1: A function of a gene is to

A. Have a unique sequence of DNA nucleotides.

B. Code for a transfer RNA molecule.
C. Code for the production of a functional protein made of nucleotides.
D. Have a unique amino acid sequence.

2: Which one of the following statements is consistent with the information provided?

A. The-two unique polypeptides in type I collagen – alpha – 1 and alpha – 2 – possess different
quaternary structures.
B. Type I collagen does not have a quaternary structure.
C. Type I collagen has a tertiary structure determined by the quaternary structures of the alpha
1 and alpha 2 polypeptides.
D. The tertiary structures of the alpha 1 and alpha 2 polypeptides determine the quaternary
structure of type 1 collagen.
3: A bacterial chromosome is cut using to different restriction enzymes, A and B. Each of these
restriction enzymes recognise and binds to a unique sequence of bases in DNA called a ‘recognition
site’.

The recognition site for A occurs at three locations on the bacterial chromosomes. The recognition
site for B occurs at two locations. These recognition sites do not overlap.

How many DNA fragments are produced by cutting the bacterial chromosome with A and B.

A. 3
B. 4
C. 5
D. 6

Refer to Source 2 when answering question 4.

4: Which one of the following statements is consistent with the information provided?

A. Antibody 3 has a three-dimensional shape that is not complementary to the SARS-CoV-2

antigen.
B. Antibody 1 and antibody 2 have the same shape as the SARS-CoV-2 antigen.
C. Antibody 2 has the same three-dimensional shape as antibody 3.
D. Antibody 1 has a three-dimensional shape that is complementary to antibody 2.

5: Which one of the following statements is not correct?

A. Ribosomal RNA synthesis occurs in the nucleolus.

B. The nucleolus is located in the nucleus.
C. The production of ribosomal proteins occurs in the nucleolus.
D. The nucleolus lacks a membrane.

Refer to Source 2 when answering question 7.

7: Which one of the four arrangements of chromosomes in source 2 would not occur during or at the
end of the division of cell A? (Ignore the effects of crossing over).

A. J
B. K
C. L
D. M

Refer to Source 3 when answering question 8.

8: When a person experiences a significant injury such as a deep cut, their body responds in several
in several ways. For example, pain receptors send nerve messages to the brain, and hormones such
as endorphins are released to help ease the pain.

A. Endorphins are faster acting.

B. The effect of endorphins lasts longer.
C. Endorphins have a less widespread action.
D. The endorphin pathway is more direct.
10: Nicotinic acetylcholine receptors (nACHRs) on neurons in the spinal cord are involved in pain
regulation in several different animals. When the neurotransmitter acetylcholine (Ach) binds to
nACHRs, it reduces the level of pain.

A compound called Rg1A, extracted from the highly toxic venom of a sea snail (Conus regius), can
also bind to these receptors and it has the same effect as ACH.

Based on this information, it can be concluded that

A. Rg1A binds to nAChRs and inhibits the response normally caused by ACh.
B. Enzymes that break down Ach ill also break down Rg1A.
C. Rg1A acts on the central nervous system and could potentially be used as a drug for pain
relief.
D. A person with low level of Ach would not experience the pain-relief benefits of Rg1A.

Questions 11 to 15

11: The process that involves the rapid development of two or more new species from a common
ancestor is called.

A. Convergent evaluation
B. Allopatric speciation
C. Interbreeding
D. Adaptive radiation

12: Temporal isolation, which maintains the separation of similar species, is an example of

A. A pre-zygotic mechanism
B. Hybrid inviability.
C. Gamete incompatibility
D. Behavioral differences

13: Genetic drift can result in the loss of alleles from the gene pool of a population.

Which one of the following processes could result in the reappearance of a lost allele in the gene
pool?

A. Natural selection
B. Mutation
C. Fertilisation
D. Crossing over
15: The ranges of results for the measurements taken are shown by a symbol on the graph, as
indicated in the key.

