Classifying living things
Classifying living things
- Scientists classify organisms — sort them into groups by shared features.
- The smallest group is the species, with a two-part name.
- The biggest groups are the kingdoms.
Species and the binomial system
- A species is a group that can reproduce to make fertile offspring.
- Each has a two-part scientific name (the binomial system), written in italics:
- first part = the genus (capital letter), e.g. Homo.
- second part = the species (small letter), e.g. sapiens.
Practice
A species is a group of organisms that:
Members of a species can breed to produce fertile offspring.
Practice
In a scientific name like Homo sapiens:
The binomial system: Genus (capital) then species (small), both in italics.
Keys and DNA
- A dichotomous key identifies an organism by giving two choices at each step until you reach its name.
- DNA shows relatedness: organisms with more similar base sequences are more closely related (a more recent ancestor).
Practice
A dichotomous key works by:
"Dichotomous" means splitting in two; each step offers two choices.
Practice
Two organisms with more similar DNA base sequences are:
More similar DNA means a more recent shared ancestor — more closely related.
The five kingdoms
- Animal, Plant, Fungus, Prokaryote (e.g. bacteria, no nucleus), Protoctist (e.g. Amoeba).
- You decide an organism's kingdom from its main features.
Practice
Which is one of the five kingdoms?
The five kingdoms are Animal, Plant, Fungus, Prokaryote and Protoctist.
You've got it
Key idea
- a species = can make fertile offspring; named by the binomial system (Genus species, italics)
- a dichotomous key uses two choices per step; more similar DNA → more closely related
- the five kingdoms: Animal, Plant, Fungus, Prokaryote, Protoctist