Classification, Biodiversity and Conservation

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Cambridge International AS & A Level Biology (9700)

Classification, Biodiversity and Conservation

The big idea: Classification sorts living things by shared features and evolutionary relationships. Biodiversity is measured by sampling fairly and counting carefully, and conservation uses everything from national parks to frozen embryos to stop species being lost.

Summary — What This Chapter Covers

Three species concepts; three domains; differences between Archaea and Bacteria; the taxonomic hierarchy.
Features of Protoctista, Fungi, Plantae and Animalia; classification of viruses by nucleic acid.
Ecosystem and niche; biodiversity at three levels; random sampling.
Quadrats, transects and mark-release-recapture (Lincoln index); Spearman’s and Pearson’s correlation; Simpson’s index of diversity.
Causes of extinction, reasons to conserve, conservation methods, assisted reproduction, invasive species, IUCN and CITES.

1. Classification

18.1

What is a species?

Concept	A species is…	Limitations
Biological	a group of organisms with similar morphology and physiology that can interbreed to produce fertile offspring, and are reproductively isolated from other species	Cannot be used for asexual organisms or fossils; hard to test for organisms that never meet
Morphological	a group of organisms that share the same physical features (structure, appearance)	Males and females or life stages may look very different; unrelated species can look alike
Ecological	a group of organisms that share the same ecological niche, using the same resources in the same way	Some species occupy different niches in different places or life stages

Three domains

Archaea: prokaryotes, often in extreme environments (hot springs, salt lakes, anaerobic mud).
Bacteria: prokaryotes.
Eukarya: all organisms with eukaryotic cells (nucleus and membrane-bound organelles).

Archaea and Bacteria are both prokaryotes (no nucleus, 70S ribosomes, circular DNA), but they differ:

	Bacteria	Archaea
Membrane lipids	Fatty acids, unbranched, joined to glycerol by ester bonds	Branched hydrocarbon chains joined to glycerol by ether bonds
Ribosomal RNA	Bacterial base sequences	Different base sequences, more similar to those of eukaryotes
Cell walls	Contain peptidoglycan (murein)	No peptidoglycan; made of other polysaccharides and proteins

The taxonomic hierarchy (Eukarya)

Domain → kingdom → phylum → class → order → family → genus → species. Each level contains fewer organisms with more features in common. Species are named by the binomial system: Genus species, e.g. Homo sapiens (genus capitalised, species lower case, italicised or underlined).

Example, the lion: Eukarya, Animalia, Chordata, Mammalia, Carnivora, Felidae, Panthera, Panthera leo.

Kingdoms of the Eukarya

Kingdom	Characteristic features
Protoctista	Eukaryotes that do not fit the other kingdoms; mostly unicellular (some multicellular, e.g. seaweeds); some photosynthetic with chloroplasts (algae), some heterotrophic (protozoa); some with cell walls, some without; may have cilia or flagella
Fungi	chitin hyphae
Plantae	cellulose
Animalia	Multicellular; heterotrophic, usually ingesting food; no cell walls; no chloroplasts; store glycogen; nervous coordination; usually able to move

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Also in the full note

Classification of viruses
Key terms
Assessing distribution and abundance
Correlation: Spearman’s rank and Pearson’s linear
Why species become extinct
Conserving endangered species
Invasive alien species

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Classification, Biodiversity and Conservation