2023 HSC Biology Exam Solutions

The Matrix Biology team is thrilled to publish the 2023 HSC Biology Exam Solutions. These are the responses for the 2023 HSC Biology exam which can be viewed here.

2023 HSC Biology Exam Solutions

Keep in mind that these answers were not written under exam conditions and may be longer than required.

Section I: Multiple Choice

Do you want the confidence to respond like this under pressure?

Section II: Extended Response

Question 21 (a)

Sugar, phosphate and base pair (nitrogen containing base)

Question 21 (b)

Question 22 (a)

Phagocytes engulf bacteria, foreign particles and dying cells to protect the body from infection. They bind to pathogens using protein markers and engulf them, initiating a digestive response by acidification in the lysosomes which destroy the contents of the particle or cell

Question 22 (b)

When a pathogen enters the body such as bacteria, antigens will stick to the host cell surface. B cells detect and identify antigens and activate memory B cells and plasma cells to produce antibodies. Antibodies are Y shaped proteins which are produced and can bind to a particular antigen. When the correct antibody is found, the correct B-cell and antibody will bind to the antigen and clone itself for identification by the cytotoxic T-cells (or cytokines) which activate cell death and apoptosis.

Question 23

Question 24 (a)

The front of the eye is made up of the transparent cornea, pupil and the lens which is located in the aqueous humor. As a light ray comes in, the light will hit the cornea and the lens which bends the light towards the retina which is at the back of the eye. The ciliary body and suspension ligaments change the shape of the lens to allow focus of close objects (shorten) and far away objects (elongated). If someone has myopia, myopia means that the ligaments are unable to bend the lens to see far sighted objects, so they are unable to be focused clearly on the retina and the image received by the optic nerve will be unclear. 

Question 24 (b)

A technology which can aid in myopia is using glasses with a concave lens. This diverges the light rays so that they focus further back, hence allowing the light to focus on the retina instead of in front. This allows someone with myopia to see clearly.

Question 25 (a)

Huntington’s Disease is autosomal dominant trait (A) and individual “H” has the genotype Aa heterozygous dominant for the trait. This is because the parents of individual H (A and B) are Aa and Aa heterozygous dominant for the trait. These individuals are heterozygous because some of the offspring (D and F) do not have the condition (aa). Parents therefore will produce 50% heterozygous Aa, 25% AA and 25% aa.

Individual H is not homozygous dominant because the offspring J and L do not express the disease. This means individual H must be Aa and individual G is aa.

Question 25 (b)

Glutamine

Question 25 (c)

The graph shows that the more CAG repeats corresponds with a lower age of onset for Huntington’s disease. For example, someone with 40 CAG repeats has the age of onset at 60 years old, whereas someone with 120 CAG repeats will have the age of onset at 0 years old.

Question 25 (d)

Individual “S” will not have the disease as this individual has a low number of CAG repeats (around 15) and the same genotype repeats as “P” who does not have the disease. Individual “U” has the same number of genotype repeats as “Q”, which is still a low number of CAG repeats (around 38) and is therefore likely to experience the same age of onset as 45 years of age as Q.

Question 26 (a)

Dependent Variable: Transmission of malaria – number of times mosquitoes landed on clothing.  Controlled Variable: Number of mosquitoes in each experiment

Question 26 (b)

Wearing clean clothing does reduce the number of times mosquitoes land on the clothing by a small amount. Whether mosquitoes are infected or non-infected does not have any correlation to the number of times they will land on the clothing. Therefore, if mosquitoes land on the clean clothing less, we can assume that wearing clean clothes will slightly decrease the transmission of malaria.

Question 27

This study was not effective in determining the link between air pollution in different cities and the symptoms experienced by individuals as there are problems with the study in reliability, accuracy, and validity. 

In terms of reliability, the study does have a large sample size and measuring three different cities is a positive and there are controlled variables such as the study period of 12 months. However, it is not specified how many individuals were measured in each city and how many males and females were in the total population for each city. This would make it difficult to understand the frequency of the disease in the general population when comparing the three cities, hence making the study unreliable as a source of information. 

In terms of accuracy and validity, the study does not indicate what kind of symptoms were experienced by individuals, and that individual symptoms could also be linked with other diseases, this means that the study is not valid in determining the link between air quality and neurological issues. The study does not specify whether the participants have a prior disease or neurological problem. This makes the participants very broad, and the numbers given not an accurate indication of air quality and neurological disorders. 

Other variables that are not controlled include the testing area, it is not specified where the test has occurred (in the workplace, outside, inside). For a fair test, a similar area in each city would need to be chosen with the least number of uncontrolled variables including weather, air conditioning. The study needs to specify where the test is taken place for it to be valid. 

This experiment is not a valid test to determine the link between air pollution and symptoms experienced. Prior understanding of past conditions, accurate area chosen, and more variables controlled would allow for a fairer test.

Question 28 (a)

Bacteria are single celled organisms which can survive in and outside the body and can reproduce on their own, whereas viruses are made of just a protein coat ang genetic material and cause infections by entering and multiplying inside the host.

Question 28 (b)

Test Diahhroea for the presence of pathogens in those infected: 1. Collect and make stool cultures – this will determine if the disease is bacterial because bacterial culture will grow. 2. PCR techniques and antigen testing can also distinguish any DNA that is found and whether it is viral or bacterial in origin. 

Question 29 (a)

A physiological adaptation of endotherms includes altering the metabolic heat production in order to maintain a stable temperature of 37 degrees Celsius. If the body temperature moves below this in mammals, it will cause vasoconstriction and shivering, if the temperature moves above this, it will cause vasodilation and sweating.

