Species and the three domains
| English | Chinese | Pinyin |
|---|---|---|
| classification | 分类 | fēn lèi |
| species | 物种 | wù zhǒng |
| domain | 域 | yù |
| Archaea | 古菌 | gǔ jūn |
| prokaryote | 原核生物 | yuán hé shēng wù |
| nucleic acid | 核酸 | hé suān |
Classifying living things
- Biologists sort all life into groups — classification 分类.
- First we need to define a species 物种.
- Then we place every organism into one of three domains 域.
Species and domains lab
Classify organisms and definitions by the level they describe.
What is a species?
- biological species — members can breed together to make fertile offspring.
- morphological species — members look alike.
- ecological species — members fill the same role in their surroundings.
A coral reef: many species make it one of Earth's most biodiverse habitats
The biological species concept defines a species as a group whose members:
The biological concept uses interbreeding to produce fertile offspring; other concepts use appearance or ecological role.
A group whose members can breed together to produce fertile ______ is a biological species.
A mule (horse × donkey) is sterile, so horses and donkeys are different species.
The three domains
- Archaea 古菌 and Bacteria — both prokaryotes 原核生物 (no nucleus). They differ in their membrane lipids, ribosomal RNA, and cell-wall make-up.
- Eukarya — all organisms whose cells have a nucleus.
The three domains and the four eukaryote kingdoms
The three domains of life are:
The largest groups are the three domains: Archaea, Bacteria (both prokaryotes) and Eukarya.
Which is true of the domains?
Archaea and Bacteria lack a nucleus (prokaryotes); Eukarya have a nucleus.
Match each group to its key feature.
Two prokaryote domains (Bacteria, Archaea) and one with a nucleus (Eukarya); a species is defined by interbreeding.
Archaea and Bacteria are both prokaryotes, while Eukarya have a nucleus.
The split into three domains is based on differences in their cells and genes, especially rRNA.
Where viruses fit
- Viruses are not placed in these groups.
- They are classified by the type of nucleic acid 核酸 they contain (DNA or RNA), and whether it is single- or double-stranded.
Viruses are classified by:
Viruses are non-cellular, so they are grouped by their nucleic acid (DNA/RNA, single/double-stranded).
You've got it
- species can be defined biologically (fertile offspring), morphologically (look alike), or ecologically (same role)
- three domains: Archaea + Bacteria (prokaryotes) and Eukarya (have a nucleus)
- viruses are classified by their nucleic acid type (DNA/RNA, single/double-stranded)