5.1 - Classification

Species and scientific naming

• A species is the smallest group organisms are sorted into.
• It's a group of similar organisms that can reproduce with one another to give fertile offspring - offspring that can themselves go on to reproduce.
• This makes a species a natural unit: its members breed together, while members of different species generally don't produce fertile offspring.

The binomial system

• Because there are so many species, each is given its own scientific name using the binomial system - an internationally agreed, two-part naming system, mostly in Latin.
• The two parts are:
  1. Genus - The first part, shared with closely related organisms, giving information about ancestry
  2. Species - The second part, the species itself
• Example: humans are Homo sapiens - Homo is the genus and sapiens is the species.
• Writing conventions:
  • The whole name is written in italics
  • Only the first letter of the genus is capitalised

Why the system is used

• The point is consistency.
• The same organism is often given many different common or local names in different places and languages - over a hundred plant species are commonly called raspberries, for instance - which causes confusion.
• A single agreed scientific name means scientists anywhere in the world refer to a species by exactly the same name, so there's no doubt about which organism is meant.

Broad grouping of organisms

• Living organisms come in an enormous range of sizes, features, and complexity - from tiny simple bacteria to large complex animals and plants.
• They can be sorted into groups according to the features they share.
• At the broadest level, familiar living things are placed into a small number of large descriptive groups, which are then subdivided into smaller and smaller groups whose members share more and more features.

Two major groups of plants

1. Flowering plants - e.g. daisies and grasses
2. Non-flowering plants - e.g. ferns and mosses

Two major groups of animals

Animals are divided according to whether they have a backbone:

1. Vertebrates - Have a backbone and an internal skeleton, e.g. mammals and birds
2. Invertebrates - Have no backbone, e.g. insects and worms