ESAT Mock Biology Esat-bio-bank-1

15 questions15 marks40Updated August 2026

The ESAT Mock Biology Esat-bio-bank-1 paper in full: all 15 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

An artificial cell is constructed using a selectively permeable membrane that is permeable to water but impermeable to sucrose. This cell is filled with a

5\%

sucrose solution and then placed into a beaker containing a

10\%

sucrose solution.

Which of the following statements is/are correct?

1. The water potential of the solution in the beaker is lower than the water potential inside the cell.
2. The volume of the cell will decrease over time.
3. Sucrose molecules will move into the cell by diffusion.

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 2

1 mark

A population of identical animal cells divides synchronously by mitosis. The total duration of one complete cell cycle is

24

hours.

- Interphase lasts

22

hours and is followed by mitosis, which lasts

2

hours.
- DNA replication occurs during a

10

-hour period within interphase.
- This replication period begins

8

hours after the start of interphase.
- Cell growth occurs during the parts of interphase when DNA is not replicating.
- At

t = 0

hours, the cells are at the very beginning of interphase.

Which of the following statements is/are correct?

1. By

t = 70

hours, exactly three rounds of cell division will have been completed.
2. At

t = 44

hours, the mass of DNA in each cell is twice the mass of DNA in each cell at

t = 6

hours.
3. In a culture starting with

100

cells at

t = 0

, there will be

400

cells at

t = 50

hours.

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

Answer: D

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Question 3

1 mark

A diploid cell from an organism has a chromosome number of

2n = 12

. This cell undergoes the meiotic cell cycle to produce sperm cells. Assume that no mutations or chromosomal abnormalities occur.

Which of the following statements is correct?

A.Each cell at the end of the first meiotic division contains $12$ chromosomes.
B.A primary spermatocyte that has completed interphase contains a total of $24$ DNA strands.
C.Each sperm cell produced contains $6$ chromosomes and $12$ DNA strands.
D.Four sperm cells are produced from one diploid cell, each containing $3$ chromosomes and $6$ DNA strands.
E.During the interphase stage of the cell cycle, the number of chromosomes increases from $12$ to $24$ .

Answer: C

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Question 4

1 mark

A species of diploid organism can reproduce both asexually (producing clones) and sexually. In this species, sex is determined by

X

and

Y

chromosomes, where

XX

is female and

XY

is male. A particular female has the genotype

GgHh

, where these two genes are located on different autosomes.

Which of the following statements is/are correct?

1. If she reproduces asexually, there is a

100\%

probability that the offspring will be female and have the genotype

GgHh

, provided no mutations occur.
2. If she mates with a male of genotype

gghh

, the probability that any single offspring is genetically identical to the mother (considering the two autosomal loci and the sex chromosomes) is

0.25

.
3. If she mates with a male of genotype

GgHh

, the probability that she produces an offspring that is male and homozygous recessive for both autosomal genes is

1/32

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 5

1 mark

In a species of mammal, sex determination follows the same

XX/XY

mechanism as in humans. A specific recessive allele (

a

) located on the

X

chromosome is embryonic lethal; any individual possessing the genotype

X^a X^a

X^a Y

dies before birth and is not included in the count of surviving offspring.

A female that is heterozygous for this lethal allele (

X^A X^a

) is mated with a normal male (

X^A Y

). Over its lifetime, this pair produces a total of

48

surviving offspring.

Assuming that the observed phenotypic ratios perfectly match the genetic probabilities, what is the ratio of males to females and the total number of

X

chromosomes present in the

48

surviving offspring?

A.ratio: $1:1$ ; total number of $X$ chromosomes: $72$
B.ratio: $1:2$ ; total number of $X$ chromosomes: $80$
C.ratio: $2:1$ ; total number of $X$ chromosomes: $64$
D.ratio: $2:1$ ; total number of $X$ chromosomes: $80$
E.ratio: $1:2$ ; total number of $X$ chromosomes: $48$

Answer: B

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Question 6

1 mark

Consider the following three statements about the

\text{DNA}

within a cell:

Statement 1: In eukaryotic cells, the nucleus is the primary site where genetic material is stored.
Statement 2: Inside the nucleus, the

\text{DNA}

is organized into structures known as chromosomes.
Statement 3: A nucleus is a characteristic feature of both eukaryotic and prokaryotic cells.

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

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 7

1 mark

An autosomal recessive condition is determined by a single gene with two alleles: the dominant allele (

D

) and the recessive allele (

d

).

In a family study:
- The original parents are both unaffected.
- They have three children: an affected daughter, an unaffected son, and an unaffected daughter.
- The unaffected son has a child with an unaffected woman. This woman’s mother was affected by the condition, while her father was homozygous dominant.
- The son and his partner have one child, who is affected.
- The unaffected daughter of the original parents has a child with a man who is homozygous dominant. Their child is a carrier of the condition.

