Respiration of yeast

 

The factor chosen to be varied is the concentration of sugar within the solution. So the other factors are to be kept as control factors to make this experiment fair. The following are the controlled factors:

• The sugar used was glucose because it is easy to decompose,
• The weight of the yeast was to be kept at 1.5g,
• The temperature of the environment was 400c so that the enzymes do not denature,
• The yeast must come from the same source, so it is the same age because this may effect the rate of reaction.

Prediction:

        I predict that the higher the temperature of the water surrounding the reaction and a higher percentage of sugar solution will produce more carbon dioxide (bubbles). This is because heat make will make the yeast atoms vibrate and split up causing yeast enzymes to combine and react producing carbon dioxide (c02).  

Method:

• We collected and set up the apparatus as shown on the diagram,
• Weighed the yeast to 1.5g,
• Filled and boil the kettle,

• Emptied the kettle content into the beaker,
• Added cold water to make the temperature 400c by using a thermometer,

• Poured 20ml3 of 0% sugar solution into a test tube,
• Put the 1.5g of yeast into the sugar solution,
• Started the stopwatch,
• Made sure the bung and delivery tube was securely on top of the test tube with the reaction in it so that carbon dioxide doesn’t escape,
• Place a test tube filled half way with water at the other end of the delivery tube so that the carbon dioxide is visible via bubbles,
• Wait for three minutes so that the sugar solution and yeast reaction goes to the same temperature as the surrounding water,
• When the three minutes are up we stared counting the bubbles for another three minuets. Then when the six minuets are up we stoped the clock and measured the finishing temperature of the surrounding water and noted the results,  
• We repeated the experiment three times to make sure it is accurate.

Apparatus:

       Spatula, test tube rack, delivery tube, measuring cylinder, test tube, stopwatch, kettle, beaker, thermometer, sugar solution, yeast and scales.

Conclusion:

    Looking at my results I have come to the conclusion that the higher the percentage of sugar solution the more carbon dioxide is produced in the amount of time given.  The relationship between my prediction and the results are similar.

Evaluation:

      I think my method explains what I did in my experiment and is simple to follow and easy to understand. Looking at my result table I can see some anomalous results this might be because of carelessness or improper use of equipment this is why the experiment was repeated three times. If I were to do the experiment again I would make sure I had more time to ensure the results are more accurate. For example I would make sure the yeast used are at the same weight and assure that the starting temperature of the water surrounding the reaction is remains at 400c.