Which one of the following statements is consistent with the information provided?

A. The measurements at 30 minutes or likely to be affected by a systematic error.

B. The measurements at 6 minutes are the least precise.
C. The measurements at 90 minutes or the most accurate.
D. The measurements at 150 minutes or likely to be affected by random error.
16 (a): State the name of the process that occurs in the nucleus of melanocytes and leads to the
production of tyrosinase from the TYR gene.

The name of the process that occurs in the nucleus of melanocytes and leads to the production of
the tyrosinase from the TYR gene is called transcription.

16 (b): By referring to the information in the source, explain how a mutation in the TYR gene can
result in a melanin-deficiency disorder.

A mutation in the TYR gene could alter the sequence of amino acids in tyrosinase, preventing it from
functioning properly. Tyrosinase is essential for the production of melanin. If the enzyme is not
functional, melanin synthesis will be reduced or absent, leading to a melanin-deficiency disorder.
16 (c): Compare the potential consequences of a mutation in the TYR gene in a melanocyte with the
potential consequences of a mutation in the same gene in a gamete.

A mutation in the TYR gene in a melanocyte will affect only that particular cell and its descendants,
leading to localized effects such as melanin deficiency in specific areas. In contrast, a mutation in a
gamete can be passed on to offspring and affect the entire organism, potentially leading to a
hereditary melanin-deficiency disorder.

UV radiation activates tyrosinase, and this leads to a change in melanin production.

16 (d): State the effect of decreased UV radiation exposure on melanin production in an individual.

Decreased UV radiation exposure would lead to reduced activation of tyrosinase, resulting in lower
melanin production.

(e) (i): Hyperpigmentation disorders result from the accumulation of excess melanin in the skin.
Tropolone, an inhibitor of tyrosinase, is a medication that is used in the treatment of
hyperpigmentation disorders.

Explain one way in which tropolone might inhibit tyrosinase.

Tropolone could bind to the active site of tyrosinase, preventing the enzyme from interacting with its
substrates, thereby inhibiting its activity.

(ii) Explain how the inhibition of tyrosinase would be effective in the treatment of
hyperpigmentation disorders.

Inhibiting tyrosinase reduces the production of melanin, which would prevent the accumulation of
excess melanin in the skin and help alleviate hyperpigmentation.
17: The SARI gene encodes the tumour suppressor protein, SARI. Decreased expression of SARI
caused by high methylation levels of the SARI gene has been implicated in a range of cancers.

(a): Explain why increased methylation of the SARI leads to reduced expression of SARI.

Increased methylation of the SARI gene likely occurs in its promoter region, which prevents the
binding of transcription factors necessary for the initiation of transcription, thereby reducing gene
expression.

Researchers have recently investigated the use of a modified CRISPR system, called ‘CRISPR- dCas9’,
to introduce epigenetic modification for the treatment of cancer. An inactivated mutant form of
‘Casp9’, called ‘dCas9’ is created, and this is unable to cut DNA. The dCas9 can be loaded with guide
RNA and will still be able to bind to a DNA sequence, such as part of the SARI gene.

(b): Explain why dCas9 is still able to bind to a specific DNA sequence, despite being inactivated.

dCas9 retains the ability to bind to specific DNA sequences because the guide RNA directs it to a
complementary sequence on the DNA. Although it cannot cut the DNA, it can still locate and bind to
the sequence based on the RNA-DNA base pairing.

An ‘epi-effector’ is an enzyme that can make epigenetic modifications.

Researchers attached an epi-effector called TET1 to the CRISPR-dCas9 complex. TET1 removes methyl
groups. Researchers used this modified CRISPR system to successfully inhibit tumour growth in mice.

(c) (i) State the effect of this CRISPR-dCas9 system to the expression of the SARI gene.

The CRISPR-dCas9 system, when combined with the epi-effector TET1, increases the expression of
the SARI gene by removing methyl groups from the SARI gene promoter. This demethylation allows
for the binding of transcription factors, leading to increased transcription and expression of the SARI
gene.

