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ESAT Mock Biology Esat-bio-bank-2

30 questions30 marks40Updated August 2026

The ESAT Mock Biology Esat-bio-bank-2 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

A diploid somatic cell from a mammal has a nuclear DNA content of

24\,\text{picograms (pg)}

during the

G_1

phase of the cell cycle. This cell undergoes the meiotic cell cycle to produce four gametes.

Which row correctly identifies the DNA content per nucleus in a cell during prophase II and the total combined nuclear DNA content of all four resulting gametes?

A.per nucleus in prophase II: $12\,\text{pg}$ ; total in four gametes: $24\,\text{pg}$
B.per nucleus in prophase II: $12\,\text{pg}$ ; total in four gametes: $48\,\text{pg}$
C.per nucleus in prophase II: $24\,\text{pg}$ ; total in four gametes: $24\,\text{pg}$
D.per nucleus in prophase II: $24\,\text{pg}$ ; total in four gametes: $48\,\text{pg}$
E.per nucleus in prophase II: $48\,\text{pg}$ ; total in four gametes: $48\,\text{pg}$

Answer: D

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Question 2

1 mark

In a specific species of grasshopper, sex is determined by the number of X chromosomes. Females are diploid (

2n = 24

) and have two X chromosomes (

XX

). Males have only one X chromosome and no corresponding Y chromosome (the

X0

system).

A single male cell undergoes the meiotic cell cycle to produce sperm cells.

Assuming no mutations or errors occur, which row correctly identifies the number of chromosomes in a male somatic cell and the number of chromosomes found in each of the four resulting sperm cells?

A.male somatic cell: $23$ ; sperm cells: two have $11$ , two have $12$
B.male somatic cell: $23$ ; sperm cells: all four have $11$
C.male somatic cell: $24$ ; sperm cells: two have $12$ , two have $12$
D.male somatic cell: $24$ ; sperm cells: two have $11$ , two have $12$
E.male somatic cell: $25$ ; sperm cells: two have $12$ , two have $13$

Answer: A

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Question 3

1 mark

A farmer is comparing two methods of cultivating plants. Method 1 involves using stem cuttings (asexual reproduction), while Method 2 involves growing plants from seeds produced by the fusion of gametes from two different plants (sexual reproduction).

Which of the following statements is/are correct?

1. Provided no mutations occur, all offspring produced by Method 1 will be genetically identical to the parent plant.
2. Method 2 will produce offspring that exhibit increased genetic variation compared to Method 1.
3. Method 2 requires two parents, whereas Method 1 involves only one parent.

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 4

1 mark

A certain species of animal is capable of both asexual and sexual reproduction. A researcher is studying the genetic makeup of the offspring produced by both methods.

Which of the following statements is/are correct?

1. Offspring produced through asexual reproduction are genetically identical to the parent, assuming no mutations occur.
2. Offspring produced through sexual reproduction inherit

100\%

of their nuclear DNA from only one parent.
3. Sexual reproduction leads to offspring that are genetically different from both the parents and from each other.

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 5

1 mark

In a laboratory experiment, two groups of human somatic cells are prepared. Group 1 contains

150

diploid cells from a healthy male donor. Group 2 contains

150

diploid cells from a healthy female donor.

Every cell in Group 1 is induced to undergo exactly one round of mitosis. Every cell in Group 2 is induced to undergo meiosis to produce four haploid cells each.

What is the ratio, in its simplest form, of the total number of

Y

chromosomes in Group 1 after mitosis to the total number of

X

chromosomes in Group 2 after meiosis?

A. $1:1$
B. $1:2$
C. $2:1$
D. $1:4$
E. $4:1$

Answer: B

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Question 6

1 mark

A particular species of eukaryotic organism has a diploid number of

2n = 12

. Consider the following statements regarding the genetic material found within the nucleus of a somatic cell from this organism:

Statement 1: In the

G_1

phase of the cell cycle, there are exactly 12 molecules of

\text{DNA}

in the nucleus.
Statement 2: During the

S

phase, the total mass of

\text{DNA}

in the nucleus doubles, but the number of chromosomes remains 12.
Statement 3: In an animal cell, the nucleus is the only organelle that contains genetic material.

Which of the statement(s) is/are correct?

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 7

1 mark

Consider a human somatic cell, which is diploid (

2n = 46

). Which of the following statements correctly describes the state or organization of the genetic material within the nucleus of this cell?

