Doc Brown's Biology AQA GCSE Additional Science-BIOLOGY 2 Revision Notes

Biology Unit B2.8 Speciation Study Notes

BIOLOGY UNIT 2 Biology 2 for GCSE Additional Science or GCSE Biology

PLEASE NOTE NEW revision summaries for the NEW AQA GCSE Biology and NEW AQA GCSE Combined Science Trilogy Biology courses: Revision for Paper 1 (Topics 1-4) and  Paper 2 (Topics 5-7) STARTING with Y10 in Sept. 2016 onwards, first exams in 2018

REVISION NOTES GUIDE SUMMARY: What do you need to know for the examinations? What do you need to able to do in the exams? In AQA GCSE Science A examinations HT means for higher tier students only. Sorry, but I don't have much time to answer questions, but if you see any apparent errors or wish to comment, please email me. All my notes, learning objectives, comments for exam revision are based on the official AQA GCSE Science A Key Stage 4 syllabus specification.

AQA GCSE Science BIOLOGY 2 Unit B2.8 Speciation

  • doc b's Earth Science NotesKnow 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 'traces' or ‘remains’ of organisms from many years ago, which are found in rocks which we find dating back thousands or millions of years ago..

    • 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, but may stay as the original material for quite some time, though eventually most become replaced by surrounding minerals so human bones might still be bones after a few thousand years, but dinosaur bones will be rock like after over 65 million years.

      • 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 in the acid water but flesh and human clothing/animal coats can be preserved in a sort of 'mummified' state).

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

      • as preserved traces of organisms by way of casts and impressions in sedimentary rock layers, 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.

    • The fossil record is incomplete for other reasons e.g.

      • only a small proportion of organisms (creatures or plants) have by chance become fossilised,

      • and there are still lots other fossils have still to be discovered, in fact new species are being regularly discovered.

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

    • From fossils we can get some idea on what the animals and plants looked like e.g. general shape, skeletal structure and sometimes, though very rarely, detail of  internal organs.

    • Generally speaking, the deeper the layer of rock containing fossils, the older the fossils and this means we can follow the development and evolution of a species or the origin of new species by looking at similarities and differences, but its the gradual changes in the structure of plants and animals over millions of years that shows the evolutionary path of a species.

  • 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.


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