In this post, our Science Team gives you the answer to the 2018 HSC Biology paper.
Now you’ve finished The 2018 HSC Biology exam, you’ll want to see how you did, right? Well, let’s take a look. The Matrix Science Team has been hard at work getting the solutions together for you. While the official exam paper has not yet been released by NESA, here are our draft suggested solutions and some explanations in case you wanted to know ASAP! Read on for the 2018 HSC Biology Exam Paper solutions.
This paper was broken into two sections.
Section 1 is in two parts and had two parts – multiple choice and short answer.
Part A – 20 multiple choice questions worth 20 marks
Part B – 10 short answer questions worth 55 marks
Section 2 is based on option topics and has five questions, one for each option. Students had to choose one question to answer hich was worth 25 marks and had mutliple parts.
We have included the answers to the two most popular option topics:
Please enjoy our solutions from the science team, below.
|1.||B||Ectotherms cannot regulate their body temperature so must bask in the sun to warm up enough to move or even digest food.|
|2.||B||Salts are transported as dissolved ions in the plasma.|
|3.||D||Cells around the pathogen can by killed to form a barrier to stop the pathogen from spreading. In some cases this will form a cyst.|
|4.||B||Mitosis produces two genetically identical cells, while meiosis produces four genetically different cells.|
|5.||A||The rate at which evolution happens is the only difference between the two theories.|
|6.||C||Beadle and Tatum used x-rays to induce mutations in bread mould.|
|7||C||The cortex resides on the outside of the kidney; the medulla is in the middle and the ureter transports the urine to the bladder.|
|8.||A||Bacteria are prokaryotes that have a cell wall, but no membrane bound organelles such as a nucleus.|
|9.||C||Sunken stomata reduce that rate that water is lost from the leaf by creating a humid environment just outside to the stomate.|
|10.||D||Artificial insemination can be used to fertilise multiple females with the sperm of a few males. Cloning produces individuals with identical genotypes.|
|11.||D||No plant with any evidence of disease is likely to be allowed to leave quarantine. Plant Z has individual raised bumps that indicate insect eggs within the leaf or sap-sucking activity.|
|12.||B||The graph for X reflects how endotherms can maintain a constant body temperature except for in extreme conditions of heat or cold.|
|13.||A||The two populations of snakes have experienced different selection pressures and have now diverged. One population has a different average jaw size to the other. Divergent evolution does not necessarily result in a new species.|
|14.||A||The condition is not dominant because there are two unaffected parents with affected children. The condition is not sex-linked recessive as an unaffected father (individual 1) has produced an affected daughter. Therefore, it is an autosomal recessive condition.|
|15.||D||Aldosterone acts on the distal tubule not the collecting duct. Large plasma proteins do not move into the bowman’s capsule.|
|16.||B||Helper T cells never differentiate into another type of cell or produce antibodies. Phagocytes are not part of the specific immune response.|
|17||D||Vaccines are most effective against the parasite when its antigens are accessible, before the parasite enters a cell. Drugs may help once the parasite enters the red blood cells. Spraying swarms and using mosquito nets will only be affective in the stages before the vector injects the parasite into a human.|
|18.||A||Red blood cells have a diameter around 8 µm. The parasite appears to be around one quarter of the diameter of the red blood cell, so around 2 µm. 0.002 mm is equivalent to 2 µm.|
|19.||C||Colour blindness is recessive, thus individual 1 will have the genotype Xa Y. Individual 2 will have inherited one recessive allele from the colour-blind father so will have the genotype XA Xa. When 1 and 2 are crossed (using a punnet square) it produces the genotypes XA XA, XA Y, Xa Xa, and Xa Y. Thus 50% of the male and female offspring will be colourblind.|
|20.||C||Organism X maintains internal salt concentration regardless of the external environment. This is an example of homeostasis. Organism Y does not regulate internal salt concentration and is demonstrating enantiostasis.|
|21 (a)||2||Responses to a decrease in body temperature in endotherms include: vasoconstriction, piloerection, shivering.|
|21 (b)||2||A negative feedback loop is used to maintain body temperature in endotherms. Thermoreceptors in the brain detect changes in body temperature and send the signal via sensory neurons to the central nervous system (interneurons of the brain or spinal cord). The central nervous system then sends a signal to an effector (muscle or gland) via motor neurons in response to the change. E.g. if temperature is too high sweat glands will be directed to produce sweat.|
|22 (a)||2||Pasteur produced two swan-neck flasks half full of broth and boiled them both. He then snapped the neck of one flask. After a few days, the broth in the damaged flask had changed colour and smelled bad while the other flask had not changed colour. This disproved the theory of spontaneous generation and showed that it is microbes in the air (not air itself) that leads to decay|
|22 (b)||3||Koch’s experiments provided evidence for the fact that microscopic pathogens can cause disease. He developed a process which allows us to identify the microorganism which causes a particular disease – this is called Koch’s postulates. Koch’s work with anthrax showed that specific microbes can be linked to specific infectious diseases.|
|23 (a)||3||The dependent variable is the weight of a plant cutting in a cylinder with water. (The whole set up is to be weight before and after exposure to light for a number of hours).|
The control is a plant cutting set up in the cylinder with water but kept in total darkness.
