2023 HSC Biology Solutions

Section I

For each multiple choice question, the correct answer is given along with an explanation of why this is the correct answer.

1. Answer: D

Explanation: Cochlear implants stimulate the auditory nerve.

2. Answer: A
   Explanation: Internal fertilisation is often employed by terrestrial animals whereas external fertilisation by aquatic animals. If terrestrial animals’ egg and sperm fuse external to the animals’ body, then it could become dehydrated.
3. Answer: C
   Explanation: BB and bb are both homozygous; only Bb is heterozygous.
4. Answer: D
   Explanation: Both the male and female part of the flower has been cut which means no self-pollination will occur.
5. Answer: B
   Explanation: Plotting the data on the table on a graph makes it clear that the correct curve is that shown in B.
6. Answer: A
   Explanation: A liver fluke must develop in a particular type of small freshwater snail.
7. Answer: D
   Explanation: tRNA has anticodon which is complementary to mRNA’s codon. tRNA carries as amino acid with which is used to form a peptide chain.
8. Answer: C
   Explanation: Innate immune system responds quickly and non-specifically to pathogens.
9. Answer: D
   Explanation: The hybrid offspring is going to have (54+60)/2=57 chromosomes as mammals are haploid. So, n=57 and 2n=114.
10. Answer: B
    Explanation: A gene is a sequence of DNA that encodes a protein.
11. Answer: A
    Explanation: Primary structure of a protein is polypeptide chain which is made up of a sequence of amino acids.
12. Answer: B
    Explanation: Decrease in serum calcium will trigger the release of PTH which will stimulate osteoclasts to degrade bone to release calcium into the blood.
13. Answer: B
    Explanation: As an example, Oidium eucalypti (fungal) → causes powdery mildew disease in Eucalyptus → plant identified infected cells and induces cell death.
14. Answer: D
    Explanation: Environmental: caused by pathogen, nutritional: caused by lack of excess of nutrition, genetic: born with the disease
15. Answer: B
    Explanation: Using a process of elimination to find the most correct answer —
    A is incorrect as we cannot determine whether the drug has antiviral properties solely from the graph,
    C is incorrect as the graph always trends downwards in the drug arm, so the drug did not increase symptoms.
    B and D are similar, but D suggests that ALL pharmaceuticals do not reduce symptoms which cannot be concluded since only one pharmaceutical was tested.
    So, B is the most correct answer.
16. Answer: C
    Explanation: Incidence = new cases/population = 246/26×10⁶ = 0.0025%
17. Answer: C

Explanation: The possibilities are as follows:

All type A

Half type A, half type O

Half type A, half type B

18. Answer: D

Explanation: Using a process of elimination to find the most correct answer —
A & B are incorrect as embryo transfer was not available in the past.
C is incorrect as recombinant DNA technologies is not yet used in wheat.
So, D is the only plausible answer.

19. Answer: D
    Explanation: First step is to always prepare the source DNA.
20. Answer: C
    Explanation: Using a process of elimination to find the most correct answer —
    A is incorrect as they do not show trisomy
    B is incorrect as you cannot tell if there is inversion on this karyotype
    D is incorrect since both karyotypes contain 14 chromosomes.
    So, C is the only plausible answer.

Section II

For each short-answer question, a sample answer is given. Where the question requires more than a simple identification, an indication is also given of how each available mark is earned by a part of the sample solution.

21. 1. Pentose sugar, phosphate group, nitrogenous base
    2. G, U, C, A (up to down)
22. 1. Ingest the pathogen hence isolating it from other cells, release of cytotoxic substances inside the phagocyte will eliminate the pathogen. [1 mark] Phagocytes can display the antigens of the engulfed pathogens on its MHCII complex assisting the adaptive immune response [1 mark]
    2. CD4 T cells recognise the antigens presented by phagocytes and gets activated. [1 mark]
       B cells encounter the pathogenic antigens in primary lymphoid organs either on their own or recognising those presented on helper T cells. [1 mark]
       Activated CD4 produce cytokines to activate B cells and B cells undergo clonal selection and differentiate into plasma cells [1 mark]
       Plasma cells produce antibodies. [1 mark]
23. 1. hCG — Promotes implantation, promotes progesterone secretion by the mother’s corpus luteum [1 mark] — first trimester [1 mark]
    2. oestrogen — Maintains uterine lining, promotes uterine hypertrophy, promotes expansion in total blood volume by mediating vasodilation, activates and regulate the production of other hormones [1 mark] — third trimester [1 mark]
24. 1. The lens is a transparent, bi-convex protein disc situated behind the pupil, responsible for refracting light towards the retina [1 mark]
       Cataract is caused as a result of ageing, excessive UV exposure, high alcohol intake, salt, and steroids etc whereby light is prevented from striking the retina. [1 mark]
       When the cells of the lens die, the protein of the cell will accumulate in the lens capsule which result in the lens being opaque rather than transparent. These proteins absorb the incoming light radiation and prevent light from passing through and striking the photoreceptor cells on the retina. [1 mark]
       [Other possible disorders could include hyperopia/myopia or glaucoma]
    2. Lens replacement: [1 mark] obliterate the old lens using ultrasound vibration [1 mark] and put in a new artificial lens [1 mark]
       [Other possible technologies could include glasses or implantable drainage device for glaucoma.]
25. 1. Both A and B are affected, but their child F is not affected. [1 mark]
       This means that A and B are heterozygous, because that is the only possible genotype combination where they can produce an offspring that is unaffected [1 mark]
       If the diseased allele is denoted by H and wildtype gene is denoted by h, the genotype of individual H can be HH or Hh [1 mark]
    2. Glutamine
    3. Inverse relationship [1 mark]  — the higher the number of repeats the younger the age of onset. [1 mark] 
    4. Question not available

