ESAT Mock Biology

27 questions27 marks40Updated July 2026

The ESAT Mock Biology paper in full: all 27 questions, each with its answer and a worked solution that shows every step. 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.

Question 1

1 mark

A student identifies the following features in a particular cell: a nucleus, mitochondria, and a cell membrane. However, the cell does not possess a cell wall.

Which of the following could be the identity of this cell?

A.a bacterium
B.a human cheek cell
C.a root hair cell
D.a leaf mesophyll cell
E.a fungal cell

Answer: B

Worked solution

To identify the cell, we must evaluate the presence or absence of specific organelles:

1. The presence of a nucleus and mitochondria indicates that the cell is eukaryotic. Bacteria are prokaryotic and lack a nucleus and membrane-bound organelles like mitochondria, so option A is incorrect.
2. The absence of a cell wall is a key identifying feature. Plant cells (such as root hair cells and leaf mesophyll cells) and fungal cells possess a cell wall. Therefore, options C, D, and E are incorrect.
3. Animal cells, such as human cheek cells, are eukaryotic (containing a nucleus and mitochondria) but do not have a cell wall.

Since the human cheek cell matches all the criteria (eukaryotic and lacking a cell wall), it is the correct answer.

Question 2

1 mark

Which of the following is a correct description of the function of the specified sub-cellular component?

A.The nucleus is the primary site of aerobic respiration within the cell.
B.The cell wall controls the movement of substances into and out of the cell.
C.The chloroplast is the site of protein synthesis in plant cells.
D.The vacuole contains cell sap and helps to maintain the cell's internal pressure.
E.The cytoplasm provides a rigid external structure to support the cell.

Answer: D

Worked solution

We evaluate each functional description:

A is incorrect. The mitochondrion, not the nucleus, is the site of aerobic respiration. The nucleus contains genetic material.
B is incorrect. The cell membrane controls the movement of substances. The cell wall is usually freely permeable and provides structural support.
C is incorrect. The chloroplast is the site of photosynthesis. Protein synthesis occurs on ribosomes (though ribosomes are not in this specific sub-list, the statement remains false for chloroplasts).
D is correct. In plant cells, the large permanent vacuole contains cell sap and pushes the cytoplasm against the cell wall, maintaining turgor pressure to keep the cell firm.
E is incorrect. The cytoplasm is the jelly-like substance where chemical reactions occur. The cell wall provides the rigid external structure.

Therefore, description D is the only correct match.

Question 3

1 mark

Which of the following sub-cellular structures are found in both a typical human liver cell and a typical leaf mesophyll cell?

1. cell membrane
2. cytoplasm
3. cell wall
4. mitochondria
5. nucleus

A.1 and 2 only
B.1, 2 and 5 only
C.1, 2, 4 and 5 only
D.1, 2, 3 and 5 only
E.1, 2, 3, 4 and 5

Answer: C

Worked solution

We must determine which structures are common to both animal (liver) and plant (mesophyll) cells:

1. Cell membrane: Found in all cells (both animal and plant).
2. Cytoplasm: Found in all cells (both animal and plant).
3. Cell wall: Found in plant cells (mesophyll) but never in animal cells (liver).
4. Mitochondria: Both liver cells and leaf mesophyll cells are eukaryotic and require energy from aerobic respiration, so both contain mitochondria.
5. Nucleus: Both are eukaryotic cells and contain a nucleus.

Structures 1, 2, 4, and 5 are found in both. Structure 3 is only found in the leaf cell. Thus, the correct combination is 1, 2, 4, and 5.

Question 4

1 mark

Which of the following statements correctly describe(s) the sub-cellular components of a typical prokaryotic cell?

1. The cell membrane contains enzymes responsible for the final stages of aerobic respiration.
2. The chromosomal DNA is enclosed within a double-membrane-bound nucleus to prevent damage from cytoplasmic reactions.
3. Plasmid DNA consists of small, circular loops that can carry accessory genes such as those for antibiotic resistance.
4. The cell wall is a rigid external layer primarily composed of cellulose.

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

Answer: C

Worked solution

Let us evaluate each statement regarding prokaryotic (bacterial) cells:

1. **Correct.** Since prokaryotes lack membrane-bound organelles like mitochondria, the enzymes and proteins required for aerobic respiration (such as the electron transport chain) are located in the cell membrane.
2. **Incorrect.** A defining feature of prokaryotes is that they do not have a 'true' nucleus. Their chromosomal DNA is located directly in the cytoplasm in a region called the nucleoid.
3. **Correct.** Plasmids are small, independent circular DNA molecules. They often carry 'extra' genes that are not essential for basic survival but provide advantages, such as resistance to specific antibiotics.
4. **Incorrect.** While bacteria do have a rigid cell wall, it is made of peptidoglycan (also called murein). Cellulose is the primary component of plant cell walls.