Variables to keep constant include: temperature, humidity, plant species, amount of water provided.
|23 (b)||2||Answers include: Transpiration, cohesion, adhesion, tension or capillary action.|
Cohesion of water molecules to one another is a mechanism for the movement of water through xylem vessels during the process of transpiration. As one water molecule moves up the xylem, cohesion causes the water molecules below it to follow.
|24 (b)||3||In 2014-2015 the flu vaccine only reduced an individual’s chance of getting the flu by 19%, while the other values recorded vary from 41-60%. The influenza vaccine works by exposing the patient’s immune system to antigens from the surface of the virus so that memory cells will be formed that recognise the antigen. However, the influenza virus has a high rate of mutation and it is possible that by the time the vaccine was produced, tested and administered to the population a new strain of flu had emerged with different antigens on its surface and spread throughout the population.|
|25 (a)||1||These three measures are from arterial blood gas analysis.|
|25 (b)||3||The patients oxygen levels are at the upper-end of normal range which indicates that the patient is getting enough oxygen. However, the CO2 levels in the blood are actually lower than normal. This means there is less CO2 to form carbonic acid with water in the body, which may explain the slightly high pH of the blood. The condition of the patient should continue to be monitored using regular arterial blood gas analysis. If the pH of the blood becomes too high the pH in body cells will become high and this will denature enzymes, preventing them from functioning properly and slowing down metabolic processes.|
|26 (a)||2||A polypeptide is a chain of amino acids that is coded for by a single gene. It has not been folded and is thus non-functional. A protein consists of one or more polypeptides that have been folded into a specific three-dimensional shape and can perform a function.|
|26 (b) i||3||A mutation in the AVP gene would result in a change in at least one codon on the mRNA transcript of the gene for ADH. Unless it is a silent mutation, this would in turn result in at least one incorrect amino acid being added by the ribosome to produce the polypeptide chain that will form the protein. If this change results in an amino acid that is chemically very different from the original one, it will result in a change in function for the ADH protein.|
|26 (b) ii||1||ADH controls the reabsorption of water by increasing the permeability of the distal convoluted tubule. If the an AVP mutation results in a dysfunctional protein, then the water will not be reabsorbed by the kidney when it should and the kidney will produce dilute urine.|
|27||4||Terrestrial mammals convert ammonia into urea in the liver. This is a less toxic substance that can be stored within the body and requires less water (but more energy) to remove. The kidney filters urea out of the blood, reabsorbing a large amount of water so that a minimal amount of water is lost e.g. 1-2L per day in humans. Metabolic water is reused and excess salt is excreted.|
|28 (a)||2||A genotype is the genetic makeup of an individual, while phenotype is the individual’s observable traits. The phenotype can be influenced by the environment as the environment affects gene expression. For example, a person may have two copies of an allele that makes people tall, but if they have poor nutrition they will be short.|
|28 (b)||4||The presence of the mites acts as a selection pressure on the population of mammals. Those individuals that are badly affected will have bald patches, a phenotype that leaves them vulnerable to the cold and more likely to die.|
Those individuals that are heterozygous for the co-dominant allele are more likely to survive and pass the allele on to their offspring, increasing the frequency of this allele in the population.