A.During interphase, the $\text{DNA}$ is packaged into 46 highly condensed chromosomes that are individually visible under a light microscope.
B.The nucleus contains 46 linear $\text{DNA}$ molecules during the $G_2$ phase of the cell cycle.
C.Each chromosome in the nucleus consists of a single $\text{DNA}$ molecule associated with proteins during the $G_1$ phase.
D.The nuclear envelope is a single-layered lipid membrane that prevents all proteins from entering the nucleoplasm.
E.The genetic material in the nucleus of a mature human sperm cell is identical in quantity and sequence to that of a somatic cell.

Answer: C

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Question 8

1 mark

In a population of

1200

mice, fur colour is determined by a single gene located on an autosome. The allele for black fur (

B

) is dominant over the allele for white fur (

b

). In this population,

15\%

of the mice have white fur. Among the mice with black fur, the ratio of the number of individuals with the genotype

BB

to the number of individuals with the genotype

Bb

is

2:1

. One somatic cell was collected from every mouse in the population.

What is the total number of alleles for white fur (

b

) in these collected cells?

A. $340$
B. $360$
C. $520$
D. $700$
E. $1040$

Answer: D

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Question 9

1 mark

An autosomal recessive condition is caused by a single gene. A male, P, has the condition. He has a child with a female, Q, who does not have the condition. Q has a brother who has the condition, but both of her parents are unaffected.

Assume that no new mutations occur. What is the probability that the first child of P and Q is a girl who has the condition?

A. $\frac{1}{3}$
B. $\frac{1}{4}$
C. $\frac{1}{6}$
D. $\frac{1}{8}$
E. $\frac{1}{12}$

Answer: C

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Question 10

1 mark

In a population of insects, a specific wing phenotype is controlled by a single gene with two alleles. The allele for normal wings (

V

) is dominant over the allele for vestigial wings (

v

). Two insects with normal wings are crossed and produce a large number of offspring, approximately 25% of which have vestigial wings. One of the normal-winged offspring is selected at random and crossed with an insect that has vestigial wings. What is the probability that the first offspring produced from this second cross will have normal wings?

A. $\frac{1}{4}$
B. $\frac{1}{3}$
C. $\frac{1}{2}$
D. $\frac{2}{3}$
E. $\frac{3}{4}$

Answer: D

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Question 11

1 mark

Which of the following statements about the human genome is/are correct?

1 The genome is the full set of genetic material (DNA) of an organism.
2 The human genome is found only within gametes (sperm and egg cells).
3 Each individual chromosome in a human cell contains the entire human genome.

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

Answer: A

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Question 12

1 mark

A scientist is studying the cells of a healthy human male. Which of the following statements is/are correct?

1 The DNA in the nucleus of a skin cell is contained within chromosomes.
2 The skin cells and the muscle cells of this individual contain the same genome.
3 The sperm cells produced by this individual contain

46

chromosomes.

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 13

1 mark

A double-stranded DNA molecule contains

1200

bases in total. The molecule is separated into its two single strands, Strand 1 and Strand 2. The following information is known about the base compositions:

1. In Strand 1,

20\%

of the bases are adenine (

A

) and

35\%

are cytosine (

C

).
2. In the whole double-stranded molecule,

25\%

of the bases are thymine (

T

).

What is the total number of thymine (

T

) bases present in Strand 1?

A. $120$
B. $150$
C. $180$
D. $210$
E. $300$

Answer: C

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Question 14

1 mark

A linear, double-stranded DNA fragment contains a total of

498

phosphodiester bonds. There are

650

hydrogen bonds holding the two strands together. What percentage of the total number of bases in this fragment is cytosine (

C

)?

(Assume each adenine–thymine pair has

2

hydrogen bonds and each guanine–cytosine pair has

3

hydrogen bonds.)

A. $20\%$
B. $25\%$
C. $30\%$
D. $35\%$
E. $40\%$

Answer: C

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Question 15

1 mark

A functional protein is formed from a single polypeptide chain. The gene coding for this protein has

450

nucleotide bases in its coding region (excluding any start or stop codons). How many amino acids are in this protein, and what primarily determines its specific three-dimensional shape?

A. $150$ amino acids; the total number of amino acids.
B. $150$ amino acids; the sequence of its amino acids.
C. $450$ amino acids; the sequence of its amino acids.
D. $450$ amino acids; the three-dimensional folding of the DNA.
E. $1350$ amino acids; the sequence of its amino acids.

