I am investigating the enzyme rennin, to see at which temperature it will clot the milk the quickest.

Thermometer,

Pipette,

Stopclock,

Test Tube rack,

2cm3 of Milk,

Rennin,

Ice.

This investigation will be kept fair by using appropriate variables. The variable I am going to change is the temperature of the water. I will be keeping the amount of rennin and the amount of milk constant. The only variable that could cause a problem is the water temperature. Some of the results will need to be repeated for the lower temperatures because when they heat up past their desired temperature it is harder for it to cool down because room temperature, for example is above 20 degrees. It is harder to keep constant temperature at a lower heat.

Observing

I will use the thermometer to find when the temperature of the water has settled. I will place the test tubes into the beakers. I will not start the stopclock until the rennin has been placed into all of the test tubes. The test tubes will be checked at 90-second intervals to see if the milk has been clotted. When clotting has occurred, I will record the time into my results table.

Diagrams

Ice Cold

Room temperature

Boiling

About Enzymes

Enzymes are proteins. They are very important substances because they control the chemical reactions that happen in our bodies. They are known as biological catalysts (substances which speed up reactions but which do not get used up themselves).

There are two main types of enzyme:

* Intracellular enzymes which control reactions that occur inside cells.

* Extracellular enzymes which control reactions that occur outside cells (digestive enzymes work outside cells in the gut).

The enzymes in our digestive system break down the complex substances into simpler ones, which can be absorbed. Enzymes work best at their optimum pH. If the stomach does not have enough acid, its enzyme will not work properly.

About Rennin

Rennin is an enzyme obtained from a young animal's (usually a calf's) stomach. It's used to curdle milk in foods such as cheese. Its role in digestion is to curdle or coagulate milk in the stomach, a process of considerable importance in the very young animal. If milk were not coagulated, it would rapidly flow through the stomach and miss the opportunity for initial digestion of its proteins.

Conclusion

The conclusion to my experiment partially matched my prediction. The two test tubes which clotted were those at room temperature (28oC) as this was temperature closest matched to the human body. If I was to do the investigation again, I would make more of an effort to ensure the temperatures were kept constant. This may have affected the actual results.