How are living things classified? Life Science Notes Ch. 1.4 How are living things classified? Life Science

History of Classification Aristotle was the first to classify organisms. He had 2 groups: plants and animals. He then further grouped them based on common characteristics. Linnaeus changed classification by looking for organisms with similar structures. Today scientists use internal and external similarities. They look at the number of chromosomes, fossils, hereditary information, and early stages of development.

Phylogeny is the evolutionary history of an organism, or how it has changed over time.

Levels of Classification

Levels of Classification There are 6 kingdoms. A kingdom is the first and largest category. The smallest classification category is species. The same species can reproduce and produce fertile offspring. Example: Two horses can mate and produce a fertile horse. A donkey and a horse can mate and produce a mule. The mule is sterile (cannot reproduce) so a donkey and horse are different species.

Scientific Names Common names can cause a lot of confusion. Different countries may call the same organism something different, or the common name may be a misnomer, like a sea horse isn’t a horse at all. Binomial nomenclature is a two-word naming system created by Linnaeus to name various species. It uses Latin. The first word identifies the genus of an organism. Genus is a group of similar species. The second word tell you characteristics about the organism.

Uses of Scientific Names They avoid mistakes – gives each species a specific name, not a general name for several species Organisms with similar evolutionary histories are classified together. This helps you know that organisms in the same genus are related. Scientific names give descriptive information. It allows information about organisms to be organized easily.

Tools for Identifying Organisms Two tools used to identify organisms are field guides and dichotomous keys. A field guide usually have descriptions and illustrations of organisms and information about where the organism lives. Dichotomous keys are a series of questions about an unknown organism that helps you figure out what the organism is.

Field Guide

Dichotomous Key