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BIOLOGY, M6 2014 HSC 33d

The data compare a segment of the eye control gene in mice to the equivalent gene segment in a range of different species. The expression of these genes is necessary for eye development to begin.
 

Note: grey highlighted bases are the same as those in the mouse gene.

  1. With reference to the data in the table, explain why it is possible for different gene sequences to produce the same protein.   (2 marks)

  2. Discuss ONE strength and ONE limitation of using the data shown to determine the evolutionary relationships between these species.   (4 marks)

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i.   Explanation

→ Differences in base sequences can still code for the same amino acid, and therefore the same protein will be produced. This is often referred to as a silent change.

→ A change producing a different amino acid can have no effect on the protein if the amino acids are chemically similar. For example leucine and isoleucine are so similar that a change in DNA sequence resulting in this change will have no effect on the protein it codes for. This is called a neutral change.


♦♦ Mean mark (i) 40%.

ii.   Strengths

→ Despite having different sequences, each polypeptide chain/protein it is a part of will go on to initiate eye development.

→ This provides evidence that a once common ancestor had the eye development gene similar to that of all species, providing evidence of their close ancestry.

→ The average rate of mutation can also be used as a measure of time since divergence from the common ancestor. For example, species 2 may have more recently diverted as it has a genetic similarity of 85% when compared to species 4, which only has 71.66% similarity.
  

Limitations

→ The study only shows the relationship of one gene which is very small in comparison to the whole genome. This is a weak comparison as the rest of the genome may have intense variation and just studying this gene could provide false information.

→ Studying only one gene also increases the risk of encountering back mutations, mutations of a variation which revert back to the original sequence, making the species seem more closely related. This can also give false information about evolutionary relationships and ancestry.


♦♦ Mean mark (ii) 41%.

BIOLOGY, M6 2014 HSC 32e

The text summarises an ethical framework for decision-making related to the use of biotechnologies.
 

Evaluate the ethics of the use of ONE specific biotechnology in relation to this framework.   (7 marks)

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→ Transgenic organisms are those in which a gene from another species has been inserted into their genome to provide a favourable characteristic to them.

→ The ‘Super Salmon’ is a genetically modified Atlantic salmon which contains genes from the Chinook salmon and Ocean Pout fish which allow it to grow to market size in colder conditions and therefore faster than wild type Atlantic salmon. This has the potential to increase the availability of salmon and therefore providing a benefit to society. However, the transgenic salmon are unnatural and the addition of the gene may effect other parts of the genome, potentially making the salmon unhealthy or harmful for consumption, providing no benefit to society.

→ Roundup-ready soybeans have an implemented gene which allows them to be immune to roundup, a herbicide sprayed onto the crops which kills weeds. While this will increase yield of soybeans as they will be unaffected by roundup, it is toxic to humans and residue could be on the soybeans at sale, providing harm to consumers. The mass use of roundup may also leak and drift into soils, and overtime ecosystems, harming surrounding environments.

→ In the cases above, the adverse effects on society and the environment of both transgenic organisms as stated above should be studied and compared to the positives to decide which has greater influence (Utilitarian Ethics).

→ The companies and groups responsible for development, distribution and sale of the transgenic organisms are also obligated to provide proof that their product does not induce any harm to society or the environment (The Precautionary Principle).

→ Since there is little evidence for short and long term safety of transgenic organisms for the environment and society, a valid case for ethical use of transgenic organisms has not yet been developed. 


♦ Mean mark 55%.

BIOLOGY, M5 2014 HSC 32a

  1. Name the process for the synthesis of a polypeptide chain from a messenger-RNA base sequence.   (1 mark)

  2. Outline the steps in the formation of a functional enzyme from polypeptide chains.   (3 marks)

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i.    Translation


♦ Mean mark (i) 40%.

ii.   Formation of a functional enzyme from polypeptide chains

→ A polypeptide will fold in a certain three-dimensional shape dependent on the amino acids, such as a sheet or a coil.

→ Multiple polypeptide chains will then link together to form a more specific shape. This shape will then go on to do a specific task as a protein.

Note: The following point is old syllabus knowledge.

→ One type of protein is an enzyme, which acts as a biological catalyst on certain substrates, primarily in metabolic reactions. The certain shape an enzyme makes due to the polypeptide chains within it is what dictates which substrate it will act on. 


♦♦ Mean mark (ii) 31%.

BIOLOGY, M8 2014 HSC 31a

The biological structure shown is part of one of the systems in the body.
 

  1. Name the biological structure.   (1 mark)

  2. Outline the steps involved in this system's response to a stimulus.   (3 marks)

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i.   Nerve cell/neuron
  

ii.   Steps involved in system’s response to a stimulus

→ A stimulus is detected by a receptor nerve cell which convert the stimulus to an electrochemical impulse, which is then carried by sensory cells to the brain.

→ The signal reaches a certain segment on the brain depending on what signal was received, where an action is determined to be carried out.

→ Motor neurons carry the signal to an effector, which carries out the response.


♦ Mean mark (ii) 48%.

 

BIOLOGY, M6 2014 HSC 29

Scientists have tried to achieve a viable embryo by fusing two ova (eggs) from the same female.

Explain whether the offspring produced using this process would be a clone of the female whose two ova were used. Use your knowledge of gamete formation and sexual reproduction to support your answer.   (5 marks)

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→ Despite coming from the same female, meiosis and processes within it cause the genetic material within each ova to be different, and thus the offspring will not be a clone.

→ During meiosis, a germ line cell will replicate, split, then split again, resulting in 4 genetically unique daughter gametes.

→ The processes of independent assortment, the random splitting of each chromosome during each stage, as well as crossing over, where like segments of homologous chromosomes can be exchanged creating new combinations, also contribute to the variability amongst daughter cells.

→ When two of these ova (gametes) are fused, the genetic material of each are contributed to the offspring, with some genes being expressed or suppressed depending on the combinations of alleles from each. In this way, the offspring will be genetically different from the female rather than a clone.


♦♦ Mean mark 36%.

BIOLOGY, M7 2014 HSC 18 MC

Two people were exposed to pathogen `P` on the same day. The graph shows the blood antibody levels for that pathogen over the following 28 days for each person.
 

Which of the following best explains these results?

  1. Person 1 had not been previously exposed to pathogen `P` but had a recent organ transplant.
  2. Person 1 had been previously exposed to pathogen `P`.
  3. Person 2 had already been vaccinated against pathogen `P`.
  4. Person 2 had recent contact with a person infected with a similar pathogen.
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`B`

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By Elimination

→ Being vaccinated against a pathogen or being exposed to a similar pathogen would lead to higher antibody counts, not lower. (Eliminate C and D).

→ Person 1’s previous exposure to the pathogen means that memory B cells can quickly and rapidly differentiate into plasma B cells, leading to higher counts of antibodies in a shorter time. An organ transplant is not relevant in this scenario. (Eliminate A).

`=>B`


♦ Mean mark 50%.

BIOLOGY, M7 2014 HSC 17 MC

When B cells are activated they divide to form a large number of antibody-secreting cells.

How is this best explained?

  1. Mitosis and gene expression produce cytotoxic cells.
  2. Mitosis and differentiation produce B cells that repair tissues.
  3. Mitosis and cell specialisation produce cells that maintain health.
  4. Mitosis and differentiation produce cells for growth and development.
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`C`

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→ Mitosis allows B cells to divide into identical plasma B cells.

