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SACE Stage 2 Biology: complete 2026 guide to the four topics

A complete 2026 guide to SACE Stage 2 Biology: the four topics (DNA and Proteins, Cells, Homeostasis, Evolution), the three science strands, and how school assessment and the external examination combine into your final result.

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SACE Stage 2 Biology is the Year 12 biology course offered by the SACE Board of South Australia. It is organised around four topics and three interwoven strands, and your final result combines school assessment (70 percent) with a single external examination (30 percent).

This page is the index. Below you will find every dot-point answer we have for SACE Stage 2 Biology in 2026, organised by topic, alongside the structural notes you need to plan your study.

The four topics in 2026

Topic 1: DNA and Proteins
The molecular core of the course: DNA structure and semi-conservative replication, gene expression through transcription and translation, the genetic code, protein structure and function, enzymes and the factors affecting their activity, gene regulation (including the lac operon), mutations and mutagens, and DNA technologies such as PCR, gel electrophoresis and the production of genetically modified organisms.
Topic 2: Cells as the Basis of Life
Cell biology: the distinction between prokaryotic and eukaryotic cells, the structure and function of organelles, the fluid mosaic membrane and transport, the surface area to volume ratio and its effect on cell size, cellular respiration, photosynthesis, and the cell cycle and mitosis.
Topic 3: Homeostasis
How organisms maintain a stable internal environment: the principles of homeostasis and negative feedback, the nervous system and nerve impulses, the endocrine system and hormones, thermoregulation, blood glucose regulation, osmoregulation and the kidney, and homeostasis in plants including transpiration.
Topic 4: Evolution
How life changes over time: the evidence for evolution, natural selection and adaptation, genetic drift and gene flow, speciation and reproductive isolation, population genetics and allele frequencies (including Hardy-Weinberg), and antibiotic resistance as a real-time example of natural selection.

The three strands

Every topic is taught and assessed through three interwoven strands:

  • Science Inquiry Skills - designing and conducting investigations, processing and analysing data, evaluating procedures, and communicating findings.
  • Science as a Human Endeavour - understanding how scientific knowledge develops, and how science influences and is influenced by society, ethics and applications.
  • Science Understanding - the biological content of the four topics, which is what the dot-point pages below cover.

How SACE Stage 2 Biology is assessed in 2026

Your final subject result combines two parts:

School assessment (70 percent).

  • Investigations Folio (30 percent). The practical component, typically a student-designed practical investigation reported in a deconstructed format, plus a science-as-a-human-endeavour investigation evaluating a contemporary biological issue.
  • Skills and Applications Tasks (40 percent). In-class tasks (commonly tests and supervised tasks) that assess your ability to apply biological understanding and inquiry skills to questions and scenarios.

External examination (30 percent). A single examination set and marked by the SACE Board, covering all four topics and drawing on all three strands.

School assessment is moderated by the SACE Board to keep standards consistent between schools, so the grades you earn at school are checked against the same statewide standard.

Our 2026 SACE Stage 2 Biology dot-point answers

Every link below is a focused answer to one part of the Biology subject outline. Each page identifies the concept, gives a worked answer, and flags the common mistakes.

Topic 1: DNA and Proteins

Topic 2: Cells as the Basis of Life

Topic 3: Homeostasis

Topic 4: Evolution

How the topics connect

The four topics build on one another. Topic 1 (DNA and Proteins) sets up the molecular basis of genes, proteins and enzymes; Topic 2 (Cells) shows where those molecules act and how cells exchange materials and release energy; Topic 3 (Homeostasis) applies enzyme and protein function to whole-organism regulation through feedback; and Topic 4 (Evolution) explains how the genetic variation introduced in Topic 1 changes across populations over time. Mutations, enzymes and negative feedback recur throughout, so understanding the molecular foundations pays off across the whole course.

How to use this hub

If you are starting the year: work through Topic 1 first, since its molecular concepts underpin enzymes (Topic 2), homeostatic control (Topic 3) and the source of variation for evolution (Topic 4).

If you are preparing your Investigations Folio: focus on Science Inquiry Skills - designing a fair test, identifying variables, processing data, and evaluating reliability and validity. Choose a dot point relevant to your practical (enzymes, transpiration, photosynthesis and osmosis are common experimental systems) and read it alongside your method.

If you are revising for the external examination: review the Science Understanding content topic by topic using the dot-point pages above, then practise applying it to unseen data and ethical scenarios. Past SACE Board examination papers and the published exemplars are the best practice resource.

For the official subject outline, assessment requirements and past examination papers, refer to the SACE Board of South Australia at sace.sa.edu.au.

The SACE system, explained

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Common questions about Biology

How is SACE Stage 2 Biology structured in 2026?
SACE Stage 2 Biology is built around four topics (DNA and Proteins, Cells as the Basis of Life, Homeostasis, and Evolution) taught through three strands: Science Inquiry Skills, Science as a Human Endeavour, and Science Understanding. Your result comes 70 percent from school assessment and 30 percent from a single external examination.
How is SACE Stage 2 Biology assessed?
School assessment is worth 70 percent and has two components: an Investigations Folio worth 30 percent and Skills and Applications Tasks worth 40 percent. The remaining 30 percent comes from the external examination set and marked by the SACE Board. The school component is moderated to keep marking consistent across schools.
What are the four topics in SACE Stage 2 Biology?
Topic 1 (DNA and Proteins) covers molecular genetics, gene expression and biotechnology. Topic 2 (Cells as the Basis of Life) covers cell types, organelles, membranes, respiration, photosynthesis and the cell cycle. Topic 3 (Homeostasis) covers negative feedback and the nervous, endocrine, thermoregulatory, glucose, kidney and plant control systems. Topic 4 (Evolution) covers evidence, natural selection, drift, gene flow, speciation and population genetics.
What are the three science strands?
The three strands are interwoven through every topic. Science Inquiry Skills covers designing investigations, handling data and drawing conclusions. Science as a Human Endeavour covers how science develops and interacts with society. Science Understanding is the biological content itself. The Investigations Folio chiefly assesses inquiry skills; the exam assesses all three.
What is in the Investigations Folio?
The Investigations Folio (30 percent) is the practical component. It typically includes a practical investigation (a student-designed experiment with a deconstructed report) and a science-as-a-human-endeavour investigation in which students evaluate a contemporary biological issue. It assesses your investigation design, analysis, evaluation and communication.
How should I prepare for the SACE Biology external exam?
The external examination is worth 30 percent and covers all four topics. Revise the Science Understanding content topic by topic using these dot-point pages, practise applying it to unseen data and scenarios (Science Inquiry Skills), and prepare to discuss social and ethical contexts (Science as a Human Endeavour). Past SACE Board exams and exemplars are the best practice resource.
What's the difference between mitosis and meiosis?
Mitosis produces two identical diploid cells (for growth and repair). Meiosis produces four genetically distinct haploid cells (for sexual reproduction).
How does protein synthesis work?
Transcription (DNA → mRNA in the nucleus) then translation (mRNA → polypeptide at the ribosome). tRNA brings amino acids that the ribosome links into the protein sequence the mRNA codes for.
What's homeostasis?
The maintenance of a stable internal environment (temperature, blood glucose, pH) despite external change — usually via negative feedback loops involving receptors, control centres, and effectors.
How does evolution by natural selection work?
Variation exists in a population → some variants survive and reproduce better in a given environment → those traits become more common over generations. Requires heritable variation, differential reproductive success, and time.
What's the difference between an antibody and an antigen?
Antigen: a molecule (often on a pathogen) that triggers an immune response. Antibody: a Y-shaped protein the immune system makes to bind specifically to that antigen.