Adaptation, Evolution and Biodiversity
This domain links the structures an organism develops to survive its habitat with the evolutionary process that produced them, and then to the variety of life that must be conserved. The exam asks for adaptation examples with the habitat named, the Lamarck-Darwin distinction, homologous versus analogous organs, and levels of biodiversity.
Adaptation
- Xerophytes (cactus): leaves reduced to spines, thick cuticle, sunken stomata, fleshy green stem for photosynthesis, deep roots.
- Hydrophytes: aerenchyma air spaces, thin cuticle, poorly developed roots.
- Mangroves of the Sundarbans: pneumatophores for aeration in waterlogged mud, vivipary (seed germinates on the parent tree), salt-excreting glands, stilt roots for support.
- Animals: streamlined fish body with gills and fins; birds with hollow pneumatic bones, feathers, air sacs and strong flight muscles; insectivorous plants such as Nepenthes trap insects to obtain nitrogen.
Evolution
- Lamarck: use and disuse of organs, inheritance of acquired characters. Darwin: variation, struggle for existence, natural selection, survival of the fittest. Darwin's finches illustrate adaptive radiation.
- Evidences: fossils, homologous organs (same basic structure, different function - forelimbs of human, bat and whale), analogous organs (different origin, same function - wings of bird and butterfly), vestigial organs (vermiform appendix, nictitating membrane).
Biodiversity
- Levels: genetic, species, ecosystem. Loss is driven by habitat destruction, pollution, overexploitation and invasive species. Conservation may be in situ (national park, sanctuary, biosphere reserve) or ex situ (zoo, botanical garden, seed bank).
Worked example
Compare the wing of a bird with the wing of a butterfly. Both are used for flight, but the bird wing is a modified forelimb with bones while the butterfly wing is a fold of cuticle with no skeleton. Same function, different origin: analogous organs, evidence of convergent evolution rather than common ancestry.
Traps that cost marks
- Cactus spines are modified leaves, not stem branches.
- Pneumatophores are negatively geotropic roots for breathing, not anchoring roots.
- Lamarck is use and disuse; Darwin is natural selection.