→ Plasma B cells are specialised cells particular to one pathogen, allowing individuals to be protected against it.

`=>C`


♦ Mean mark 56%.

BIOLOGY, M6 2014 HSC 16 MC

What is the best explanation for the successful development of transgenic species?

  1. Artificial pollination works across the plant kingdom.
  2. Nuclear transplantation from cell to cell is easily achieved.
  3. DNA in the biosphere is composed of the same chemical components.
  4. Genes from different animals within the one species are easily combined.
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`C`

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→ The development of transgenic species is only possible since all nucleotides in all of the worlds’ life is chemically identical.

`=>C`


♦♦ Mean mark 35%.

BIOLOGY, M5 2014 HSC 15 MC

Goltz Syndrome is a condition in humans that adversely affects the skin. It is inherited as a dominant gene carried on the X chromosome.

A man with Goltz Syndrome and a woman who does NOT have the trait have two children, a boy and a girl.

Which of the following is correct about the inheritance of Goltz Syndrome in these children?

  1. Both children have the syndrome.
  2. The girl has the syndrome and the boy does not.
  3. The girl has the syndrome and the boy is a carrier.
  4. The girl has a 50% chance of having the syndrome and the boy has a 0% chance.
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`B`

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→ A woman with the genotype XgXg will not have Goltz and a male with XGY will have Goltz.

→ A cross between these individuals will mean that all girls will have Goltz as they have to have the XG allele from the father, and no boys will have Goltz, as they have to inherit the Y chromosome from the father, and both X chromosomes from the mother do not have the gene for Goltz.

`=>B`


♦ Mean mark 48%.

BIOLOGY, M7 2014 HSC 12-13 MC

Refer to the following information to answer Questions 12 and 13.

A student conducted a first-hand investigation using nutrient broth, beakers and an S-shaped delivery tube in an attempt to model Pasteur's experiment.

The equipment and data collected are shown.
 

Question 12

The data collected by the student are

  1. quantitative because data were collected for fourteen days.
  2. qualitative because the appearance of the broth is described.
  3. qualitative because this is a model of a past scientific experiment.
  4. quantitative because the results were recorded for two different beakers.

Question 13

The student's results were different from Pasteur's results.

Which of the following provides the best explanation for the difference?

  1. The nutrient broth was different from Pasteur's.
  2. The nutrient broth always goes cloudy as it ages.
  3. The nutrient broth was not boiled thoroughly on Day 1 .
  4. The nutrient broths were both exposed to oxygen from the outside air.
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Question 12

By Elimination

→ Quantitative data is one in which numerical values are obtained for comparison. (Eliminate A and D).

→ The data then must be qualitative as it includes a description of the broth’s appearance.

`=>B`

Question 13

→ The apparatus matches that of Pasteur’s, so the best explanation for flask 2 also going cloudy would be due to not thoroughly boiling the broth before the experiment, and therefore not eliminating any bacteria already present.

`=>C`


♦ Mean mark 53%.

ENGINEERING, TE 2017 HSC 16 MC

Television programs that show high levels of activity often have lower picture quality.

This is because television signals are transmitted using

  1. digital modulation at low compression levels.
  2. digital modulation at high compression levels.
  3. analogue modulation at low compression levels.
  4. analogue modulation at high compression levels.
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`B`

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→ Modern television signals are transmitted using digital modulation, so the answer must be A or B.

→ The lower picture quality is the result of the TV being unable to decompress the highly compressed signal quickly.

`=>B`


♦♦ Mean mark 39%.

ENGINEERING, CS 2017 HSC 10 MC

Which of the following statements describes Hooke's Law?

  1. Pressure acting on an object varies proportionally with depth.
  2. Pressure acting on an object in a confined fluid is uniform in all directions.
  3. Force induced in an object by stretching it is initially proportional to its extension.
  4. Force acting on an object is equal to the stress divided by the cross-sectional area.
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`C`

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→ Hooke’s Law states that when an object is extended or stretched in the elastic range the extension is proportional to the force applied.

→ That is, stress is proportional to strain below the elastic limit.

`=>C`


♦ Mean mark 45%.

ENGINEERING, PPT 2017 HSC 8 MC

Which row of the table correctly identifies how the properties of a cold worked metal are changed after annealing?
 

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`B`

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→ Generally, annealing is the heat treating of a metal to produce a soft (decrease in hardness), stress reduced (decrease in internal residual stress) state.

→ By decreasing the hardness and internal stress, the ductility will increase as well.

`=>B`


♦ Mean mark 49%.

ENGINEERING, TE 2017 HSC 7 MC

Wireless networks operate in two distinct frequency bands: 2.4 GHz and 5 GHz.

Which of the following statements is correct?

  1. 5 GHz waves experience lower attenuation and have a lower bandwidth
  2. 5 GHz waves experience higher attenuation and have a higher bandwidth
  3. 2.4 GHz waves experience lower attenuation and have a higher bandwidth
  4. 2.4 GHz waves experience higher attenuation and have a lower bandwidth
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`B`

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→ Lower frequencies (2.4GHz) are characterised by lower bandwidth but also good range coverage due to their lower attenuation.

→ Higher frequencies such as 5GHz are subject to higher attenuation especially when they encounter solid objects.

`=>B`


♦♦ Mean mark 38%.

ENGINEERING, PPT 2016 HSC 27b

The table compares the `\text{CO}_2` emissions of three transport systems - car, train and aircraft.
 

For each transport system shown in the `\text{CO}_2` emissions table, explain how an engineering innovation in that transport system has affected the environment.   (7 marks)

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Innovations in car transport include:

→ Fuel injection, turbo engines, power to weight ratio, tyre variants, engine management systems, ABS breaks, regenerative braking and reduction in drive train losses.

Show Worked Solution

Innovations in car transport include:

→ Fuel injection, turbo engines, power to weight ratio, tyre variants, engine management systems, ABS breaks, regenerative braking and reduction in drive train losses.

Environmental Impacts

→ Improved power to weight ratios have led to greater fuel efficiency (less consumption).

→ This has resulted from innovations in the strength of aluminium alloys and the use of carbon fibre composite components both of which make the car lighter.

→ Cars with more aerodynamic shapes are also being routinely produced, which reduces drag.

→ Therefore, modern cars that are more aerodynamically designed and built with lighter materials, have considerably less drag, and thus CO2 emissions are reduced.
  

Innovations in rail transport include:

→ Turbo driven diesel engines, magnetic levitation braking, disc brakes, electric trains with AC versus DC motors and efficient track alignment.

Environmental Impacts

→ The use of AC motors in the drive train, rather than DC, has been the most positive modern innovation in rail transport.

→ VVVF (variable voltage variable frequency) drives, control the voltage and torque on modern AC machines, creating greater efficiencies, as DC machines lose electricity as heat.

→ Regenerative braking can be employed by AC machines as a train descends or slows down.

→ These improved efficiencies result in less diesel fuel on country trains and less electricity on city trains, leading to a reduction in CO2 emissions.

  
Innovations in air transport include:

→ The use of composites to create more aerodynamic shapes and reduced weight, improved efficiency in turbofans, reduced drag and the removal of rivet-induced turbulence through the use of adhesives.

Environmental Impacts

→ Fuel efficiency is greatly improved through the use of modern turbofan engines that optimise the entrainment of by bypass air, which produces 90% of the total thrust of the engine.

→ The use of flow control devices and winglets on wings, minimise wing tip vortices, improving lift and reducing drag.

