18.1.317-18 · Selection, Evolution, Classification and Conservation
Eukarya — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
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18.1.3 Eukarya — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the taxonomic ranks and how organisms of domain Eukarya are classified.Domain — the highest rank.Kingdom.Phylum.Class.Order.Family.Genus.Species — the lowest rank.Mnemonic for the ranks below do…
- Protoctists
- Classification
- Peptidoglycan
- Mnemonic for the ranks below domain: Kings Play Chess On Fancy Gold Squares
- The hierarchy groups similar organisms so evolutionary relationships are easier to understand
- Higher ranks contain more organisms with less similarity; lower ranks contain fewer organisms with more similarity
Section 1 of 9Taxonomic ranks
- Domain — the highest rank.
- Kingdom.
- Phylum.
- Class.
- Order.
- Family.
- Genus.
- Species — the lowest rank.
- Mnemonic for the ranks below domainKings Play Chess On Fancy Gold Squares.
Section 2 of 9How the hierarchy works
1
The hierarchy groups similar organisms so evolutionary relationships are easier to understand.
2
Similar species are grouped in a genus, genera in a family, families in an order, orders in a class, classes in a phylum, phyla in a kingdom and kingdoms in a domain.
3
Higher ranks contain more organisms with less similarity; lower ranks contain fewer organisms with more similarity.
4
Each group nests inside the next with no overlap.
Section 3 of 9Eukarya and its characteristics
Eukarya and its characteristics
Eukarya contain the hierarchy of kingdom, phylum, class, order, family, genus and species.
Eukaryote cells have a nucleus with a double membrane and membrane-bound organelles, linear DNA with histones and 80S ribosomes.
Eukaryote cells are larger than prokaryote cells, typically 10 to 100 micrometres.
Section 4 of 9Classifying a wolf and a hibiscus
| Rank | Wolf | Hibiscus |
|---|---|---|
| Domain | Eukarya | Eukarya |
| Kingdom | Animalia | Plantae |
| Phylum | Chordata | Angiospermae |
| Class | Mammalia | Dicotyledonae |
| Order | Carnivora | Malvales |
| Family | Canidae | Malvaceae |
| Genus | Canis | Hibiscus |
| Species | lupus | rosa-sinensis |
Section 5 of 9Binomial naming
Binomial naming
A Latinised species name always has two words: the genus and the species.
- The Latin name therefore gives the last two taxonomic ranks.
Genus has a capital letter and species a lower-case letter, both in italics (or underlined when handwritten).
Binomial names are the same worldwide and avoid confusion from common names.
Section 6 of 9The four kingdoms
The domain Eukarya is divided into Protoctista, Fungi, Plantae and Animalia.
All have membrane-bound nuclei and organelles, giving compartmentalised cells.
Protoctists
- Protoctists unicellular or colonial, nutrition autotrophic, heterotrophic or both, e.g. Plasmodium, Amoeba and Chlorella.
Fungi
- Fungi heterotrophs feeding by extracellular digestion, with chitin walls and spores.
Plantae
- Plantae multicellular autotrophs with cellulose walls.
Animalia
- Animalia multicellular heterotrophs with no cell walls.
Section 7 of 9More from the specification
More from the specification
Three-domain classification system
- The three-domain system divides cellular life into Archaea, Bacteria,
- and Eukarya based on ribosomal RNA sequences, membrane lipid structure,
- and fundamental biochemical features.
Distinguishing Archaea and Bacteria
- Bacteria possess cell walls containing peptidoglycan and glycerol ester membrane lipids,
- whereas Archaea possess unique branched ether-linked lipids and lack peptidoglycan in their cell walls.
Domain Eukarya characteristics
- Organisms in the domain Eukarya possess true membrane-bound nuclei, linear DNA associated with histones,
- and 80S ribosomes in cytoplasm alongside membrane-bound organelles.
Viruses in biological classification
- Viruses are considered non-cellular entities and do not fit into the three-domain concept because they lack metabolic machinery and ribosomal RNA, requiring a host cell to replicate.
Three-domain classification system
- The three-domain system divides cellular life into Archaea, Bacteria,
- and Eukarya based on ribosomal RNA sequences, membrane lipid structure,
- and fundamental biochemical features.
Distinguishing Archaea and Bacteria
- Bacteria possess cell walls containing peptidoglycan and glycerol ester membrane lipids,
- whereas Archaea possess unique branched ether-linked lipids and lack peptidoglycan in their cell walls.
Domain Eukarya characteristics
- Organisms in the domain Eukarya possess true membrane-bound nuclei, linear DNA associated with histones,
- and 80S ribosomes in cytoplasm alongside membrane-bound organelles.
Viruses in biological classification
- Viruses are considered non-cellular entities and do not fit into the three-domain concept because they lack metabolic machinery and ribosomal RNA, requiring a host cell to replicate.
Three-domain classification system
- The three-domain system divides cellular life into Archaea, Bacteria,
- and Eukarya based on ribosomal RNA sequences, membrane lipid structure,
- and fundamental biochemical features.
Distinguishing Archaea and Bacteria
- Bacteria possess cell walls containing peptidoglycan and glycerol ester membrane lipids,
- whereas Archaea possess unique branched ether-linked lipids and lack peptidoglycan in their cell walls.
Domain Eukarya characteristics
- Organisms in the domain Eukarya possess true membrane-bound nuclei, linear DNA associated with histones,
- and 80S ribosomes in cytoplasm alongside membrane-bound organelles.
Viruses in biological classification
- Viruses are considered non-cellular entities and do not fit into the three-domain concept because they lack metabolic machinery and ribosomal RNA, requiring a host cell to replicate.
Archaea
- Prokaryotes with ether-linked membrane lipids and no peptidoglycan.
Bacteria
- Single-celled microorganisms, much smaller than plant or animal cells.
Classification
- Grouping organisms by shared features and relationships.
Lipids
- Concentrated energy, insulation, cell membranes.
Feature
- An observable characteristic.
Peptidoglycan
- The cell wall material of bacteria.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Hierarchy | Nested arrangement of groups in which each rank contains lower ranks. |
| Genus | Rank containing similar species. |
| Species | Lowest taxonomic rank. |
| Kingdom | Rank below domain; Eukarya has four. |
| Phylum | Rank below kingdom. |
| Binomial | Two-word Latin name of a species. |
Section 9 of 9Exam technique
1
Writing species name with an upper-case species or without the genus — the format is Genus species.
2
Placing ranks in the wrong order — domain, kingdom, phylum, class, order, family, genus, species.
3
Saying domain is lower than kingdom — domain is the highest rank.
4
Saying protoctists are all animal-like — they include plant-like algae.
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