Therefore, only statements 1 and 3 are correct.

Question 5

1 mark

A cell is examined under a microscope and found to possess the following features:
- a cell wall
- DNA
- no mitochondria

Which of the following statements about this cell could be correct?

1. The cell is a bacterium and its chromosomal DNA is located in the cytoplasm.
2. The cell is a mature plant cell.
3. The genetic material is organized into a single circular chromosome.
4. The cell contains plasmid DNA.

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

Answer: D

Worked solution

We must identify the cell type based on the provided features:
- **Cell Wall:** This rules out animal cells.
- **DNA:** Present in all living cells.
- **No Mitochondria:** This is the key distinguishing factor. Eukaryotic cells with cell walls (such as plant cells and fungal cells) possess mitochondria for aerobic respiration. Prokaryotic cells (bacteria) lack all membrane-bound organelles, including mitochondria.

Since the cell has a wall but no mitochondria, it must be a prokaryote.

1. **Could be correct.** In bacteria, DNA is found freely in the cytoplasm because there is no nucleus.
2. **Incorrect.** Plant cells are eukaryotic and contain mitochondria to perform aerobic respiration, regardless of whether they also contain chloroplasts.
3. **Could be correct.** The chromosomal DNA in most bacteria is a single circular molecule.
4. **Could be correct.** Many bacteria contain plasmids in addition to their chromosomal DNA.

Statements 1, 3, and 4 are consistent with the features of a prokaryotic cell.

Question 6

1 mark

A student lists four structures found in the human body:

1. The lining of the small intestine
2. A white blood cell
3. The liver
4. The respiratory system

What is the correct order of these structures, starting from the simplest level of organisation to the most complex?

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

Answer: B

Worked solution

We must categorise each structure by its level of organisation:

1. The lining of the small intestine is an epithelium, which is a tissue (a group of similar cells working together).
2. A white blood cell is a single cell.
3. The liver is an organ (made of several tissues like nervous, connective, and epithelial tissues).
4. The respiratory system is an organ system (comprising the trachea, bronchi, lungs, etc.).

The order of complexity from simplest to most complex is: Cell

\to

Tissue

\to

Organ

\to

Organ System.
This corresponds to the sequence: 2 (cell)

\to

1 (tissue)

\to

3 (organ)

\to

4 (system).

Question 7

1 mark

Which of the following descriptions accurately matches a human structure to its level of organisation?

A.Red blood cell: a tissue found within the circulatory system.
B.Pancreas: an organ that produces digestive enzymes and hormones.
C.Muscle fibre: a tissue that enables the movement of limbs.
D.Large intestine: an organ system involved in water absorption.
E.Brain: a tissue that coordinates nervous impulses.

Answer: B

Worked solution

We evaluate the level of organisation for each option:

A is incorrect. A red blood cell is an individual cell. Blood itself is considered a tissue, but a single cell is the cellular level.

B is correct. The pancreas is an organ because it is made of different tissues (endocrine and exocrine glandular tissues, connective tissue, etc.) working together for specific functions.

C is incorrect. In biological terms, a 'muscle fibre' is a single muscle cell. Skeletal muscle (the whole structure) is an organ, and muscle tissue is the group of cells.

D is incorrect. The large intestine is an organ. It is part of the digestive system, which is the organ system.

E is incorrect. The brain is an organ, not a tissue. It is composed of nervous tissue, connective tissue (meninges), and blood vessels.

Question 8

1 mark

A student investigated the change in mass of potato tissue in different sucrose solutions. Three identical potato cylinders, each with an initial mass of

10.0\text{ g}

, were placed in three different sucrose solutions (X, Y, and Z) for 60 minutes. The cylinders were then removed, blotted dry, and reweighed. The final masses were recorded as:

- Solution X:

10.0\text{ g}

- Solution Y:

11.5\text{ g}

- Solution Z:

8.5\text{ g}

Which of the following statements is correct?

A.Solution X has a higher water potential than the potato cells.
B.Solution Y has a higher water potential than the potato cells.
C.Solution Z has a higher water potential than the potato cells.
D.The concentration of sugar in solution Z is lower than the concentration of sugar in the potato cells.
E.The change in mass in solution Y was caused by the active transport of water into the cells.