→ Efficiency is therefore improved leading to reduced fuel consumption and a consequent reductions in CO2 emissions.


♦ Mean mark 51%.

Environmental Impacts

→ Improved power to weight ratios have led to greater fuel efficiency (less consumption).

→ This has resulted from innovations in the strength of aluminium alloys and the use of carbon fibre composite components both of which make the car lighter.

→ Cars with more aerodynamic shapes are also being routinely produced, which reduces drag.

→ Therefore, modern cars that are more aerodynamically designed and built with lighter materials, have considerably less drag, and thus CO2 emissions are reduced.
  

Innovations in rail transport include:

→ Turbo driven diesel engines, magnetic levitation braking, disc brakes, electric trains with AC versus DC motors and efficient track alignment.

Environmental Impacts

→ The use of AC motors in the drive train, rather than DC, has been the most positive modern innovation in rail transport.

→ VVVF (variable voltage variable frequency) drives, control the voltage and torque on modern AC machines, creating greater efficiencies, as DC machines lose electricity as heat.

→ Regenerative braking can be employed by AC machines as a train descends or slows down.

→ These improved efficiencies result in less diesel fuel on country trains and less electricity on city trains, leading to a reduction in CO2 emissions.

  
Innovations in air transport include:

→ The use of composites to create more aerodynamic shapes and reduced weight, improved efficiency in turbofans, reduced drag and the removal of rivet-induced turbulence through the use of adhesives.

Environmental Impacts

→ Fuel efficiency is greatly improved through the use of modern turbofan engines that optimise the entrainment of by bypass air, which produces 90% of the total thrust of the engine.

→ The use of flow control devices and winglets on wings, minimise wing tip vortices, improving lift and reducing drag.

→ Efficiency is therefore improved leading to reduced fuel consumption and a consequent reductions in CO2 emissions.

ENGINEERING, PPT 2016 HSC 22c

An electrical connector is screwed onto a threaded rod. A flat plate is then secured to the connector by a bolt screwed into a threaded hole.
 

Complete the scaled sectioned front view with the parts assembled.   (6 marks)
 

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The image below should be adjusted to the appropriate scale.

Show Worked Solution

The image below should be adjusted to the appropriate scale.

Key points for this drawing:

  • Do not dimension unless asked
  • Section lines should be at 45 degrees and 3 mm apart
  • No not section threads/bolts
  • Ensure correct bolts dimensions used for the bolt
  • The gap in the middle shows that the pieces DO NOT sit flush
  • Swap direction of section lines for adjoining areas

♦♦ Mean mark 43%.

ENGINEERING, CS 2016 HSC 21ai

The reinforced concrete modules shown are designed for public seating. A typical use would be as a bus shelter.

Outline benefits of using this type of modular seating system.   (3 marks)

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→ Reusable moulds can be used to manufacture the modules off-site and then delivered to the site.

→ The completed modules can then be delivered to the site, resulting in fewer site disruptions.

→ More modules can be added as required.

Show Worked Solution

→ Reusable moulds can be used to manufacture the modules off-site and then delivered to the site.

→ The completed modules can then be delivered to the site, resulting in fewer site disruptions.

→ More modules can be added as required.


Mean mark 54%.

ENGINEERING, PPT 2016 HSC 26c

Structural steel `text{I}`-beams are used to make a crane were hot-rolled then normalised.

Explain why normalising was chosen as the heat treatment process. Support your answer with a labelled sketch of the resulting microstructure.   (4 marks)


 

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Advantages of normalising:

→ An increase in strength. Grain size strengthening is achieved due to the fine uniform grain structure produced by normalising.

→ When compared to other strengthening methods it is relatively economical.

→ Normalising relieves stress.
 

Show Worked Solution

Advantages of normalising:

→ An increase in strength. Grain size strengthening is achieved due to the fine uniform grain structure produced by normalising.

→ When compared to other strengthening methods it is relatively economical.

→ Normalising relieves stress.
 


♦ Mean mark 43%.

ENGINEERING, CS 2016 HSC 26b

What are redundant truss members?   (2 marks)

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Redundant truss members:

→ A truss that carries no load under the conditions present.

→ It is important to note that as load conditions change, the truss may not actually remain redundant. 

Show Worked Solution

Redundant truss members:

→ A truss that carries no load under the conditions present.

→ It is important to note that as load conditions change, the truss may not actually remain redundant. 


♦ Mean mark 46%.

ENGINEERING, CS 2016 HSC 26a

A simplified diagram of a pin jointed truss of a hammerhead crane is shown. It is lifting a load of 54 kN.
 

  1. Calculate the reactions at supports `A` and `B`.   (4 marks)
  1. Determine the magnitude and nature of the force in member `M`.   (2 marks)
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i.     Reaction at `A` = 249 kN ↑

Reaction at `B` = 123 kN @ 12.7° acting down and to the right.

ii.   Force in `M` = 121 kN (Compression)

Show Worked Solution

i.

`text{R}_(BH)-27=0`

`text{R}_(BH)=27`

`text{From the diagram,}\ \ text{R}_(BH)=27\ text{kN →}`

+\({\circlearrowleft}\)`sumM_B` `=0`  
`0` `=27xx2+54xx5-75xx1-R_Axx1`  
`R_A` `=54+270-75`  
  `=249\ text{kN ↑}`  
     
+ ↑`sumF_V` `=0`  
`0` `=249-75-54+R_B`  
`R_B` `=129-249`  
  `=-120\ text{kN}`  
  `=120\ text{kN ↓}`  

 

`R_A=249\ text{kN @ 0° ↑}`

`text{Reaction at}\ B:`

Reaction at `A` = 249 kN acting vertically, up

Reaction at `B` = 123 kN @ 12.7° acting down and to the right.
  


Mean mark (i) 52%.

ii.   `theta = tan^(-1)(20/40)=26.6°`

   

`F` `=sqrt(108^2+54^2)`  
  `=sqrt(14\ 580)`  
  `=120.747…`  

  
Force in `M` = 121 kN (Compression)


♦ Mean mark (ii) 49%.

ENGINEERING, AE 2016 HSC 25aii

An image of a small drone is shown.
 


  

Nylon propellers are used on drones whereas carbon fibre composite propellers are used on commercial aircraft.

Describe a suitable manufacturing method for each type of propeller.   (3 marks)

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Nylon propellers

→ Injection moulded

→ A screw feeds nylon pellets into a heat chamber.

→ As the screw rotates, a combination of pressure, friction and external heat melts the nylon.

→ Molten nylon is pumped into multi-cavity moulds for setting. 
 

Carbon fibre composite propellers

→ A mould is laid with an impregnated carbon fibre sheet and placed into a vacuum bag.

→ An autoclave is used to evacuate the bag so the assembly can be heated and then allowed to set.

Show Worked Solution

Nylon propellers

→ Injection moulded

→ A screw feeds nylon pellets into a heat chamber.

→ As the screw rotates, a combination of pressure, friction and external heat melts the nylon.

→ Molten nylon is pumped into multi-cavity moulds for setting. 
 

Carbon fibre composite propellers

→ A mould is laid with an impregnated carbon fibre sheet and placed into a vacuum bag.

→ An autoclave is used to evacuate the bag so the assembly can be heated and then allowed to set.


♦♦ Mean mark 36%.

ENGINEERING, AE 2016 HSC 25ai

An image of a small drone is shown.
 


