AQA GCSE Combined Science: Biology

Revision Notes

6.3.4 Evidence for Evolution

Evolution in Bacteria

  • The theory of evolution by natural selection is now widely accepted and many sources of data are now available to support the theory of evolution
  • One very clear piece of evidence for evolution is antibiotic resistance in bacteria
  • An antibiotic is a chemical that can kill or inhibit the growth and reproduction of bacteria
  • Antibiotics are extremely useful to humans as some bacteria are pathogenic and can cause life-threatening disease
  • Bacteria reproduce, on average, every 20 minutes and therefore evolution occurs in a much shorter time span
  • Like all other organisms, within a population, there will be variation caused by mutations
  • A chance mutation might cause some bacteria to become resistant to an antibiotic (eg penicillin)
  • When the population is treated with this antibiotic, the resistant bacteria do not die
  • This means they can continue to reproduce with less competition from non-resistant bacteria, which are now dead
  • Therefore the genes for antibiotic resistance are passed on with a much greater frequency to the next generation
  • Over time the whole population of bacteria becomes antibiotic-resistant because the bacteria are best suited to their environment

Evidence for Darwin's Theory

  • Darwin’s theory of evolution by natural selection is now widely accepted
  • Evidence for Darwin’s theory is now available as it has been shown that characteristics are passed on to offspring in genes
  • Our understanding of genetics has made clear the mechanism by which natural selection can occur
  • There is further evidence for evolution in the fossil record and our knowledge of how resistance to antibiotics evolves in bacteria

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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