Cladistics turns molecular data into evolutionary trees. This HL lesson covers A3.1 Diversity of organisms, A3.2 Classification & cladistics, A4.1 Evolution & speciation and A4.2 Conservation of biodiversity.
You will use the species concept, build and interpret cladograms, apply a molecular clock, and quantify biodiversity with Simpson's index.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.
A species is typically a group that interbreeds to produce fertile offspring, named with a binomial (genus + species). Species differ in traits and in chromosome number, yet share a universal genetic code.
The species concept is harder to apply to asexual, extinct or ring species — a good evaluation point.
Cladistics groups organisms into clades — an ancestor and all its descendants — using shared derived characteristics, especially DNA and amino-acid sequences.
A cladogram shows branching relationships; each node is a common ancestor. A molecular clock uses the roughly constant rate of neutral mutations to estimate when lineages diverged.
Sequence data can force reclassification, as when the figworts were reorganised on molecular evidence.
Sort each item as evidence, a mechanism, or a conservation strategy.
Evidence for evolution includes homologous structures, the fossil record, biogeography, selective breeding and molecular data.
Speciation follows reproductive isolation: allopatric (geographic barrier) or sympatric (e.g. polyploidy, behaviour). Divergence may be gradual or punctuated.
A biodiversity crisis is driven by habitat loss, overexploitation, invasive species, pollution and climate change.
Diversity indices such as Simpson's track richness and evenness over time.
Match each cladistics term to its meaning.
A3.1: species and binomial naming; limits of the species concept
A3.2 (HL): clades and cladograms from sequences; molecular clocks; reclassification
A4.1: homology as evidence; allopatric vs sympatric speciation
A4.2: in-situ vs ex-situ; Simpson's index tracks biodiversity
Press Finish to see your score.
You have worked through Theme A: Unity & Diversity — Organisms & Ecosystems for IB Diploma Biology. 🎉
Your stars: 0 / 0
Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.