Answer: B

Worked solution

To solve this, we analyze the direction of water movement by osmosis, which occurs from a region of higher water potential to a region of lower water potential.

1. In Solution X, there is no change in mass (

10.0\text{ g} \rightarrow 10.0\text{ g}

). This indicates no net movement of water, meaning the solution is isotonic and has a water potential equal to the potato cells.
2. In Solution Y, the potato gained

1.5\text{ g}

(

10.0\text{ g} \rightarrow 11.5\text{ g}

). Since the mass increased, water must have moved into the potato cells by osmosis. This means Solution Y had a higher water potential than the potato cells.
3. In Solution Z, the potato lost

1.5\text{ g}

(

10.0\text{ g} \rightarrow 8.5\text{ g}

). This means water moved out of the cells, indicating Solution Z had a lower water potential than the potato cells.
4. A lower water potential corresponds to a higher sugar concentration. Since Solution Z has a lower water potential than the potato, it must have a higher sugar concentration than the potato cells. Thus, statement D is incorrect.
5. Osmosis is a passive process; the mass change is not due to active transport. Statement E is incorrect.

Statement B is the only correct conclusion.

Question 9

1 mark

A cell from a marine organism maintains an internal sodium ion (

Na^+

) concentration of

15\text{ mmol dm}^{-3}

, despite living in seawater where the sodium ion concentration is

450\text{ mmol dm}^{-3}

.

Which of the following processes is directly responsible for maintaining this concentration difference?

A.Sodium ions moving out of the cell by diffusion.
B.Sodium ions moving into the cell by active transport.
C.Sodium ions being pumped out of the cell using energy from respiration.
D.Water moving out of the cell by osmosis to balance the sodium concentration.
E.Sodium ions moving into the cell by diffusion until an equilibrium of $232.5\text{ mmol dm}^{-3}$ is reached.

Answer: C

Worked solution

1. The internal concentration of

Na^+

15\text{ mmol dm}^{-3}

, while the external concentration is

450\text{ mmol dm}^{-3}

.
2. Due to the steep concentration gradient (

450 > 15

), sodium ions will naturally tend to diffuse into the cell (passive movement from high to low concentration).
3. To maintain the low internal concentration of

15\text{ mmol dm}^{-3}

, the cell must counteract this inward diffusion by moving sodium ions back out of the cell.
4. Moving sodium ions out of the cell is movement against the concentration gradient (from

15\text{ mmol dm}^{-3}

450\text{ mmol dm}^{-3}

).
5. This process is active transport, which requires energy from respiration (ATP).
6. Option A and B describe the wrong directions for those processes. Option D describes the movement of water, not the maintenance of ion concentrations. Option E describes what would happen if the cell were dead or failed to maintain the gradient, not how the gradient is maintained.

Therefore, the correct answer is C.

Question 10

1 mark

The table below shows some characteristics of three types of movement across cell membranes.

| row | process | direction of net movement | energy required from respiration |
| :--- | :--- | :--- | :--- |
| 1 | diffusion | down a concentration gradient | no |
| 2 | osmosis | from low to high water potential | no |
| 3 | active transport | against a concentration gradient | yes |
| 4 | diffusion | against a concentration gradient | yes |
| 5 | active transport | down a concentration gradient | no |

Which row(s) correctly describe the characteristics of the named process?

A.1 only
B.1 and 3 only
C.2 and 3 only
D.3 and 5 only
E.1, 2, and 3

Answer: B

Worked solution

We evaluate each row based on the biological definitions of transport processes:

- Row 1: Correct. Diffusion is the passive (no energy) movement of particles down a concentration gradient (from high to low).
- Row 2: Incorrect. Osmosis is the movement of water from a region of higher water potential to a region of lower water potential.
- Row 3: Correct. Active transport moves substances against a concentration gradient (from low to high) and requires energy (ATP) from respiration.
- Row 4: Incorrect. Moving against a gradient using energy describes active transport, not diffusion.
- Row 5: Incorrect. Active transport requires energy and moves substances against, not down, a gradient.

Since only rows 1 and 3 are correct, the answer is B.

Question 11

1 mark

A population of 2000 cells in a tissue culture is studied. It is found that 200 cells are in mitosis, and 800 cells are in the

S

phase of the cell cycle. All other cells are in either the

G1

G2

phase. The total duration of one full cell cycle is 20 hours.

