Characteristics and Classification

All living things show seven characteristics: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition (MRS GREN). Organisms are classified into groups by shared features, from kingdom down to species. The binomial system gives each species a two-part Latin name: genus then species, e.g. Homo sapiens. A dichotomous key identifies an organism through a series of two-way choices.

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Section 1 of 14

Learning objectives

List the characteristics of living organisms.
Describe the binomial system and classification hierarchy.
Use dichotomous keys.
Recognise the main groups of vertebrates and arthropods.

Pause and think

A car moves, uses fuel and gives off waste gases. Why isn't it alive?

Section 2 of 14

Core idea

Start hereSorting life

Scientists have named about 2 million species and estimate millions more are undiscovered. Classification gives every one of them a place and a unique name.

The big idea

Living things share seven characteristics. They are classified by shared features (and DNA) into groups from kingdom to species, and named with two Latin words.

1. Is it alive?

Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition

2. Using a key

A simple dichotomous key

Drawing diagram…

Each step splits the group in two.

Worked exampleClassifying a vertebrate

An animal has moist skin, lays jelly-coated eggs in water and its young have gills.

Goal: Group.
Strategy: Match features.

$\text{moist skin, eggs in water}$
Not reptile (dry scales) or bird.
$\text{young with gills}$
Metamorphosis from tadpole.

AnswerAmphibian.

✓ CheckFrogs fit all three ✓.

Key takeawayBinomial names Genus species, in italics (or underlined when handwritten), genus with a capital letter.

Pause and think

Why are dolphins classified with humans rather than with sharks?

Summary

MRS GREN.
Kingdom → species.
Keys: paired questions.

Species: Organisms that can interbreed to produce fertile offspring.
Binomial system: Naming species with genus and species names.
Dichotomous key: Identification key with two choices at each step.

HistoryLinnaeus. Swedish botanist Carl Linnaeus introduced the binomial system in 1753. Before that, plant names could be long Latin descriptions of a dozen words.

Fun factName it after a celebrity. New species are sometimes named after famous people: there's a horse fly called Scaptia beyonceae and a beetle called Agra schwarzeneggeri.

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