26. 

1. Dependent variable: number of mosquitos that land on clothing. [1 mark]
   Controlled variable: number of mosquitos inside the container, number & types (e.g., material, shape, function) of clothing pieces in inside the container, size of the container. [1 mark]
2. First need to calculate the average [1 mark]
   Container A (infected, dirty) 16.6
   Container B (uninfected, dirty) 5.6
   Container C (infected, clean) 11.6
   Container D (uninfected, clean) 4.2
   
   Infected mosquitos are more likely to land on clothing, especially dirty clothing [1 mark]
   Wearing clean clothes will reduce the risk of malaria transmission [1 mark]
   
   27.
   For this question, you should address the following points: Choice of study design [1 mark], host environment and agent factors [1 mark], measurement of outcome [1 mark], threats to validity – random & systematic errors & confounding factors [3 marks], conclusion [1 mark]
   The following is a sample answer:
   This is an analytic cohort study investigating the question “how is the disease caused or transmitted and why?” It is used to test the hypothesis formulated in descriptive epidemiology, with the hypothesis being “air pollution is linked to organic brain disorders”. [1 mark] Analytic epidemiological studies examine the host, environment and agent (e.g. pathogen, vectors, chemicals, etc) as potential factors that may be responsible for causing the disease. [1 mark] In this study, the host factors being studied is age and gender, the environmental factor is different city of residence, and the agent factor is the air pollutant. [1 mark] In this study, the sample size is n=500 in each city, which is a good sample size, but it did not specify the number of times data has been collected, or how it is collected. This means the random error could be large if the data has not been averaged. [1 mark]  In terms of systematic errors, it is unknown whether the sample of 500 subjects from each city is representative of the entire population of the city, therefore selection bias could be likely. The level of information bias, which is caused by errors in measurement and recording, is also unknown. [1 mark] Confounding factors such as as background medical conditions – especially neurological and respiratory conditions, recent acute illness, and location of living within the city – e.g., next to industrial facilities or not, have not been considered. [1 mark] Furthermore, simply assessing the % of sample with symptoms is not enough, the time period for which they had the symptoms, the severity of symptoms, which symptoms do the subjects have, etc, should also be assessed. It is also unknown whether the scientists who performed the study has any conflict of interest. Overall, there is very limited information provided to accurately evaluate this study. [1 mark]
   

28. 1. Bacterial pathogens are prokaryotic organisms, it contains circular DNA, ribosomes etc making it a functional cell on its own [1 mark], whereas virus only has a genome that could be DNA or RNA and some proteins [1 mark].
       OR
       Bacteria can be obligate or facultative parasite [1 mark], whereas virus is an obligate parasite only. [1 mark].

b. Draw blood (or CSF, if the disease is neurological; urine, if the disease causes urinary symptoms) the from patients who are currently affected by the disease, and culture the blood in a dish [1 mark], if there are growth of organisms then it is bacterial, otherwise it is viral because virus cannot be cultured on a dish. [1 mark]

29.