  

Explain how this drone achieves flight.   (3 marks)

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→ The weight of the drone is counteracted by rotating propellers that produce vertical thrust (lift).

→ The drone will achieve flight if the vertical thrust exceeds the weight.

→ Controlled climb or descent is achieved by varying the speed of the motor.

→ The direction of flight or thrust can be affected by a change in the rotational speed of the propellers.

→ Power for flight is supplied by battery systems.

Show Worked Solution

→ The weight of the drone is counteracted by rotating propellers that produce vertical thrust (lift).

→ The drone will achieve flight if the vertical thrust exceeds the weight.

→ Controlled climb or descent is achieved by varying the speed of the motor.

→ The direction of flight or thrust can be affected by a change in the rotational speed of the propellers.

→ Power for flight is supplied by battery systems.


Mean mark 54%.

ENGINEERING, PPT 2016 HSC 24d

A mild steel nut and bolt is used to hold a bumper bar onto the chassis of a truck. The bolt needs to withstand a maximum shear load of 2 kN.
 

If the maximum shear stress of the material is 56 MPa and the factor of safety is 2, calculate the minimum bolt diameter.   (3 marks)

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`9.5\ text{mm}`

Show Worked Solution

`text{Max load = 2000 N,  Max Shear = 56 MPa}`

`text{Factor of Safety = 2}`

`sigma_A = sigma/2 = 28\ text{MPa}`

`sigma_A` `=P/A`  
`A` `=P/sigma_A`  
`(pid^2)/4` `=P/sigma_A`  
`d^2` `=(4P)/(pi sigma_A)`  
  `=(4 xx 2000)/(pi xx 28\ 000\ 000)`  
  `=9.09 xx 10^(-5)`  
`d` `=9.53 xx 10^(-3)`  
  `=9.5\ text{mm (min)}`  

Mean mark 55%.

ENGINEERING, PPT 2016 HSC 24b

Give reasons for selecting an aluminium alloy for the side panel of the truck.   (2 marks)

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Reasons for using aluminium alloy:

→ Easily shaped, fabricated and installed.

→ Good strength to weight ratio.

→ Waterproof and resistant to corrosion.

Show Worked Solution

Reasons for using aluminium alloy:

→ Easily shaped, fabricated and installed.

→ Good strength to weight ratio.

→ Waterproof and resistant to corrosion.


♦ Mean mark 49%.

ENGINEERING, CS 2016 HSC 23b

This diagram shows the cross-section of a highway pavement drawn using AS 1100 drawing standards.
 

  1. Outline the properties of asphalt that make it suitable for highway pavement surfaces.   (3 marks)
  1. Why are geotextiles used in the construction of highway pavements?   (3 marks)
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i.    Successful answers should include 3 of the following:

Asphalt suitability

→ More durable than gravel and easier to lay than concrete.

→ Easily shaped and moulded to the contour of the road.

→ Can be driven on minutes after laying.

→ Can be easily repaired.

→ A smooth surface can be produced by pressing aggregate into substrate.

→ Flexibility allows for earth movement.
 

ii.   Reasons for using geotextiles:

→ Geotextiles are used to prevent the blockage of underground drainage by filtering silt from drainage below the surface.

→ They can also be used to prevent silt from undermining the road base, which can lead to road collapse.

Show Worked Solution

i.    Successful answers should include 3 of the following:

Asphalt suitability

→ More durable than gravel and easier to lay than concrete.

→ Easily shaped and moulded to the contour of the road.

→ Can be driven on minutes after laying.

→ Can be easily repaired.

→ A smooth surface can be produced by pressing aggregate into substrate.

→ Flexibility allows for earth movement.

ii.   Reasons for using geotextiles:

→ Geotextiles are used to prevent the blockage of underground drainage by filtering silt from drainage below the surface.

→ They can also be used to prevent silt from undermining the road base, which can lead to road collapse.


♦♦ Mean mark (ii) 38%.

ENGINEERING, CS 2018 HSC 23b

The steel used in the chassis members was tested.

The load–extension graph represents the data collected during the testing of a specimen of the steel.
 

Before testing, the specimen was 1020 mm long with a cross-sectional area of 100 mm².

  1. Calculate Young's modulus for this steel.   (4 marks)
  1. Describe the physical changes that occur in the specimen tested in part (i) when a 20 kN load is applied and then removed, compared to when a 30 kN load is applied and then removed.   (2 marks)
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i.   Young’s modulus

`F = 20 xx 10^3\ text{N}, l = 1020\ text{mm},  e = 1\ text{mm},  text{A} = 100\ text{mm}^2`

`E` `=(Fl)/(eA)`  
  `=(20 xx 10^3 xx1020)/(1 xx 100)`  
  `=204 xx 10^3`  
  `=204\ text{GPa}`  

 

ii.   → Elastic deformation is produced by the 20 kN load.

→ After initial stretching the specimen returns to its original length.

→ Plastic deformation is produced by the 30 kN load.

→ The specimen stays deformed subsequent to release.

Show Worked Solution

i.   Young’s modulus

`F = 20 xx 10^3\ text{N}, l = 1020\ text{mm},  e = 1\ text{mm},  text{A} = 100\ text{mm}^2`

`E` `=(Fl)/(eA)`  
  `=(20 xx 10^3 xx1020)/(1 xx 100)`  
  `=204 xx 10^3`  
  `=204\ text{GPa}`  

 


♦ Mean mark (i) 51%.

ii.  → Elastic deformation is produced by the 20 kN load.

→ After initial stretching the specimen returns to its original length.

→ Plastic deformation is produced by the 30 kN load.

→ The specimen stays deformed subsequent to release.

ENGINEERING, PPT 2018 HSC 20 MC

A box with weight `W` and subject to a friction force `F` is being pulled up an inclined plane by a force `P`.
 

The force `R` is the resultant of which two forces?

  1. `P` and `W`
  2. `P` and `N`
  3. `F` and `W`
  4. `F` and `N`
Show Answers Only

`D`

Show Worked Solution

→ `R` is used as the resultant of `F` and `N`, usually used to calculate `P` and employ the 3 force rule.

`=>D`


♦ Mean mark 42%.

ENGINEERING, TE 2018 HSC 19 MC

Which heat-treated metal is used for contact springs in electrical switches?

  1. OFHC copper
  2. Phosphor bronze
  3. Copper beryllium
  4. Tough pitched copper
Show Answers Only

`C`

Show Worked Solution

→ Beryllium copper is used in contact springs due to its conductivity and low sparking characteristics.

`=>C`


♦ Mean mark 47%.

ENGINEERING, TE 2018 HSC 15 MC

Which of the following electronic circuits functions as a NAND logic gate?
 

 

Show Answers Only

`D`

Show Worked Solution

→ NAND gates produce a high output (in this case turn the light on) as long as the 2 conditions are not BOTH met.

→ The gates in these diagrams represent inputs being met (closed) or not met (open).

→ In `D`, if both gates close the circuit will be complete without turning the light on as ‘both conditions have been met’. 

`=>D`


♦♦ Mean mark 34%.

ENGINEERING, PPT 2018 HSC 14 MC

Which row of the table correctly describes the property changes that occur after tempering quench-hardened steel?
 

Show Answers Only

`A`

Show Worked Solution

→ Tempering of hardened steel is designed to reduce the brittleness of the material without significantly impacting its hardness (minimal loss).

→ This increases the toughness as tempering usually involves an increase in ductility.

`=>A`


Mean mark 51%.