(ii) Explain how this CRISPR-dCas9 system is able to inhibit tumour growth in mice?

The CRISPR-dCas9 system, with TET1 attached, demethylates the promoter region of the SARI gene,
resulting in increased expression of the SARI tumour suppressor protein. The elevated levels of SARI
inhibit tumour cell proliferation and promote tumour suppression mechanisms, leading to the
inhibition of tumour growth in mice. By restoring the function of SARI, the system reactivates its role
in preventing uncontrolled cell division, thereby reducing tumour progression.

Refer to the source when answering part (d).

(d) Discuss how the information in the source illustrate the interaction between science and society.
Questions 18 (a) to (e) (iii)

18: Refer to source 1 when answering parts (a) to (d).

(a) Describe the different between the cells of the haploid male honeybees and the cells of the
diploid female honeybees.

Male honeybees are haploid, meaning their cells have one set of chromosomes because they
develop from unfertilized eggs. Female honeybees are diploid, with two sets of chromosomes, as
they develop from fertilized eggs.

(b) State the name of the type of cell division represented in the diagram by X.

The cell division at X is meiosis, which produces haploid egg cells in females, necessary for sexual
reproduction.
 (c) By referring to Y and Z in the diagram, explain why the sperm cells produced by a honeybee
are genetically identical to the egg cell that produced the honeybee.

The sperm cells in male honeybees are genetically identical to the egg cell that produced the
male because they develop from it through mitosis, without fertilization or genetic
recombination.

(d) State the role of fertilisation, and its importance in honeybees.

Fertilisation combines haploid sperm and egg to create diploid females, adding genetic diversity to
the colony, which helps improve resilience to environmental changes and diseases.

Refer to source 2 when answering part (e).

(e) (i) State the dependent variable in this investigation.

The dependent variable in this investigation is the percentage mortality (deaths) of the honeybees
after 5 days.

(ii) Based on the data in the graph, write a conclusion about the impact of temperature on the effect
of these insecticides on honeybees.

The data suggests that higher temperatures (35°C) increase the mortality rate of honeybees
exposed to insecticides compared to lower temperatures (23°C), indicating that temperature
intensifies the toxic effects of these insecticides.
 (iii) Explain how the researchers could have reduced the effect of random error on these
data.

Researchers could have reduced random error by increasing the sample size (using more honeybees)
and repeating the experiment multiple times to get more consistent results.

Question 19 (a) to (d) (ii)

The cell cycle is regulated by internal and external factors.

(a) Describe the role of the checkpoint in G1 of the cell cycle.

The G1 checkpoint, also known as the restriction point, ensures that the cell is ready for DNA
replication in the S phase. It checks for sufficient cell size, adequate energy reserves, and the absence
of DNA damage. If any issues are detected, the cell cycle is halted, allowing the cell time to repair the
damage, grow, or undergo apoptosis if the damage is irreparable.

An ‘immortalised cell line’ is a population of cells that, due to mutation, can continue undergoing
division indefinitely.

(a) Explain how a mutation can led to uncontrolled cell division.

A mutation in genes that regulate the cell cycle, such as proto-oncogenes or tumor suppressor genes,
can result in uncontrolled cell division. For example, a mutation in a proto-oncogene can turn it into
an oncogene, leading to the overproduction of proteins that promote cell division. Alternatively,
mutations in tumor suppressor genes like p53 can disable the mechanisms that halt the cell cycle or
initiate apoptosis in damaged cells, allowing cells to divide uncontrollably.

HeLa cells are produced by immortalised cell line derived from human cervical cancer cells in 1951.
They were the first human cells to be successfully grown in culture and have been used for a variety
of purposes.

(b) State two requirements of culturing cells, such as HeLa cells.

(i) Requirement 1

A sterile environment to prevent contamination from bacteria, fungi, or other microorganisms that
could interfere with the growth and health of the cultured cells.

