Is this the official SCSA Human Bio reference?

No. SCSA does not provide a Human Biology formula sheet; Human Bio is a knowledge subject, not a calculation subject. This is an Educatta-prepared revision summary, intended as a study companion, not for use in the exam itself.

How should I use this cheat sheet?

Print it, pin it above your desk, and revisit weekly through Term 3. By exam day, you should be able to reproduce every section from memory, then check against this sheet for gaps.

Does this cover Year 11 content?

This sheet focuses on Year 12 (Units 3 & 4); homeostasis, immunity, disease, DNA, evolution, biotechnology. For Year 11 reproduction and inheritance content, see our Year 11 Human Biology reference card.

WACE Human Biology Cheat Sheet (Year 12)

Homeostasis; the framework

Definition: Maintenance of stable internal conditions within narrow limits despite external change.
Components: Receptor (detects stimulus) → Control centre (compares to set point; usually hypothalamus) → Effector (restores set point).
Negative feedback: Response opposes the change. The default mechanism.
Positive feedback: Response amplifies the change. Examples: childbirth (oxytocin), blood clotting.

Three feedback loops you must know

System	Receptor	Control	Effector → Effect
Thermoregulation	Skin & hypothalamus thermoreceptors	Hypothalamus (~37 °C set point)	Sweat glands, blood vessels, muscle (shiver) → restore temp
Blood glucose	Pancreatic α/β cells	Pancreas + liver	Insulin (β) lowers BG; glucagon (α) raises BG
Osmoregulation	Hypothalamic osmoreceptors	Posterior pituitary (ADH)	Kidney tubules → ↑ water reabsorption

Mnemonic for thermoregulation: "Cool down = Sweat, Vasodilation, Slow metabolism. Warm up = Shiver, Vasoconstriction, Pilo-erection, ↑ thyroxin."

Immunity; the three lines of defence

1st line (non-specific): Skin, mucous, cilia, stomach acid, lysozyme in tears, normal flora.
2nd line (innate): Inflammation, fever, phagocytosis (macrophages, neutrophils), NK cells, complement, interferons.
3rd line (adaptive): B-cells (humoral) + T-cells (cell-mediated). Specific. Slower. Has memory.

	B-cells	T-cells
Mature in	Bone marrow	Thymus
Acts on	Free antigen	Infected/abnormal cells
Effectors	Plasma cells → antibodies	Helper (CD4), Cytotoxic (CD8)
Memory	Yes	Yes

Antibody actions: Neutralisation, agglutination, opsonisation, complement activation.
Active immunity: Body makes own antibodies. From infection (natural) or vaccination (artificial). Has memory.
Passive immunity: Antibodies received from elsewhere. From placenta/breastmilk (natural) or injection (artificial). No memory.

Disease; infectious vs non-infectious

Pathogen	Examples	Treatment
Bacteria	TB, Strep, Salmonella	Antibiotics
Virus	HIV, influenza, COVID-19	Antivirals (limited)
Fungi	Tinea, Candida	Antifungals
Protozoa	Malaria, Giardia	Antiprotozoals
Prion	CJD	None

Transmission: Droplet, fomite, food/water, vector (mosquito), sexual, vertical (mother→fetus).
Endemic / epidemic / pandemic: Constant in a population / sudden ↑ in a region / across multiple countries.
Non-infectious diseases: Cancer (mutation → uncontrolled cell division), cardiovascular (atherosclerosis → MI/stroke), Type 2 diabetes (insulin resistance), asthma, autoimmune.

DNA, gene expression & mutation

DNA structure: Double helix; sugar-phosphate backbone; bases A-T (2 H-bonds), G-C (3 H-bonds); antiparallel 5'→3' / 3'→5'.
Replication: Semi-conservative. Helicase unwinds → DNA polymerase adds free nucleotides → two identical daughter strands. Site: nucleus, S-phase.
Transcription: Nucleus. DNA → mRNA. RNA polymerase reads template (3'→5'). U replaces T. Introns spliced out.
Translation: Ribosome (cytoplasm or RER). mRNA codons read 3 at a time. tRNA brings amino acids. Peptide bonds form polypeptide. Start: AUG (Met). Stop: UAA, UAG, UGA.
Point mutations: Substitution (silent, missense, nonsense), insertion, deletion (frameshift).
Chromosomal mutations: Deletion, duplication, inversion, translocation. Aneuploidy: trisomy 21 (Down), XXY (Klinefelter), XO (Turner).
Germline vs somatic: Germline = heritable. Somatic = not passed on. Causes: mutagens (UV, radiation, chemicals), replication errors, viruses.

