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ESAT Mock Biology Esat-bio-bank-3

30 questions30 marks40Updated August 2026

The ESAT Mock Biology Esat-bio-bank-3 paper in full: all 30 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

Which of the following statements regarding genetic inheritance in humans is/are correct?

1. A phenotype is the observable characteristic of an organism, which is determined by its genotype and its interaction with the environment.
2. An autosome is any chromosome that is not a sex chromosome.
3. A recessive allele will always be expressed in the phenotype of a heterozygous individual.

A.1 only
B.2 only
C.3 only
D.1 and 2 only
E.1, 2 and 3

Answer: D

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Question 2

1 mark

Achondroplasia is a type of dwarfism caused by a mutation in the

FGFR3

gene. It is an autosomal dominant condition. Individuals who inherit two copies of the mutant allele (

D

) do not survive to birth. Individuals with one mutant allele (

D

) and one normal allele (

d

) have achondroplasia. Individuals with two normal alleles (

d

) are of average height.

Which of the following statements is/are correct?

1. It is impossible for a live-born child to be homozygous for the mutant allele.
2. In a mating between two individuals with achondroplasia, the probability of a live-born child having average height is

\frac{1}{4}

.
3. Most human phenotypes, such as height and weight, are the result of the inheritance of multiple genes rather than a single gene.

A.1 only
B.1 and 2 only
C.1 and 3 only
D.2 and 3 only
E.1, 2 and 3

Answer: C

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Question 3

1 mark

A family tree shows the inheritance of an autosomal recessive condition. Two parents, both unaffected by the condition, have three children: one son who has the condition, and two daughters who do not have the condition.

One of these unaffected daughters (Individual X) has a child with a man (Individual Y) who is a known carrier (heterozygous) for the condition.

Assuming no new mutations occur, what is the probability that the first child of X and Y is a boy with the condition?

A. $\frac{1}{4}$
B. $\frac{1}{6}$
C. $\frac{1}{8}$
D. $\frac{1}{12}$
E. $\frac{1}{16}$

Answer: D

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Question 4

1 mark

Consider a healthy human with no genetic mutations. Which of the following statements is/are correct?

1. A skin cell contains the genes for proteins that are only expressed in the brain.
2. A mature human red blood cell contains the same number of chromosomes as a liver cell.
3. In a human, the genome is stored within the nucleus as a single, continuous molecule of DNA.

A.1 only
B.2 only
C.3 only
D.1 and 2 only
E.2 and 3 only

Answer: A

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Question 5

1 mark

A double-stranded DNA molecule contains a total of 1000 deoxyribose sugar molecules. In one of its strands (strand 1),

15\%

of the nitrogenous bases are adenine and

25\%

are cytosine. In the whole double-stranded molecule,

30\%

of the bases are guanine.

Which of the following statements about this DNA molecule is/are correct? (Assume no mutations.)

1 Strand 2 contains 75 adenine bases.
2 The whole molecule contains 200 thymine bases.
3 Strand 1 contains 175 guanine bases.

A.1 only
B.2 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: D

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Question 6

1 mark

A segment of double-stranded DNA is

N

base pairs long. It is found that

15\%

of the total nitrogenous bases in this segment are cytosine.

Which of the following is the correct expression for the total number of hydrogen bonds between the two strands in this DNA segment?

A. $1.15N$
B. $2.15N$
C. $2.30N$
D. $2.70N$
E. $2.85N$

Answer: C

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Question 7

1 mark

A protein

P

is a functional protein consisting of two different polypeptides,

X

and

Y

. Polypeptide

X

consists of

150

amino acids. Polypeptide

Y

is

40\%

longer than polypeptide

X

. Each polypeptide is coded for by a separate, unique gene. The coding region of each gene starts with a start codon (which codes for an amino acid) and ends with a stop codon (which does not code for an amino acid). Which of the following is correct?

A.The coding region of the gene for polypeptide $Y$ contains $630$ nucleotides.
B.The total number of amino acids in one molecule of protein $P$ is $210$ .
C.The coding region of the gene for polypeptide $X$ contains exactly $453$ nucleotides.
D.The three-dimensional shape of protein $P$ is determined by the total number of amino acids, regardless of their sequence.
E.A mutation in the gene for $X$ will always change the three-dimensional shape of the functional protein $P$ .

