly the same experiment with 22ºC and then 40ºC.  In the preliminary experiment, I am going to use limewater instead of water and therefore prove that Carbon Dioxide is the gas that is being given off in the bubbles as when Carbon Dioxide is given off into limewater the limewater turns milky.

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  The results I got for my preliminary experiment were as follows:

  I am going to change the temperatures that I use in my main experiment as I don’t think I have enough and 22ºC is a very random temperature so instead of using the temperatures above I am going to use 10ºC, 20ºC, 30ºC, 40ºC and 50ºC.  I am going to use these temperatures, as they are round numbers; they increase by 10ºC, which is what I want in order to prove if my prediction was correct.  They are probably going to be easy temperatures ...

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