AQA GCSE Science BIOLOGY 2 Unit B2.8 Speciation

• Know and understand that changes in the environment of plants and animals may cause them to die out.

• Know and understand that the fossil record shows that new organisms arise, flourish, and after a time become extinct.

• Know and understand that the record also shows changes that lead to the formation of new species.

• You should be able to use your skills, knowledge and understanding to suggest reasons why scientists cannot be certain about how life began on Earth.

  • The uncertainty arises from the lack of enough valid and reliable evidence.

AQA GCSE Science BIOLOGY Unit B2.8.1 Old and new species

• a) Know and understand that evidence for early forms of life comes from fossils.

• b) Know and understand that fossils are the ‘remains’ of organisms from many years ago, which are found in rocks.

  • Know that fossils may be formed in various ways:

    • from the hard parts of animals that do not decay easily eg bones, shells or teeth,

    • from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent eg insects in solidified amber resin (no air/microbes can get in), glaciers or permafrost ground (too cold for decay microorganisms to function) or very acid peat bogs (pH too low for microbes to function, the bones dissolve rapidly but flesh and human clothing/animal coats can be preserved in a sort of 'mummified' state).

    • when parts of the organism are replaced by other materials as they decay - eg mineralisation from surrounding sediments of sand or shale layers,

    • as preserved traces of organisms, eg footprints, burrows and rootlet traces.

• c) Know and understand that many early forms of life were soft-bodied, which means that they have left few traces behind.

  • What traces there were have been mainly destroyed by geological activity.

• d) Know and understand that we can learn from fossils how much or how little different organisms have changed as life developed on Earth.

• e) Know and understand that extinction may be caused by:

  • changes to the environment over geological time - eg think of plate tectonic movement over millions of years from warm equatorial areas to cold arctic areas of the Earth's surface,

  • new predators - one species can consume another!, we humans have been responsible for many extinctions by 'over hunting'!

  • new diseases - eg an animal's immune system unable to cope with a new mutant bacteria or virus,

  • new, more successful, competitor for food invading a particular habitat,

  • a single catastrophic event, eg massive volcanic eruptions, collisions with asteroids (huge impact 65 million years ago may be responsible for the extinction of dinosaurs), onset of an ice age

  • through the cyclical nature of speciation - the evolution of a new species.

• f) Know and understand that new species arise as a result of:

  • A species is group of similar organisms that can interbreed to give fertile offspring.

  • Speciation is the development of a new species and can happen when populations of the same original species becomes so different (genetically) that they can no longer interbreed to give fertile offspring.

  • Speciation can occur via isolation – two populations of a species become separated, eg geographically,

    • In the two geographical regions, the climate might be different, the other plants and animals may be different.

      • However, if each population can survive, by the process of natural selection, two distinct species can evolve (or perhaps one population remains the same, but the other has to adapt to a different environment).

    • For Foundation Tier students ideas are restricted to knowledge and understanding of isolation,

  • HT only: genetic variation – each population has a wide range of alleles that control their characteristics,

  • HT only: natural selection – in each population, the alleles that control the characteristics which help the organism to survive are selected and passed on to the next generation - 'survival of the fittest'.

  • HT only: speciation – the populations become so different that successful interbreeding is no longer possible.

    • Therefore breeding continues separately within each distinct population - in time producing further genetic distinction.