Section 4Section 4How are living things How are living things

classified?classified?

A. Classification systemsA. Classification systems

1.1. Aristotle classified organisms more Aristotle classified organisms more than 2000 years ago.than 2000 years ago.

2.2. Carolus Linnaeus introduced a Carolus Linnaeus introduced a system based on similar structures system based on similar structures of organisms. of organisms.

Modern systems based on Modern systems based on phylogenyphylogeny – – the evolutionary history of an organism. the evolutionary history of an organism.

Today’s classification system separates Today’s classification system separates organisms into 6 organisms into 6 kingdomskingdoms..

1.1. Kingdoms are the first and Kingdoms are the first and largestlargest category.category.

2.2. The smallest classification category is a The smallest classification category is a speciesspecies..

3.3. Organisms that belong to the same Organisms that belong to the same species can mate and produce species can mate and produce fertile fertile offspring.offspring.

B. Binomial nomenclature – two-word B. Binomial nomenclature – two-word system used by Linnaeus to name species system used by Linnaeus to name species

1.1. First word identifies the First word identifies the genusgenus, or group of , or group of similar species.similar species.

2.2. Second word tells something about the Second word tells something about the species – what is looks like, where it is found, species – what is looks like, where it is found, or who discovered it.or who discovered it.

3.3. Why use scientific names?Why use scientific names?

1.1. To avoid mistakesTo avoid mistakes

2.2. To show that organisms in the same genus To show that organisms in the same genus are related.are related.

3.3. To give descriptive information.To give descriptive information.

4.4. To allow information to be organized To allow information to be organized easily.easily.

C. Tools for identifying organismsC. Tools for identifying organisms

1.1. Field guides – descriptions and Field guides – descriptions and illustrations or organisms.illustrations or organisms.

2.2. Dichotomous keys – detailed lists of Dichotomous keys – detailed lists of identifying characteristics that identifying characteristics that include scientific names.include scientific names.