(ii) Requirement 2

A nutrient-rich culture medium, containing essential amino acids, vitamins, glucose, and growth
factors to support cell metabolism, growth, and division.

(c) Discuss one application and one limitation of using cells, such as HeLa cells, in scientific
research.
(i) Application
 HeLa cells have been widely used in cancer research, vaccine development (such as the polio
vaccine), and studying the effects of toxins, drugs, and radiation on human cells. Their ability to
divide indefinitely makes them a valuable tool for long-term studies in various biological and
medical fields.

(ii) Limitation

A limitation of using HeLa cells is that they are derived from cancerous cells, which may not behave
like normal, healthy cells. This can limit their applicability to studies that aim to understand normal
cellular processes, as their abnormal division and mutation rates may not reflect typical human cell
behavior.

Question 20 (a) to (f) (ii)

Refer to Source 1 when answering questions 20.

(a) State the function of the ribosome in bacterial cells.

It has been hypothesised that the first cells that formed more than 3 billion years ago contained RNA,
but not DNA.

(b) State two probable functions of RNA in the first cells.

(i) Function 1

(iii) Function 2
One method of identifying bacterial species involves sequencing the gene that codes for the 16S
rRNA molecule.

(c) (i) State why the gene for the 16S rRNA molecule is an appropriate target for DNA
sequencing.

(ii) Explain how the results of rRNA gene sequencing can be used to identify a new species.

(iii) Explain why scientists may need to consider other target genes, as well as the 16S rRNA
gene, when identifying bacterial species.

(iv) Describe another method, other than gene sequencing, that could be used to determine
how closely two bacterial species are related.

It is often difficult to extract enough material to perform rRNA gene sequencing, and therefore the
target gene requires amplification before it can be sequenced.

(d) Explain why heating and cooling cycles are required for the amplification of target gene.

Antibiotics are chemicals that kills bacteria or stop them from multiplying. One problem with the use
of antibiotics for treating patients with bacterial diseases is that this may result in a population of
bacteria that is more resistant to the antibiotics.

(e) Explain how an antibiotic could act as a selection pressure, resulting in a population of
bacteria that is more resistant to the antibiotic than the original population.

Refer to source 2 when answering part (f).

 (f) (i) Explain how M. cookie and M. abscesses can be different species, even though they both
have 95.7% similarity to the new strain of Mycobacterium.

(iii) Scientists used the data in the table to determine that the new strain of Mycobacterium
was a new species.

State how the data support this idea.

Question 21 (a) to (c)

Refer to the source when answering questions 21.

(a) Explain how low genetic diversity in the Kangaroo Island koala population could affect the
survival of the population in the future.

By 2019, the estimated size of the koala population on Kangaroo Island was 50000. In January 2020,
fires devasted approximately 40% of Kangaroo Island and reduced the Koala population by an
estimated 85%.

(b) Explain how genetic drift, caused by the fires, could further endanger the Kangaroo Island
Koala population.

Despite the devastation caused by the fires, the Koala population is expected to recover as the
ecosystem recovers.

(c) Name and describe the process following environmental changes, such as that caused by the
Kangaroo Island fires, which leads over time to changes in the mix of species.

Question 22 (a) to (b) (ii)

Metformin is a medication that is often prescribed for the treatment of type 2 diabetes mellitus. It
enhances the effect of insulin and

Blocks the action of glucagon in the liver.

(a) Insulin and glucagon regulate the concentration of a substance in the blood.
(i) State the name of the substance in the blood that is regulated by insulin and glucagon.
(ii) By referring to the roles of insulin and glucagon, explain the effect of metformin on the
blood concentration of this substance.

A rare form of diabetes insipidus, which can result from a lack of antidiuretic hormone (ADH). A
common symptom of the disease is a change in the amount of urine produced.
 (b) (i) State and explain the change in urine production in a patient who has diabetes insipidus
as a result of a lack of ADH.

