Biology AS Planning Exercise.

This denaturation means that the enzyme molecule is not soluble and so it will cease to work. This is because the properties of an enzyme depend on their specific tertiary structure. When enzymes are exposed to high temperatures they vibrate extremely energetically so that the mentioned bonds start to break. To begin with the active site’s specific shape is altered so the substrate will not be a perfect fit. This decreases the rate of reaction up to a point where the substrate is not able to fit into the active site and so the reaction ceases. (Ref③). As the graph shows, the temperature at which the rate of an enzyme controlled reaction begins to decrease at 45°C, therefore suggesting that this is the lowest temperature    

                                                                     at which the cells are killed.

Preliminary Experiments.

1. Prepare a water bath at 38°C. Add a test tube containing 8cm3 of 10% yeast suspension mixed with 2cm3 of 10% glucose solution.
2. Leave for 3 minutes and then add a drop of 1% Methylene Blue solution. Time how long it takes for the Methylene Blue solution to go colourless.
3. Repeat with varying volumes of glucose solution and yeast suspension.

Results.

I will use 8cm3 yeast suspension and 2cm3 glucose solution as my preliminary experiments showed these two volumes to be effective in achieving the shortest time in reducing the Methylene Blue.

Factors Kept Constant.

1. Volume of glucose solution (2cm3)
2. Volume of yeast suspension (8cm3)
3. Concentration of glucose solution (10%)
4. Concentration of yeast suspension (10%)
5. Type of yeast

Apparatus.

Boiling Tubes

Water Bath

Thermometer

Stop-Clock

Yeast Suspension

Glucose Solution

Glass Rod

Sticky Labels

Tongs

5cm3 Syringe

10cm3 Syringe

Methylene Blue

Method.

1. Prepare the water bath at 30°C.
2. Place 8cm3 10% yeast suspension and 2cm3 10% glucose solution using a 10cm3 syringe (for the yeast suspension) and a 5cm3 syringe (for the glucose solution) into a boiling tube.
3. Add a drop of 1% Methylene Blue.
4. Stir with a glass rod.
5. Place the boiling tube into the water bath using the tongs.
6. Start the stop-clock. Observe the colour of the boiling tube and at the moment it returns the original yeast cololur stop the stop-clock.
7. Note the time taken for the solution to turn colourless.
8. Repeat the experiment a further 2 times.

9. Repeat the above experiment with the following temperatures:- 35°C, 40°C, 45°C, 50°C, 55°C, 60°C.

Reliability/Precision of Results.

The experiment will be done a minimum of 3 three times to achieve an accurate value for the lowest temperature. Carrying out the experiment 3 times will ensure that if any of the first two experiments produce anomalous results a more accurate average will be obtained to show the lowest temperature.

To get the most reliable results for temperature I will be testing a set of temperatures ranging from 30-60°C (increasing in multiples of 5). To obtain even more accurate results I will then carry out another set of experiments in which the range of temperatures are closer to the value obtained in the initial experiment e.g. increasing temperatures by1°C.

I will use separate syringes for the yeast suspension and glucose solution because the amount of each used differs. This will reduce error in the measuring of each.

Possible Dangers.

1. Spillage of Methylene Blue⇨stain.
2. Obstructions⇨resulting in a spillage or breakage.
3. Water bath⇨possible burns.

How to Minimise Them.

1. Wear a lab coat & take extra care not to spill it.
2. Ensure that additional items of clothing & other obstructions are out of the way.
3. Take care to avoid spillage’s by using tongs to place the test tubes into the water bath. After the experiment is finished leave 20 minutes before removing it. Wear gloves to protect your hands.

Table of Results.

Calculations.

I will use the average time values to calculate the rate.

Rate = 100/time

Graph.

   0          30              35          40          45         50        55        60        

                Temperature  (°C)

                 

Interpretation of Results.

After 45°C there will be a decline in the time taken for the Methylene Blue to go colourless. This will be shown on the graph by being the peak of the rate.

Validity of Results.

 

A fundamental part of this experiment is to time how long it takes for the Methylene Blue to lose its colour. However, this presents a problem as an individuals interpretation of when this occurs can vary, therefore affecting the results due to human error.

Bibliography.

① http://www.yobrew.co.uk/fermentation.php

② Introduction to Advanced Biology – Clegg 2000

③ Advanced Biology – Mary Jones & Geoff Jones 1997