GCSE Biology - Classification, variation, evolution, genes and inheritance

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The vertebrates are animals with a backbone. Scientists separate this group into smaller groups because of their features:

  • how the animal takes in oxygen – lungs, gills or through the skin
  • thermoregulation – maintains own temperature(homeotherms)or temperature varies with surroundings(poikilotherms)
  • reproduction – internal or external fertilisation, lay eggs(oviparous)or give birth to live young(viviparous).
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Group Characteristics

FishGills, external fertilisation, Oviparous, poikilotherm

AmphibianSome lungs or gills, external fertilisation, Oviparous, poikilotherm

ReptileLungs, internal fertilisation, Oviparous, poikilotherm

BirdLungs, internal fertilisation, Oviparous, homeotherm

MammalLungs, internal fertilisation, Vivaparous, homeotherm

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What is species?

Organisms of the same species:

- have more characteristics in common than they do with organisms of a different speciescan

- interbreed to produce fertile offspring.

Sometimes a species may have different kinds or breeds that show great variation but the individuals still belong to the same species. Different breeds of pedigree dog are like this.

A species is defined as organisms that produce fertile offspring but this is sometimes limited as some organisms do not always reproduce sexually, and some hybrids are fertile

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The first rank in this system is called a kingdom. There are five kingdoms, based upon what an organism's cells are like:

  1. animalia (all multicellular animals)
  2. plantae (all green plants)
  3. fungi (moulds, mushrooms, yeast)
  4. prokaryotae (bacteria, blue-green algae)
  5. protoctista (Amoeba, Paramecium).
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Classification is the method used by scientists to order living organisms. All species have a unique classification that results in a binomial name. Vertebrates are an example of a classification group. Keys can be used to help to identify individual organisms.

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Further Divisions

Further divisions

There are several further ranks before we reach a particular species. In order, these are:

  • kingdom
  • phylum
  • class
  • order
  • family
  • genus
  • species.
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Kingdom characteristics

Animalia; Multicellular, no cell wall or chlorophyll, heterotrophic feeders.

Plantae; Multicellular, have cell walls and chlorophyll, autotrophic feeders.

Fungi; Multicellular, have cell walls, do not have chlorophyll, saprophytic feeders.

Proctista; Usually unicellular, with a nucleus eg amoeba.

Prokaryotes; Unicellular, with no nucleus eg bacteria. Examples: bacteria and blue-green algae

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