Pepsin is an enzyme that is present in gastric juice. Gastric juice is secreted into the stomach of humans and many other animals. Egg albumen (egg white) contains a high proportion of protein. $$$10 \%$$$ albumen solution is a cloudy-white colour. This becomes colourless when pepsin is added to the $$$10 \%$$$ albumen solution. A student used a colorimeter to follow the progress of the hydrolysis of protein by pepsin. The student decided to investigate the effect of pH on the rate of protein hydrolysis by pepsin. From the internet the student found out that pepsin is inactive at $$$\mathbf{p H 6 . 5}$$$ and above. (i) The student was provided with a colorimeter and standard laboratory apparatus. Describe a method that the student could use to investigate the effect of pH on the rate of protein hydrolysis by pepsin and to determine the optimum pHof pepsin. Your method should be set out in a logical order and be detailed enough to allow another person to follow it. Details of how to prepare and use the colorimeter should not be included. . . . . . . . . . . . . . . . . . . (ii) Complete the sketch graph in Fig. 1.3 to predict the effect of pH on the rate of protein hydrolysis by pepsin.

Biology

IGCSE&ALevel

CAIE

Exam No：9700_s25_qp_51 Year：2025 Question No：1(b)

Answer:

Knowledge points:

3.1.1 state that enzymes are globular proteins that catalyse reactions inside cells (intracellular enzymes) or are secreted to catalyse reactions outside cells (extracellular enzymes)

3.1.2 explain the mode of action of enzymes in terms of an active site, enzyme–substrate complex, lowering of activation energy and enzyme specificity, including the lock-and-key hypothesis and the induced-fit hypothesis

3.1.3 investigate the progress of enzyme-catalysed reactions by measuring rates of formation of products using catalase and rates of disappearance of substrate using amylase

3.1.4 outline the use of a colorimeter for measuring the progress of enzyme-catalysed reactions that involve colour changes

3.2.1.1 temperature

3.2.1.2 pH (using buffer solutions)

3.2.1.3 enzyme concentration

3.2.1.4 substrate concentration

3.2.1.5 inhibitor concentration

3.2.2 explain that the maximum rate of reaction (Vmax) is used to derive the Michaelis-Menten constant (Km) which is used to compare the affinity of different enzymes for their substrates

3.2.3 explain the effects of inhibitors, both competitive and non- competitive, on the rate of enzyme activity

3.2.4 investigate the difference in activity between an enzyme immobilised in alginate and the same enzyme free in solution, and state the advantages of using immobilised enzymes

Answer:

Knowledge points:

Solution:

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