Consider the following statements:
1. The

S

phase of the cell cycle for these cells lasts 8 hours.
2. The combined duration of the

G1

and

G2

phases is 10 hours.
3. A cell in the

G2

phase contains twice as many chromosomes as a cell in the

G1

phase.

Which of the statements is/are correct?

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

Answer: D

Worked solution

To evaluate the statements, we calculate the time spent in each phase based on the proportion of cells observed.

Statement 1: The proportion of cells in the

S

phase is

\frac{800}{2000} = 0.4

(or

40\%

). The duration of the

S

phase is

0.4 \times 20\text{ hours} = 8\text{ hours}

. Statement 1 is correct.

Statement 2: First, find the time spent in mitosis. The proportion of cells in mitosis is

\frac{200}{2000} = 0.1

. The duration of mitosis is

0.1 \times 20\text{ hours} = 2\text{ hours}

. The total cell cycle is the sum of interphase (

G1 + S + G2

) and mitosis (

M

). Therefore,

G1 + S + G2 + M = 20\text{ hours}

. We know

S = 8\text{ hours}

and

M = 2\text{ hours}

, so

G1 + G2 = 20 - 8 - 2 = 10\text{ hours}

. Statement 2 is correct.

Statement 3: During the

S

phase of interphase, DNA replication occurs. This doubles the amount of DNA (mass), but the number of chromosomes (counted by centromeres) remains the same (

2n

) until the chromatids separate during the later stages of mitosis. Thus, a cell in

G2

has the same number of chromosomes as a cell in

G1

, even though it has double the DNA mass. Statement 3 is incorrect.

Since statements 1 and 2 are correct, the answer is D.

Question 12

1 mark

In a certain species of insect, sex is determined by the

XO

system. Females are

XX

(

2n = 12

) and males are

XO

(

2n = 11

).

A male insect cell undergoes mitosis to produce two daughter cells. During this specific division, a nondisjunction event occurs where the sister chromatids of the

X

chromosome fail to separate and both move to the same pole. All other chromosomes separate and migrate normally to opposite poles.

Which of the following correctly describes the chromosome count and sex chromosome composition of the two resulting daughter cells?

A.Cell 1: 11 ( $X$ ); Cell 2: 11 ( $X$ )
B.Cell 1: 12 ( $XX$ ); Cell 2: 10 ( $O$ )
C.Cell 1: 12 ( $X$ ); Cell 2: 10 ( $X$ )
D.Cell 1: 13 ( $XX$ ); Cell 2: 9 ( $O$ )
E.Cell 1: 11 ( $XX$ ); Cell 2: 11 ( $O$ )

Answer: B

Worked solution

1. Determine the starting state: A male cell has

2n = 11

chromosomes. This consists of 10 autosomes (5 pairs) and 1

X

chromosome (the

O

indicates the absence of a second sex chromosome).

2. Analyze DNA replication (

S

phase): Before mitosis, every chromosome replicates. The 10 autosomes become 10 pairs of sister chromatids, and the 1

X

chromosome becomes 1 pair of sister chromatids (two identical

X

strands).

3. Analyze Mitosis with nondisjunction: Usually, one chromatid from every pair goes to each pole, resulting in two cells with 11 chromosomes (

10 \text{ autosomes} + 1 \, X

).

4. Calculate the effect of

X

nondisjunction:
- For the autosomes: 10 chromatids move to Pole 1 and 10 move to Pole 2.
- For the

X

chromosome: Both sister chromatids move to Pole 1, and zero move to Pole 2.
- Cell 1 (Pole 1):

10 \text{ autosomes} + 2 \, X \text{ chromosomes} = 12

chromosomes total (Composition:

XX

).
- Cell 2 (Pole 2):

10 \text{ autosomes} + 0 \, X \text{ chromosomes} = 10

chromosomes total (Composition:

O

).

Therefore, the daughter cells have 12 and 10 chromosomes respectively, with

XX

and

O

compositions.

Question 13

1 mark

In a particular species of beetle, the diploid number of chromosomes is

2n = 20

. A single diploid cell in this beetle undergoes the complete process of meiosis to produce gametes.

Which of the following identifies the number of daughter cells produced and the number of chromosomes in each daughter cell?