ENGINEERING, CS 2018 HSC 10 MC

In a ductile material, which two stresses are used to calculate the factor of safety (FOS)?

  1. Working and yield
  2. Working and compressive
  3. Bending and yield
  4. Bending and compressive
Show Answers Only

`A`

Show Worked Solution
`sigma_(text{allowable})` `= sigma_(text{yield})/text{FOS}`  
`text{FOS}` `= sigma_(text{yield})/sigma_(text{allowable})`  
     

`→ sigma_(text{allowable})` is working stress.

→ FOS is calculated using yield and working stress in ductile materials.

`=>A`


♦ Mean mark 42%.

ENGINEERING, CS 2019 HSC 21b

A bus shelter is shown.

   

A laminated timber beam is used as part of the roof construction for this bus shelter.

Apart from cost and aesthetics, justify why laminated timber would be selected for this structure.   (2 marks)

Show Answers Only

→ Laminated timber can create a stronger and more rigid beam by eliminating knots and imperfections.

→ It is fire resistant.

→ Compared to steel, laminate has a superior strength to weight ratio.

Show Worked Solution

→ Laminated timber can create a stronger and more rigid beam by eliminating knots and imperfections.

→ It is fire resistant.

→ Compared to steel, laminate has a superior strength to weight ratio.


♦♦ Mean mark (b) 33%.

ENGINEERING, CS 2019 HSC 21c

A bus shelter is shown.

   

Describe a testing procedure that could be used to determine the structural strength of the laminated timber beam. Support your answer with a labelled sketch.   (4 marks)

Show Answers Only

Traverse Bend Test

→ Used to measure the beam’s flexural strength.

→ A single or double point load is applied to a beam supported at both ends.

→ The measured deflection is plotted onto a load/deflection graph.
 

Show Worked Solution

Traverse Bend Test

→ Used to measure the beam’s flexural strength.

→ A single or double point load is applied to a beam supported at both ends.

→ The measured deflection is plotted onto a load/deflection graph.
 


♦ Mean mark 39%.

ENGINEERING, CS 2019 HSC 21d

A pictorial sketch of a laminated timber beam used in a bus shelter is shown. This beam has a second moment area of `117 × 10^(-6)\ text{m}^(4)`. The maximum applied bending moment is 17 kNm.
 

  1. Calculate the maximum bending stress present in the beam.   (3 marks)
Show Answers Only

`18.2\ text{MPa}`

Show Worked Solution

Second Moment of Area (`l`)`= 117 times 10^(-6)\ text{m}^(4)`

Maximum Bending Moment (`M`)`= 17 times 10^(3)\ text{N}`

Distance (Neutral axis → outside of beam) = 125 mm

`=> y = 0.125\ text{m}`

`:.\ text{Bending Stress}_text{max}` `=(My)/l`  
  `=(0.125 times 17 times 10^(3))/(117 times 10^(-6)`  
  `=18.2\ text{MPa}`  

ENGINEERING, PPT 2017 HSC 25b

A small truck chassis rail has been made from rectangular hollow section (RHS) steel. The RHS has been cold formed from an alloy steel with a yield strength of 500 MPa. A manufacturer's sign on the chassis rail is shown below.
 

  1. Explain why the chassis rail should normally not be drilled or welded.   (3 marks)
  1. A large reinforcing plate that supports a new attachment is to be welded onto the chassis rail according to the manufacturer's specifications.   
  2. Use the diagram below to draw and label the macrostructure of the weld area, including the surrounding chassis rail and reinforcing plate.   (2 marks)
     

Show Answers Only

i.   Welding

→ The chassis rail steel becomes molten when welded at temperatures exceeding the A1 temperature.

→ Columnar grains may form on some parts of the weld upon cooling.

→ Martensite may form on cooling, creating a brittle, hard microstructure with less strength than that of the steel chassis (500 MPa).

Drilling

→ Stress raisers are produced by drilling the flanges.

→ Fatigue failure is initiated by surface roughness that can occur around the drill hole.

Show Worked Solution

i.   Welding

→ The chassis rail steel becomes molten when welded at temperatures exceeding the A1 temperature.

→ Columnar grains may form on some parts of the weld upon cooling.

→ Martensite may form on cooling, creating a brittle, hard microstructure with less strength than that of the steel chassis (500 MPa).

Drilling

→ Stress raisers are produced by drilling the flanges.

→ Fatigue failure is initiated by surface roughness that can occur around the drill hole.
 


♦♦ Mean mark (i) 39%.

ii.


♦♦ Mean mark (ii) 27%.

ENGINEERING, TE 2020 HSC 27b

An orthographic drawing of a toggle switch is shown.
 

 

Produce a pictorial drawing of the toggle switch when viewed from the direction indicated by arrow A.   (6 marks)

Use a scale of 2:1.

Show Answers Only

Notes on this drawing: 

→ Ensure correct scale of 2:1 is used

→ Ensure drawing is completed from the correct viewing direction

→ Drawing must be isometric as indicated by viewing direction

→ Do not show hidden detail or centrelines on pictorial drawing

→ Do not show dimensions unless explicitly asked

→ There is not a specific standard for drawing pictorial threads, show some working/attempt to show that a thread is present

Show Worked Solution

Notes on this drawing: 

→ Ensure correct scale of 2:1 is used

→ Ensure drawing is completed from the correct viewing direction

→ Drawing must be isometric as indicated by viewing direction

→ Do not show hidden detail or centrelines on pictorial drawing

→ Do not show dimensions unless explicitly asked

→ There is not a specific standard for drawing pictorial threads, show some working/attempt to show that a thread is present


Mean mark 53%.

ENGINEERING, AE 2018 HSC 25c

 A two-engine aircraft with mass 330 tonnes is climbing at 15°. Each engine produces 510 kN of thrust. The aircraft maintains a constant velocity.

  1. Complete the space diagram by indicating the four key forces of flight for this situation.   (2 marks)
     
     

  1. Determine the induced drag force for this situation.   (3 marks)
Show Answers Only

i.

ii.   `166\ text{kN}`

Show Worked Solution

i.

ii.  `text{Find Induced drag} (D):`

`text{Weight}\ (W)` `=text{m} xx text{g} `  
  `=330 xx 10^3 xx 10`  
  `=33 xx 10^5\ text {N}`  

 

`text{Thrust}\ (T)` `=510 xx 10^3 xx 2`  
  `=102 xx 10^4` N  

 

`T` `= D + W\ sin\ gamma`  
`D` `= T-W\ sin\ gamma`  
  `=102 xx 10^4  –  33 xx 10^5\ sin15^\circ`  
  `=165\ 897.1512`  
  `=166 xx 10^3`  
  `=166\ text{kN}`  

♦♦ Mean mark (ii) 34%.

ENGINEERING, AE 2018 HSC 25b

Explain how the angle of attack of an aircraft in flight influences the lift generated by the wings. Use a labelled sketch to support your answer.   (3 marks) 

Show Answers Only

→ When the angle of attack is zero,there is no lift, but drag is still encountered.

→ The lower the angle of attack, the weaker these forces will become.

→ The higher the angle of attack, the higher the lift and drag forces become.

→ With increased angle of attack, upper surface separation point of air flow transfers to the trailing edge from the leading edge.

→ When the critical angle of attack is reached, the wing’s maximum coefficient of lift is produced and upper surface flow is increasingly disconnected.

