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Want to see how you went in the 2025 Biology HSC exam? Read on for the 2025 Biology HSC exam answers!
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The Matrix Biology team is thrilled to publish the 2025 HSC Biology Exam Solutions. These are the answers for the 2025 HSC Biology exam, which you can view here once NESA publishes.
Keep in mind that these answers were not written under exam conditions and may be longer than required.
See a full list of the latest HSC Biology Exam Solutions here.
| Question | Answer | Solution |
| 1 | B | Genetically identical to parent amoeba. Amoeba (eukaryote) divides via binary fission using mitosis (nuclear division, then cytokinesis) resulting in identical daughter cells. |
| 2 | D | Electromagnetic. UV light is an electromagnetic wave, this would be a “physical” mutagen. Biological refers to pathogens (virus, bacteria), chemical refers to molecules that interact with DNA molecules (eg. tobacco smoke). |
| 3 | A | Phagocytes engulf pathogens, Lymphocytes (includes T cells & B cells) produce antibodies (it is the plasma B cells specifically). |
| 4 | B | Genetic drift. This refers to random events influencing survival in a population. Natural selection refers to survival due to adaptive traits. |
| 5 | B | High population density and rarely dying from the disease will increase transmission of disease (eg. COVID). When diseases have a high mortality rate, it does not transmit rapidly as symptoms are obvious and thus less transmission will occur (eg. Ebola). |
| 6 | D | Acquired passive. Acquired means receiving immunity rather than developing it yourself (natural), the word artificial could have been used as well. Injection of antibodies is passive immunity (the antibodies will work to flag pathogens), while injection of antigens (eg. in a vaccine) would be active immunity as the body has to develop its own antibodies. |
| 7 | C | Endotherm with constant body temperatures despite a fluctuating air temperature due to metabolic warm-bloodedness. |
| 8 | D | Co-dominance refers to two phenotypes being visible, with no traditional dominant/recessive pattern. |
| 9 | A | Dialysis was made to replace the kidney function of removing toxic nitrogenous wastes (urea) from the blood using passive diffusion between blood and dialysis fluid. Glucose is not normally removed because the body does not usually control glucose with the kidney. |
| 10 | C | Mortality rates for measles were, on average, declining since 1950. After the 1975 vaccine, the number drops to near zero. The decline precedes the vaccine. |
| 11 | C | High vaccination rates protect the % of people who are not vaccinated (eg. children, immunocompromised). This is also known as herd immunity. |
| 12 | D | A female with a chromosomal mutation, specifically trisomy 21 (3 copies of chromosome 21). Female is indicated by 2 X chromosomes. |
| 13 | A | Increases prevalance. When a treatment is developed, this will prolong survival rate, resulting in more people having the disease in the population. Prevalence means, how common a disease is in the population. Incidence means, new cases diagnosed in a period of time (which would be unchanged). |
| 14 | A | Antibodies have a binding site that perfectly matches antigens found on the pathogen. A is the only antibody with a matching grabbing-shape to an antigen seen on the pathogen. |
| 15 | C | Sounds are picked up by the microphone, converted into electrical signals, which is sent TO the implant found in the coclea, the implant sends a signal to the cochlea electrodes, which then stimulates the auditory nerve (as it is found connected to the organ of corti in the cochlea). |
| 16 | A | The offspring are clones of each other. This diagram shows the offspring embryo of a male and female sheep being split into parts (much like identical siblings) and implanted into different surrogates. This is called ’embryo splitting’. |
| 17 | C | The diagram is depicting meiosis. 4 individual chromosomes are replicated into replicated chromosomes (made up of 2 chromatids attached at a centromere), homologous chromosomes are seperated in two rounds of cell division, resulting in a gamete with 2 individual chromosomes. |
| 18 | B | All female offspring will have the bar-eye dominant mutation as they inherit their X from their fathers (which have bar-eyes). Males only inherit the Y chromosome from dad so they will not have the trait. Males will inherit the normal copy of the gene from their mom. |
| 19 | C | 58% of 120 million base pairs is 69.6 million base pairs of adenine=thymine (totalling 139.2 million nucleotides). The question is asking for the number of thymine NUCLEOTIDES. So the answer is 69.6 million thymine nucleotides, (and there will also be 69.9 million adenines). |
| 20 | D | Individual B affected with this cancer has regulating proteins that switch on the oncogene (cancer-causing gene) related to this cancer. We cannot state that these proteins are the direct cause of this cancer based on the information provided. There is likely some people who have the regulating proteins who do NOT have cancer, but are at risk of it depending on other risk factors or other mutations. |
Example:
– Skin: has many layers of waterproof cells that shed off along with skin-surface pathogens as the skin grows. Pathogens cannot penetrate the skin without an open wound.