Individuals that are homozygous are infertile and cannot pass the allele on to their offspring, but because individuals that are heterozygous have an advantage they are likely to survive, reproduce, and pass the allele on to the next generation. Thus, despite the disadvantage produced by the allele it is still maintained within the population.
|29 (a)||2||During interphase the DNA is replicated within the cell in preparation for cell division. DNA replication involves the enzyme helicase which unwinds the DNA double helix into two separate strands by breaking the hydrogen bonds between the bases.|
DNA polymerase enzymes then travel along each strand adding complimentary nucleotides until two identical DNA copies have been formed, each containing half of the original strand.
|29 (b)||5||During prophase I chromatin condenses to form chromosomes consisting of two identical chromatids.|
There is one maternally inherited chromosome and one paternally inherited. This is visible in the model as chromosomes with different colours.
During prophase I the homologous chromosomes join together (synapsis) and swap segments in a process known as crossing over. The result is chromosomes with both maternal and paternal segments, visible as different coloured segments of chromosomes in the model. This results in new combinations of alleles.
In telophase the nuclear envelope dissolves and the chromosomes begin to decondense into chromatin. Cytokinesis completes the division of the cell into two unique daughter cells.
|30||8||In the one hundred years between 1900 and 2000, developments in the identification, treatment and prevention of disease have increased life expectance for all ages listed in the graph above. However, the greatest increase in life expectancy was seen in new-borns, which suggests that the risk of death between birth and age 20 has been dramatically reduced. In part this is due to developments in preventing childhood diseases with techniques such as hygiene practices, vaccination and antibiotics.|
The work of Louis Pasteur and Robert Koch identified microbes as the cause of disease. Koch developed postulates to establish which specific microbe was associated with a disease. Pasteur experimented with vaccinations and developed a method of heating food products to kill off contaminating microbes (now known as pasteurisation). Once microbes were identified as the cause, efforts could focus on preventing the spread of microbes in order to prevent disease.
Hygiene practices were introduced to encourage medical practitioners, food preparers and the general public to wash their hands regularly to prevent the spread of microbes. In many countries water filtration systems were introduced to provide clean drinking water to the public via methods such as filtration and chlorination. Quarantine requirements were developed to prevent the spread of diseases in plants, animals and people through international travel (e.g. shipping ports, airports, border crossings).
An important technique to prevent disease is vaccination. Once a microbe has been identified as the cause of a disease, the antigens from its’ surface can be isolated and used in a vaccination. Once injected into the body, the immune system learns to recognise the antigen and produce memory cells which will be activated if the pathogen is encountered. The introduction of wide-scale vaccination campaigns in the 20th century lead to a dramatic decrease in deaths from diseases such as polio which now only occurs in around 3 countries. Smallpox has now been completely eradicated saving millions of lives. Diseases such as measles, mumps and rubella are now very rare in developed countries with childhood vaccination schedules. This has had a major impact on the life expectancy of people at birth.
New treatments for disease such as antivirals and antibiotics have had a huge impact. When antibiotics were first introduced in the 1940s they could easily cure what were once deadly bacterial infections. Antibiotics have saved millions of lives, but in recent years many bacteria have become resistant to antibiotics and new treatments must be found. As a result recent strategies have shifted from treatment to prevention.
There was a dramatic increase in expected life span over the 20th century. This is particularly evident in new-borns, where the life expectancy increased from around 47 years to 73 years. This increase is due to biological developments in identification, treatment and prevention of disease during this time.
