52 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
The central region of the A band that contains myosin filaments but no actin; it shortens and may disappear during contraction.
The place in which a community, species, population or organism lives, described by its geographical location, physical location and type of ecosystem.
The clearing, draining, burning or fragmentation of a habitat so that it can no longer support the species that lived there.
A ring-shaped prosthetic group with an iron ion (Fe²⁺) at its centre; each haem group in haemoglobin binds one oxygen molecule.
A conjugated globular protein in red blood cells made of four polypeptides, each with a haem group containing iron, which binds oxygen for transport.
A sex-linked genetic disease in which blood clots slowly or not at all, caused by a recessive allele of an X-linked gene for a clotting factor (factor VIII or IX).
A plant adapted to grow in soil or water with a high salt concentration, for example by excluding or excreting salt.
Describes a nucleus or cell that has one set of chromosomes (n), with one chromosome of each type.
The equations and
The state of a population in which allele and genotype frequencies stay constant between generations, as the Hardy–Weinberg equation predicts, because there is no selection, mutation, migration or non-random mating and the population is very large.
The number of times the heart beats per minute (bpm), equal to the pulse rate.
An enzyme that unwinds the DNA double helix and separates the two strands by breaking the hydrogen bonds between complementary bases.
A lymphocyte that is activated by antigen presented by a macrophage and then activates B-lymphocytes that recognise the same antigen; it is the cell infected by HIV.
An animal that feeds on plants or parts of plants; herbivorous mammals typically have large, flat molars for grinding.
The eating of plants or parts of plants by animals.
The protection of a whole population, including non-immune individuals, from an infectious disease when a large enough proportion of the population is immune that transmission is greatly reduced.
Describes a characteristic that is passed from parents to offspring through the genes in their gametes.
An organism, or a flower, that has both male and female reproductive organs and so produces both male and female gametes.
The 1952 experiment that used T2 bacteriophages labelled with ³⁵S (protein) or ³²P (DNA) to show that DNA, not protein, enters bacteria during infection and is the genetic material.
An organism that obtains carbon compounds from other organisms and uses them to synthesise the carbon compounds it needs.
Having two different alleles of a gene, for example Rr.
A monosaccharide with six carbon atoms, formula C₆H₁₂O₆, such as glucose, fructose or galactose; usually found as a ring of five carbons and one oxygen.
A base or amino acid sequence that has remained identical or very similar over long periods of evolution, in distantly related species.
A synovial joint that allows movement in one plane only (flexion and extension), as at the knee and elbow.
A basic protein around which eukaryote DNA is wound to package it into chromosomes; prokaryote DNA is not associated with histones.
The addition or removal of chemical groups, such as methyl or acetyl groups, on amino acids in histone proteins, which changes how tightly DNA is packed and so affects transcription.
Human immunodeficiency virus: a retrovirus, transmitted in body fluids, that infects and destroys helper T-lymphocytes and leads to AIDS.
A mode of heterotrophic nutrition in which food is ingested, digested internally, absorbed and assimilated, and undigested material is egested; used by animals.
The maintenance of the internal environment of an organism within preset limits, despite fluctuations in the external environment.
A member of the family Hominidae, the great apes: humans, chimpanzees, gorillas, orangutans and their extinct relatives such as Paranthropus.
A pair of chromosomes, one from each parent, with the same length, centromere position and sequence of genes, though not necessarily the same alleles.
A structure that is similar in basic arrangement in different species because it was inherited from a common ancestor, even if it now has a different function.
Having two identical alleles of a gene, for example RR or rr.
The transfer of genetic material between organisms other than from parent to offspring, for example between different bacterial species by conjugation, transformation or transduction.
A chemical signal secreted by an endocrine gland directly into the blood, which carries it to target cells that have receptors for it.
Treatment with oestrogen, often combined with a progestogen, to replace the hormones that the ovaries stop secreting at the menopause.
A biome with very low, unpredictable rainfall (under about 250 mm a year), very high daytime temperatures and sparse, drought-adapted vegetation.
A glycoprotein hormone secreted by the embryo (trophoblast) and later the placenta, which maintains the corpus luteum in early pregnancy; its presence in urine is the basis of pregnancy tests.
The offspring of a cross between two different species (or two genetically different varieties); hybrids between species are often sterile.
The inability of a hybrid between two species to produce viable gametes, usually because its chromosomes from the two parent species cannot pair in meiosis.
The attraction between a partially positive hydrogen atom in one polar molecule and a partially negative atom, such as oxygen or nitrogen, in another polar molecule or another part of the same large molecule.
A reaction in which a covalent bond is broken by the addition of a water molecule, whose –H and –OH become part of the two products; used to digest polymers into monomers.
Attracted to water and able to dissolve in it; ions and polar molecules are hydrophilic because their charges attract water molecules.
Not attracted to water and insoluble or poorly soluble in it; non-polar substances such as fats and oils are hydrophobic.
The clustering of non-polar R-groups away from water in a protein, caused by water molecules hydrogen bonding with each other and excluding the non-polar groups.
An opening in the deep sea floor that releases hot, mineral-rich water; vent communities are based on chemoautotrophic bacteria rather than sunlight.
A change in membrane potential that makes the inside more negative than the resting potential, as after an action potential or during an inhibitory postsynaptic potential.
Describes a solution with a higher concentration of solutes than another solution, such as the cytoplasm of a cell; water moves by osmosis into it from the less concentrated solution.
One of the thin, branching threads that make up the body of most fungi; aseptate hyphae have no cross walls, so many nuclei share one continuous cytoplasm.
A region at the base of the brain that monitors the blood and receives nervous input, and controls the pituitary gland, linking the nervous system with the endocrine system.
A tentative, testable explanation of an observation, from which predictions can be made and checked by experiment or further observation.
Describes a solution with a lower concentration of solutes than another solution, such as the cytoplasm of a cell; water moves by osmosis out of it into the more concentrated solution.