Answer: C

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Question 8

1 mark

A functional protein is a homodimer (it consists of two identical polypeptide subunits). The coding region of the gene for this protein contains

1206

nucleotide bases. This coding region includes exactly one start codon (which codes for an amino acid) and one stop codon (which does not code for an amino acid).

Which of the following statements is/are correct?

1. A single molecule of the functional protein contains a total of

802

amino acids.
2. The specific three-dimensional shape of the protein is determined by the sequence of the amino acids in its polypeptides.
3. A substitution mutation that changes the

100

th triplet in the gene to a stop codon would result in a shorter polypeptide.

A.1 only
B.2 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: E

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Question 9

1 mark

A mutation in a gene changes a DNA triplet from

GCA

to

GCG

. Both triplets code for the amino acid alanine.

Consider these three statements:
1. The sequence of nucleotides in the DNA has changed.
2. The primary structure of the encoded protein has changed.
3. This mutation is likely to have no effect on the phenotype of the organism.

Which of the statements is/are correct?

A.1 only
B.3 only
C.1 and 2 only
D.1 and 3 only
E.1, 2 and 3

Answer: D

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Question 10

1 mark

The table describes three different mutations that occur in the DNA of a gene coding for an enzyme.

| Mutation | Description |
| :--- | :--- |
| 1 | A substitution that results in the same amino acid being added to the polypeptide chain. |
| 2 | A substitution that replaces one amino acid with a different one in a region of the protein away from the active site. |
| 3 | An insertion of a single nucleotide at the start of the coding sequence. |

Based on the principle that most mutations have no effect on the phenotype, some have a small effect, and others determine the phenotype, which row correctly identifies the most likely phenotypic effect of each mutation?

A.1: no effect; 2: small effect; 3: determine phenotype
B.1: small effect; 2: no effect; 3: determine phenotype
C.1: no effect; 2: determine phenotype; 3: small effect
D.1: determine phenotype; 2: small effect; 3: no effect
E.1: no effect; 2: no effect; 3: determine phenotype

Answer: A

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Question 11

1 mark

Which of the following statements about the process and medical applications of genetic engineering are correct?

1. Restriction enzymes isolate a target gene by breaking the covalent phosphodiester bonds in the DNA sugar-phosphate backbone at specific recognition sites.
2. DNA ligase is used to join a human gene and a plasmid by catalyzing the formation of hydrogen bonds between complementary base pairs at the sticky ends.
3. Recombinant human insulin is generally considered safer for treating diabetes than insulin extracted from animal pancreases because it is chemically identical to the insulin produced by the human body.

A.1 only
B.1 and 2 only
C.1 and 3 only
D.2 and 3 only
E.1, 2 and 3

Answer: C

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Question 12

1 mark

A researcher isolates three types of human stem cells and records their characteristics:

- Cell X: Stem cells taken from the inner cell mass of a 5-day-old blastocyst that can differentiate into any body cell type.
- Cell Y: Stem cells taken from a 2-cell stage embryo that have the potential to develop into a complete multicellular organism.
- Cell Z: Stem cells taken from adult bone marrow that can differentiate into a limited number of different blood cell types.

Which of the following rows correctly identifies the potency of these cells?

A.X: pluripotent; Y: totipotent; Z: multipotent
B.X: totipotent; Y: pluripotent; Z: multipotent
C.X: pluripotent; Y: multipotent; Z: totipotent
D.X: multipotent; Y: totipotent; Z: pluripotent
E.X: multipotent; Y: pluripotent; Z: totipotent

Answer: A

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Question 13

1 mark

Stem cells have significant potential for medical use, but their application involves several risks and ethical considerations.

Which of the following statements is/are correct?

1. Pluripotent stem cells carry a higher risk of forming tumours (teratomas) compared to multipotent adult stem cells.
2. Using a patient's own adult stem cells (autologous) reduces the risk of immune rejection compared to using embryonic stem cells from a donor.
3. A primary ethical objection to the use of embryonic stem cells is that the extraction process typically results in the destruction of a human embryo.