A.Daughter cells: $2$ ; chromosomes per cell: $20$
B.Daughter cells: $4$ ; chromosomes per cell: $10$
C.Daughter cells: $4$ ; chromosomes per cell: $20$
D.Daughter cells: $2$ ; chromosomes per cell: $10$
E.Daughter cells: $8$ ; chromosomes per cell: $10$

Answer: B

Worked solution

According to the specification for meiosis (B3.2.a), meiosis involves two cell divisions starting from a single diploid cell. This results in the production of four daughter cells. Each of these daughter cells is haploid, meaning they contain a single copy of each chromosome, which is half the diploid number (

n

). Given the diploid number

2n = 20

, the haploid number is

n = 20 / 2 = 10

. Therefore, there are

4

daughter cells, each with

10

chromosomes.

Question 14

1 mark

The meiotic cell cycle consists of interphase followed by meiosis. Which of the following statements correctly describes the events of interphase that occur before the first division of meiosis?

A.The cell grows in size and the DNA is replicated.
B.The cell undergoes two successive divisions without DNA replication.
C.The DNA content is halved to prepare for the production of haploid cells.
D.Chromosomes are distributed into four daughter cells.
E.Homologous chromosomes pair up and then immediately separate.

Answer: A

Worked solution

The specification (B3.2.a) defines the meiotic cell cycle as including interphase and meiosis. Interphase is the phase where the cell prepares for division; it specifically involves cell growth and DNA replication so that there is enough genetic material to be distributed. Options B, D, and E describe events that occur during the meiotic divisions themselves, not during interphase. Option C is incorrect because DNA content increases during interphase due to replication.

Question 15

1 mark

Human somatic cells are diploid, containing

46

chromosomes. Which of the following is a correct description of the role of meiosis and fertilisation in the human life cycle?

A.Meiosis produces four genetically identical cells to ensure trait stability.
B.Fertilisation involves two diploid cells fusing to form a tetraploid zygote with $92$ chromosomes.
C.Meiosis produces haploid gametes with $23$ chromosomes so that fertilisation results in a diploid zygote with $46$ chromosomes.
D.Meiosis produces two haploid gametes that each contain $46$ chromosomes.
E.Fertilisation is the process that reduces the chromosome number to ensure the offspring is haploid.

Answer: C

Worked solution

Meiosis produces haploid gametes, which in humans contain

23

chromosomes (half of the diploid number of

46

). This reduction is essential because, during fertilisation, two gametes (sperm and egg) fuse. Since

23 + 23 = 46

, this restores the diploid number in the resulting zygote (B3.2.b). Option A is incorrect because meiosis produces genetically different cells. Option B and D are numerically incorrect. Option E describes the role of meiosis, not fertilisation.

Question 16

1 mark

An organism reproduces asexually through binary fission. Which of the following statements about its offspring is/are correct?

1. In the absence of mutation, the offspring are genetically identical to the parent.
2. The offspring are produced via the fusion of two haploid gametes.
3. The offspring will always have the same phenotype as the parent, regardless of environmental conditions.

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

Answer: A

Worked solution

Statement 1 is correct: Asexual reproduction involves one parent and produces offspring that are clones, meaning they are genetically identical to the parent unless a mutation occurs. Statement 2 is incorrect: The fusion of two haploid gametes is a characteristic of sexual reproduction; asexual reproduction typically involves processes like mitosis or binary fission without gamete fusion. Statement 3 is incorrect: Although offspring are genetically identical, phenotype is determined by the interaction between the genotype and the environment (

Phenotype = Genotype + Environment

). Therefore, different environmental conditions can lead to phenotypic variation between the parent and its clones.

Question 17

1 mark

A student is comparing the mechanisms of inheritance in sexual and asexual reproduction. Which of the following statements is/are correct?

1. In sexual reproduction, offspring inherit

100\%

of their nuclear DNA from a single parent.
2. Asexual reproduction results in offspring with exactly the same combination of alleles as the parent, excluding mutations.
3. Genetic variation observed in the offspring of sexual reproduction is solely the result of new mutations.

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

Answer: B

Worked solution

Statement 1 is incorrect: In sexual reproduction, offspring typically inherit

50\%

of their nuclear DNA from each of the two parents. Statement 2 is correct: Asexual reproduction produces clones that are genetically identical to the parent, meaning they possess the same combination of alleles. Statement 3 is incorrect: While mutations do provide a source of variation, sexual reproduction introduces significant genetic variation through meiosis (independent assortment and crossing over) and the random fusion of gametes during fertilisation.

Question 18

1 mark

A population of

100

protozoa reproduces asexually, with each individual dividing into two exactly once every

4

hours. Simultaneously, a population of

100

insects reproduces sexually. In the insect population, each pair produces

4

offspring every

4

hours, after which the parents die. Assume an equal sex ratio in every insect generation.

