UEE Biology key terms

The small region of an enzyme where substrate molecules bind and the chemical reaction is catalysed, determined by the protein's three-dimensional shape and complementary to the substrate.

Loss of a protein's functional three-dimensional shape caused by heat, extreme pH or chemicals, which destroys hydrogen bonds and other weak interactions without breaking peptide bonds.

A protein (occasionally RNA) that acts as a biological catalyst, lowering activation energy and speeding up a specific reaction without being consumed, and is sensitive to temperature and pH.

The minimum energy that reacting molecules must possess for a collision to result in a chemical reaction; enzymes reduce this barrier rather than changing the overall energy yield.

The net movement of water across a partially permeable membrane from a region of higher water potential to a region of lower water potential, driven by differences in solute concentration.

A measure of the tendency of water to move from one region to another, expressed in pressure units; pure water at atmospheric pressure has a value of zero and solutes lower it.

Shrinkage of the protoplast away from the cell wall when a plant cell loses water by osmosis in a hypertonic solution, causing the vacuole to shrink and the membrane to pull inward.

The first stage of respiration in the cytoplasm, where one glucose molecule is split and oxidised to two pyruvate molecules, yielding a net gain of two ATP and two reduced NAD.

A series of reactions in the mitochondrial matrix that oxidises acetyl groups derived from pyruvate, releasing carbon dioxide and reducing NAD and FAD to carry electrons to the electron transport chain.

A membrane protein complex that uses the flow of protons down an electrochemical gradient to phosphorylate ADP, producing ATP in mitochondria and chloroplasts.

The movement of protons across a membrane through ATP synthase, driven by an electrochemical gradient established by electron transport, which couples oxidation reactions to ATP synthesis.

One of two or more alternative forms of a gene occupying the same locus on homologous chromosomes and differing in nucleotide sequence, which may produce different phenotypes.

The genetic constitution of an organism with respect to one or more genes, usually stated as the combination of alleles present, such as homozygous or heterozygous.

The observable characteristics of an organism resulting from the interaction between its genotype and the environment, including biochemical, physiological and morphological traits.

An allele that is expressed in the phenotype even when only one copy is present, masking the effect of a recessive allele in a heterozygote.

The fixed position of a gene on a chromosome, at which the alternative alleles of that gene are found on homologous chromosomes.

The tendency of genes located close together on the same chromosome to be inherited together, so their alleles do not assort independently and recombinant offspring are fewer than expected.

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis, producing new combinations of alleles on recombinant chromosomes.

A reduction division producing four haploid cells from one diploid cell through two successive divisions, generating genetic variation by independent assortment and crossing over.

Synthesis of a messenger RNA molecule from a DNA template by RNA polymerase, occurring in the nucleus of eukaryotes and the cytoplasm of prokaryotes.

The process at ribosomes in which the base sequence of mRNA is decoded into a specific sequence of amino acids, using tRNA molecules that carry matching anticodons.

A sequence of three consecutive bases in mRNA that specifies one amino acid or a stop signal during protein synthesis; the genetic code is degenerate and non-overlapping.

A change in the base sequence of DNA, such as substitution, deletion or insertion, which may alter the polypeptide produced or have no effect at all.

The loss of water vapour from the aerial parts of a plant, mainly through stomata, which drives the upward movement of water in the xylem and cools the leaves.

Pores in the leaf epidermis, each bounded by two guard cells, that allow gas exchange and control water loss by opening and closing in response to environmental and hormonal signals.

Vascular tissue of dead, lignified hollow cells that transports water and dissolved mineral ions upward from the roots to the shoots, also providing structural support.

The transport of sugars and other organic solutes through the phloem from sources such as mature leaves to sinks such as roots, fruits and growing tissues.

A directional growth response of a plant towards or away from an external stimulus such as light or gravity, mediated by the unequal distribution of auxin.

A plant hormone, principally indoleacetic acid, that promotes cell elongation, controls apical dominance and mediates responses such as phototropism and gravitropism.

The maintenance of a stable internal environment within narrow limits despite external change, achieved by negative feedback control of variables such as temperature, blood glucose and water potential.

A control mechanism in which a change in a variable is detected and triggers a response that counteracts the change, restoring the variable towards its set point.

The control of water and solute balance in body fluids, achieved in mammals mainly by the kidneys adjusting water reabsorption under the influence of ADH.

The differential survival and reproduction of individuals because of heritable variation in traits, leading to changes in allele frequencies across generations and adaptation to the environment.

The formation of new species when populations become reproductively isolated and diverge genetically, for example through geographical separation followed by accumulation of different mutations.

The system of naming species with two Latinised names, the genus followed by the species epithet, both italicised, providing a universal and stable scientific label.

A group of organisms with similar morphology and physiology that can interbreed to produce fertile offspring, though the concept is applied with difficulty to asexual organisms.

The position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer, determined by the number of energy-transfer steps from the start.

The passage of energy between trophic levels in a food chain, which is inefficient because much energy is lost as heat, in movement and in uneaten or undigested material.

The maximum population size of a species that an ecosystem can sustain indefinitely given the available resources, often represented as the plateau of a logistic growth curve.

The ability of bacteria to survive and multiply in the presence of an antibiotic, arising by mutation or gene transfer and spread by selection when antibiotics are used.

Administration of antigens from a pathogen, or weakened forms of it, to stimulate an immune response and produce memory cells that give protection against later infection.

A statistical relationship in which two variables change together, which does not by itself establish that one variable causes the other.

A comparison group in an experiment that is treated identically to the experimental group except for the variable being tested, allowing the effect of that variable to be isolated.