Aerobe (obligate aerobe) - organisms that require oxygen for cellular respiration and cannot live without it.
Alga -(pl. algae) an organism of a wide diversity of protists (q.v.), mostly aquatic and mostly unicellular.
Asexual reproduction - a type of reproduction involving only one parent that produces genetically identical offspring by budding or division of a single cell or the entire organism into two or more parts.
Autotrophs - organisms that use energy from the sun (photoautotrophs (q.v.)) or from the oxidation of inorganic substances (chemoautotrophs (q.v.)) to make organic molecules from inorganic ones.
Bacterium - (pl. bacteria) a prokaryotic (q.v.) cell with chromosomes not enclosed in a nuclear membrane.
Chemoautotrophs - organisms that need only carbon dioxide as a carbon source, but that obtain their energy by oxidising inorganic substances (q.v.) photoautotrophs)
Chitin - a structural polysaccharide of an amino sugar found in fungal cell walls and the exoskeleton of all arthropods
Competition - (ecological) the use of the same resource by two or more species, when the resource is present in insufficient supply for the combined needs of the species.
Cytoplasm - entire contents of the cell exclusive of the nucleus (q.v.) and bounded by the plasma membrane.
Decomposer - saprophytic (q.v.) fungi and bacteria that absorbs nutrients from non-living organic material (e.g. corpses, fallen plant material, waste products) and convert them into inorganic forms.
Detritivore - consumers that derive energy from organic wastes and dead organisms from all trophic levels.
Endocytosis - the cellular uptake of macromolecules and particulate substances by localised regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.
Eukaryote - a type of cell with a membrane-enclosed nucleus (q.v.) and membrane-enclosed organelles (q.v.), found in protists (q.v.), plants, animals and fungi (q.v.).
Facultative anaerobe - organisms that make ATP by aerobic respiration if oxygen is present, but switch to fermentation under anaerobic conditions ((q.v.) obligate anaerobe)
Fission - reproduction of a prokaryote (q.v.) by division of a cell into two comparable progeny cells.
Fungus - (pl. fungi) a (usually) multicellular eukaryote (q.v.), with extracellular digestion.
Heterotrophs - organisms that obtain their organic food molecules by eating other organisms or their by-products.
Host - an organism that harbours a parasite (q.v.) and provides it with nourishment.
Hypha - the filaments making up the body of a fungus.
Medium (pl. media) - the environment in which a micro-organism grows,
Microbiology - the scientific study of microscopic organisms, particularly bacteria (q.v.), unicellular algae (q.v.), protists (q.v.), fungi (q.v.) and viruses(q.v.).
Mutualism - a symbiotic (q.v.) relationship in which both the host and the symbiont (q.v.) benefit.
Mycelium - the densely branched network of hyphae (q.v.) of a fungus.
Mycorrhiza - mutualistic (q.v.) associations of plant roots and fungi.
Nucleic acid - biological molecules (DNA and RNA) that allow organisms to reproduce.
Nucleoid region - the region of a prokaryotic cell (q.v.) consisting of a concentrated mass of DNA.
Nucleus - the information centre of the cell which contains the chromosomes and is bounded by double membrane
Obligate anaerobe - organisms that cannot use oxygen and are poisoned by it.
Organelle - a body with a specialised function, suspended in the cytoplasm (q.v.) and found in eukaryotic (q.v.) cells.
Organism - any living creature.
Parasite -organisms that absorb their nutrients from the body fluids of living hosts.
Parasitism - the attacking and consumption of a host (q.v.) organism by predators (q.v.) that are much smaller than it is; may be internal or external; sometimes but not always kills the host.
Phagocytosis - a type of endocytosis (q.v.) involving large particulate substances.
Photoautotrophs (phototrophs) - organisms that harness light energy to drive the synthesis of organic compounds from carbon dioxide.
Photoheterotrophs - organisms that use light to generate ATP, but that must obtain their carbon in organic form ((q.v.) photoautotrophs)
Plasmid - a small ring of DNA that carries accessory genes separate form those of a bacterial chromosome.
Prokaryote - a type of cell lacking a membrane-enclosed nucleus (q.v.) and membrane- enclosed organelles (q.v.); found only in the bacteria.
Protist - eukaryotic (q.v.) organisms that do not fit the definition of plant, animal or fungus (q.v.).
Respiration - oxidation of the end products of glycolysis with the storage of energy in ATP. The oxidant can be oxygen but some bacteria use nitrate or sulphate.
Saprophyte - organisms that act as decomposers (q.v.) by absorbing nutrients from dead organic matter.
Secondary metabolite - compound produced by an organism (prokaryote and eukaryote) that is not required for the existence of the organism.
Sexual reproduction - a type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the two parents.
Spore - an asexual reproductive cell capable of developing into a new individual; in prokaryotes (q.v.), a resistant cell capable of surviving unfavourable periods.
Substrates - the components of a medium (q.v.) used by micro-organisms for growth.
Symbiont - the smaller participant in a symbiotic (q.v.) relationship, which lives on or in the host.
Symbiosis - an ecological relationship between organisms of two different species that live together in direct contact.
Toxin - a toxic protein, usually of microbial origin.
Virus - a non-cellular obligatory parasite (q.v.) of cells which, in its simplest form, consists of a nucleic acid (q.v.) in a protein coat