Which of the following statements is/are correct?

1. At

t = 8\,\text{hours}

, the protozoa population is

400

.
2. At

t = 8\,\text{hours}

, the insect population is

800

.
3. Sexual reproduction in the insect population generates more genetic variation than the asexual reproduction in the protozoa population.

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

Answer: D

Worked solution

Statement 1 is correct: The protozoa double every

4

hours. At

t = 0

N = 100

. At

t = 4\,\text{hours}

N = 100 \times 2 = 200

. At

t = 8\,\text{hours}

N = 200 \times 2 = 400

.

Statement 2 is incorrect: For the insects,

100

individuals form

50

pairs. At

t = 4\,\text{hours}

50\,\text{pairs} \times 4 = 200

offspring (the parents die). These

200

offspring form

100

pairs. At

t = 8\,\text{hours}

100\,\text{pairs} \times 4 = 400

offspring. The insect population is

400

, not

800

.

Statement 3 is correct: Sexual reproduction involves two parents and the reshuffling of alleles through meiosis and fertilisation, which leads to increased variation compared to asexual reproduction where offspring are clones of the parent.

Question 19

1 mark

Which of the following statements concerning human chromosomes is/are correct for a healthy individual?

1. A skin cell contains

44

autosomes.
2. A sperm cell contains

22

autosomes.
3. A mature red blood cell contains

22

pairs of autosomes.

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

Answer: C

Worked solution

Statement 1 is correct: A healthy human somatic cell (like a skin cell) contains

46

chromosomes in total. This consists of

22

pairs of autosomes (

44

in total) and

1

pair of sex chromosomes (

XX

XY

).

Statement 2 is correct: Gametes (like sperm cells) are haploid and contain half the number of chromosomes of a somatic cell (

23

in total). This consists of

22

autosomes and

1

sex chromosome (

X

Y

).

Statement 3 is incorrect: Mature human red blood cells do not have a nucleus and therefore contain no chromosomes, autosomes or otherwise.

Since statements 1 and 2 are correct, the answer is C.

Question 20

1 mark

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

1. Most phenotypic characteristics are the result of the interaction of multiple genes.
2. Characteristics determined by a single gene typically show continuous variation across a population.
3. Human height is an example of a characteristic typically controlled by multiple genes.

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

Answer: D

Worked solution

Let's evaluate each statement based on the principles of monohybrid and polygenic inheritance.

Statement 1 is correct. According to specification detail B4.3.d, most phenotypes are the result of multiple genes (polygenic inheritance) and only some result from single gene inheritance.

Statement 2 is incorrect. Phenotypes resulting from single-gene inheritance typically show discrete (discontinuous) variation, where individuals fall into distinct categories (e.g., blood type or the presence/absence of a condition). Continuous variation, where a characteristic shows a wide range of values (like a bell curve), is typically the result of multiple genes interacting with each other and the environment.

Statement 3 is correct. Height is a classic example of a polygenic characteristic, as it is determined by the combined effect of many different genes and is further influenced by environmental factors such as nutrition.

Since statements 1 and 3 are correct, the correct option is D.

Question 21

1 mark

In a particular species of plant, the allele for red flowers (

R

) is dominant over the allele for white flowers (

r

). A researcher performs a cross between a heterozygous red-flowered plant and a white-flowered plant.

If

400

offspring are produced from this cross, what is the expected number of plants with white flowers?

A.0
B.100
C.200
D.300
E.400

Answer: C

Worked solution

Step 1: Identify the genotypes of the parents. The red-flowered plant is heterozygous, so its genotype is

Rr

. The white-flowered plant expresses the recessive phenotype, so its genotype must be homozygous recessive,

rr

.

Step 2: Perform the monohybrid cross (

Rr \times rr

). The possible gametes from the heterozygous parent are

R

and

r

. The only possible gamete from the white parent is

r

.

Step 3: Determine the offspring genotypes using a Punnett square:
-

R \times r \rightarrow Rr

(red flowers)
-

R \times r \rightarrow Rr

(red flowers)
-

r \times r \rightarrow rr

(white flowers)
-

r \times r \rightarrow rr

(white flowers)

Step 4: Calculate the probability. The ratio of genotypes is

1 Rr : 1 rr

. Therefore,

50\%

of the offspring are expected to have white flowers (

rr

).

Step 5: Apply the probability to the total number of offspring.

0.50 \times 400 = 200

.

The final answer is C.

