Before you write
- Identify the instruction, the scientific context and every part you must answer.
- Choose the relevant mechanism, relationship or equation.
- Make each link explicit. Then check units, direction, assumptions and whether you answered the whole question.
The NESA key-word glossary helps interpret instructions. Read the word in its subject and question context, rather than applying a fixed paragraph template.
Biology · Explain a mechanism
Meiosis and variation
Practice question (4 marks): Explain two ways meiosis can produce genetically different gametes.
Try your answer before opening the worked response.
Show the worked response and criteria
During prophase I, crossing over between non-sister chromatids of homologous chromosomes exchanges DNA segments. This can create new combinations of alleles on a chromosome. At metaphase I, each homologous pair can orient independently of the other pairs. Their separation during meiosis I can therefore place different combinations of maternal and paternal chromosomes into the cells that become gametes.
Where the reasoning earns credit
- Crossing over between non-sister chromatids of homologous chromosomes (1).
- Links that exchange to new allele combinations (1).
- Independent orientation and separation of homologous pairs (1).
- Links that process to different chromosome combinations in gametes (1).
Common gap: listing “crossing over and independent assortment” without explaining what each process changes.
Chemistry · Cause and effect
Temperature and equilibrium
Practice question (3 marks): In a closed system, A ⇌ B is at equilibrium and the forward reaction is endothermic. Explain the effect of a sustained temperature increase on the equilibrium amount of B.
Show the worked response and criteria
A temperature increase favours the endothermic direction, which absorbs energy. Here that is the forward reaction, so the equilibrium composition shifts towards B and its equilibrium amount increases. The forward and reverse reactions continue; at the new equilibrium their rates are equal.
- Identifies the endothermic direction as favoured by the temperature increase (1).
- Applies that direction to the stated forward reaction (1).
- Concludes that the equilibrium amount of B increases (1).
Common gap: saying the reaction “stops at equilibrium” or that a catalyst would produce the same change in equilibrium composition.
Physics · Calculate and state direction
Force in circular motion
Practice question (4 marks): A 1,000 kg vehicle travels at a constant speed of 20 m s−1 around a circular path of radius 50 m. Calculate the magnitude of the net force and state its direction.
Show the worked response and criteria
For uniform circular motion, Fnet = mv2/r.
Fnet = (1,000 × 202)/50 = 8,000 N.
The net force acts towards the centre of the circular path. Although speed is constant, the changing direction of velocity means the vehicle accelerates.
- Selects the correct net-force relationship (1).
- Substitutes the given mass, speed and radius correctly (1).
- Gives 8,000 N, including the force unit (1).
- States that the net force is towards the centre (1).
Common gap: using mv/r, omitting the force unit, or concluding that constant speed means zero net force.