Natural selection & evidence for evolution

Natural selection: Variation exists → heritable via genes → selection pressure → differential survival & reproduction → allele frequency shifts. Types: directional, stabilising, disruptive.
Other mechanisms: Gene flow (migration), genetic drift (founder effect, bottleneck), mutation.
Speciation: Allopatric (geographic isolation) or sympatric (within range).
Fossils: Transitional forms; relative + radiometric dating.
Comparative anatomy: Homologous (common ancestor) vs analogous (convergent) vs vestigial structures.
Molecular evidence: DNA/protein similarity → molecular clocks; cytochrome c, mtDNA.
Biogeography: Species distribution reflects continental drift & isolation.

Hardy-Weinberg: p² + 2pq + q² = 1, where p + q = 1. Population in equilibrium when no selection, mutation, drift, gene flow, random mating.

Hominin evolution timeline

Species	Date	Key feature	Brain size
A. afarensis ("Lucy")	~4 mya	Bipedal, small canines	~400 cc
H. habilis	~2.5 mya	First stone tools (Oldowan)	~600 cc
H. erectus	~1.8 mya	Fire, hand axes, migration out of Africa	~900 cc
H. heidelbergensis	~700 kya	Common ancestor of Sapiens & Neanderthals	~1200 cc
H. neanderthalensis	~400 kya	Cold-adapted, burial rituals	~1500 cc
H. sapiens	~300 kya	Symbolic art, language, agriculture	~1350 cc

Trends: bipedalism · ↑ cranial capacity · ↓ prognathism · smaller teeth · longer juvenile period · increasing tool sophistication.

Biotechnology

PCR (polymerase chain reaction): Amplifies DNA. Cycle: denaturation (~95 °C, separates strands) → annealing (~55 °C, primers attach) → extension (72 °C, Taq polymerase adds nucleotides). Repeat 25-30x.
Gel electrophoresis: Separates DNA fragments by size. Negatively charged DNA moves toward + electrode. Smaller fragments travel further.
Restriction enzymes: Cut DNA at specific recognition sequences. Create sticky or blunt ends.
DNA profiling: STR (short tandem repeat) analysis. Used in forensics, paternity, ancestry.
Gene therapy: Replacing or supplementing a defective gene with a functional copy. Vector usually a virus.
Ethics: Privacy of genetic data; consent for testing; GMO concerns; designer traits; gene-editing equity.

Common mistakes that cost marks

Negative vs positive feedback

Negative feedback opposes the change (the default for homeostasis). Positive feedback amplifies it (childbirth, clotting). Calling thermoregulation "positive feedback" is the #1 error every year.

B-cells vs T-cells confusion

B-cells make antibodies; they're factory workers. T-cells attack infected cells directly; they're soldiers. Mixing the two in long-response questions costs marks instantly.

Forgetting "semi-conservative"

DNA replication produces two daughter strands, each with one original strand and one new strand. Saying "two new strands" or "two original strands" is wrong, every time.

Genotype vs phenotype ratios

Monohybrid cross gives 1:2:1 genotype but 3:1 phenotype. Students quote one when the question asks the other. Read the prompt twice.

Missing specific examples

"Natural selection happens when..." gets fewer marks than "Natural selection: peppered moths went from light-coloured (camouflage on lichen) to dark-coloured during the Industrial Revolution as soot darkened tree bark." Examples convert.

Innate vs adaptive immunity

Innate = fast, non-specific, no memory (skin, phagocytes, fever). Adaptive = slow, specific, has memory (B-cells, T-cells). Vaccination triggers adaptive only.

Mutation isn't always bad

Many mutations are silent (no protein change). Some are beneficial (e.g. lactase persistence, sickle-cell heterozygote advantage in malaria zones). Saying "mutations are harmful" loses marks in evolution questions.

Hominin dates

Sapiens ~300 kya, not "millions of years ago". Australopithecines ~4 mya. Mixing these is common; make a timeline and revise it weekly.

Print and pin this

Print this page double-sided. Pin it above your desk. Cover it and try to write each section from memory weekly through Term 3. Where you stumble is your study map for that week.

WACE Human Biology Cheat Sheet