Question 22

1 mark

A population of

200

plants is studied for a single gene with two alleles,

B

and

b

. The distribution of genotypes in the population is as follows:
-

30\%

are homozygous dominant (

BB

)
-

50\%

are heterozygous (

Bb

)
-

20\%

are homozygous recessive (

bb

)

What is the total number of recessive alleles (

b

) present in this population of

200

plants?

A.40
B.100
C.140
D.180
E.200

Answer: D

Worked solution

Step 1: Calculate the number of individuals for each genotype.
- Total population =

200

plants.
-

BB

plants:

0.30 \times 200 = 60

plants.
-

Bb

plants:

0.50 \times 200 = 100

plants.
-

bb

plants:

0.20 \times 200 = 40

plants.

Step 2: Calculate the number of recessive alleles (

b

) contributed by each genotype. Each plant has two alleles for the gene.
-

BB

plants:

60 \times 0 = 0

recessive alleles.
-

Bb

plants:

100 \times 1 = 100

recessive alleles.
-

bb

plants:

40 \times 2 = 80

recessive alleles.

Step 3: Sum the recessive alleles.
Total

b

alleles =

0 + 100 + 80 = 180

.

The final answer is D.

Question 23

1 mark

A human sperm cell is compared to a human liver cell from the same healthy individual. Which of the following statements is/are correct?

1 The sperm cell contains

23

pairs of chromosomes.
2 The liver cell contains the full genome of the individual.
3 The sperm cell and the liver cell contain the same mass of DNA.

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

Answer: B

Worked solution

We evaluate each statement regarding the comparison between a gamete (sperm) and a somatic cell (liver):

1. **The sperm cell contains

23

pairs of chromosomes.** Sperm cells are haploid gametes produced by meiosis. They contain one set of

23

chromosomes, not

23

pairs (which would be

46

chromosomes). Statement 1 is incorrect.

2. **The liver cell contains the full genome of the individual.** Liver cells are diploid somatic cells. They contain a complete set of the individual's genetic material (the genome) organized into

46

chromosomes in the nucleus. Statement 2 is correct.

3. **The sperm cell and the liver cell contain the same mass of DNA.** Because the liver cell is diploid (

2n

) and the sperm cell is haploid (

n

), the liver cell contains approximately double the mass of nuclear DNA compared to the sperm cell. Statement 3 is incorrect.

Only statement 2 is correct, so the answer is B.

Question 24

1 mark

A functional protein consists of a single polypeptide chain of

240

amino acids. Which of the following statements is/are correct?

1. The coding region of the gene for this protein contains at least

720

nucleotide bases.
2. The specific three-dimensional shape of this protein is determined by the sequence of its amino acids.
3. If the

100

th amino acid is changed from leucine to valine, the three-dimensional shape of the protein will definitely be destroyed.

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

Answer: C

Worked solution

Statement 1 is correct. Each amino acid is coded for by a triplet of

3

bases. For a polypeptide of

240

amino acids, the gene must contain

240 \times 3 = 720

bases. Additionally, genes include a stop codon (another

3

bases), so the coding region contains

723

bases, which is 'at least

720

'.

Statement 2 is correct. This is a fundamental principle of protein synthesis (specification point 5.3c): the sequence of amino acids (primary structure) determines how the chain folds into its functional 3D shape.

Statement 3 is incorrect. While changing an amino acid *can* alter the 3D shape and function (e.g., sickle cell anemia), it does not 'definitely' destroy the protein. If the change occurs in a less critical part of the protein or involves amino acids with similar chemical properties (like leucine and valine), the shape may remain largely functional.

Question 25

1 mark

A template strand of DNA has the nucleotide sequence shown below:

3' \text{- TAC CCG TTT GGC -} 5'

Which of the following is correct?

A.The mRNA sequence produced from this template is $3' \text{- AUG GGC AAA CCG -} 5'$ .
B.The sequence of the coding (non-template) DNA strand is $5' \text{- ATG GGC AAA CCG -} 3'$ .
C.There are a total of $12$ codons in the mRNA produced from this sequence.
D.A substitution mutation in the first base of the second triplet is less likely to change the amino acid than a substitution in the third base of that triplet.
E.This sequence of DNA bases contains the code for $12$ different amino acids.

Answer: B

Worked solution

A is incorrect: While the base pairing is correct, the mRNA is synthesized in the

5'

3'

direction antiparallel to the template. The correct mRNA sequence is

5' \text{- AUG GGC AAA CCG -} 3'

.