Answer: B

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Question 16

1 mark

A polypeptide is synthesized using the information in a gene. The coding region of this gene consists of

603

nucleotides. This sequence includes exactly one stop codon, which is a triplet of bases that does not code for an amino acid. Every other triplet in the sequence codes for exactly one amino acid. How many amino acids will be linked together to form the polypeptide?

A. $200$
B. $201$
C. $600$
D. $603$
E. $1809$

Answer: A

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Question 17

1 mark

The table shows some DNA triplets and the amino acids they code for.

| DNA triplet | Amino acid |
| :--- | :--- |
|

TCT

| serine |
|

TCC

| serine |
|

TCA

| serine |
|

TCG

| serine |
|

ACT

| threonine |
|

GCT

| alanine |
|

CCT

| proline |
|

TAT

| tyrosine |
|

TGT

| cysteine |
|

TTT

| phenylalanine |

A mutation occurs in the DNA triplet

TCT

, which codes for serine. The mutation is a single base substitution where one of the three bases is replaced by one of the other three possible DNA bases. Each possible substitution is equally likely.

What is the probability that this mutation results in a change to the amino acid sequence of the encoded protein?

A. $\frac{1}{9}$
B. $\frac{2}{9}$
C. $\frac{1}{3}$
D. $\frac{2}{3}$
E. $\frac{8}{9}$

Answer: D

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Question 18

1 mark

Which of the following statements about gene mutations is/are correct?

1. A mutation always involves a change in the sequence of nucleotides in the DNA.
2. If a mutation occurs in a non-coding region of the DNA, it is impossible for it to have any effect on the phenotype of the organism.
3. A single base substitution is more likely to have no effect on the phenotype than a single base insertion within the coding region of a gene.

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

Answer: D

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Question 19

1 mark

Which of the following statements concerning the process, benefits, and risks of genetic engineering is/are correct?

1. Using human insulin produced by genetically modified bacteria is generally safer for patients than using insulin extracted from animal pancreases because it is chemically identical to human insulin and less likely to cause an allergic reaction.
2. Restriction enzymes function as 'molecular glue' used to join an isolated human gene to a bacterial plasmid by forming new covalent phosphodiester bonds.
3. A potential environmental risk of cultivating genetically modified (GM) crops is the transfer of modified genes to wild relative plant species via cross-pollination, which could provide them with a selective advantage.

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 20

1 mark

A researcher attempts to produce a recombinant plasmid by inserting a gene for a fluorescent protein into a plasmid vector. The plasmid contains two functional genes:

kan^R

(providing resistance to the antibiotic kanamycin) and

tet^R

(providing resistance to the antibiotic tetracycline). The restriction enzyme used to insert the fluorescent protein gene cuts the plasmid at a single site located within the

tet^R

gene.

Following the transformation process, bacteria were grown on a master plate containing no antibiotics, resulting in

500

colonies. These colonies were then transferred to two different types of selective agar plates using replica plating:

-

320

colonies were able to grow on the plate containing kanamycin.
-

110

colonies were able to grow on the plate containing tetracycline.

Assuming that all bacteria containing a plasmid (recombinant or original) express the

kan^R

gene, and only those with the original plasmid express the

tet^R

gene, how many of the

500

initial colonies contain the recombinant plasmid?

A.110
B.180
C.210
D.320
E.390

Answer: C

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Question 21

1 mark

A single human zygote (

2n = 46

) undergoes exactly three successive rounds of mitosis. The resulting cells, known as blastomeres, are then separated for analysis.

Which of the following statements is/are correct?

1. After these divisions, there are 8 cells, and each is totipotent with the potential to develop into a complete multicellular organism.
2. At this stage, the cells have already differentiated to become pluripotent, meaning they can differentiate into any cell type but can no longer form a complete organism.
3. Each of these cells contains 23 chromosomes, as the DNA content is halved during early embryonic cleavage to facilitate specialization.

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

Answer: A

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Question 22

1 mark

A clinical researcher is evaluating two different types of stem cells for use in a regenerative medicine trial to repair damaged heart tissue in a patient.

- Source X: Embryonic stem cells obtained from a donor blastocyst.
- Source Y: Adult stem cells obtained from the patient’s own bone marrow.

Which of the following statements correctly describe(s) the likely benefits or risks of these sources?

1. Source X cells are pluripotent and can differentiate into a wider range of cell types than Source Y cells, but they carry a higher risk of forming tumors (teratomas).
2. Source Y cells are multipotent and, because they are autologous (from the patient's own body), they avoid the risk of immune rejection associated with Source X.
3. A primary benefit of using Source Y is that these cells are totipotent, allowing them to be easily reprogrammed into any specialized cell type needed for the surgery.