A.1 only
B.3 only
C.1 and 2 only
D.2 and 3 only
E.1, 2, and 3

Answer: E

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Question 14

1 mark

Consider two different scenarios involving the reproduction of rice plants over 50 generations:

Scenario 1: A farmer identifies the plants with the highest grain yield each year and uses only their seeds to plant the next generation.
Scenario 2: A wild population of rice grows in a natural wetland, where environmental factors such as seasonal flooding and competition for sunlight determine which plants survive to produce seeds.

Which of the following statements is/are correct?

1. Scenario 1 is an example of artificial selection, while Scenario 2 is an example of natural selection.
2. Over 50 generations, Scenario 1 is likely to result in a greater decrease in genetic diversity than Scenario 2.
3. In both scenarios, the process of selection leads to a change in the frequency of specific alleles within the population over time.

A.1 only
B.2 only
C.1 and 2 only
D.1 and 3 only
E.1, 2 and 3

Answer: E

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Question 15

1 mark

Selective breeding has been used for centuries to produce modern breeds of domestic dogs from a common wolf-like ancestor.

Which of the following are likely consequences of this process for a modern breed that has been heavily selected for specific physical traits?

1. An increase in the frequency of alleles that are beneficial to human requirements but may be detrimental to the health of the dog.
2. A higher probability of individuals being homozygous for deleterious recessive alleles compared to the ancestral population.
3. An increased capacity of the breed to adapt to a rapidly changing natural environment compared to the ancestral population.

A.1 only
B.3 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: C

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Question 16

1 mark

A population of a species of bird is studied on an isolated island. Beak depth in this species is an inherited characteristic. During a decade of significant environmental change, where small seeds became scarce and large, thick-shelled seeds became the primary food source, scientists recorded the average beak depth of the population every two generations.

| Generation | Average beak depth /

\text{mm}

|
| :--- | :--- |
| 2 |

8.6

|
| 4 |

8.9

|
| 6 |

9.3

|
| 8 |

9.8

|

Which of the following statements about this population is/are correct?

1. The change in average beak depth is an example of a change in the inherited characteristics of a population over time.
2. The scarcity of small seeds acted as a selective pressure on the population.
3. Individual birds with small beaks adapted to the drought by growing larger beaks during their lifetime to crack the remaining seeds.

A.1 only
B.2 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: C

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Question 17

1 mark

A student is researching the development of antibiotic resistance in a population of bacteria. They propose several statements to explain how a population of

1.0 \times 10^7

bacteria could become resistant to a specific antibiotic after being exposed to it.

Which of the following of the student's statements is/are correct?

1. The antibiotic induces specific mutations in the DNA of the bacteria to ensure their survival.
2. Antibiotic resistance is an example of evolution through natural selection.
3. Natural selection acts on genetic variants already present in the population, favouring those with phenotypes best suited to the environment.

A.2 only
B.3 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: D

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Question 18

1 mark

Three different plant genotypes (

G_1

,

G_2

, and

G_3

) were grown in two different light intensities, 'Dim' and 'Bright', while all other environmental factors were kept identical. The mean heights of the plants are recorded in the table below:

| Genotype | Height in Dim light | Height in Bright light |
| :--- | :--- | :--- |
|

G_1

|

12\,\text{cm}

|

18\,\text{cm}

|
|

G_2

|

15\,\text{cm}

|

21\,\text{cm}

|
|

G_3

|

14\,\text{cm}

|

14\,\text{cm}

|

Which of the following statements is/are correct?

1. For genotype

G_3

, the variation in height caused by changing from 'Dim' to 'Bright' light is zero.
2. The difference in height between

G_1

and

G_2

when grown in the 'Dim' light environment is entirely due to genetic factors.
3. A plant with a height of

14\,\text{cm}

must possess genotype

G_3

.

A.1 only
B.2 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: C

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Question 19

1 mark

A physiological trait is measured in a large population and is found to follow a normal distribution. Researchers studied the trait in pairs of twins to determine the sources of variation, calculating the correlation coefficients (

r

) as follows:

- Monozygotic (MZ) twins reared together:

r = 0.88

- Monozygotic (MZ) twins reared apart:

r = 0.65

- Dizygotic (DZ) twins reared together:

r = 0.42

Which of the following statements is/are correct?

