Fermentation of different sugars by yeast.

After this we could see from the results that as the temperature increased, the rate at which gas accumulated also increased. However, when it reached around 40c it slowed down and it was even slower at 50c. We can see that the temperature is a variable that we will have to control. By reading Biology 2 I have found out that the optimal temperature for the yeast to work at is 37c. That is the temperature at which I will try and keep the sugar and yeast mixtures at.

Studying fermentation via dough rising

We have also seen that fermentation can be measured by looking at how the level of the dough rises at frequent intervals. By looking at this we can see the rate of fermentation, by exploiting this manifestation of anaerobic respiration. Then by changing the substrates or the temperature we can see the effect of them on respiration. Although we will be able to compare the results of different substrates from this experiment quite easily, the procedure seems to be quite inaccurate and prone to human errors.

Investigation into the speed at which yeast ferments different sugars

There is a simple technique to determine how and at what speed yeast ferments different sugars. Equal volumes of yeast cells and a sugar solution are drawn into a barrel of a syringe. If gas is produced from the fermentation an equivalent amount liquid will be displaced from the barrel into a capillary tube. By measuring the amount of liquid displaced after frequent intervals over a period of 30 minutes, it will be possible to determine the rate at which fermentation takes place.

If we repeat the method for different sugars we will be able to work out how fermentation differs from sugar to sugar.

For my actual experiment for this experiment I will use a similar method to the one above, but try and keep the temperature at 37c by using a water bath, if possible.

Scientific Knowledge

The sugars that I will use in this experiment are:

* Glucose

* Fructose

* Sucrose

* Lactose

* Maltose

Glucose and Fructose are both monosaccharides, which means that they exist as single molecules. They are very similar; in fact they both have the same chemical formula, C6H12O6. The only difference is that they are arranged slightly differently.

The other sugars, that are going to be used, are all disaccharide, which means that they are two monosaccharide sugar molecules joined together by a glycosidic bond.

Sucrose is made when a molecule of glucose is bonded with a molecule of fructose.

Lactose is made when a molecule of glucose is boned with a molecule of Galactose.

Maltose is formed when a molecule of glucose is boned with another molecule of glucose.

The molecules are all bonded together by glycosidic bonds. This bond is formed by condensation. Two OH groups line up alongside each other. One combines with a hydrogen atom of the other to form a water molecule. This forms a water molecule and in the process a bond is formed between the two sugar molecules. See example below.

Yeast

Yeast is a micro-organism which breaks down sugars to form alcohol and Carbon Dioxide.

Variables

* Temperature

* Yeast Concentration

* Type of Sugar

* Sugar Concentration

The variables that I will control are temperature, yeast concentration and sugar concentration. This will then allow me to change the type of sugar that I will use. By doing this I will find out how different sugars effect fermentation.

Method

. Set up the equipment as shown in the diagram

2. Fill up 2.5cm3 of glucose solution into the barrel of a syringe. Fill up the rest of that barrel with 2.5 cm3 of yeast suspension.

3. Gently rotate the barrel so that the solution is mixed properly.

4. Connect the syringe with the rubber tubing.

5. Now connect the rubber tubing with the capillary tubing so that syringe is connected with the tubing.

6. Slowly lower the plunger of the syringe, just until the meniscus can be seen in the capillary tubing. Start the stopwatch.

7. At intervals of 1 minute, record the amount of liquid displaced for the next 20 minutes.

8. Repeat steps 2-7 with fructose solution instead of glucose.

9. Repeat steps 2-7 with sucrose solution instead of glucose.

0. Repeat steps 2-7 with lactose solution instead of glucose.

1. Repeat steps 2-7 with maltose solution instead of glucose.

2. Now repeat the whole experiment, so that the results are reliable.

3. Fill in the table.

Reliability of Method

To make sure that our experiment would be reliable we took a number of precautions. First of all we decided that we would repeat the experiment for all of the different sugars. Also we decided to take a large number of recordings at short intervals, 1 minute. The measurements should be accurate due to the fact that we will look at the meniscus at eye level. Stirring the yeast will also increase the reliability.

Risk Assessment

General good laboratory practice should be sufficient We should also wash hands after the experiment. A lot of the equipment is made with glass, so they will also have to be handled with care. All stools must be tucked in so that people won't trip over them.