40 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
Nicotinamide adenine dinucleotide: a coenzyme that carries hydrogen in respiration; it is reduced when it accepts two electrons and a proton, and oxidised when it passes them to the electron transport chain.
A hydrogen carrier in photosynthesis; it is reduced by two electrons from photosystem I and a proton to form reduced NADP, which supplies hydrogen to the Calvin cycle.
The process by which individuals with heritable traits that make them better adapted to their environment survive and reproduce more than others, so the alleles for those traits become more common in the population over generations.
An area of land or water that is protected and managed for the conservation of its wildlife, habitats and natural features.
A gland at the base of a flower that secretes nectar, a sugary liquid that attracts and rewards pollinating animals.
A control mechanism in which a change in a variable triggers a response that reverses the change, returning the variable towards its set value.
The theory that combines Darwin's natural selection with Mendelian and population genetics, so that evolution is described as a change in allele frequencies in a population's gene pool over generations.
An insecticide that binds to nicotinic acetylcholine receptors in insect synapses and is not broken down by acetylcholinesterase, so it blocks synaptic transmission.
The functional unit of the kidney: a tubule consisting of Bowman's capsule, proximal convoluted tubule, loop of Henle and distal convoluted tubule, draining into a collecting duct.
A bundle of nerve fibres from many neurons, surrounded by a protective sheath of connective tissue; a nerve may contain sensory fibres, motor fibres or both.
An elongated extension of a neuron, either an axon or a dendrite, along which electrical impulses are conducted.
An action potential propagated along a nerve fibre, carrying a signal from one end of a neuron to the other.
A synapse between a motor neuron and a skeletal muscle fibre, at which acetylcholine is released to stimulate contraction.
A cell of the nervous system, made of a cell body with a nucleus and elongated nerve fibres, that carries electrical impulses.
A neuron that secretes a hormone into the blood instead of releasing a neurotransmitter at a synapse, as in the hypothalamus.
A signalling chemical released by a presynaptic neuron that diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane.
The division of resources between species with overlapping niches, so that each uses a different part of the resource and both can coexist.
A ligand-gated ion channel in postsynaptic membranes that opens when acetylcholine binds to it, allowing positive ions, mainly Na⁺, to diffuse into the cell.
A nitrogen-containing ring molecule attached to carbon 1′ of the pentose in a nucleotide; the five bases are adenine, cytosine, guanine, thymine and uracil.
A branch point on a cladogram, representing the last common ancestor of the groups that branch from it and the point at which its lineage split.
A short gap in the myelin sheath of an axon where the membrane is exposed and voltage-gated channels are concentrated, so action potentials can occur.
Describes a material that cannot be broken down into simpler substances by decomposers such as bacteria and fungi, so it persists in the environment.
A DNA sequence that is not translated into a polypeptide, such as promoters, enhancers, introns, telomeres and the genes for tRNA and rRNA.
Inhibition in which the inhibitor binds reversibly to an allosteric site, changing the active site so the reaction cannot be catalysed; increasing substrate concentration does not overcome it.
ATP production in which electrons flow from water through photosystem II, the electron transport chain and photosystem I to NADP, producing ATP, reduced NADP and oxygen.
The failure of homologous chromosomes (in anaphase I) or sister chromatids (in anaphase II) to separate during meiosis, producing gametes with an extra or a missing chromosome.
An amino acid that an organism can synthesise from other amino acids or compounds, so it need not be obtained from the diet.
A base substitution that changes a codon for an amino acid into a stop codon, so translation ends early and the polypeptide is shortened.
A sterile 0.9% w/v solution of sodium chloride in water, approximately isotonic with human blood plasma, used for intravenous fluids, washing wounds and storing tissues.
The double membrane that surrounds the nucleus of a eukaryote cell, perforated by nuclear pores.
A protein-lined opening through both membranes of the nuclear envelope that controls movement of molecules such as mRNA and proteins between the nucleus and cytoplasm.
An enzyme that hydrolyses nucleic acids (DNA or RNA) by breaking the bonds between their nucleotides.
A polymer of nucleotides that stores or transmits genetic information; the two nucleic acids are DNA and RNA.
The region of a prokaryote cell that contains its main DNA molecule, a naked, circular loop not enclosed by a membrane.
A dense region inside the nucleus of a eukaryote cell where ribosomal RNA is made and ribosome subunits are assembled.
The unit of DNA packing in eukaryotes: about 147 base pairs of DNA wrapped about 1.65 turns around an octamer of eight histones, held in place by histone H1.
The monomer of nucleic acids, consisting of a pentose sugar, a phosphate group and a nitrogenous base.
The organelle of eukaryote cells that contains the chromosomes, enclosed by a double membrane with pores; it controls the cell through the genes that are transcribed.
A statement that there is no difference, effect or association between the variables being studied, so that any observed difference is due to chance.
The continuous movement of a chemical element, such as carbon, nitrogen or phosphorus, between organisms and the abiotic environment, in which decomposers release it from dead matter in inorganic forms that producers reuse.