|31 (a) i||2||Any two: Cornea, aqueous humour, lens, vitreous humour.|
|31 (a) ii||2||Beam A will strike the fovea while beam B will strike the periphery of the retina. At the fovea there is better perception of colour and also more detail detected as there are more cones than the periphery and they are packed into a small space. On the periphery there are more rods than cones so there is less detection of detail or colour, but good detection of light and dark.|
|31 (b)||4||Air is moved out from the lungs to the upper respiratory tract by the contraction of abdominal muscles and relaxing of the diaphragm. The air passes through the larynx and produces vibrations in the vocal cords, resulting in audible sounds. The frequency of these vibrations determines the pitch of the sound, since they are directly proportional to each other. Sounds of different pitches are controlled by the position and tension of the vocal cords. Increasing the tension of the vocal folds increases the frequency at which it vibrates, resulting in a higher pitched sound. On the other hand, reducing the tension of vocal folds decreases the frequency of the sound, which results in lower pitches.|
|31 (c) i||2||Adult A has far more overlap in the range of detection for each of the three cones. Adult A also has a greater number of green and red cones that respond within their wavelength ranges.|
|31 (c) ii||3||In adult B there is less overlap between the wavelengths detected by each of the three cones. In fact, the red and green cones do not overlap at all. These overlaps are important in the detection of intermediate colours such as orange which requires stimulation of red and green cones at the same time. Adult B will not be able to detect certain intermediate colours as the brain will not receive the correct combination of signals from the cones. They may also may be less sensitive to green and red as less cones respond and send signals to the brain in comparison to adult A.|
|31 (e)||7||Humans are able to detect the colours of the visible spectrum, ranging from 440-700 nm and hear sounds from 20Hz – 20 000 Hz. The diet of our human ancestors consisted partially of fruit, and hence by differentiating between different colours, ancestral humans would be able to distinguish between ripe and unripe fruit. The sound frequency range they can detect is more than adequate for verbal communication. Due to evolution however, different groups of organisms have different needs and abilities to detect electromagnetic radiation or sound. Thus, the models of hearing and sight are different for other animals.|
The occurrence of colour vision corresponds to their use of colour in the environment. For example, planarians live in a dark environment and hence do not require any colour vision. They possess a basic eye-cup structure to only detect direction and intensity of light, but there is no need for colour as a form of visual communication, hence there is no need for colour vision.
In contrast, bees are insects which possess compound eyes composed of a large number of singular photoreceptor units called ommatidia. Each ommatidia has its own lens, pigment and receptor cells. This results in trichromatic colour vision (UV, blue, green, orange but not red). Colour and UV is used as the means by which flowers are able to “communicate their whereabouts” to the bees for pollination. Honey bees detect a portion of the ultraviolet spectrum in addition to the blue-green end of the visible spectrum, ranging from 300-700 nm. Thus, colour vision in bees allows the organisms to quickly locate pollen and nectar.
Snakes are able to detect light from 480-850 nm which includes the infrared part of the spectrum. As infrared light is produced by heat, snakes can use this sense to detect warm blooded prey at night when hunting.
Sound is a particularly versatile form of communication and mammals such as humans have ears made up of an outer, middle, and inner ear segment. The inner ear includes the cochlea that converts sound into mechanical vibration of the ear hairs (stereocilia) and then into electrical signals that are sent to the brain. However sound detection mechanisms vary widely between animals. Different animals have different ranges of detection. For example bats can detect between 10 000 and 150 000 Hz as they use ultrasound for echolocation. By contrast elephants hear between 5 – 12 000 Hz as they use infrasound for communication.
Insects do not have a cochlea but have a Tympanum membrane on the front legs or abdomen that detect vibrations in air and Chordotonal organs located in the legs that detect vibration through surfaces.
Fish have hard Otoliths that vibrate and cause hair cells to move, triggering sensory neurons. These are used for detection of high frequency sound while a Lateral line system (involving stereocilia in cupula) is used for detection of lower low frequency sounds. The swim bladder is used as a resonance chamber. Thus the models of hearing and vision in animals is very different to that of humans as animals have very different needs.
|33 (a) i||2||Diploid cells have twice as many chromosomes as haploid cells. In diploid cells there is one maternal and one paternal chromosome in each homologous pair while in haploid cells the homologous chromosomes have undergone crossing over. Each chromosome now contains a mixture of maternal and paternal genetic material.|
|33 (a) ii||2||Diploid cells have twice as many chromosomes as haploid cells. In diploid cells there is one maternal and one paternal chromosome in each homologous pair while in haploid cells the homologous chromosomes have undergone crossing over. Each chromosome now contains a mixture of maternal and paternal genetic material.|
|33 (b)||4||Genes are copied onto mRNA and then the bases are read by the ribosomes in groups of three (a codon). Each codon corresponds to an amino acid.|
A base substitution will replace just one base on the DNA. This will change a single codon on the mRNA and one incorrect amino acid will be included in the polypeptide. In some cases, a silent mutation will occur and the codon will still code for the same amino acid.
or example, if the first base was changed from A to G the DNA sequence would read GTC AGT CGT ACG ATC GCA TA and the mRNA would read as CAG UCA GCA UGC UAG CGU AU. Only the first amino acid will be affected.
