Ecology & Evolution is a core part of IB Biology. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Natural selectionDifferential reproduction by trait fitness
VariationGenetic differences in a population
FitnessReproductive success of a phenotype
Homologous structureSame origin, different function (limbs)
Analogous structureSame function, different origin (wings)
Convergent evolutionUnrelated species evolve similar traits
BinomialGenus + species (Homo sapiens)
TaxonGroup at any classification level
CladeGroup sharing a common ancestor
CladogramTree based on derived traits
DomainHighest taxon: Bacteria/Archaea/Eukarya
SpeciesGroup interbreeding to produce fertile offspring
Allele frequencyp (dominant) and q (recessive), p+q=1
Hardy-Weinbergp²+2pq+q²=1 under no evolution
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Are characteristics gained during life (like big muscles) inherited?✗ Yes, acquired characteristics are inherited. ✓ No — only genetic variation is passed on.
Why do organisms evolve?✗ Because they want or need to change. ✓ Random variation plus selection of advantageous traits — no intent.
Is continuous variation (like height) controlled by a single gene?✗ Yes, one gene controls it. ✓ No — it is polygenic (many genes) and affected by environment.
Which way do arrows point in a food chain?✗ From predator to prey, because predators eat prey. ✓ From prey to predator, showing the direction of energy flow.
Is energy recycled in an ecosystem?✗ Yes, the same energy goes round and round forever. ✓ No — energy flows through and is lost as heat; only nutrients are recycled.
Practise Ecology & Evolution — free games
Test yourself with these quick revision games for this topic:
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