(iii) State the effect of diabetes insipidus on blood volume.

Question 23 (a) and (b)

Narcolepsy is a medical condition in which patients experience overwhelming drowsiness, or even an

uncontrolled urge to sleep.

Methylphenidate is a medication that improves alertness and general performance. It is used to treat
narcolepsy by reducing the ability of nerve cells to absorb dopamine that they have secreted.
Dopamine is a neurotransmitter that increases alertness.

(a) Describe the role of neurotransmitters.

Neurotransmitters are chemical messengers that transmit signals between nerve cells (neurons) or
from neurons to muscles. When an electrical signal (action potential) reaches the end of a neuron,
neurotransmitters are released from synaptic vesicles into the synapse (the gap between neurons).
These chemicals then bind to receptors on the receiving neuron, triggering an electrical response,
continuing the transmission of the signal. Neurotransmitters play essential roles in regulating a wide
range of physiological processes, such as mood, memory, and muscle movement.

(b) Explain the effect that methylphenidate will have on nerve function and how this may be
used to treat narcolepsy.

Methylphenidate inhibits the reabsorption (reuptake) of dopamine by nerve cells, which increases
the amount of dopamine available in the synaptic cleft. This enhanced dopamine availability leads to
increased stimulation of the postsynaptic neurons. Since dopamine is associated with increased
alertness and wakefulness, the action of methylphenidate helps maintain higher dopamine levels,
improving alertness and performance. By reducing drowsiness and fatigue, this medication helps
manage narcolepsy by promoting wakefulness in individuals affected by the condition.

Question 24 (a) to (c)

After a major ecological disturbance, such as a flood, the area affected often experience significant
loss of biodiversity and severe ecosystem damage.

(a) (i) State the name of the process that results in an area affected by a flood having a different
mix of species after ecosystem recovers.

The process is called ecological succession.

 (ii) Explain how the mix of species present after the ecosystem recovers from a flood may change
over time.

After a flood, the ecosystem undergoes succession, where early colonizing species (pioneer species)
are typically fast-growing, hardy plants and organisms that can quickly establish in the disturbed
environment. Over time, these pioneer species alter the environment, such as by enriching the soil
with nutrients, making it more suitable for slower growing, more complex species. As the ecosystem
matures, more diverse species, such as trees, shrubs, and a variety of animal species, gradually
replace the pioneer species, leading to increased biodiversity and a more stable community.

(iv) State the likely effect on the gene pool of a population that is affected by a major
ecological disturbance, such as a flood.

A major ecological disturbance, like a flood, can significantly reduce population sizes, leading to
genetic drift. This random loss of individuals may result in a smaller gene pool with reduced
genetic diversity, which could make the population more vulnerable to diseases and
environmental changes, affecting long-term survival.

Human activities can also affect the biodiversity of an ecosystem.

(b) Describe two human activities that could lead to a reduction in the biodiversity of an
ecosystem.
(i) Activity 1

Deforestation – The clearing of forests for agriculture, urban development, or logging destroys
natural habitats, leading to a decline in species that rely on those ecosystems for survival, thus
reducing biodiversity.

(ii) Activity 2

Pollution – The release of harmful substances into the environment, such as industrial waste,
pesticides, or plastics, can degrade habitats and cause harm or death to species. This results in a
decline in biodiversity as fewer species can survive in polluted environments.

(c) Explain why humans have an obligation to prevent the extinction of species.

Humans have a moral and ethical responsibility to protect biodiversity because each species plays a
crucial role in maintaining the balance and functioning of ecosystems. The loss of species can lead to
ecosystem collapse, affecting resources that humans rely on, such as food, clean air, and water.
Additionally, preventing extinction helps preserve natural heritage, maintains ecological integrity, and
supports future scientific research, medical discoveries, and cultural significance. Protecting species
ensures the sustainability of ecosystems for future generations.