– Stomach acid: made of HCl, this acid destroys many pathogens that are accidentally consumed from food and water, preventing infection.
– Mucus lining: moist tissue contains mucus which acts to trap pathogens.
Example:
– Yeast (unicellular eukaryotes) reproduce asexually via budding, where daughter cells grow off parent cells until they bud off and live as independent organisms. Offspring are identical to parent yeast cells.
– Mushrooms can reproduce sexually by producing haploid spores that germinate into mycelium, which can conjugate with other haploid mycelium to produce a new diploid fruiting body.
Example:
– Viruses invade respiratory tract cells by inserting their genetic material (DNA or RNA). The inserted genetic material hijacks host cell machinery to produce new viruses, which are expelled when the infected host coughs or sneezes, infecting new individuals.
– Some bacteria have sticky fimbriae on their surface so they can adhere to the urinary tract in urinary tract infections. This allows them to reproduce without being expelled.
Compare (similarities and differences):
– Similarities: artificial insemination and artificial pollination are methods used to control breeding or crosses between individuals in selective breeding for desirable traits.
– Differences:
– Artificial pollination is used in plant agriculture; it involves manually transferring pollen from the male anther of a plant to the female stigma, leading to fertilisation of ovules in the ovary.
– Artificial insemination is used in animal agriculture; it involves manually inserting semen (and thus haploid sperm cells) into the female reproductive tract.
Mechanism A (in response to an increase in body temperature): sweating, vasodilation, increasing exposed surface area.
Mechanism B (in response to a decrease in body temperature): shivering, vasoconstriction, huddling.
Example:
– Shivering maintains homeostasis as it involves muscle contractions, which require more fuel to be burned in cellular respiration to make ATP. A by-product of this mechanism is the release of metabolic heat.
– Vasoconstriction decreases the diameter of blood vessels; this reduces the amount of heat and blood flowing to the extremities (hands, feet), which could otherwise be lost to the environment.
Evaluate: make a judgement.
– The Cancer Council’s suggestion to use sun protection at UV levels of 3 or higher is better advice than the information provided by the sunscreen product (to use between 10 a.m. and 4 p.m.).
– This is apparent when analysing the UV level data, which shows UV levels above 3 from 8 a.m. to 7 p.m. This time range far exceeds the product’s suggested period. Perhaps on a winter day the sunscreen advice is adequate, but it is not applicable year-round.
– It is important to wear adequate sun protection during high UV levels as it protects the skin from exposure to mutagenic UV light, a risk factor for developing skin cancer.
Visual disorder: can be myopia (nearsightedness) or hyperopia (farsightedness).
Example (myopia):
– Myopia is a disorder of the eye where the focal length of images is too short, with images focusing in front of the retina due to excessive converging power of the eye.
– Concave lenses are used to correct myopia as they diverge light before it reaches the eye, which contains the cornea and lens that converge light.
– The result is that the image, which previously focused in front of the retina, now focuses on the retina to produce a clear image.
– LASIK for myopia involves reshaping the cornea to be flatter, reducing the converging power of the cornea so light can focus on the retina.