1. Fairy Penguin are able to thermoregulate their core body temperature as their muscle glands are activated [1 mark], resulting in involuntary shivering to produce heat energy. [1 mark]

• Thick, waxy cuticle [1 mark]: Eucalyptus and Banksia plants have thick cuticle that insulates water from excessive sunlight as it reduces the internal temperature. By doing so, the thick cuticle reduces the rate of evaporation [1 mark]
• Shiny Leaves [1 mark]: Eucalyptus plants have shiny leaves that help reflect sunlight and therefore help reduce the spike in internal temperature due to heat energy from sunlight. Again, this minimises the rate of transpiration and therefore serves to help minimise dehydration [1 mark]
  

30. Vaccination is used to prevent disease caused by pathogens, as it induces antibody production in the body before the infection. It is a form of acquired immunity [1 mark]. However, the antibody level needs to be above a certain threshold (in the case of tetanus – 0.01IU/mL) in order for it to be sufficient to prevent disease [1 mark].  In this graph, a 5-dose tetanus schedule is illustrated, where the vaccine is given at 2, 6, 18 months, 4 years, and 13 years of age [1 mark]. This schedule is used so that the antibody level does not fall below 0.01IU/mL between each dose, and the level after the 5^th dose is sufficiently high that it theoretically would not fall below 0.01IU/mL during the person’s lifetime. The higher the initial level of antibody post vaccination, the slower the level falls [1 mark]. A booster shot should also be recommended for people aged 65 and over; because eventually the antibody level could fall below 0.01 IU/mL and therefore the majority of recorded cases occurred in this age group [1 mark].
 

31. For this question, you should address the following points: Technology name [1 mark], how it works [1 mark], how it is used in medical application [1 mark]  and what benefit this technology brings [1 mark]
    The following is a sample answer:

• Recombinant DNA technology used in gene splicing to produce drugs in biotechnology [1 mark]
• Gene splicing is a technique used in recombinant DNA technology that involves using same restriction enzyme to cut a desired gene and a plasmid. The gene is then inserted into an open (cut) plasmid and strengthened using ligase enzyme. [1 mark]
• Gene splicing therefore is a technique that set up the bacteria so that it contains the desired gene which is replicated as the bacteria undergo binary fission. [1 mark]
• Thus, through gene splicing technique, recombinant DNA technology is able to produce large quantities of genes specifying for substances such as antibiotics, insulin and many other drugs and hormones. This effectively increases the availability and lowers the cost of drugs for patients globally. [1 mark]
  
  

32. For this question, you should address the following points: Describe trend of graph [3 marks], discuss the risks of small gene pool [2 marks] and discuss the benefit of introduction of possums from another region [2 marks]

The following is a sample answer:
Since 1996, the population of possum has been declining, and started declining at a faster rate after the 1998 bushfire. It recovered very slightly from around n=35 to n=7 between in the year 1999 but the 2000 bushfire caused a decline again. It started recovering in 2001 but another bushfire in 2002 made it decline again. Since then, the populations show a small increase in number in one year, but the next year it will decline again; the number of possums that has died is more than the small increase in number the previous year. This leads to the pattern where the population size of possum in Mt Buller has been declining overall since 1996 (n=90) until the introduction of males from Mt Bogong in 2012 (n=40), since which it raised to n=160 in 2016. This is because, the gradual contraction of possum population has caused a contraction in the gene pool, and the breeding of these genetically similar possums in Mt Buller regions produce offspring that are susceptible to the same environmental insults e.g., diseases, changes in climate conditions etc. A gene pool that is too small will also cause genetic diseases, as it causes more recessive disease alleles to become homozygous. 6 males from Mt Bogong region gave the Mt Buller possums genetic diversity such that they are now more resilient to environmental insults and has less genetic diseases.

33. 

Similarities 

• Both can reproduce sexually. [1 mark]
• Zygotes are both 2n. [1 mark]

Differences

• Fungi can reproduce asexually by spores whereas humans cannot produce asexually. [1 mark]
• The human zygote undergoes mitosis to form a foetus, whereas fungi zygote undergoes meiosis to form a spore which germinates to form a mycelium. [1 mark]

34.

Selective breeding: decrease biodiversity because only cows that have high milk production are allowed to breed. [1 mark]

Artificial insemination: decrease biodiversity because one bull can have many offspring, whereas other bulls which could have produced offspring are stripped of the opportunity to breed. [1 mark]

Whole organism cloning: Decrease biodiversity because a clone is genetically identical to its parent. [1 mark]

Hybridisation: Increase biodiversity because two species of cows which may not normally breed with one another are given the opportunity to do so. [1 mark]

Transgenic organism: Increase biodiversity because a new gene is introduced. But if selectively bred later it could cause decrease in biodiversity. [1 mark]

35.

1. Substitution 
2. Can cause silent, missense, or nonsense mutation. [1 mark]
   – A silent mutation is when a single base pair gets swapped out on the DNA, but the mutated RNA sequence produces the same amino acid. Codons are set up so that there are many ways to produce the same amino acid. If one nucleotide is changed, it will usually still produce the same amino acid. [1 marks]
   – A missense mutation is when a nucleotide gets changed, resulting in a different amino acid in the protein. [1 mark]
   – A nonsense mutation occurs when a base change causes an early stop codon. This causes the protein to be too short and almost always results in a non-functioning protein. [1 mark]