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

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 2

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 3

1 mark

Five cylinders of equal size were cut from the same potato, blotted dry, weighed, and each left for

60

minutes in a different concentration of sucrose solution at the same temperature. Each cylinder was then blotted dry and reweighed.

| sucrose concentration /

\text{mol dm}^{-3}

0.00

0.20

0.40

0.60

0.80

|
|---|---|---|---|---|---|
| percentage change in mass |

+15.0

+9.0

+3.0

-3.0

-9.0

|

Which of the following statements is/are correct?

1. The water potential of the potato cells is equal to the water potential of a

0.50\,\text{mol dm}^{-3}

sucrose solution.
2. The concentration of sucrose in the potato cells must be

0.50\,\text{mol dm}^{-3}

.
3. A cylinder of initial mass

5.00\,\text{g}

left in the

0.80\,\text{mol dm}^{-3}

solution would have a final mass of

4.55\,\text{g}

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

Answer: F

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Question 4

1 mark

Two cubes are cut from the same block of agar. Cube X has sides of length

10\,\text{mm}

and cube Y has sides of length

6\,\text{mm}

. Both are placed in a dye that diffuses into agar at a steady rate, penetrating

2.0\,\text{mm}

inwards from every face in

10

minutes.

Which row correctly gives the percentage of the volume of cube X that is still uncoloured after

10

minutes, and the cube with the greater surface area to volume ratio?

A.percentage of X uncoloured: $21.6$ , greater surface area to volume ratio: X
B.percentage of X uncoloured: $21.6$ , greater surface area to volume ratio: Y
C.percentage of X uncoloured: $51.2$ , greater surface area to volume ratio: X
D.percentage of X uncoloured: $51.2$ , greater surface area to volume ratio: Y
E.percentage of X uncoloured: $60.0$ , greater surface area to volume ratio: X
F.percentage of X uncoloured: $60.0$ , greater surface area to volume ratio: Y
G.percentage of X uncoloured: $78.4$ , greater surface area to volume ratio: X
H.percentage of X uncoloured: $78.4$ , greater surface area to volume ratio: Y

Answer: B

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Question 5

1 mark

A single diploid plant cell, in a species with a diploid number of

14

, completes interphase and then divides by mitosis. One of the two daughter cells then completes interphase and a full meiotic division. The other daughter cell does not divide again, and no cells die.

What is the total number of chromosomes present in all the cells that exist at the end of this process?

A. $21$
B. $28$
C. $35$
D. $42$
E. $56$
F. $70$

Answer: D

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Question 6

1 mark

In rabbits, black coat colour is determined by a dominant allele

B

and brown coat colour by the recessive allele

b

. The gene is autosomal.

A black rabbit, R, is crossed with a brown rabbit, and some of the offspring are brown. Rabbit R is then crossed with a second black rabbit, S, which is known to have had one brown parent.

What is the probability that the cross between R and S produces at least one brown offspring in a litter of four?

(Assume no mutations, and that each offspring is independent.)

A. $\tfrac{1}{4}$
B. $\tfrac{27}{64}$
C. $\tfrac{81}{256}$
D. $\tfrac{175}{256}$
E. $\tfrac{255}{256}$
F. $1$

Answer: D

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Question 7

1 mark

A sample of double-stranded DNA contains

1200

nucleotides in total. Of these,

20

per cent contain the base cytosine. The whole of one of the two strands is a single gene, and the entire strand is read as triplets.

Which row gives the number of nucleotides in the sample that contain adenine, and the number of amino acids in the polypeptide that this gene codes for?

A.nucleotides containing adenine: $240$ , amino acids: $200$
B.nucleotides containing adenine: $240$ , amino acids: $400$
C.nucleotides containing adenine: $360$ , amino acids: $200$
D.nucleotides containing adenine: $360$ , amino acids: $400$
E.nucleotides containing adenine: $480$ , amino acids: $200$
F.nucleotides containing adenine: $480$ , amino acids: $400$
G.nucleotides containing adenine: $720$ , amino acids: $200$
H.nucleotides containing adenine: $720$ , amino acids: $400$

Answer: C

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Question 8

1 mark

A student investigated the digestion of starch by an amylase. At each temperature, a fixed volume of starch solution was mixed with a fixed volume of amylase solution at the same pH. Samples were tested with iodine solution at regular intervals and the time taken for the iodine to stop turning blue-black was recorded.

| temperature /

^\circ\text{C}

10

20

30

40

50

60

|
|---|---|---|---|---|---|---|
| time taken / s |

300

150

75

40

90

| iodine still blue-black after

600

|

The rate of reaction is taken to be proportional to

\tfrac{1}{\text{time taken}}

.

Which of the following statements is/are correct?

1. The rate of reaction at

40\,^\circ\text{C}

is eight times the rate at

10\,^\circ\text{C}

.
2. At

60\,^\circ\text{C}

the active site of the amylase no longer binds starch.
3. The results show that the optimum temperature for this amylase is

40\,^\circ\text{C}

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

Answer: C

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Question 9

1 mark

A student estimated the number of dandelion plants in a rectangular field measuring

80\,\text{m}

50\,\text{m}

. Ten quadrats, each

0.5\,\text{m}

0.5\,\text{m}

, were placed at random positions in the field and the dandelions in each were counted:

4, \ 0, \ 6, \ 2, \ 0, \ 8, \ 6, \ 4, \ 0, \ 5

What is the best estimate of the total number of dandelion plants in the field?

A. $14\,000$
B. $28\,000$
C. $56\,000$
D. $80\,000$
E. $224\,000$
F. $560\,000$

Answer: C

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Question 10

1 mark

A leafy shoot is sealed into a bubble potometer whose capillary tube has an internal diameter of

1.0\,\text{mm}

. The apparatus is airtight and the rate of water uptake is taken to equal the rate of transpiration.

In still air, the air bubble moves along the scale from the

12\,\text{mm}

mark to the

72\,\text{mm}

mark in

4.0

minutes.

Which row gives an expression for the rate of transpiration in

\text{mm}^3

per minute, and a change that would increase it?

A.rate: $\pi \times (0.5)^2 \times 15$ , change: increasing the humidity of the air around the shoot
B.rate: $\pi \times (0.5)^2 \times 15$ , change: increasing the movement of air around the shoot
C.rate: $\pi \times (0.5)^2 \times 18$ , change: increasing the humidity of the air around the shoot
D.rate: $\pi \times (0.5)^2 \times 18$ , change: increasing the movement of air around the shoot
E.rate: $\pi \times (1.0)^2 \times 15$ , change: increasing the humidity of the air around the shoot
F.rate: $\pi \times (1.0)^2 \times 15$ , change: increasing the movement of air around the shoot
G.rate: $2\pi \times (0.5) \times 15$ , change: increasing the humidity of the air around the shoot
H.rate: $2\pi \times (0.5) \times 15$ , change: increasing the movement of air around the shoot

Answer: B

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