→ If you pass the critical angle of attack (around 10° to 20°) the lift from the airfoil will drop to zero and the aircraft will stall.
 

Show Worked Solution

→ When the angle of attack is zero,there is no lift, but drag is still encountered.

→ The lower the angle of attack, the weaker these forces will become.

→ The higher the angle of attack, the higher the lift and drag forces become.

→ With increased angle of attack, upper surface separation point of air flow transfers to the trailing edge from the leading edge.

→ When the critical angle of attack is reached, the wing’s maximum coefficient of lift is produced and upper surface flow is increasingly disconnected.

→ If you pass the critical angle of attack (around 10° to 20°) the lift from the airfoil will drop to zero and the aircraft will stall.
 


Mean mark 51%.

ENGINEERING, CS 2018 HSC 23c

The chassis for a motor vehicle could be made from a solid steel bar or hollow steel tube. Both the bar and the tube have the same mass and cost per metre.
 

Justify why a hollow tube would be used in preference to a solid bar to build the vehicle chassis.   (3 marks)

Show Answers Only

→ Hollow tube has a higher second moment of area and is therefore more rigid.

→ Because the chassis is exposed to continual flexural forces and moments when the vehicle is moving, rigidity is important.

→ Stiffness is therefore a major design requirement.

→ The hollow tube also provides damage protection for any electrics cabling.

Show Worked Solution

→ Hollow tube has a higher second moment of area and is therefore more rigid.

→ Because the chassis is exposed to continual flexural forces and moments when the vehicle is moving, rigidity is important.

→ Stiffness is therefore a major design requirement.

→ The hollow tube also provides damage protection for any electrics cabling.

♦♦ Mean mark 35%.

ENGINEERING, PPT 2018 HSC 22d

To operate successfully, a laser diode requires 2.3 V while drawing a current of 25 mA.
 

For the circuit shown, calculate the required resistor value `R` needed to produce the correct operating voltage.   (3 marks)

Show Answers Only

`268\ text{Ohms}`

Show Worked Solution
`V` `= V_(total) \ – \ V_(led)`  
  `= 9-2.3`  
  `= 6.7\ text{V}`  

 

`R` `= V/I`  
  `= 6.7\(25 xx 10^(-3))`  
  `= 268\ text{Ohms}`  

♦ Mean mark 43%.

ENGINEERING, TE 2018 HSC 22c

The following three types of diode are used in telecommunication circuits.
 

Describe the function of each diode in telecommunication circuits.   (4 marks)

Show Answers Only

Zener diode

→ Voltage regulator.

→ Allows current to flow above an assigned voltage (zener voltage).

→ Stable reference voltage for a range of current values.
 

Laser diode

→ Focused light beam produced when current present in the circuit.

→ Pulses of light transmitted down optical fibre, allowing transmission of digital data.
 

Light emitting diode

→ When current present in the circuit a wide beam of light is emitted.

→ Frequently used so show power is on.

Show Worked Solution

Zener diode

→ Voltage regulator.

→ Allows current to flow above an assigned voltage (zener voltage).

→ Stable reference voltage for a range of current values.
 


♦♦ Mean mark 39%.

Laser diode

→ Focused light beam produced when current present in the circuit.

→ Pulses of light transmitted down optical fibre, allowing transmission of digital data.
 

Light emitting diode

→ When current present in the circuit a wide beam of light is emitted.

→ Frequently used so show power is on.

ENGINEERING, CS 2018 HSC 2 MC

The diagram shows a scaffold with diagonal braces.
 

When loaded, the diagonal braces are typically subjected to which pair of forces?

  1. Torsion and shear
  2. Torsion and tension
  3. Compression and shear
  4. Compression and tension
Show Answers Only

`D`

Show Worked Solution

→ Bracing members can only carry tension, or both tension and compression.

`=>D`


♦ Mean mark 53%.

ENGINEERING, AE 2017 HSC 26b

Orthogonal and pictorial drawings of a sheet metal electrical cable cover are given below.
 

  1. Draw a half-development of the electrical cable cover. Use the centre line to position the development.   (4 marks)
     

  1. A 20 mm diameter hole is to be punched through the top of the electrical cable cover before folding.
  2. The ultimate shear stress of the material used to manufacture the cover is 110 MPa.
  3. Calculate the force required to punch out the hole if the thickness of the sheet metal is 0.5 mm.   (3 marks)
Show Answers Only

i.   
         

ii.   `3.46\ text{kN}`

Show Worked Solution

i.   
         

Key Points for this Drawing:

  • Find true length of each line from the diagrams given
  • Do not dimension
  • Only complete a half development, not a full development
  • Use lighter lines for the the bends/folds and heavier lines for the outline
  • Label all points
ii.    `delta_S` `=F_S/A_S`
  `F_S` `=delta_S xx A_S`

 
`A_S = pid xx t=pi xx 20 xx 0.5 = 31.4\ text{mm}^2`

`:.F_S` `= 110 xx 31.4`  
  `=3455.7\ text{N}`  
  `=3.46\ text{kN}`  

♦ Mean mark (ii) 42%.

ENGINEERING, AE 2022 HSC 27b

The top and front views of a transition piece in an aircraft air conditioning duct are shown.

Complete a half-pattern development of the transition piece, starting from the line `a`-1 given below.   (6 marks)
 

     

Show Answers Only

 

Notes on this drawing:

→ Ensure you find the true length of lines

→ Ensure fold lines are lighter than the outline

→ Since the half development cuts through a side, ensure you use a break line

→ Do not dimension

→ Only complete a half development and not a full development

Show Worked Solution

 

Notes on this drawing:

→ Ensure you find the true length of lines

→ Ensure fold lines are lighter than the outline

→ Since the half development cuts through a side, ensure you use a break line

→ Do not dimension

→ Only complete a half development and not a full development


♦ Mean mark 40%.

ENGINEERING, CS 2017 HSC 27b

An engineering team has been contracted to design a multi-function lifting device for a coastal container wharf.

The table shows some of the engineering design elements for this lifting device.
 

Explain how the lifting device can be tested and evaluated to determine if the criteria for the listed engineering elements are met.   (6 marks)

Show Answers Only

Show Worked Solution


♦ Mean mark 46%.

ENGINEERING, CS 2017 HSC 25a

A pin-jointed truss designed to support a roadside sign is shown.
 

  1. Determine the magnitude and direction of the reactions at `A` and `B`.   (4 marks)
  1. Determine the magnitude and nature of the force in member `C`.   (2 marks)
  1. Explain why concrete would be a suitable material to support the roadside sign around point `D`.   (2 marks)
Show Answers Only

i.   `R_B=37\ text{N} larr`

`R_A=44.7\ text{kN}, \ theta=26.6^(@)`
 

ii.   `F_C=17\ text{kN (compression)}`
 

iii.   Suitability of concrete

→ Easily poured and formed around the sign.

→ Relatively quick to cure.

→ Weather resistant.

→ Hardens and sets with high strength and hardness.

Show Worked Solution

\[\textbf{i}. \ \ \ce{->[\ce{+}]} \sum M_A = 0 \]

`3xx1.5-20 xx3+R_(B)xx1.5=0`

`4.5-60+1.5R_(B)=0`

`1.5R_(B)` `=55.5`  
`R_(B)` `=(55.5)/(1.5)`  
  `=37\ text{N} larr`  

 

Mean mark 56%.