1. The normal distribution of the trait suggests that it is likely to be polygenic.
2. The data suggest that environmental factors have no influence on this trait.
3. The greater correlation in MZ twins reared apart (

r = 0.65

) compared to DZ twins reared together (

r = 0.42

) indicates a genetic basis for the variation.

A.1 only
B.3 only
C.1 and 2 only
D.1 and 3 only
E.2 and 3 only

Answer: D

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Question 20

1 mark

Amylase is an enzyme that catalyses the breakdown of starch into maltose. Trypsin and pepsin are protease enzymes that break down proteins. Amylase and trypsin both have an optimum pH of approximately

7.5

, while pepsin has an optimum pH of approximately

2.0

.

Three test tubes are prepared with the following contents and incubated at

37\,^\circ\text{C}

and pH

7.5

:

- Tube 1: amylase and starch
- Tube 2: amylase and trypsin
- Tube 3: amylase and pepsin

In which of the tube(s) will the concentration of functional amylase molecules decrease significantly during the incubation?

A.Tube 1 only
B.Tube 2 only
C.Tube 1 and 2 only
D.Tube 2 and 3 only
E.1, 2 and 3

Answer: B

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Question 21

1 mark

A student compares the decomposition of hydrogen peroxide (

2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2

) using two different catalysts: the enzyme catalase and the inorganic catalyst manganese(IV) oxide (

M\text{nO}_2

).

Which of the following properties are shared by **both** catalase and manganese(IV) oxide?

1. They increase the rate of reaction by providing an alternative pathway with a lower activation energy.
2. They are biological molecules primarily composed of amino acids.
3. They are not consumed by the reaction, meaning their mass remains constant.
4. Their catalytic activity is destroyed if the reaction mixture is boiled.

A.1 and 2 only
B.2 and 4 only
C.1 and 3 only
D.1, 3 and 4 only
E.1, 2, 3 and 4

Answer: C

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Question 22

1 mark

Which of the following statements about the mechanism of enzyme action is/are correct?

1. The active site is a specific region of the enzyme molecule where the substrate binds.
2. The tertiary structure of the protein determines the specific three-dimensional shape of the active site.
3. Enzymes are consumed during the reaction and must be resynthesised by the cell before the reaction can occur again.

A.1 only
B.2 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: C

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Question 23

1 mark

A student investigates enzyme specificity using the enzymes lactase (which hydrolyses lactose into glucose and galactose) and sucrase (which hydrolyses sucrose into glucose and fructose). Four test tubes are prepared with the following contents:

Tube 1:

5\,\text{cm}^3

lactose solution +

1\,\text{cm}^3

lactase solution
Tube 2:

5\,\text{cm}^3

sucrose solution +

1\,\text{cm}^3

lactase solution
Tube 3:

5\,\text{cm}^3

lactose solution +

1\,\text{cm}^3

lactase solution that has been boiled and cooled
Tube 4:

5\,\text{cm}^3

sucrose solution +

1\,\text{cm}^3

sucrase solution

All tubes are incubated at

35\,^\circ\text{C}

for 15 minutes. Which tube(s) will contain free glucose at the end of the incubation period?

A.1 only
B.4 only
C.1 and 4 only
D.2 and 3 only
E.1, 2 and 4 only

Answer: C

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Question 24

1 mark

A student investigated the effect of pH and temperature on the rate of starch breakdown by an amylase enzyme. The student recorded the time taken (in minutes) for the starch to be completely digested under various conditions. The results are shown in the table below:

| pH | Time at

25^\circ\text{C}

(minutes) | Time at

35^\circ\text{C}

(minutes) |
| :--- | :--- | :--- |
| 3.0 | 40 | 20 |
| 7.0 | 10 | 5 |
| 11.0 | No reaction | No reaction |

Which of the following statements is/are correct?

1. At pH 7.0, the temperature coefficient (

Q_{10}

) for the rate of this reaction between

25^\circ\text{C}

and

35^\circ\text{C}

is 2.0.
2. The lack of reaction at pH 11.0 suggests the enzyme has denatured, resulting in a loss of the specific shape of its active site.
3. At

25^\circ\text{C}

, the rate of reaction at pH 7.0 is 300% greater than the rate of reaction at pH 3.0.

