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AEHBY Semester 2 Exam Cheatsheet

01/09/2026

Human Biology Semester 2 COMPLETE STUDY GUIDE (Units 1&2 – A-Grade Sheet)

Everything that appears in every paper (2022–2024). Red = traps.

Exam Structure (same every year)

  • Section 1: 30 MC, 30 marks, 40 min.
  • Section 2: Short answer, 7 Q, 50%, 90 min.
  • Section 3: Extended answer, Unit 1 & Unit 2 choice questions, 20% each.
  • Total 100%, 3 hours.

1. Science Skills (guaranteed Q1 area)

  • Control group: acts as a comparison, so the effect of the treatment on the experimental group can be seen.
  • Controlled variable: something kept the same for all groups so it does not affect the results.
  • Hypothesis: a clear statement linking the independent and dependent variable (e.g. “The combination of radiation and chemotherapy will reduce the size of tumours”).
  • Identify IV vs DV – IV is what you change, DV is what you measure.

2. Mitosis & Meiosis (HIGHEST priority)

Mitosis (identical cells; growth & repair):

  • Prophase: nucleolus disappears, nuclear membrane breaks down, centrioles migrate to poles, chromatin condenses into chromosomes, spindle forms from microtubules.
  • Metaphase: chromosomes line up at the equator.
  • Anaphase: centromeres divide, chromatids/chromosomes move to opposite poles.
  • Telophase: nuclear membranes and nucleoli reform, chromosomes uncoil, spindle disappears, cytokinesis.

Meiosis (variation; gametes):

  • Crossing over (prophase I)

  • Non-disjunction (anaphase I or II)

  • Independent assortment

  • crossing over = exchange of genetic material between homologous chromatids.

  • non-disjunction = two chromosomes (or chromatids) fail to segregate during anaphase I (or II).

  • Genetic uniqueness from: random assortment, crossing over, random fertilisation (NOT non-disjunction – it causes disorders).

  • Oogenesis: oogenesis stops at prophase II after ovulation; meiosis I completed at ovulation.

3. Genetics: Punnett Squares + Pedigrees

  • Autosomal recessive (e.g. CF, Crohn’s): two unaffected parents heterozygous (Nn×Nn) → 25% affected, 50% carriers, 25% unaffected. Probability a child inherits condition = 25%.
  • X-linked recessive (colour blindness, haemophilia): males more affected; affected sons get allele from carrier mother.
  • Why autosomal not X-linked (pedigree evidence): an affected daughter has an unaffected father; if it were X-linked recessive, the father would be affected/cannot be a carrier.
  • Third child probability: independent events – each child has same probability (e.g. 25% affected, so 75% unaffected).

4. Cell Transport + Osmosis

  • Osmosis: net movement of water from a region of higher water concentration to lower water concentration across a semi-permeable membrane, down the concentration gradient.
  • Direction: water moves into the cell if the extracellular fluid has a higher water concentration (lower solute concentration).
  • Active transport vs diffusion: diffusion passive down gradient; active transport needs ATP, against gradient.

5. Digestive System

  • Small vs large intestine (contrast): small intestine contains villi, large does not; small is longer; small has smaller diameter.
  • Diarrhoea from large-intestine inflammation: one role of the large intestine is to absorb water; if it cannot, water is not absorbed, giving watery faeces = diarrhoea.
  • Elimination vs excretion: elimination removes undigested material from the body; excretion is the removal of metabolic wastes.
  • Enzymes: amylase (starch→disaccharides), pepsin/trypsin (protein→amino acids), lipase + bile (fat→fatty acids + glycerol). Optimal pH (pepsin pH 2, others ~pH 7-8).

6. Respiration + ATP

  • Anaerobic: glucose is broken down through glycolysis, producing two pyruvate molecules, and enough energy for a net yield of two ATP; no oxygen required; occurs in the cytosol.
  • Aerobic: needs oxygen, produces far more ATP, occurs in mitochondria.
  • ATP: ADP + a third phosphate bonded forms ATP; this is a high-energy bond; energy is released when broken.
  • Alveoli adaptations: thin one-cell-thick walls, large surface area, moist surfaces, surrounded by blood capillaries.
  • Breathing in: air flows from high pressure to low pressure; diaphragm contracts/ribs move out.

7. Nephron / Kidney

  • Filtration: glomerulus under high pressure (different diameters of afferent/efferent arterioles) forces small molecules (water, glucose, urea, ions) through the thin one-cell-thick glomerular wall into Bowman’s capsule.
  • Reabsorption: components of filtrate are returned to the blood capillaries (selective).
  • Secretion: materials are added to the filtrate from the blood.
  • Label: proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct.