`uarr sumF_(V)=0`

`R_(AV)=20\ text{kN} +uarr`
  

\[\ce{->[\ce{+}]} \sum F_H = 0 \]

`R_(AH)=37+3=40\ text{kN} rarr^(+)`

`R_A` `=sqrt(20^(2)+40^(2))`  
  `=sqrt2000`  
  `=44.7\ text{kN}`  

 

`tan\  theta` `=(R_(AV))/(R_(AH))`  
  `=20/40`  
  `=0.5`  
`:.theta` `=26.6^(@)`  

 

\[\textbf{ii}. \]

`text{Taking moments about X:}`

\({+ \circlearrowleft} \Sigma M_X = 0\)

`0` `=-1.5 xxF_(C)+1.5 xx20-1.5 xx3`  
`0` `=-F_(C)+20-3`  
`F_(C)` `=17\ text{kN (compression)}`  

 


♦♦ Mean mark (ii) 38%.

iii.   Suitability of concrete

→ Easily poured and formed around the sign.

→ Relatively quick to cure.

→ Weather resistant.

→ Hardens and sets with high strength and hardness.


♦ Mean mark (iii) 52%.

ENGINEERING, PPT 2017 HSC 24b

A child and sled with a combined mass of 23 kg are being pulled along a horizontal snow-covered surface using a rope.
 

The coefficient of static friction between the sled and the snow is 0.14.

  1. Draw a free-body diagram that indicates the forces acting on the sled. Label the diagram.   (2 marks)
  1. Calculate the tension in the rope immediately before the point at which the sled and child begin to move.   (3 marks)
Show Answers Only

i.
       

 

ii.   `text{32 N}`

Show Worked Solution
i.
       

Mean mark (i) 57%.

ii.   `text{Weight}\ = mg = 23 xx 10 = 230\ text{N}`     

`text{Solving for}\ T:`

`tan^(-1)(0.14) = 8°`

`text{Using the sine rule:}`

`T/(sin8°)` `=230/(sin92°)`  
`T` `=(230 xx sin8°)/(sin92°)`  
  `=32.0\ text{N}`  

  
`:.\ text{Tension in the rope = 32 N}`


♦ Mean mark (ii) 40%.

ENGINEERING, PPT 2017 HSC 24a

Sleds are used to slide loads over soft surfaces such as grass, sand and snow. They can be made using polypropylene.

  1. Explain how the properties of polypropylene make it a suitable material for this application.   (3 marks)
  1. Describe a suitable manufacturing method to make a sled from polypropylene.   (3 marks)
Show Answers Only

i.   Polypropylene properties

→ Low coefficient of friction, lightweight and durable with excellent flexural strength.

→ In the manufacturing process, polypropylene is a good material for injection moulding which makes it easy to produce.
 

ii.  Manufacturing method:

→ Polymer pellets are introduced into an injection moulding machine.

→ A heating unit surrounding the exterior of the machine and internal friction heat the pellets.

→ They are forced into a steel mould under pressure.

→ After solidifying, the mould halves are separated and removed using injector pins.

→ Cooling, removal of surplus flash and polishing complete the process.

Show Worked Solution

i.   Polypropylene properties

→ Low coefficient of friction, lightweight and durable with excellent flexural strength.

→ In the manufacturing process, polypropylene is a good material for injection moulding which makes it easy to produce.
 

ii.  Manufacturing method:

→ Polymer pellets are introduced into an injection moulding machine.

→ A heating unit surrounding the exterior of the machine and internal friction heat the pellets.

→ They are forced into a steel mould under pressure.

→ After solidifying, the mould halves are separated and removed using injector pins.

→ Cooling, removal of surplus flash and polishing complete the process.


♦ Mean mark (ii) 53%.

ENGINEERING, PPT 2017 HSC 21c

The diagram shows a gear train.
 

The mechanical advantage of the gear train is 1.6 : 1 with an efficiency of 80%.

Calculate the number of teeth on the driven gear.   (3 marks)

Show Answers Only

`18\ text{teeth}`

Show Worked Solution
`n` `=(MA)/(VR)`  
`VR` `=(MA)/n`  
  `=1.6/0.8`  
  `=2`  

 

`VR` `=text{Driven}/text{Driver}`  
`:.\ text{Driven}` `=VR xx text{Driver}`  
  `=18\ text{teeth}`  

♦ Mean mark 48%.

ENGINEERING, PPT 2019 HSC 24b

Normalised high-tensile steel has been chosen for the manufacture of a wing support beam.

  1. Draw and label the microstructures of a normalised high-tensile steel and an annealed high-tensile steel.   (2 marks)
     

  1. Explain how the microstructure produced by normalising high-tensile steel improves the steel's suitability for this application.   (2 marks)
Show Answers Only

i.    Microstructures

 

ii.    → The strength of the steel is markedly increased.

→ Normalising produces finer and more uniform grains.

Show Worked Solution

i.    Microstructures


♦♦♦ Mean mark (i) 26%.

ii.    → The strength of the steel is markedly increased.

→ Normalising produces finer and more uniform grains.


♦ Mean mark (ii) 41%.

BIOLOGY, M8 2019 HSC 33b

Alzheimer's disease causes destruction of brain tissue, dementia and eventually death.

The gene with the greatest known effect on the risk of developing late-onset Alzheimer's disease is called APOE. It is found on chromosome 19.

The APOE gene has multiple alleles, including e2, e3 and e4 .

  1.  What are multiple alleles?   (2 marks)

  2. The table shows the risk of developing Alzheimer's disease for various APOE genotypes compared to average risk in the population.
     

   

  1. Analyse the data to assess the risk of developing Alzheimer's disease associated with the e2, e3 and e4 alleles.   (4 marks)

Show Answers Only

i.     → Alleles are the different variations of the same gene.

→ While most genes only have two alleles, dominant and recessive, some genes have 3 or more versions of itself. This phenomena is referred to as the gene having “multiple alleles”.
  

ii.  Analysis of data 

→ The table indicates that the alleles follow a hierarchy and have influence over the risk of Alzheimer’s, with certain combinations masking effects of others or amplifying them.

→ The e2 allele in both a homozygous genotype and coupled with e3 reduces the risk of Alzheimer’s by 40%. This suggests that the e2 allele is the one which reduces the risk of Alzheimer’s and can mask the effect of e3.

→ However, when coupled with e4, the risk of developing Alzheimer’s is 2.6 times more likely. This suggests that e4 is the more dominant allele.

→ The e4/e3 genotype also makes Alzheimer’s 3.2 times more likely in those individuals, and the e4/e4 genotypes makes it 14.9 times more likely. We can then make the conclusion that the e4 allele makes Alzheimer’s much more common in any genotype where it is present.

→ The e3 allele seems to be completely neutral and almost completely masked by both e2 and e4. In its homozygous genotype, it has no effect on the risk of developing Alzheimer’s, and when heterozygous with either e2 or e4, has little to no effect on the risk in comparison the e2 and e4’s homozygous genotypes.

→ It would then be accurate to conclude that the allele hierarchy is e3<e2<e4, with e3 being neutral and having no known effect, e2 reducing the risk of Alzheimer’s and e4 greatly increasing the risk of developing Alzheimer’s.

Show Worked Solution

i.     → Alleles are the different variations of the same gene.

→ While most genes only have two alleles, dominant and recessive, some genes have 3 or more versions of itself. This phenomena is referred to as the gene having “multiple alleles”.
 


