Biodiversity is the variety of living organisms such as microorganisms, animals and plants that interact with one another. (p.144)
Taxonomy is the field of biology that classifies, identifies and names organisms systematically. (p.144)
Organisms are classified by physical features in a taxonomic hierarchy, identified with dichotomous keys, and named with binomial nomenclature. (p.144)
Carolus Linnaeus is known as the father of taxonomy. (p.144)
All organisms are classified into six kingdoms: Archaebacteria, Eubacteria, Protista, Fungi, Plantae and Animalia, based on cell type, number of cells and nutrition. (p.145)
Archaebacteria are prokaryotic unicellular organisms without peptidoglycan in the cell wall, living in extreme environments such as hot, salty or anaerobic places. (p.146)
Eubacteria are prokaryotic unicellular organisms with peptidoglycan cell walls, classified by shape. (p.146)
Protista are eukaryotes, unicellular or multicellular, autotrophic or heterotrophic, grouped as protozoa, algae and slime moulds. (p.147)
Fungi are eukaryotic heterotrophs with chitin cell walls, existing as hyphae in a mycelium. (p.147)
Plantae are eukaryotic multicellular photoautotrophs that reproduce sexually or asexually. (p.147)
Animalia are eukaryotic multicellular heterotrophs, most of which can move and reproduce sexually. (p.147)
The taxonomic hierarchy is domain, kingdom, phylum, class, order, family, genus and species. (p.148)
Members of the same species can interbreed to produce viable fertile offspring. (p.148)
In binomial nomenclature, the first word is the genus (capital letter) and the second is the species (lowercase); names are italicised, or underlined separately if handwritten. (p.149)
A dichotomous key identifies organisms using a series of couplets of contrasting statements based on observable features. (p.151)
8.2 Biodiversity
Biodiversity has three levels: genetic diversity, species diversity and ecosystem diversity. (p.152)
Genetic diversity is gene variation within and between populations of the same species. (p.152)
Species diversity includes species richness and species evenness in a community. (p.152)
Ecosystem diversity refers to the biotic communities and ecological processes in land, sea and aquatic ecosystems. (p.152)
A phylogenetic tree shows evolutionary relationships among organisms; classification uses homologous structures that share a common ancestor. (p.153)
Land plants evolved from green algae, through non-vascular plants (mosses), seedless vascular plants (ferns), gymnosperms and angiosperms. (p.154)
In situ conservation keeps species in their natural habitat, e.g. national parks and forest reserves. (p.154)
Ex situ conservation protects species outside their natural habitat, e.g. zoos and botanical gardens. (p.154)
8.3 Microorganisms and Viruses
Microorganisms are microscopic organisms, mostly unicellular, that include bacteria, protozoa, algae, fungi and viruses. (p.155)
Bacteria have no nuclear membrane; their DNA is a nucleoid, and some carry plasmids. (p.155)
Bacteria are 1 to 10 micrometres long and occur as cocci, vibrios, bacilli or spirilla. (p.155)
Protozoa are animal-like unicellular organisms that move by pseudopodia, cilia or flagella, and are mostly found in aquatic habitats. (p.156)
Euglena sp. is an autotrophic protozoan with chloroplasts. (p.156)
Algae have chloroplasts and are autotrophs, but have no true leaves, stems or roots; they live in ponds, lakes and oceans. (p.157)
Fungi have chitin cell walls, no chlorophyll, and are heterotrophic parasites or saprophytes that live in dark, moist places. (p.157)
Viruses are not cellular, are made of nucleic acid and a protein capsid, are 20 to 400 nm in size, and reproduce only inside host cells. (p.158)
Nitrifying bacteria Nitrosomonas sp. and Nitrobacter sp. convert ammonium to nitrite and then to nitrate for plant uptake. (p.159)
Denitrifying bacteria convert nitrates back into nitrogen gas. (p.159)
Phytoplankton are microorganisms that photosynthesise and act as producers in aquatic food chains. (p.160)
Saprophytic fungi and bacteria are decomposers that break down dead organisms and waste into simple compounds returned to the soil. (p.160)
In parasitism, the parasite benefits and the host is harmed; Plasmodium sp. is a parasite transmitted by Anopheles mosquitoes that causes malaria. (p.161)
Symbionts live close to a host: ectosymbionts live outside host cells (e.g. ectomycorrhiza) and endosymbionts live inside host cells (e.g. Trichonympha sp. in termites). (p.161)
Pathogens are organisms that cause disease, including viruses, bacteria, protozoa and fungi. (p.162)
Vectors are organisms that transmit pathogens, e.g. Aedes aegypti (dengue), Musca domestica (flies), and Periplaneta americana (cockroaches) for Salmonella typhi. (p.163)
Pathogens cause disease by damaging cells, disrupting cell functions or releasing toxins that disrupt the immune system. (p.163)
Wolbachia bacteria are used in Malaysia against dengue by injecting them into Aedes aegypti eggs to limit the dengue virus. (p.162)