A.1 only
B.3 only
C.1 and 2 only
D.2 and 3 only
E.1, 2 and 3

Answer: E

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Question 25

1 mark

An enzyme-catalysed reaction was studied under different conditions. The following information is known about the enzyme and the reaction:

- The optimum pH for the enzyme is 7.0. At pH 5.0, the enzyme's activity is

25\%

of its activity at pH 7.0.
- Between

15^\circ\text{C}

and

25^\circ\text{C}

, the temperature coefficient (

Q_{10}

) for the rate of reaction is 2.0.
- In an initial experiment at pH 7.0 and

15^\circ\text{C}

, it took 10 minutes to produce

40\,\text{mg}

of product.

If the experiment is repeated at pH 5.0 and

25^\circ\text{C}

using the same initial mass of substrate (which is in excess), how long will it take to produce

40\,\text{mg}

of product?

A.5 minutes
B.10 minutes
C.20 minutes
D.40 minutes
E.80 minutes

Answer: C

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Question 26

1 mark

Which of the following rows correctly identifies a digestive enzyme, a primary site of its production in the human body, and the products formed from its substrate?

A.Enzyme: Amylase; Produced in: Salivary glands; Products: Amino acids
B.Enzyme: Protease; Produced in: Salivary glands; Products: Maltose
C.Enzyme: Lipase; Produced in: Pancreas; Products: Fatty acids and glycerol
D.Enzyme: Amylase; Produced in: Stomach; Products: Glucose
E.Enzyme: Lipase; Produced in: Liver; Products: Fatty acids and glycerol

Answer: C

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Question 27

1 mark

During heavy physical activity, human muscle cells transition from purely aerobic respiration to a combination of aerobic and anaerobic respiration. Consider the following three statements regarding these processes:

1. The word equation for anaerobic respiration in animal cells is:

\text{glucose} \rightarrow \text{ethanol} + \text{carbon dioxide}

.
2. Carbon dioxide is a waste product of aerobic respiration that acts to increase the pH of the blood plasma as its concentration rises.
3. Aerobic respiration releases a significantly greater amount of energy per molecule of glucose than anaerobic respiration.

A.1 and 2 only
B.3 only
C.1 and 3 only
D.2 and 3 only
E.1, 2, and 3

Answer: B

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Question 28

1 mark

A student is investigating the metabolic processes within a mammalian liver cell. They consider three specific points regarding cellular respiration:

1. In the word equation for anaerobic respiration in animals, the total mass of the products formed is equal to the total mass of the glucose consumed.
2. The process of aerobic respiration occurs partly in the cytoplasm and partly within the mitochondria.
3. Lactic acid is a product of anaerobic respiration that must eventually be removed or broken down because it can interfere with cellular function.

Which of these points is/are correct?

A.1 only
B.2 only
C.1 and 2 only
D.2 and 3 only
E.1, 2, and 3

Answer: E

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Question 29

1 mark

A healthy adult has a resting heart rate of

60

beats per minute (

\text{bpm}

) and a stroke volume of

75\text{ ml}

. During a period of intense exercise, their heart rate increases to

150\text{ bpm}

and their stroke volume increases by

20\%

.

What is the cardiac output during exercise, and what is the percentage increase in cardiac output compared to the resting state?

(Note:

1\text{ litre} = 1000\text{ ml}

)

A. $11.25\text{ L/min}$ and $150\%$
B. $13.5\text{ L/min}$ and $200\%$
C. $13.5\text{ L/min}$ and $300\%$
D. $15.0\text{ L/min}$ and $233\%$
E. $11.25\text{ L/min}$ and $250\%$

Answer: B

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Question 30

1 mark

A simplified diagram of a spinal reflex arc consists of a sensory neurone, a relay neurone, and a motor neurone, with synapses connecting them in the spinal cord.

Consider the following statements regarding this reflex arc:

1. If the sensory neurone is severed, the individual will still feel the stimulus but will be unable to perform the reflex action.
2. At each synapse, the signal is transmitted via the diffusion of chemical neurotransmitters across a gap.
3. The motor neurone carries electrical impulses from the central nervous system to an effector, such as a muscle.
4. This reflex arc is typically slower than a voluntary response because it must pass through the spinal cord.

Which of the statements are correct?

A.1 and 2 only
B.2 and 3 only
C.3 and 4 only
D.1, 2 and 3 only
E.2, 3 and 4 only

Answer: B

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