Question 29 (b)

Adaptations of plants to maintain water:

1. Leaves are covered by a waxy cuticle (such as in eucalyptus) on the outer surface, which decreases the water loss. In areas where it is hot and there is higher evaporation, leaves will have a thicker waxy cuticle.

2. Stomata are tiny holes in the underside of the leaf which allow gaseous exchange. Stomata will close when the plant is exposed to high temperatures and high evaporation rates (drought conditions) in order to preserve water.

Question 30

Vaccinations are an excellent tool to support the adaptive immune system and induce long term immunity. The vaccine is a killed or weakened form of the diseased organism which is administered most often intravenously. This allows the immune system enough time to respond to the disease without the disease-causing huge consequences to the health of the host. Each time a vaccination is given as per the diagram, there is an increase in antibody levels. This is because the adaptive immune system actives memory B-cells which then activate cytotoxic t-cells which kill the virus causing apoptosis. Between the 1st and 3rd doses the immune system is building up memory t-cells so that by the time the 4th and 5th doses are given, there is a strong antibody response to tetanus and the vaccinations can be spread apart. The advantage of this is that if the host is exposed to the pathogen in the future, the chance of bad infection is very low, as the adaptive immunity has already been built up significantly. This makes vaccines an effective preventative method to stop the spread and severity of tetanus.

Question 31

Genetic Technology: IVF (could also do cloning or PCR) 

In-vitro fertilisation is a series of procedures which can lead to a successful pregnancy with supply of an egg and sperm. During IVF mature eggs are collected and fertilised by sperm. Then a procedure is done to place of the fertilised eggs (embryos) into the uterus where the baby will develop into a foetus. IVF is the most effective treatment for infertility and has a wide range of implications. It also allows for genetic testing to be completed on both parents to ensure the child does not carry any life-threatening diseases. Further, the process of using the embryos allows scientists extra tools to do further research on genetic frequency of diseases and whether disease genes are carried through families.

Question 32

Environmental and genetic factors have a large impact on populations of Pygmy possums. During bushfires, the habitat of the pygmy possum changes dramatically causing food sources to be scarcer due to decreased vegetation and water availability decreases due to evaporation and high temperatures. As a result, we can see a large decrease in the population of pygmy possums in the Mount Buller population after every bushfire, which continues to influence the overall population to a low point of under 10 individuals from 2005 to 2007. 

The population took a slow increase in the absence of fires and with the introduction of 6 males to the population from Mount Bogong in 2007. The 6 males from another isolated population probably increased the genetic diversity as this was also an isolated population during the bushfires, however not so far removed that the Bogong population would not interbreed with the Buller population. In 2012 there was another bushfire, however the population continued to increase because 6 more males were introduced to the Mount Buller population. This increase in genetic diversity allowed the species time to adapt to the changing conditions and drier climate, hence being an effective rehabilitation strategy to increase the population size of the Pygmy possum in isolated populations. 

Question 33

Similarities: 

• Both fungi and human reproduction use two methods of cell reproduction – mitosis and meiosis. 
• Fungi and human reproduction form zygotes from 2 different individuals with 2n chromosomes from 2 different nuclei.

Differences: 

• Fungi reproduce through sexual reproduction and asexual spores, humans reproduce through only sexual reproduction, using mitosis for cell replication within the system only. 
• Fungi produces spores which then germinate to produce mycelium which can be formed asexually or sexually, but humans produce egg and sperm cells which must fuse together to form a zygote.

Question 34

The process of refining and improving biotechnologies has led to many advancements in techniques which can be used concurrently to improve productivity. Overtime, technologies have become more and more specific from selective breeding involving the whole animal selecting cows with the best traits to breed and have more effective offspring, right down to the DNA and genes in transgenic species – which involves altering the genome of the individual by introducing foreign DNA sequences from other species; often transferred using CRISPR technology. These technologies have helped scientists understand the importance of phenotypic traits and genotype and its overall effect on the output of the organism. For example, artificial insemination has proven to be an effective way of using one individual to fertilise many embryos, hence being more cost effective. Hybridisation of Bos taurus and Bos indicus species has given farmers tools to increase production using favourable traits which makes production more profitable, and technologies such as Transgenic species can make production of milk cheaper and more manageable with the introduction of human milk protein, hence decreasing the effect on the environment of over production. 

However, the use of these technologies is not widely used because these technologies are still very new and expensive to undertake, and there are many ethical issues involved. Many people are not comfortable with the use of genetically modified organisms (specifically hybridisation and transgenic species). For example, genetic alterations may have unintended negative consequences on the animal, or may have unintended on human health. The effects impact of transgenic species requires more research in order to change perceptions of the problems it may cause. Many also believe technologies such as cloning have an ethical dilemma because the organism does not live as long and often has more health concerns, and the current success rate of cloning in Australia is low. 

Although all these technologies are useful in helping increasing productivity and scientific understanding, more research and trials are needed for more recent DNA technologies to ensure they are safe and acceptable for long term public use. 

Question 35 (a)

Substitution (Type of point mutation)

Question 35 (b)

If this mutation occurred within coding DNA, there may be a range of consequences. If RNA polymerase copies the new C-G onto messenger RNA, the RNA will transfer G-C instead of A-T to the ribosome. When the corresponding t-RNA strand is recruited, a different amino acid will be brought over and hence attached. This will change the structure of the polypeptide chain which will then change the structure of the protein. This may have no effect but may also end in the protein not forming correctly which disenables it to carry out normal functioning. Alternatively, if the modified U-G strain is copied by the RNA, this may cause the polymerase to interpret this as a stop codon, hence stopping the protein from being produced altogether.