Edexcel GCSE B1 Revision Notes

Topic 1 – Classification, variation and inheritance

CLASSIFICATION

·         Classification – sorting organisms into groups based on their characteristics

·         The five kingdoms ->

o   Animalia:

§  Multicellular

§  Heterotrophic feeders -eating and digesting other organisms

§  No cell walls

§  Complex cell structure with nucleus

o   Plantae:

§  Multicellular

§  Autotrophic feeders – make their own food through photosynthesis

§  Cell walls made of cellulose

§  Complex cell structure with nucleus

o   Fungi:

§  Multicellular

§  Cell walls not made of cellulose

§  Saprophytic feeders – digest other organisms outside the body

§  Complex cell structure with nucleus

o   Protoctista:

§  Unicellular

§  Complex cell structure with nucleus

o   Prokaryotae:

§  Unicellular

§  Simple cell structure with no nucleus

·         There is no kingdom for viruses because:

o   They are non-living (do not exhibit many life processes)

o   They’re not made up of cells (no cell organelles)

o   They can only exist inside ‘host’ cells

·         As you progress from kingdom -> phylum -> class -> order -> family -> genus -> species, the groups are smaller and the organisms share more and more characteristics in common

Naming species:

o   Binomial system- Latin words- made up of genus then species, e.g humans are Homo Sapiens

·         The binomial naming system is in Latin:

o   Because common names given to organisms can sometimes be misleading:

§  E.g robins in America (Turdus migratorius) and robins in the UK (Erithacus rubecula) are different species

o   So that scientists all over the world can communicate clearly, whatever their language

VERTEBRATES AND INVERTEBRATES

·         Vertebrates are animals that have a supporting rod that runs the length of the body, e.g. a backbone

·         All vertebrates belong to the phylum Chordata

·         Animals that don’t have a backbone are called invertebrates

Grouping vertebrates into classes:

·         1. Vertebrates can be grouped into classes according to how they absorb oxygen for respiration:

o   Fish – gills to take in oxygen from the water

o   Amphibians – young amphibians have gills but adult amphibians usually have lungs and can absorb oxygen through their moist skin

o   Mammals, reptiles, birds – lungs

·         2. Vertebrates can be grouped into classes according to how they reproduce:

o   External fertilisation – i. female releases eggs into the water, where they’re fertilised by the sperm released by an adult male (fish and amphibians)

o   Internal fertilisation- egg is fertilised inside the body:

§  Organisms which lay eggs are known as oviparous (reptiles and birds)

§  Organisms which give birth to live young are known as viviparous (mammals)

·         3. Vertebrates can be grouped into classes according to the way in which they thermoregulate:

o   Homeotherms e.g mammals, birds – keep…