SACE Biology: DNA and proteins, cells, homeostasis and evolution

What the four topics ask of you

The outline names its own skills too: biologists use pathway and flow diagrams in Topic 3, and mathematical models of gene pools in Topic 4. Our Cell Biology course and Human Physiology course cover the basics of Topics 2 and 3.

The 70/30 split and the exam

The SACE Board sets the school assessment at 70%: an Investigations Folio worth 30% (one or two practical investigations and one investigation with a science as a human endeavour focus) and Skills and Applications Tasks worth 40% (three or four tasks). The external examination is Assessment Type 3, 30%, and lasts 130 minutes.

The outline says that questions may be of different types, may need an understanding of science as a human endeavour, and may ask you to apply understanding from more than one topic. All the assessment design criteria can be assessed in the exam, so expect data interpretation and experimental design questions alongside recall.

Worked examples

Why cells stay small

A cube-shaped cell with sides of 2 μm has a surface area of 6 × 2² = 24 μm² and a volume of 2³ = 8 μm³, so the surface area to volume ratio is 3. A cube with sides of 4 μm has a surface area of 96 μm² and a volume of 64 μm³, so the ratio is 1.5. Doubling the side halves the ratio, which means the cell has less membrane for every unit of cytoplasm to supply, and this is why large cells struggle to exchange materials fast enough.

Check a similar calculation in the Cell Biology course, then press Mark:

Template to mRNA to protein

A template DNA strand reads 3′ TAC GGT CAT 5′. Transcription gives mRNA 5′ AUG CCA GUA 3′ (A pairs with U in RNA, and the strands run in opposite directions). The three codons then code for methionine, proline and valine in that order. Marks come from the base pairing rule, the direction, and naming which molecule you are describing at each step.

Negative feedback

If blood glucose rises after a meal, receptors detect the change, the pancreas releases insulin, cells take up glucose and the level falls. When the level returns to the set point, insulin release drops. Use the stimulus-response words the outline uses: stimulus, receptor, control centre, effector, response.

Grades, SATAC and your ATAR

The final result is reported from A+ to E−. SATAC turns the school and exam results into a raw score out of 15, with the school part contributing up to 10.5 and the exam part up to 4.5, then scales it before building the university aggregate from 90 credits of Stage 2 study. Biology is a 20-credit subject, so it can be one of the three subjects that count in the first 60 credits.

Dates

Use the daily paper as a trial

Your school sets trial exams in South Australia, and the Board publishes past papers on the subject page. The free daily paper on the Year 12 Biology track is a short timed trial of 8 questions worth 25 to 35 marks, marked as you go. It is not a full 130-minute exam.

• It fits well: gene expression, mutation, evolution and speciation, homeostasis, hormones and nervous control are in its rotation and in the outline.
• It does not fit: muscle contraction, the kidney in detail, gene technology steps and Hardy-Weinberg are not named in Stage 2, and the paper cannot test the human endeavour and investigation parts of the exam.
• The Year 11 Biology paper revises cell structure and transport before Topic 2.

Exam answers

Answers and a worked mark scheme come with each daily paper once it has been marked. They are Uni-Sine's own, not official SACE Board answers.

Mistakes in SACE Biology

• Mixing up the template strand and the coding strand when writing mRNA.
• Describing negative feedback as the body "turning off" a response without naming the receptor and effector.
• Using "evolve" for a single organism.
• Giving a ratio without units or a comparison, when the question says "explain".

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