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Comparative anatomy: homologous and analogous organs sheet
3-mark answer frame

What are homologous and analogous organs? Explain how each supports evolution, with examples.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Define homologous organs. Organs with the same basic structure and origin but different functions.
  2. 2 · Give examples and the kind of evolution. Forelimbs of whale, bat, cheetah and human (humerus, radius, ulna, carpals, metacarpals, phalanges); thorn of Bougainvillea and tendril of Cucurbita. Divergent evolution; shows common ancestry.
  3. 3 · Define analogous organs. Organs with different structure and origin but similar function.
  4. 4 · Give examples and the kind of evolution. Wings of butterfly and bird; eye of octopus and mammal; sweet potato and potato. Convergent evolution.
  5. 5 · Draw the forelimbs if time allows. [Diagram: forelimbs of human, cheetah, whale and bat with bones labelled]

Scoring tip: Always write the type of evolution next to each kind of organ: divergent for homologous, convergent for analogous.