By contrast, a frameshift mutation will change all of the codons in the gene from the point where the mutation occurred, potentially resulting in many more amino acids being incorrectly coded. This is more likely to result in a dysfunctional protein.
For example, if a G was inserted at the beginning of the DNA sequence it would read GAT CAG TCG TAC GAT CGC ATA and the mRNA would read as CUA GUC AGC AUG CUA GCG UAU. All of the amino acids in this sequence would be incorrect and the protein product would likely be dysfunctional. (In fact the fourth codon is now a stop codon and the polypeptide will not be completed. This is a nonsense mutation.)
|33 (c) i||2||People with Lynch syndrome have an 80% chance of getting colon cancer in their lifetime, which is very high compared to the general population which has a lifetime risk below 10%. The risk of endometrial cancer is also much higher, being 60% in someone with Lynch syndrome compared to less than 10% in the general population (of women).|
|33 (c) ii||3||As Lynch syndrome is autosomal dominant an individual only needs to inherit one copy of the faulty allele in order to have the condition. The individuals in the graph that were diagnosed with cancer most likely had it as a result of Lynch syndrome.|
However, Lynch syndrome does not cause cancer in 100% of individuals that are carrying the allele so some individuals in the family that do not have cancer may still be carrying the allele. The female that was diagnosed with colon cancer at age 37 is likely to have inherited lynch syndrome from the mother who was carrying the allele but did not have cancer.
This means that 3/4 of the second generation had at least one allele for lynch syndrome and suggests that the parents in the first generation both were heterozygous for lynch syndrome.
|33 (e)||7||The process of producing cloned transgenic mice with a gene for a human disease requires a complex understanding of genes and gene technologies. Even before DNA was discovered an understanding of genetic inheritance was established by researchers such as Mendel and Morgan (who discovered sex-linkage).|
The Watson and Crick model of DNA allows to understand the double helix structure of the DNA molecule and how DNA is composed of the four bases (Adenine, Thymine, Guanine and Cytosine). This allows us to examine the ‘code’ that makes up living things and was the first step in enabling researchers to manipulate that code. Beadle and Tatum established that sections of the DNA called ‘genes’ were providing the code for the production of proteins, or polypeptides more specifically.
Eventually the process of transcription and translation was discovered, whereby a gene is copied as mRNA which is then read by a ribosome. The ribosome assembles amino acids based on the code on the mRNA.
In order to research diseases, the genes that are responsible for them had to be identified. The human genome project successfully located all coding genes on the human genome. It did not identify what they did but enabled scientists to map the location of genes and begin the process of identifying what each gene does and its potential role in disease. Once a disease-causing gene is identified, DNA sequencing enables scientists to identify the exact code of a disease-causing gene such as muscular dystrophy.
This understanding of genes and DNA eventually lead to the development of transgenic organisms, where a gene from one species is inserted into the genome of another. For example, the muscular dystrophy gene can be removed from a human cell and inserted into the plasmid of a bacteria. The bacterium is allowed to reproduce by binary fission to produce many copies of the gene. The gene can then be inserted into a mouse egg nucleus, with the resulting offspring containing the gene in all of its cells.
Tissue cells can then be taken from the offspring and used to produce clones. The tissue cells are fused with enucleated egg cells, and thus are the only contributors of genetic information. All of the offspring will be identical to the transgenic tissue donor. This process requires an understanding of how genetic information is contained in the nucleus.
Models such as these are now regularly produced in order to study different human diseases. These models only exist due to the accumulation of knowledge about genes and gene technologies.