– Both technologies fix the short focal length but through different strategies.
– Group A contains animals that use internal fertilisation, whereas Group B contains animals that use external fertilisation as reproductive strategies.
– Monotremes, snakes, and birds (Group A) use internal fertilisation as it provides a moist environment for gametes to meet without drying out in the terrestrial environment these animals live in.
– As the reproductive tract is limited in size, fewer eggs are produced, and the mothers are more involved in protecting and rearing offspring.
– In contrast, crabs, sea urchins, and squids use external fertilisation as these are aquatic animals; gametes meet in fertilisation outside of the body.
– The moist external environment is vast, requiring large numbers of eggs to maximise chances of fertilisation.
– Other points for internal: offspring require energy investment from the mother; sexual selection for a suitable mate.
– Other points for external: timed release of gametes; eggs may be eaten by predators.
– Alpha-gal (antigen) is presented by a macrophage to X: a naïve helper T cell. Helper T cells coordinate an immune response by activating other lymphocytes.
– X presents the antigen to Y: a naïve B cell. Helper T cells find a naïve B cell that recognises the alpha-gal antigen perfectly (clonal selection).
– Y differentiates into memory B cells and Z: plasma B cells. Memory B cells recognise the same antigen in future exposures to initiate a secondary immune response.
– Z produces antibodies that flag alpha-gal antigens for destruction by macrophages. Plasma B cells mass-produce antibodies with binding sites that perfectly match the antigen.
– The tick bite initiates the primary immune response; from the initial exposure, it takes around two weeks for plasma B cells to begin producing antibodies.
– When meat containing alpha-gal is eaten, it triggers the secondary immune response, as there are still circulating antibodies from the primary response that can bind to the alpha-gal antigen.
– Antibody production in the secondary response is faster and in greater quantity than in the primary response, resulting in higher levels of circulating antibodies.
– Memory B and T cells are produced after a primary immune response to recall antigens that the body has previously encountered.
– Memory B cells differentiate into antibody-producing plasma cells, and memory T cells differentiate into cytotoxic T cells that kill infected cells.
– Memory cells produce long-term immunological memory; with more exposures to a given antigen, the greater and more permanent the immune response, as evidenced by remaining antibody concentrations.
– An infectious disease is a disease that can be transmitted from infected individuals to others via some form of transmission.
– The Varroa mite is a macroparasite that lives on European honey bees, often resulting in death. They can easily reproduce and infest whole colonies.
– Prevention is more effective than treatment as it is impossible to reverse the consequences of infection.
Examples:
– Pesticides specific to Varroa mites can be applied to deliveries when receiving agricultural imports. This prevents pests from infecting native honey bees.
– Proper sanitation from exporting and importing companies, such as cleaning shipping containers and materials that touch imports (e.g. gloves), helps prevent contamination.
– Regular monitoring of imported bee and agricultural products to check for mite infection. Infected products should be destroyed (incinerated) before they spread pathogens.
– First, the SERPINE gene in humans must be removed using restriction enzymes.
– Then, many copies of the gene are produced using either recombinant DNA techniques with E. coli or polymerase chain reaction.
– These amplified genes are then injected into the nuclei of mosquito embryos, where they integrate into nuclear DNA via enzymes.
– Adult mosquitoes will produce the PAI-1 protein, blocking invasion by Plasmodium parasites.
Evaluate: make a judgement using every example; discuss whether genetic technologies are beneficial to the world. What are the societal, cultural, and economic impacts of genetic technologies? Does the good outweigh the bad?
Examples:
– DNA amplification such as PCR allows us to make many copies of genetic material so it can be manipulated in other technologies.
– DNA sequencing allows for disease diagnosis and understanding human evolution, but may lead to genetic discrimination if information is not kept private.
– DNA profiling allows for paternity testing, forensic work, and unique identification of individuals from DNA samples.