B is correct: The coding (non-template) strand is complementary to the template strand and has the same polarity and sequence as the mRNA (substituting T for U). Complementary to

3' \text{- TAC CCG TTT GGC -} 5'

5' \text{- ATG GGC AAA CCG -} 3'

.

C is incorrect: The mRNA consists of

4

triplets (codons), not

12

12

is the number of individual bases.

D is incorrect: Due to the 'wobble' effect or redundancy of the genetic code, the third base of a triplet is more likely to result in a silent mutation (no change in amino acid) than the first or second base. Therefore, a first-base mutation is *more* likely to change the amino acid.

E is incorrect: The sequence contains

12

bases, which form

4

triplets, coding for

4

amino acids.

Question 26

1 mark

A scientist is studying the effects of three different mutations in a gene that codes for a digestive enzyme in a population of organisms. The mutations are described below:

1. A single base substitution in the DNA sequence that results in the same amino acid being incorporated into the protein.
2. A single base substitution that occurs in a non-coding region (intron) of the gene.
3. A single base insertion at the very beginning of the coding sequence of the gene.

Which of the following statements is/are correct?

1. Mutation 1 is considered a mutation because it changes the sequence of nucleotides in the DNA.
2. Mutations 1 and 2 are more likely to have no effect on the phenotype than Mutation 3.
3. Mutation 3 is an example of a mutation that is likely to determine the phenotype of the organism.

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

Worked solution

Statement 1 is correct. By definition, a gene mutation is a change in the sequence of nucleotides in the DNA. Even if the genetic code's degeneracy means the amino acid sequence remains the same (a silent mutation), the DNA sequence itself has been altered.

Statement 2 is correct. Mutations 1 and 2 occur in locations or ways that typically do not alter the final protein's structure or function (silent mutations and non-coding region mutations). Mutation 3 is a frameshift mutation at the start of the gene, which will change almost every amino acid in the protein, likely resulting in a non-functional enzyme. Thus, 1 and 2 are much more likely to have no effect on the phenotype than 3.

Statement 3 is correct. The ESAT specification states that while most mutations have no effect, others can determine the phenotype. A major structural change, such as a frameshift at the start of a coding sequence, usually results in a complete loss of function for that protein, which directly determines the resulting phenotype (e.g., the inability to digest a certain nutrient).

Question 27

1 mark

The following DNA sequence represents a segment of the coding strand of a gene:

\text{5'-GTC GCT AAA TAG-3'}

A mutation occurs where the cytosine (

C

\text{GUC}

| Valine |
|

\text{GCU}

| Alanine |
|

\text{GUA}

| Valine |
|

\text{AAA}

| Lysine |
|

\text{AAU}

| Asparagine |
|

\text{UAG}

| STOP |
|

\text{UAA}

| STOP |

Which of the following statements is/are correct?

1. The deletion of the 5th nucleotide changes the sequence of nucleotides in the DNA.
2. A substitution of the 12th nucleotide (guanine,

G

) for an adenine (

A

) would be expected to have no effect on the phenotype.
3. The deletion mutation results in a stop codon being reached earlier in the sequence than in the original gene.

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

Answer: C

Worked solution

Statement 1 is correct. Any deletion, insertion, or substitution in the DNA sequence constitutes a change in the sequence of nucleotides.

Statement 2 is correct. The 12th nucleotide is the

G

in the sequence

\text{TAG}

. If

G

is substituted for

A

, the sequence becomes

\text{TAA}

. Since this is the coding strand, the mRNA codons will be

\text{UAG}

(original) and

\text{UAA}

(mutated). Both are STOP codons. Because the termination of the protein remains at the same location, there is no change to the amino acid sequence, and thus no effect on the phenotype.

Statement 3 is incorrect. Let's analyze the frameshift from the deletion at the 5th position:
Original codons:

\text{GTC}

(1),

\text{GCT}

(2),

\text{AAA}

(3),

\text{TAG}

(4 - STOP).
Mutated sequence (delete 5th char 'C'):

\text{GTC}

(1),

\text{GTA}

(2),

\text{AAT}

(3),

\text{AG...}

(4).
From the table, the new codons are Valine (1), Valine (2), and Asparagine (3). The original STOP codon (

\text{TAG}

) at the 4th position has been destroyed. Therefore, the mutation does not result in a stop codon being reached earlier; rather, the original stop is lost and the protein will continue until a new stop codon is encountered in the shifted frame.

Only statements 1 and 2 are correct.