♦♦♦ Mean mark (i) 24%.

ii.  Analysis of data 

→ The table indicates that the alleles follow a hierarchy and have influence over the risk of Alzheimer’s, with certain combinations masking effects of others or amplifying them.

→ The e2 allele in both a homozygous genotype and coupled with e3 reduces the risk of Alzheimer’s by 40%. This suggests that the e2 allele is the one which reduces the risk of Alzheimer’s and can mask the effect of e3.

→ However, when coupled with e4, the risk of developing Alzheimer’s is 2.6 times more likely. This suggests that e4 is the more dominant allele.

→ The e4/e3 genotype also makes Alzheimer’s 3.2 times more likely in those individuals, and the e4/e4 genotypes makes it 14.9 times more likely. We can then make the conclusion that the e4 allele makes Alzheimer’s much more common in any genotype where it is present.

→ The e3 allele seems to be completely neutral and almost completely masked by both e2 and e4. In its homozygous genotype, it has no effect on the risk of developing Alzheimer’s, and when heterozygous with either e2 or e4, has little to no effect on the risk in comparison the e2 and e4’s homozygous genotypes.

→ It would then be accurate to conclude that the allele hierarchy is e3<e2<e4, with e3 being neutral and having no known effect, e2 reducing the risk of Alzheimer’s and e4 greatly increasing the risk of developing Alzheimer’s.


♦♦ Mean mark (ii) 40%.

BIOLOGY, M5 2019 HSC 33a

Alzheimer's disease causes destruction of brain tissue, dementia and eventually death.

The diagram shows the effect of Alzheimer's disease on the brain.

Amyloid beta protein is produced in the human brain throughout life. In people with Alzheimer's disease, it accumulates in excessive amounts.

Outline the main steps that brain cells use to make proteins such as amyloid beta.   (3 marks)

Show Answers Only
  1. A complementary mRNA strand is transcribed from a section of DNA by RNA polymerase in the nucleus.
  2. mRNA moves to the cytoplasm where it binds to ribosomes.
  3. Each 3 nucleic bases (a codon) has a corresponding anticodon of tRNA with an amino acid attached.
  4. The amino acids are ‘stitched’ together in a chain by the ribosomes, forming a polypeptide chain.
  5. The single polypeptide chain or multiple polypeptide chains are folded to form a protein.
Show Worked Solution

     Steps that brain cells use to make proteins such as amyloid beta

  1. A complementary mRNA strand is transcribed from a section of DNA by RNA polymerase in the nucleus.
  2. mRNA moves to the cytoplasm where it binds to ribosomes.
  3. Each 3 nucleic bases (a codon) has a corresponding anticodon of tRNA with an amino acid attached.
  4. The amino acids are ‘stitched’ together in a chain by the ribosomes, forming a polypeptide chain.
  5. The single polypeptide chain or multiple polypeptide chains are folded to form a protein.

♦ Mean mark 41%.

ENGINEERING, TE 2019 HSC 26b

A simple circuit diagram of the AM radio receiver is shown.
 

  1. Complete the table giving the function of each of the circuit components listed.   (5 marks)
     

  1. Complete the table by drawing the waveform at positions B and C.   (2 marks)
     

  1. This AM radio receiver produced a demodulated electrical signal with a small current. The speakers in the earphones converted this signal into sound.
  2. Explain why the speakers in the earphones required a high impedance (resistance) in order to produce sound of sufficient volume to be heard.   (2 marks)
Show Answers Only

“

Show Worked Solution

i.  


♦ Mean mark (i) 47%.

ii.  


♦♦♦ Mean mark (ii) 22%.

iii.   → An external power source is not used to power this radio.

→ The signal picked up by the aerial powers the speakers.

→ If the impedance (resistance) is high an audible signal can be generated by the speaker at a low current.

→ Because the earphone impedance is high, the sensitivity of the coil improves, resulting in a more accurately tuned signal.

→ The sound would be inaudible if the impedance is low, as the power to the earpiece would also be low.


♦♦♦ Mean mark (iii) 15%.

BIOLOGY, M5 2020 HSC 32b

The rabies virus is a single-stranded RNA virus. It contains and codes for only five proteins. The diagrams show the structure and reproduction of the virus.
 

 

  1. Use the information provided in Diagram 1 to explain why the rabies virus cannot be classified as a cellular pathogen.   (3 marks)

  2. After infection the virus reproduces in muscle cells near the bite site and in the central nervous system. This requires the single-stranded rabies RNA to be transcribed, translated and replicated in the cytoplasm of host cells. These processes are shown in Diagram 2.
  3. Use the information provided in Diagrams 1 and 2 to explain the role of viral RNA polymerase in the reproduction of the virus.   (5 marks)

Show Answers Only

i.   Rabies virus cannot be a singular pathogen:

→ This pathogen contains only a single strand of RNA which only codes for five proteins.

→ Cellular pathogens such as bacteria contain a much larger genome in the form of DNA that allows the pathogen to perform complex processes without relying on a host.
 

ii.   The Role of Viral RNA 

→ The viral RNA polymerase (which is made from L and P proteins) is responsible for the production of the viral proteins and RNA, components of the rabies viruses.

→ RNA polymerase is responsible for transcription of viral RNA into mRNA, which is then used by the host’s ribosomes to produce respective viral proteins.

→ RNA polymerase is also responsible for the replication of the viral RNA. In this process, a complementary RNA strand is produced from the original RNA strand. This strand is then used as a template for RNA polymerase to rapidly produce more RNA, complementary to the template. The new RNA will therefore be identical to the original.

→ In this way, RNA polymerase is essential in producing viral proteins and new RNA strands which form new rabies virus particles.

Show Worked Solution

i.   Rabies virus cannot be a singular pathogen:

→ This pathogen contains only a single strand of RNA which only codes for five proteins.

→ Cellular pathogens such as bacteria contain a much larger genome in the form of DNA that allows the pathogen to perform complex processes without relying on a host.


♦♦ Mean mark (i) 33%.

ii.   The Role of Viral RNA 

→ The viral RNA polymerase (which is made from L and P proteins) is responsible for the production of the viral proteins and RNA which are components of the rabies viruses.

→ RNA polymerase is responsible for transcription of viral RNA into mRNA, which is then used by the host’s ribosomes to produce viral proteins.

→ RNA polymerase is also responsible for the replication of the viral RNA. In this process, a complementary RNA strand is produced from the original RNA strand. This strand is then used as a template for RNA polymerase to rapidly produce more RNA, complementary to the template. The new RNA will therefore be identical to the original.

→ In this way, RNA polymerase is essential in producing viral proteins and new RNA strands which form new rabies virus particles.


♦♦♦ Mean mark (ii) 29%.

BIOLOGY, M7 2020 HSC 32a

Rabies is a disease that can affect all mammals and is caused by the rabies virus. It is transmitted by the bite of an infected animal. Without treatment it almost always results in death.
 


Use the information provided to identify TWO features of the rabies infection that facilitate transmission of the pathogen to a new host.   (2 marks) 

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Successful answers should include two of the following:

→ The rabies virus can travel through the nervous system which allows it to reach the salivary glands.

→ The virus can then be directly transmitted to another host with a bite from the infected host.

→ The virus can replicate in muscle after an infected bite.

Show Worked Solution

Successful answers should include two of the following:

→ The rabies virus can travel through the nervous system which allows it to reach the salivary glands.

→ The virus can then be directly transmitted to another host with a bite from the infected host.

→ The virus can replicate in muscle after an infected bite.


Mean mark 51%.