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

Answer: C

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Question 23

1 mark

The following statements compare the processes of natural selection and selective breeding. Which of the following statements is/are correct?

1. Both processes rely on the existence of genetic variation within the starting population.
2. Selective breeding typically results in a faster change in a population's characteristics than natural selection.
3. In both processes, the selection pressure causes specific mutations to occur that are beneficial to the individual's survival or to human needs.

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

Answer: B

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Question 24

1 mark

A population of a specific crop plant has been selectively bred for high sugar content for many generations. Which of the following are likely consequences of this process when compared to the original wild population?

1. A reduction in the genetic diversity of the gene pool.
2. An increase in the proportion of the population that is homozygous for certain genes.
3. A greater ability of the population to survive a sudden outbreak of a new fungal pathogen.

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

Answer: C

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Question 25

1 mark

A population of bacteria was treated with an antibiotic. Initially,

99.9\%

of the bacteria died. The remaining

0.1\%

survived and reproduced. After several generations, the entire population was found to be resistant to the antibiotic.

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

1. The antibiotic acted as a selective pressure on the population of bacteria.
2. The mutations for resistance were caused by the presence of the antibiotic.
3. The development of antibiotic resistance in this population is an example of evolution through natural selection.

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

Answer: C

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Question 26

1 mark

On a remote island, a species of bird eats seeds. The population shows a range of beak sizes. After a severe drought, only plants with large, hard-cased seeds survive. Within two generations, the average beak size in the bird population increases significantly.

Which of the following statements explain this observation?

1. There was extensive genetic variation in beak size within the original population.
2. The birds with larger beaks had a phenotype that was better suited to the environment after the drought.
3. The average beak size increased because the drought caused individual birds to grow larger beaks during their lifetime to crack the harder 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 27

1 mark

A specific phenotypic trait,

X

, is measured in a population of organisms. The value of

X

is determined by the organism's genotype at one locus (alleles

A

and

a

) and the local temperature (

T

) during development, according to the following rules:

- Genotype

AA

:

X = T + 10

- Genotype

Aa

:

X = T + 5

- Genotype

aa

:

X = T

The environment can vary such that

10 \le T \le 20

.

Which of the following statements is/are correct?

1. The total range of possible values for trait

X

in this population is

10

to

30

.
2. An organism with

X = 22

must have the genotype

AA

.
3. If the temperature is held constant at

T = 15

, all observed variation in

X

is genetic.

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

Answer: D

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Question 28

1 mark

The height of a specific plant species is investigated in two experimental groups:

- Group A consists of genetically identical individuals (clones). Their heights range from

20\,\text{cm}

to

30\,\text{cm}

.
- Group B consists of genetically non-identical individuals. Their heights range from

15\,\text{cm}

to

45\,\text{cm}

.

Both groups were grown under the same wide range of light and nutrient conditions. Which of the following statements must be true?

1. The phenotypic variation observed within Group A is

100\%

environmental.
2. The phenotypic variation observed within Group B is caused by both genetic and environmental factors.
3. If an individual in Group B is

25\,\text{cm}

tall, it must have the same genotype as the plants in Group A.

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 29

1 mark

A substance isolated from a living cell is analyzed. The following observations are recorded:

1. It is composed of a long chain of amino acids.
2. It increases the rate of decomposition of hydrogen peroxide,

\text{H}_2\text{O}_2

.
3. Its mass remains constant at

10.0\,\text{mg}

throughout the reaction.

Which of the following terms correctly describe this substance?

- P: a protein
- Q: a catalyst
- R: a reactant

A.P only
B.Q only
C.P and Q only
D.P and R only
E.P, Q and R

Answer: C

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Question 30

1 mark

A student is given a liquid containing an unknown biological molecule. They add the molecule to a solution of substrate at

37\,^\circ\text{C}

and monitor the reaction. Which of the following sets of observations would best support the conclusion that the molecule is an enzyme?

A.The molecule is a protein and the total amount of product in the solution decreases over time.
B.The molecule is a carbohydrate and the reaction rate increases significantly when it is added.
C.The molecule is a protein and the reaction rate increases while the molecule's mass remains constant.
D.The molecule is a lipid and it provides the energy required for the reaction to reach completion.
E.The molecule is a protein and it is converted into a different substance by the end of the reaction.

Answer: C

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