ESAT Mock Biology Esat-bio-tb8-1

3 questions3 marks40Updated August 2026

The ESAT Mock Biology Esat-bio-tb8-1 paper in full: all 3 questions, each with its answer. ESAT is the Engineering and Science Admissions Test. Sit it cold under exam timing, mark it, then work back through anything you missed using the solutions below.

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Question 1

1 mark

A biologist studies a digestive protease that catalyses the hydrolysis of a peptide substrate. Two separate flasks (1 and 2) are set up with identical initial substrate concentration and identical enzyme concentration, at

37\,^\circ\text{C}

, but different pH values either side of the enzyme's optimum pH of

7.0

: flask 1 is at pH

5.0

and flask 2 is at pH

9.0

. At these two pH values the enzyme has equal, reduced catalytic activity (the pH-activity curve is symmetric about pH

7.0

over this range). The reaction in each flask is left to run to completion (until all the substrate has been converted to product).

Which of the following statements is/are correct?

1. The initial rate of product formation is equal in flasks 1 and 2.
2. The final (total) mass of product formed is equal in flasks 1 and 2.
3. The time taken to reach completion is equal in flasks 1 and 2.

A.1 and 3 only
B.2 only
C.1 only
D.2 and 3 only
E.1 and 2 only
F.1, 2 and 3
G.3 only
H.none of them

Answer: E

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Question 2

1 mark

An enzyme has an optimum temperature of

40\,^\circ\text{C}

and an optimum pH of

7.0

. A student runs four separate identical experiments (P, Q, R, S) with the same enzyme and substrate concentrations, varying only temperature and pH as shown:

Experiment P:

30\,^\circ\text{C}

, pH

7.0

Experiment Q:

40\,^\circ\text{C}

, pH

5.0

Experiment R:

50\,^\circ\text{C}

, pH

7.0

Experiment S:

40\,^\circ\text{C}

, pH

9.0

It is known that: moving

10\,^\circ\text{C}

below the optimum temperature (with pH fixed at the optimum) roughly halves the rate; moving

10\,^\circ\text{C}

above the optimum temperature (with pH fixed at the optimum) causes a much larger fall in rate than an equivalent move below the optimum, because denaturation compounds the loss of kinetic energy benefit; and the enzyme's pH-activity curve is symmetric about pH

7.0

, with pH

5.0

or pH

9.0

(at the optimum temperature) reducing the rate to the same fraction,

f

, where

f > \tfrac{1}{2}

.

Which of the following correctly ranks the initial rates of reaction from highest to lowest?

A. $R > P > Q = S$
B. $P = R > Q = S$
C. $R > Q = S > P$
D. $P > R > Q = S$
E. $P > Q = S > R$
F. $Q = S > P > R$
G. $Q = S > R > P$
H. $Q = S > P = R$

Answer: F

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Question 3

1 mark

A student investigates a soil bacterium's protease enzyme. The graph of relative reaction rate against pH is bell-shaped, symmetric about the optimum pH of

6.0

, with the rate falling to zero at pH

2.0

and at pH

10.0

(the enzyme is irreversibly denatured outside this range and never recovers activity, even if the pH is later returned to

6.0

). A separate experiment shows the enzyme is thermally stable at all temperatures used below, and that (at pH

6.0

) the temperature coefficient

Q_{10} = 2.0

between

10\,^\circ\text{C}

and

50\,^\circ\text{C}

, with the rate continuing to rise up to at least

50\,^\circ\text{C}

(no thermal denaturation occurs in this experiment).

A sample of enzyme and substrate is first incubated at pH

1.0

and

20\,^\circ\text{C}

for 10 minutes (no measurable product forms), then the pH is adjusted to

6.0

while keeping the temperature at

20\,^\circ\text{C}

, and finally the temperature is raised to

40\,^\circ\text{C}

while pH is held at

6.0

. At

6.0

and

20\,^\circ\text{C}

the rate was measured (before this sequence, in a separate control) to be

3\,\text{mg}\,\text{min}^{-1}

.

What is the rate of product formation, in

\text{mg}\,\text{min}^{-1}

, once the final conditions (pH

6.0

40\,^\circ\text{C}

) are reached?

A. $24\,\text{mg}\,\text{min}^{-1}$
B. $1.5\,\text{mg}\,\text{min}^{-1}$
C. $0\,\text{mg}\,\text{min}^{-1}$
D. $3\,\text{mg}\,\text{min}^{-1}$
E. $12\,\text{mg}\,\text{min}^{-1}$
F. $6\,\text{mg}\,\text{min}^{-1}$

Answer: C

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