Edexcel Biology B1, classification

Organisms are classified into The Five Kingdoms:

• Animalia- multicellular, do not have cell walls, do not have chlorophyll, feed heterotrophically (unable to make own food)
• Plantae- multicellular, have cell walls, have chlorophyll, feed autotrophically (make their own food, by photosynthesis)
• Fungi- multicellular, have cell walls, do not have chlorophyll, feed saprophytically (feed off of dead organisms/ decaying material)
• Protoctista- unicellular, has a nucleus, an example is algae
• Prokaryotes- unicellular, do not have a nucleus, an example is bacteria

The Five Kingdoms are subdivided into:

• Phylum
• Class
• Order
• Family
• Genus
• Species

• Viruses are considered as being non-living.
• They are unable to reproduce themselves, so invade cells to make them reproduce the virus.

For this reason, viruses are not classified into any of the five kingdoms.

The phylum Chordata contains animals that have a supporting rod running the length of their bodies, for example the backbone in vertebrates.

Vertebrates are divided into 5 classes:

• Amphibians
• Birds
• Fish
• Mammals
• Reptiles

Which group a vertebrate is in depends on:

• Oxygen absorption methods- lungs, gills, skin
• Reproductive methods- internal or external fertilisation, oviparous or viviparous
• Thermoregulation- homeotherms or poikilotherms

However some vertebrates are difficult to classify- e.g. the duck-billed platypus.

The term species is often defined as "organisms that produce fertile offspring".

Limitations of this definition:

• Not all organisms produce sexually so some hybrids are fertile.
• Some organisms can produce asexually but are still classed as the same species.
• Many closely related species can interbreed producing offspring that is classed as another species.
• Closely related species can sometimes produce fertile offsping, for example in some species of duck.