Fundamentals
The core facts every aspirant should own — each a titled nugget with a real-world story, the concept in plain words, and a memory trick. Works even when the internet doesn't.
300 fundamentals
“Unfolded, your intestinal lining could cover a tennis court.”
Most nutrients are absorbed through villi, which hugely increase surface area.
Memory trick: Villi = surface for absorption.
“Bile is dish-soap for fat, breaking it up so enzymes can attack.”
Bile (from the liver) emulsifies fats into droplets; it contains no enzymes.
Memory trick: Emulsifier, not enzyme.
“Your lungs hold ~300 million alveoli — a huge surface for trading gases.”
O₂ and CO₂ swap by diffusion across thin, moist alveolar walls.
Memory trick: Diffusion across thin walls.
“Haemoglobin is a molecular bus, seating four oxygen passengers at a time.”
Most oxygen is carried by haemoglobin in red blood cells.
Memory trick: Hb carries O₂.
“Two loops keep clean and dirty blood from mixing, unlike a fish's single loop.”
Blood passes through the heart twice per circuit — to the lungs and to the body.
Memory trick: Pulmonary + systemic loops.
“A tireless double-pump beating ~100,000 times a day.”
Two atria receive blood; two ventricles pump it — left side oxygenated, right deoxygenated.
Memory trick: Left = oxygenated.
“The pulmonary artery is the odd one out — an artery carrying deoxygenated blood.”
Arteries carry blood away from the heart at high pressure; veins return it with valves.
Memory trick: Arteries: away; veins: toward.
“About a million nephrons per kidney clean your entire blood volume many times a day.”
The kidney's filtering unit — ultrafiltration then selective reabsorption.
Memory trick: Filter, then reabsorb the good stuff.
“The liver converts poisonous ammonia into safer urea for disposal.”
Humans excrete nitrogen mainly as urea, which is less toxic than ammonia.
Memory trick: Urea = our nitrogen waste.
“Your brain wires ~86 billion of these into the most complex network known.”
The nerve cell that carries impulses via dendrites (in), an axon (out) and synapses.
Memory trick: Dendrites in, axon out.
“Thoughts are sparks that leap gaps using chemical messengers.”
Electrical within a neuron; chemical (neurotransmitter) across a synapse.
Memory trick: Within = electric; across = chemical.
“You drop a hot pan before your brain even registers the pain.”
A fast, involuntary response routed through the spinal cord, bypassing the brain.
Memory trick: Spinal shortcut for speed.
“A drop of hormone can change your whole body's behaviour.”
Chemical messengers from ductless (endocrine) glands, carried by blood to target organs.
Memory trick: Endocrine = ductless, into blood.
“This pancreatic tug-of-war keeps your blood sugar in a safe band.”
Insulin lowers blood glucose (storage); glucagon raises it — they are antagonists.
Memory trick: Insulin puts glucose IN.
“A monk counting peas discovered the hidden rules of heredity.”
Dominance, segregation and independent assortment govern how traits pass on.
Memory trick: Alleles segregate cleanly.
“Two tall plants can hide different genetic recipes inside.”
Genotype is the genetic makeup (Tt); phenotype is the visible trait (tall).
Memory trick: Genes vs appearance.
“3 tall to 1 short — the ratio that cracked genetics open.”
A single-trait cross gives a 3:1 phenotype ratio (1:2:1 genotype) in F2.
Memory trick: 3:1 seen; 1:2:1 underneath.
“It's the father's chromosome contribution that tips the coin.”
XX is female, XY is male; the sperm decides the child's sex.
Memory trick: XY = male; sperm decides.
“Watson and Crick's twisted ladder is the most famous molecule in biology.”
A double helix with complementary base pairing: A–T and G–C.
Memory trick: A–T, G–C, always.
“DNA copies itself by unzipping and rebuilding each half — proven by Meselson and Stahl.”
Each new DNA molecule keeps one old strand and one new strand.
Memory trick: Half old, half new.
“Genes are recipes; proteins are the dishes finally served.”
Genetic information flows DNA → RNA → protein.
Memory trick: Transcribe then translate.
“The genetic code reads three letters at a time, like a molecular Morse.”
A triplet of mRNA bases that codes for one amino acid.
Memory trick: 3 bases → 1 amino acid.
“It's survival of the best-fitted, not merely the strongest.”
Individuals best adapted to their environment survive and reproduce more.
Memory trick: Best-adapted, not strongest.
“A human arm and a whale flipper share bones; a bird wing and insect wing don't.”
Homologous organs share ancestry but differ in function; analogous organs share function but not ancestry.
Memory trick: Homologous = same origin.