8. Reproduction + Hormones + Foetal Development

  • Ovulation = release of the egg/secondary oocyte from the ovary; triggered by luteinising hormone (LH).
  • Menstrual cycle: oestrogen thickens the endometrium; progesterone maintains it; LH surge causes ovulation; hCG maintains the corpus luteum in early pregnancy.
  • Development of milk-secreting glands: prolactin/oestrogen+progesterone.
  • Pre-labour uterine contractions = oxytocin.
  • First trimester = most vulnerable to teratogens (organ formation).
  • Foetal circulation – ductus venosus allows blood to bypass the liver.
  • Spina bifida prevented by folic acid.
  • Listeria from unpasteurised/improperly prepared food.

9. Sperm + Gametes

  • Sperm head: acrosome contains digestive enzymes released to penetrate the corona radiata; contains the DNA.
  • Midpiece: many mitochondria (produce ATP for tail movement).
  • Tail/flagellum: movement.

10. Blood + Blood Groups + Transfusion

  • Components: erythrocytes (carry O₂ via haemoglobin), leucocytes (defence against microorganisms), platelets (clotting), plasma.
  • Platelet clotting: platelets stick to the rough surface of damaged blood vessels, then form threads of insoluble protein called fibrin.
  • Haemoglobin combines with O₂ (oxyhaemoglobin) and CO₂ (carbaminohaemoglobin).
  • ABO system: O = no antigens, universal donor; AB = no antibodies, universal recipient. Blood group B plasma has anti-A antibody.
  • Rh factor = an antigen on red blood cells; Rh+ has it, Rh− doesn’t.
  • Agglutination: antibodies bind to incompatible antigens on donor red blood cells.

11. Muscles + Joints + Bones

  • Muscle types: skeletal = striated, voluntary; cardiac = striated, involuntary, has intercalated discs; smooth = non-striated.
  • Agonist/antagonist/synergist: agonist = prime mover, antagonist = opposes it, synergist = assists.
  • Flexion (decrease angle) vs extension (increase angle); adduction (toward midline) vs abduction (away).
  • Tendon connects muscle to bone; ligament connects bone to bone; articular cartilage at joint surfaces.
  • Types of joints: synovial (hinge, condyloid, gliding, ball-and-socket), cartilaginous, fibrous.
  • Osteoporosis: imbalance between osteoclasts (break down bone) and osteoblasts (build bone) – more breakdown than build.
  • Sarcomere: smallest functional unit of a muscle; contains actin (thin) and myosin (thick) filaments.

12. DNA / Protein Synthesis

  • DNA base pairing: Adenine-T, and Cytosine-G (in RNA, U instead of T). Weak hydrogen bonds between bases allow easy separation for replication.
  • DNA replication importance: DNA must be duplicated so daughter cells have the same number of chromosomes/amount of DNA after cell division.
  • Transcription: DNA → mRNA in nucleus.
  • Translation: mRNA codons bind to tRNA anticodons at the ribosome; each tRNA carries a specific amino acid; amino acids join to form a polypeptide.
  • Non-disjunction/cytogenetics: disorders from abnormal chromosome numbers.

13. Stem Cells + Nanotech + Other

  • Stem cell potency order: totipotent (zygote) > pluripotent (blastocyst) > multipotent (adult/bone marrow).
  • Bone marrow producing red blood cells is an example of multipotent stem cells.
  • STIs: chlamydia = bacterial (often silent, causes infertility); genital herpes = viral; gonorrhoea = bacterial; syphilis = bacterial. Tubal ligation = surgical, not reversible, no STI protection.
  • Contraception barrier (STI protection): condoms.
  • Spina bifida → folic acid; teratogen vulnerability → first trimester.

Extended-Answer Scenarios (Unit 1 / Unit 2 choice)

Typical Unit 1 Q: scientific investigation (lung cancer trial analysed above) → control group, controlled variables, hypothesis, graph interpretation, conclusion, and a stoichio-free biology analysis.

Typical Unit 2 Qs: cell membrane transport (osmosis/active), genetics (Punnett + pedigree), nephron/kidney, hormones/foetal development, muscles/joints.

For every extended answer: use the scientific method structure (hypothesis → method → results → conclusion), define terms the question asks to define, and link variables to the data.

Final Checklist

  • Say “down its concentration gradient”; name the specific process.
  • Mitosis phases in order from prophase (know all 4).
  • Autism/CF/Crohn’s = autosomal recessive; colour blindness/haemophilia = X-linked recessive.
  • Punnett square shows genotype ratio; state probability as %.
  • “Control group = comparison; controlled variable = kept the same.”
  • Elimination vs excretion (undigested vs metabolic waste).
  • Agonist vs antagonist; tendon vs ligament.