If one living diploid somatic cell is taken from each of the following eight individuals, what is the total number of recessive alleles (

d

) that would be found?
- the two original parents
- their three children
- the son's partner
- the son's affected child
- the daughter's carrier child

A. $4$
B. $6$
C. $8$
D. $10$
E. $12$

Answer: D

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Question 8

1 mark

In a species of bird, feather color is determined by a single gene that is not sex-linked. The allele for blue feathers (

B

) is dominant over the allele for green feathers (

b

). While most phenotypic traits in this species are polygenic (controlled by multiple genes), feather color follows a simple monohybrid inheritance pattern.

In a population of 2000 birds, scientists observed the following:
- 400 birds have green feathers.
- 1000 birds are heterozygous for feather color.
- All other birds have blue feathers and are homozygous.

Assuming no mutations have occurred, what are the total numbers of dominant (

B

) and recessive (

b

) alleles in this population?

A.dominant alleles: 1600; recessive alleles: 1400
B.dominant alleles: 1200; recessive alleles: 800
C.dominant alleles: 2200; recessive alleles: 1800
D.dominant alleles: 2000; recessive alleles: 2000
E.dominant alleles: 3000; recessive alleles: 1000

Answer: C

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Question 9

1 mark

A healthy human male has a mutation in a single gene located on his

X

-chromosome. The

Y

-chromosome does not carry a copy of this gene. Which of the following statements is/are correct?

1 This mutation is part of the individual’s genome.
2 The mutation is present in every healthy, diploid cell in the individual’s body.
3 The mutation is present in approximately

50\%

of the individual’s sperm cells.

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

Answer: E

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Question 10

1 mark

A double-stranded DNA molecule contains a total of

4000

nucleotides. In one of the strands (strand 1), there are

600

guanine (

G

) bases and

400

adenine (

A

) bases. In the whole double-stranded molecule,

20\%

of the bases present are cytosine (

C

). How many thymine (

T

) bases are present in strand 1?

A. $200$
B. $400$
C. $600$
D. $800$
E. $1200$

Answer: D

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Question 11

1 mark

A functional protein,

P

, is composed of three polypeptide subunits: two identical

\alpha

-chains and one

\beta

-chain. The total number of amino acids in a single molecule of protein

P

700

, and the

\beta

-chain contains

50\%

more amino acids than a single

\alpha

-chain. Each unique type of polypeptide is coded for by a specific 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). What is the total number of nucleotide bases in the coding regions of the unique genes required to synthesise protein

P

A. $1500$
B. $1506$
C. $2100$
D. $2109$
E. $3012$

Answer: B

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Question 12

1 mark

The following steps describe the process of genetically engineering a bacterium to produce a human protein:

Step 1: A specific human gene is cut from human DNA using restriction enzymes.
Step 2: A bacterial plasmid is isolated and cut open using the same restriction enzymes.
Step 3: The human gene and the plasmid are joined using DNA ligase to form a recombinant plasmid.
Step 4: The recombinant plasmid is inserted into a bacterium.

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

1. Restriction enzymes are used in both Step 1 and Step 2.
2. DNA ligase is used in Step 3 to join the DNA fragments together by forming new chemical bonds.
3. One benefit of this technology is that large quantities of the human protein can be produced using bacterial cultures.

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 13

1 mark

A clinical researcher is evaluating three sources of human stem cells for potential use in treating a patient with a degenerative heart condition:

- Source 1: Cells obtained from a human embryo at the 4-cell stage.
- Source 2: Cells obtained from the inner cell mass of a 5-day-old human blastocyst.
- Source 3: Adult stem cells obtained from the patient's own bone marrow.

Which of the following statements is/are correct?

1. Cells from Source 1 are totipotent and have the potential to develop into a complete multicellular organism, whereas cells from Source 2 are pluripotent.
2. Cells from Source 3 are pluripotent and can differentiate into any cell type provided the correct chemical signals are present.
3. The medical use of Source 2 cells generally carries a higher risk of both immune rejection and tumor formation than the use of Source 3 cells.

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

Answer: C

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Question 14

1 mark

A farmer aims to increase the yield of a crop by using selective breeding. She only saves and plants the seeds from the plants that produced the largest fruits in the previous season.

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

1 The genetic diversity of the crop population is likely to decrease over time.
2 Like natural selection, this process results in a change in the frequency of alleles within the population.
3 The selection pressure in this process is provided by the environment rather than by human choice.

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 15

1 mark

A scientist monitors a large population of bacteria in a laboratory. At

t = 0

, an antibiotic is added to the growth medium. Initially, the population size decreases by

99.9\%

, but after several days, the population size returns to its original level and all individuals are found to be resistant to the antibiotic.

A student proposed the following statements to explain these observations:

1 The initial population possessed extensive genetic variation, including alleles that conferred resistance to the antibiotic.
2 The presence of the antibiotic caused the sensitive bacteria to develop specific mutations for resistance in order to survive.
3 The change in the inherited characteristics of the bacterial population over time is an example of evolution.

Which of the student's statements could be correct?

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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