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Grade 11-12 (age 16-18)

high school Biodiversity & Classification

The millions of species on Earth are classified by shared features and relatedness into the levels domain, kingdom, phylum, class, order, family, genus and species. The largest level, the domain, has three members, Bacteria, Archaea and Eukarya, and Archaea are more closely related to Eukarya than to Bacteria. The species diversity of an area takes into account both how many species there are (species richness) and how evenly individuals are shared among them (evenness), and biodiversity has to be protected at three levels: genetic, species and ecosystem. In the diagram you can see how the three domains branch, the four kingdoms of Eukarya, and how the diversity index and evenness change as you shift the distribution of 20 individuals among four species.

Why We Classify Living Things

💡 Like a Library Catalog
①Just as a library needs a catalog by subject to find books, millions of species have to be organized systematically before we can work with them
②Organisms are sorted into groups (taxa) by shared features such as body structure, development and genetic information
③Today, comparing DNA base sequences and the amino acid sequences of proteins reveals relationships between organisms more precisely
④Classification reflects evolutionary history, so the closer two taxa are, the more recently they split from a common ancestor

The Three-Domain System and Levels of Classification

Levels of Classification

The Eight Levels of Biological Classification

Species Diversity: Richness and Evenness

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🔍 Changing the Distribution
①Four species with 20 individuals in all have the same species richness, but species diversity differs with how evenly the individuals are shared
②When one species (A) takes almost all, the diversity index H′ = −Σ pᵢ ln pᵢ is small
③When the four species have 5 individuals each, H′ reaches its maximum, ln 4 ≈ 1.39, and evenness J′ = H′ ÷ ln 4 equals 1
④Species diversity reflects both richness and evenness, and ecosystems tend to be more stable when both are high

The Three Levels of Biodiversity

Biodiversity
genetic diversity + species diversity + ecosystem diversity
the three levels are linked, so a loss at one level brings losses at the others
💡 What the Three Levels Mean
①Genetic diversity: how much genes differ between individuals of one species; the higher it is, the more likely some individuals survive environmental change or disease
②Species diversity: the number of species in an area and how evenly individuals are spread among them
③Ecosystem diversity: how varied the habitats are, such as forests, wetlands, grasslands and seas
④Varied ecosystems hold varied species, and varied species make complex food webs that keep ecosystems stable
⑤Tropical rainforests have especially high species diversity because the climate is stable, energy is plentiful and habitats are varied

Summary

🎯 Exam Points
①Three domains: Bacteria (no nuclear membrane, peptidoglycan in the cell wall), Archaea (no nuclear membrane, many species in extreme environments), Eukarya (nuclear membrane)
②Archaea are more closely related to Eukarya than to Bacteria
③Levels of classification: domain, kingdom, phylum, class, order, family, genus, species
④Scientific names follow binomial nomenclature: the genus (capitalized) and species epithet (lowercase), in italics
⑤Species diversity = richness + evenness; biodiversity has three levels: genetic, species and ecosystem
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