B1 - Topic 1 - Classification, Variation and Inheritance

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Unit B1 – Influences on Life


Topic 1 – Classification, Variation and Inheritance










Binomial Naming System


·         Easier to identify existing and new species

·         To see how closely organisms are related

·         To identify biodiversity in and area and protect biodiversity hotspots

·         Named using the genus and species

·         Species must be able to have fertile offspring


-        Multi-cellular

-        Cell wall (cellulose)

-        Complex cell structure

-        Saprophytic feeders (no chlorophyll)



-        Mostly uni-cellular

-        Complex cell structure



-        Uni- cellular

-        Simple cell structure (no nucleus)



-        Multi-cellular

-        No cell wall

-        Complex cell structure

-        Heterotrophic feeders (no chlorophyll)



-        Multi-cellular

-        Cell wall (cellulose)

-        Complex cell structure

-        Autotrophic feeders (chlorophyll)



Viruses do not count as living organisms as they do not show all 7 life processes:

-        Don’t respire

-        Don’t feed

-        Don’t use senses

-        Can’t reproduce without being in a living cell

-        Don’t excrete

-        Don’t grow or move

Phylum Chordata


Vertebrates have a back bone (supporting rod that runs the length of their body)


Vertebrates                                       Invertebrates

Mammals                                            Molluscs (snails)

Amphibians                                        Sponges

Birds                                                      Arthropods (insects)
Reptiles                                                                Coelenterates (Jelly fish)

Fish                                                        Worms


Classifying Vertebrates


Oxygen Consumption - Organisms can be characterised by the way they absorb oxygen 

Fish: Have gills to gain oxygen from water

Amphibians: Have gills when young then have lungs but can absorb oxygen through moist skin too

Mammals, Reptiles and Birds: Have lungs


Thermoregulation - Organisms can be characterised by how their internal body temperature is controlled            

Homeotherms: Keep body temperature constant and often warmer than surroundings by reactions occurring all over the body

Poikilotherms: Body temperature varies based on the surroundings


Reproduction - Organisms can be characterised by how the reproduce

Mammals: Viviparous – fertilisation occurs internally and the mother gives birth to young which she feeds milk

Fish: Fertilisation occurs externally

Reptiles: Oviparous – lay eggs


Difficulty with Classification


·         Species: A group of organisms that can interbreed and produce fertile offspring

·         Some organisms do not breed by sexual reproductions, eg bacteria and fungi, so it is difficult to classify them as the same species

·         The definition of a species is not always clear because two closely related species can breed and produce hybrids

·         Hybrids are usually infertile but not always

·         A ring species is a group of related populations living in neighbouring areas that can interbreed – populations furthest apart cannot however

·         An example is the herring gull




·         Two causes of variation: genes and environment

·         The combining of genes from the


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