– Gene therapy enables treatment of genetic diseases by inserting healthy copies of genes to replace defective ones.
– CRISPR-Cas9 allows for DNA editing, but requires more study due to off-target effects. Its use can be controversial, for example, designing babies through IVF.
– Pharming uses transgenic bacteria to produce human proteins such as insulin to treat diabetes.
– Transgenic crops increase agricultural yield, helping food supply for a growing population, but create risks like monocultures vulnerable to disease.
– The pedigree shows an autosomal recessive pattern of inheritance, meaning affected individuals need two copies of the disease allele.
– There is an unaffected couple with affected children; this pattern is typical of recessive traits as both parents are carriers.
– There is an affected couple with all affected children; this is also consistent with recessive traits.
– It is important to justify that it is not X-linked recessive, e.g. equal numbers of males and females are affected and male carriers are seen.
– The DNA template strand must be converted into the mRNA sequence: CAG UAU GUC GAC.
– This mRNA strand translates into the amino acid chain: glutamine – tyrosine – valine – aspartic acid.
– Compared to the mutated amino acid sequence, valine has been replaced by isoleucine.
– This type of mutation is a missense mutation, as the DNA mutation affected one codon and led to coding for a different amino acid.
To justify the features of your epidemiological design, you need to design a study that collects all of the information provided in the graph:
– Collect data over 60 years, noting that the trends fluctuate in risk even 40 years after exposure.
– Collect data from children and adults.
– Collect medical information yearly to track disease diagnosis rates.
– Collect data from populations in regions A, B, and C simultaneously.
To ensure reliability:
– Collect data from as large a sample size as possible.
– Ensure diagnosis by qualified doctors.
– Include diverse participants (males and females of all age groups).
– Data from regions A and C are essential; without them, region B could not be identified as the at-risk group. Regions A and C act as the control groups within the same population.
– Cell S is a germline cell, meaning it is a gamete precursor that undergoes meiosis. Meiosis of one diploid parent cell results in four genetically unique haploid daughter cells due to two rounds of division and crossing over of homologous chromosomes in prophase I.
– Cell R is a somatic cell, meaning it replicates through mitosis. Mitosis of one diploid parent cell results in two genetically identical diploid daughter cells. Mitosis occurs for growth and repair.
– Individual 1 is the mother of Individual 2. The gamete produced by Individual 1’s germline cell is a haploid egg cell that combines with a haploid sperm cell to produce the zygote, Individual 2.
– Mutation A occurs in the germline cells of Individual 1; this means it affects only the gamete-producing cells in the ovary. Cell U (somatic in Individual 1) is unaffected by either mutation.
– Mutation A, assuming it is on one chromosome, can be passed down to cells V and W in Individual 2 if inherited via the egg cell that formed Individual 2.
– Cell X in Individual 2 is a gamete; it has a 50% chance of containing Mutation A, as gametes contain a random half of parental chromosomes.
– Mutation B affects only cell W and no others, as it is a somatic mutation found in only half of the somatic cells of Individual 2.
– Allele frequency is calculated as (total number of copies of a chosen allele) / (total number of gene copies in the population). The denominator can also be calculated as population × 2.
– Smaller populations show larger fluctuations in allele frequencies because sample size is smaller. Certain alleles may disappear or dominate as the population is less stable.
– Gene flow is the migration of new individuals into a population; newcomers introduce more gene copies and may carry new or uncommon alleles.
– For a population with 20 individuals, gene flow greatly impacts the gene pool composition. New individuals likely carry alleles not already present. The graph shows two alleles disappearing after many generations.
– For a population with 2000 individuals, gene flow has a smaller impact because large populations already carry greater allele diversity. Migration may slightly shift allele proportions but rarely introduces new alleles if they are already present.
Written by Matrix Science Team
The Matrix Science Team are teachers and tutors with a passion for Science and a dedication to seeing Matrix Students achieving their academic goals.
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