The Living World

Lesson

Part 1 — the variety of life, why we sort it, and the three great domains.

In this lesson you will

Explain why the diversity of life makes classification necessary
Distinguish identification, nomenclature and classification
Describe the three domains of life and place an organism in its domain
Define taxonomy and systematics

Concept

Biodiversity: the variety of life

Biodiversity is the variety of living organisms on Earth. Life is found in cold mountains, deserts, deep oceans, hot springs and rainforests. The number of species that are known and described is about 1.7 to 1.8 million, and new species are still being found.

Table of habitats and some of the organisms that live in them
Habitat	A few of its inhabitants
Rainforest canopy	Orchids, monkeys, hornbills, beetles
Hot desert	Cacti, camels, lizards, scorpions
Open ocean	Algae, jellyfish, whales, many bacteria
Hot spring	Heat-loving prokaryotes called archaea
Soil	Fungi, earthworms, bacteria, roots

Concept

Why do we need classification?

Classification is the grouping of organisms into convenient categories on the basis of observable characters. It is needed because nobody can study millions of species one by one.

Table of problems that classification solves
Problem without classification	Help from classification
Millions of species to learn	Groups let us study a few examples and apply the pattern to many
Local names differ from place to place	One agreed scientific name for each organism
A new organism is found	Its characters show where it belongs and what it resembles
Relationships are unclear	Groups reveal which organisms are close relatives

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