I am going to investigate the ability of Pepsin on Gelatin. I aim to investigate the effect of temperature on the rate of action of Pepsin on Gelatin.

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                Robert Hutton 4K

Investigation into the action of Pepsin

I am going to investigate the ability of Pepsin on Gelatin. I aim to investigate the effect of temperature on the rate of action of Pepsin on Gelatin.

Apparatus List

Black and white filmstrip, pepsin solution, water baths, 400 cm³ measuring cylinder, small tubes, 200 cm³ beakers, stopwatch, 0°c -100°c thermometer, scissors, tweezers, syringes.

Preliminary Work

The student spent time experimenting with different quantities of pepsin and other controlled factors to try to find out which quantities would work the best. It decided that a 2cm by 2cm black and white filmstrip should be used. This is because it fits inside the specimen tube, it stays still in the specimen tube and it easy to see. In the preliminary experiment a 1cm by 1cm filmstrip was used and it was difficult to see. I decided to use 14ml of pepsin in each test tube because it is just enough to completely submerge the filmstrip. A 2% solution of pepsin has been proven to be the most effective in previous experiments. The volume of the pepsin was chosen to be 20ml.

Variables

  • The volume of pepsin that is used
  • The amount of filmstrip that is used
  • Temperature of the pepsin
  • The concentration of the pepsin solution that is used
  • The apparatus that is used.
  • The method that is used.
  • Quality of film
  • pH of pepsin

The variable will be temperature. This will be measured with a thermometer. The following non-variable parameters will be used (determined by preliminary work) –

20ml of pepsin

2cm by 2cm of filmstrip

2% solution of pepsin

Black and white film

The student has elected to perform the following readings –

22°c

42°c

54°c

61°c

79°c

Prediction

The student predicts that the gelatin will be digested quickest at 37°c -42°c. Unto this temperature range, the gelatin will digest slower. Enzymes do not work efficiently at lower temperatures (they are also denatured at higher temperatures), so at any temperature less than 30°c the rate of digestion will be very slow. This is because they lack the energy given by heat, so they cannot function as quickly. A rise in temperature should increase the rate of reaction until it reaches 50°c. A rise of just 10°c in temperature can double the rate of reaction around the optimum temperature for cell reactions, which is 37°c – 42°c (body temperature). After 42°c, the rate of digestion will fall, until the gelatin is not digested at all. This is because when pepsin is heated above 50°c for a prolonged period of time, it is denatured. This is a property of proteins, and pepsin, as with other enzymes, is a protein. Any very high temperature will denature the pepsin. The reason that denaturing an enzyme disables it is that when an enzyme is denatured, the shape is altered. The shape of an enzyme is very important. Every enzyme is used specifically with one type of molecule, and its shape is designed to fit only that type of molecule. When an enzyme’s shape changes, it no longer fits the molecules it is meant to, meaning it ceases to function.

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Procedure

The student will cut 2 cm by 2cm pieces of black and white filmstrip and place them specimen tubes for each temperature. The student will then measure out 20ml of 2% pepsin solution. I will add this to a specimen tube and repeat until all test tubes are full. I will put one test tube in a beaker containing room temperature water (testing the temperature at 22°c), one in a water bath heated to 42°c, one in a water bath heated to 54°c, one in a water bath heated to 61°c, and one in a water bath ...

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*** This is a reasonably good summary of the investigation but it lacks the attention to detail needed to gain more stars. There is a lack of appropriate biological terminology in many places, and there are inconsistencies in the interpretation of the data.