ESAT Challenge Biology Esat-bio-challenge-2

10 questions10 marks20Updated August 2026

The ESAT Challenge Biology Esat-bio-challenge-2 paper in full: all 10 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 genetic condition caused by a recessive allele affects

1

person in

10\,000

. Assuming the population is in Hardy-Weinberg equilibrium, approximately what proportion of the population are carriers?

A. $1$ in $25$
B. $1$ in $50$
C. $1$ in $100$
D. $1$ in $200$
E. $1$ in $5000$

Answer: B

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Question 2

1 mark

Two unaffected parents have a child with an autosomal recessive condition, and later a second child who is unaffected. That second child has children with an unrelated person who is known to be a carrier. What is the probability that their first child is affected?

A. $\tfrac12$
B. $\tfrac13$
C. $\tfrac14$
D. $\tfrac16$
E. $\tfrac18$

Answer: D

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Question 3

1 mark

A fly heterozygous at two linked loci is test crossed. The

1000

offspring fall into four phenotypic classes, of sizes

415

385

112

and

88

. What is the map distance between the two loci?

A. $10$ cM
B. $12$ cM
C. $20$ cM
D. $40$ cM
E. $50$ cM

Answer: C

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Question 4

1 mark

Complete oxidation of one mole of glucose releases about

2870\,\text{kJ}

. Suppose

32

moles of ATP are synthesised per mole of glucose, and that ATP hydrolysis releases about

30.5\,\text{kJ mol}^{-1}

. What is the approximate efficiency of energy capture?

A. $60\%$
B. $12\%$
C. $24\%$
D. $34\%$
E. $48\%$

Answer: D

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Question 5

1 mark

A plant cell has a solute potential of

-800\,\text{kPa}

and a pressure potential of

+300\,\text{kPa}

. It is placed in a solution of water potential

-700\,\text{kPa}

. What happens?

A.Water enters the cell and its pressure potential rises.
B.There is no net movement of water.
C.Solute leaves the cell down its concentration gradient.
D.Water leaves the cell and it becomes fully plasmolysed.
E.Water leaves the cell and its pressure potential falls.

Answer: E

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Question 6

1 mark

An enzyme obeys

\text{rate}=\frac{V_{\max}[S]}{K_m+[S]},

with

V_{\max}=100\,\mu\text{mol min}^{-1}

and

K_m=2.0\,\text{mmol dm}^{-3}

. What is the rate, in

\mu\text{mol min}^{-1}

, at a substrate concentration of

6.0\,\text{mmol dm}^{-3}

A. $25$
B. $50$
C. $60$
D. $75$
E. $100$

Answer: D

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Question 7

1 mark

A person has a tidal volume of

500\,\text{cm}^3

, a breathing rate of

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

, and an anatomical dead space of

150\,\text{cm}^3

. Calculate the alveolar ventilation rate in

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

A. $1.8$
B. $4.2$
C. $6.0$
D. $7.8$
E. $42$

Answer: B

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Question 8

1 mark

An ecologist marks and releases

100

beetles. In a later sample of

120

beetles,

20

are marked. It is then discovered that marking makes a beetle slower and therefore easier to catch. Which statement is correct?

A.The estimate is $600$ , and the true population is probably larger.
B.The estimate is $600$ , and the true population is probably smaller.
C.The estimate is $600$ , and it is unbiased.
D.The estimate is $240$ , and the true population is probably larger.
E.The estimate is $2400$ , and it is unbiased.

Answer: A

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Question 9

1 mark

A bacterium has a single circular chromosome of

6.0\times10^{6}

base pairs, replicated from one origin, bidirectionally, with each replication fork advancing at

1000

base pairs per second. Grown in a rich medium, the same bacterium is observed to divide every

20

minutes. Which statement is correct?

A.One round of replication takes $100$ minutes, so the observed division time must be an error.
B.One round of replication takes $50$ minutes, so the forks must in fact move faster than stated.
C.One round of replication takes $50$ minutes, and a new round begins before the previous one has finished.
D.One round of replication takes $20$ minutes, because replication starts at many origins at once.
E.One round of replication takes $50$ minutes, so each daughter cell inherits an incomplete chromosome.

Answer: C

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Question 10

1 mark

Isolated membrane vesicles containing ATP synthase are equilibrated in a buffer at pH

8

, then transferred abruptly into a medium at pH

4

. A burst of ATP synthesis is observed, with no electron transport taking place at any stage. What does this demonstrate?

A.Electron transport is required for ATP synthesis.
B.A proton gradient alone is sufficient to drive ATP synthesis.
C.ATP synthase catalyses electron transfer directly.
D.The ATP was made by substrate-level phosphorylation.
E.Low pH denatures ATP synthase, releasing bound ATP.

Answer: B

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