Enzymes are biological catalysts.
(a) Describe what is meant by a catalyst.
(b) State the type of biological molecule enzymes are made of.
(c) The rates of enzyme activity of two different enzymes, A and B, were recorded at different temperatures. Fig. 2.1 shows the results:
(i) Compare the effect of temperature on the rate of enzyme activity for enzymes A and B. Use data from Fig. 2.1 to support your answer.
(ii) State the part of an enzyme that has a complementary shape to a substrate.
(iii) State one factor, other than temperature, that would affect the rate of enzyme activity.
(d) The box on the left contains the word ‘Enzymes’. The boxes on the right contain some sentence endings.
Draw three lines from the box on the left to make three correct sentences.
▶️ Answer/Explanation
Ans:
(a) A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It lowers the activation energy required for the reaction to proceed.
(b) Enzymes are made of proteins (or amino acids), which fold into specific 3D structures to catalyze biochemical reactions.
(c)(i) Both enzymes A and B show an increase in activity with temperature up to an optimum, followed by a decline due to denaturation. Enzyme A has a lower optimum temperature (~40°C) compared to B (~45°C), and A is active at lower temperatures while B remains active at higher temperatures.
(c)(ii) The active site of an enzyme binds specifically to the substrate due to its complementary shape.
(c)(iii) pH affects enzyme activity, as deviations from the optimal pH can alter the enzyme’s structure and reduce its efficiency.
(d) Enzymes are linked to:
1. are involved in all metabolic reactions,
2. are necessary to sustain life,
3. are used to make fruit juice (e.g., pectinase in juice extraction).
(a) Tick (✓) all the boxes that describe enzymes.
(b) Fig. 2.1 shows the effect of pH on the activity of three different digestive enzymes, X, Y and Z.
Using the information in Fig. 2.1:
(i) State the optimum pH of enzyme Z.
(ii) State a pH value at which both enzymes X and Y are active.
(iii) State a pH value at which enzyme Y is completely denatured.
(iv) Enzyme X is a protease. Describe its location and action in the digestive system.
(v) Enzyme Y is produced by the salivary glands. State the substrate and product of enzyme Y.
(c) State the type of digestion that uses enzymes.
(d) State one factor, other than pH, that affects enzyme activity.
▶️ Answer/Explanation
2(a)
Box 2: ✓ (Enzymes are involved in all metabolic reactions.)
Box 3: ✓ (Enzymes are proteins.)
Enzymes are biological catalysts that speed up metabolic reactions without being consumed. They are proteinaceous in nature, which is why Box 3 is ticked. Box 2 is correct because enzymes participate in all metabolic pathways.
2(b)
(i) The optimum pH of enzyme Z is 9 (highest activity at pH 9).
(ii) A pH where both X and Y are active is 5 (both show activity at this pH).
(iii) Enzyme Y is denatured at pH 2 (no activity at strongly acidic pH).
(iv) Location: Stomach. Action: Breaks down proteins into amino acids.
(v) Substrate: Starch. Product: Maltose/simple sugars.
From the graph, enzyme Z peaks at pH 9. Both X and Y are active around pH 5. Protease (X) acts in the stomach, while salivary amylase (Y) digests starch.
2(c)
Chemical digestion (enzymes catalyze the breakdown of food molecules).
Enzymes facilitate chemical digestion by hydrolyzing complex molecules into simpler absorbable forms.
2(d)
Temperature (enzyme activity is highly temperature-sensitive).
Enzymes have an optimal temperature range; deviations (too high/low) reduce activity or cause denaturation.