Species and the three domains
Introduced| English | Meaning |
|---|---|
| classification/ˌklæsɪfɪˈkeɪʃn/ | Arranging items or organisms into groups according to shared features or a defined system. |
| species/ˈspiːsiːz/ | A group of organisms whose members can usually interbreed to produce fertile offspring. |
| domain/dəˈmeɪn/ | The highest major taxonomic rank in the three-domain system, which distinguishes Bacteria, Archaea and Eukarya. |
| Archaea/ɑːˈkɪə/ | A domain of single-celled organisms without a membrane-bound nucleus, evolutionarily distinct from bacteria. |
| prokaryote/ˈprɒkərɪəʊt/ | An organism whose cells lack a membrane-bound nucleus and other membrane-bound organelles. |
| nucleic acid/njuːˈklɪɪk ˈæsɪd/ | A polymer of nucleotides that stores or transmits genetic information, such as DNA or RNA. |
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:
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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.
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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:
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The largest groups are the three domains: Archaea, Bacteria (both prokaryotes) and Eukarya.
Which is true of the domains?
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Archaea and Bacteria lack a nucleus (prokaryotes); Eukarya have a nucleus.
Match each group to its key feature.
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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.
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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:
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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)