B1 - Classification

Classification is the method that scientists use to order living organisms - put into groups with similar characteristics.

• Animalia - multicellular, no cell wall or chlorophyll, heterotrophic feeders.
• Plantae - multicellular, have cell walls, have chlorophyll, autotrophic feeders.
• Fungi - multicellular, have cell walls, do not have chlorophyll, saprophtic feeders.
• Prokaryotae - unicellular, no nucleus.
• Protoctista - usually unicellular, have a nucleus.

• Kingdom e.g. animal
• Phylum e.g. vertebrate
• Class e.g. mammal
• Order e.g. carnivore
• Family e.g. cat
• Genus e.g. big cat
• Species e.g. lion

Classification allows scientists to identify an individual species, wherever they are

Binomial classification is important because it can:

• Clearly identify species
• Study and conserve species
• Target conservation efforts

Animals in the phylum 'chordata' are animals with a supporting rod running the length of the body, e.g. spine/ backbone.

Scientists do not classify viruses as a living thing. This is because:

• It does not show all seven processes for life.
• When it enters a cell it changes the way a cell works so it can make copies of the virus.

Vertebrates are separated into smaller groups because of their features:

• How the animal takes in oxygen - lungs, gills or through 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).

Five groups of vertebrates (and characteristics):

• Fish - gills, external fertilisation, oviparous, poikilotherm.
• Amphibian - some lungs or gills, external fertilisation, oviparous, poikilotherm.
• Reptile - lungs, internal fertilisation, oviparous, poikilotherm.
• Bird - lungs, internal fertilisation, oviparous, homeotherm.
• Mammal - lungs, internal fertilisation, viviparous, homeotherm.

Classifying vertabrates can be difficult, as some fall into more than one group, for example, sharks are fish but give birth to live young and use internal fertilisation.

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.

Organisms of the same species:

• Have more characteristics in common than they do with organisms of a different species.
• Can interbreed to produce fertile offspring.

Some classification can be complicated by:

• Variation within a species.
• Hybridisation (closely related species breed to produce offspring that have characteristics of both - the hybrids are often infertile).
• Ring species - neighbouring populations of species may have slightly different characteristics but can still interbreed as part of a chain but the two ends of the chain can't interbreed.

Keys are used to help identify a species. Keys can either be branching or a series of paired statements and are based on the physical characteristics of the species.