WACE ATAR Human Biology cheat sheet

Human Biology

• Homeostasis: negative feedback reverses a deviation from set point (sensor → control centre → effector); positive feedback amplifies it (e.g. oxytocin in labour, clotting cascade).

• Cell transport: diffusion and osmosis are passive (down gradients); facilitated diffusion uses channels/carriers without ATP; active transport (e.g. Na+/K+ pump) moves solutes against gradients using ATP.

• Osmolarity rule: water moves toward the compartment with higher solute concentration; red blood cells lyse in hypotonic and crenate in hypertonic solutions.

• Surface area to volume ratio decreases as organism size increases, so large organisms need specialised exchange surfaces and transport systems.

• Enzyme activity: rate rises with substrate concentration until Vmax; temperature above optimum and pH outside optimum denature enzyme tertiary structure, reducing rate irreversibly.

• Blood glucose: insulin (beta cells of islets of Langerhans) lowers glucose by promoting uptake and glycogenesis; glucagon (alpha cells) raises it via glycogenolysis and gluconeogenesis.

• Gas exchange: alveolar partial pressure gradients drive O2 in and CO2 out; haemoglobin saturation follows an S-shaped curve, shifting right with higher CO2, lower pH (Bohr effect) and higher temperature.

• Nephron decision rule: glucose and amino acids are reabsorbed by active transport in the proximal tubule; water follows osmotically in the loop of Henle; ADH increases collecting-duct water permeability.

• Thermoregulation: hypothalamus detects blood temperature; responses include vasodilation/sweating (cooling) and vasoconstriction/shivering/erector pili contraction (warming); fever resets the set point.