69 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
A statistical test that compares the means of two samples to decide whether the difference between them is significant, using the size of the difference relative to the variation within the samples.
A biome with long, very cold winters, short cool summers and low to moderate precipitation, dominated by evergreen coniferous trees.
A heat-stable DNA polymerase from the thermophilic bacterium Thermus aquaticus, used in PCR because it is not denatured at about 95 °C.
A group of organisms at any level of a classification, such as a species, genus, family or kingdom.
The science of identifying, naming, describing and classifying organisms into groups.
A region of repeated short DNA sequences at each end of a eukaryotic chromosome that protects the chromosome from damage and from shortening during replication.
The last phase of mitosis, in which chromosomes reach the poles and uncoil and a nuclear membrane forms around each group.
A biome with warm summers, cool or cold winters and moderate rainfall through the year, dominated by deciduous broadleaved trees.
A bacteriophage that can follow either the lytic cycle or the lysogenic cycle; bacteriophage lambda is an example.
The strand of DNA that is transcribed; the mRNA made from it has a complementary base sequence. Also called the antisense strand.
Reproductive isolation caused by populations breeding or flowering at different times of day, season or year, so that they do not interbreed.
A specimen placed in a drop of liquid (water or stain) on a glass slide and covered with a cover slip, for viewing with a light microscope in a single session.
A tough, inelastic cord of fibrous connective tissue that joins a muscle to a bone and transmits the force of contraction to it.
A branch of a cladogram that ends at a tip, leading to a single species or group that is not divided further on the diagram.
The molecule that accepts electrons at the end of an electron transport chain; in aerobic respiration it is oxygen, which combines with electrons and protons to form water.
A consumer that feeds on secondary consumers; it occupies the fourth trophic level.
The overall three-dimensional folding of a single polypeptide, held by hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions between R-groups.
A cross between an individual of unknown genotype (or a heterozygote) and a homozygous recessive individual, so that the offspring phenotypes show the alleles in the gametes of the first individual.
One of the two male gonads, held in the scrotum, which produces sperm in its seminiferous tubules and secretes testosterone.
The main male sex hormone, a steroid made mainly in the testes; being non-polar, it diffuses through plasma membranes to receptors inside target cells.
The disproved hypothesis that DNA is a simple repeating unit of the four bases in equal amounts, which would make it unable to carry genetic information.
In science, a well-tested explanation of a wide range of observations that is supported by a large body of evidence and is used to make predictions; it is more than a guess.
The ability of a substance to transfer heat by conduction; water conducts heat more than 20 times faster than air.
An organism that lives and grows best at high temperatures, typically above 45 °C, such as Thermus aquaticus in hot springs.
A sensory receptor that detects temperature; peripheral thermoreceptors in the skin and central thermoreceptors in the hypothalamus send information to the hypothalamus.
The maintenance of body temperature within narrow limits by negative feedback, balancing heat gained from metabolism and the surroundings with heat lost to the surroundings.
The classification of all cellular organisms into three domains, Bacteria, Archaea and Eukarya, based mainly on differences in the base sequences of ribosomal RNA.
The membrane potential, about −50 mV, that must be reached for enough voltage-gated sodium channels to open to start an action potential.
An enzyme formed from the inactive plasma protein prothrombin during clotting, which converts soluble fibrinogen into insoluble fibrin.
The formation of a blood clot (thrombus) inside an intact blood vessel, which may block it.
A flattened membrane sac inside a chloroplast that holds chlorophyll and is the site of the light-dependent reactions of photosynthesis.
A pyrimidine base (T) found only in DNA, which pairs with adenine by two hydrogen bonds.
Two adjacent thymines on the same DNA strand joined by covalent bonds after absorbing UV radiation; the dimer distorts the helix and can cause errors in replication.
An iodine-containing hormone secreted by the thyroid gland, under control of the hypothalamus and pituitary gland, that raises the metabolic rate of body cells and so increases heat production.
The volume of air breathed in or out in one normal breath at rest, about 0.5 dm³ in an adult.
A critical threshold at which a small additional change pushes an ecosystem into a different state, which is often self-sustaining and difficult or impossible to reverse.
A group of similar cells, often with the material between them, that work together to perform a particular function.
The fluid that surrounds the cells of a tissue, formed from blood plasma forced out of capillaries; it has a similar composition to plasma but contains very few proteins and no red blood cells.
A very large elastic protein running from the Z-line to the M-line of a sarcomere; it holds myosin in place, prevents overstretching and recoils to help the sarcomere return to its resting length.
Regulation of the populations in a community by consumers at higher trophic levels, such as predators limiting the numbers of herbivores.
Describes a stem cell that can differentiate into any type of cell, including extra-embryonic cells such as the placenta, and so can form a whole organism.
The synthesis of RNA using a DNA strand as a template, carried out by RNA polymerase.
A protein that binds to a specific DNA sequence, such as a promoter, and helps or prevents the binding of RNA polymerase, controlling transcription of a gene.
The complete set of RNA molecules transcribed from the genome in a cell at a particular time.
A line across a habitat along which organisms are sampled at regular intervals, used to study how their distribution changes along an environmental gradient.
The synthesis of a polypeptide on a ribosome, with an amino acid sequence determined by the codons of mRNA.
The transport of organic compounds, mainly sucrose and amino acids, in solution through the sieve tubes of the phloem from sources to sinks.
A receptor protein that spans the plasma membrane, with a binding site for a hydrophilic ligand outside the cell, a hydrophobic region in the membrane and a region inside that passes on the signal.
A bacterial enzyme that forms peptide cross-links between peptidoglycan chains in the cell wall; the target of penicillin.
The loss of water vapour from the leaves and stems of a plant, by evaporation from mesophyll cell walls and diffusion out through the stomata.
A lipid formed from one glycerol molecule and three fatty acids joined by ester bonds in three condensation reactions; fats and oils are triglycerides.
A three-carbon sugar phosphate; formed by the lysis of hexose bisphosphate in glycolysis, and the product of the Calvin cycle in photosynthesis.
The presence of three copies of a particular chromosome in a cell instead of the normal two, for example trisomy 21, which causes Down syndrome.
Transfer RNA: a folded RNA molecule with an anticodon at one end and a specific amino acid attached at its 3′ end, which it brings to the ribosome.
A series of indirect effects passing down a food chain when a change in the population of a consumer, such as a top predator, alters the populations at lower trophic levels.
The position of an organism in a food chain, defined by the number of feeding steps between it and the producers.
A biome with high temperatures (about 25–28 °C) and heavy rainfall (usually over 2,000 mm) all year, dominated by tall, broadleaved evergreen trees.
A directional growth response of a plant to a directional stimulus; growth towards the stimulus is positive and growth away from it is negative.
A long regulatory protein lying along the actin filament that covers the myosin-binding sites in relaxed muscle and is moved aside when Ca²⁺ binds to troponin.
A regulatory protein complex on the thin filament; when calcium ions bind to it, it moves tropomyosin so that the myosin-binding sites on actin are exposed.
An abnormal mass of tissue formed by uncontrolled cell division.
A gene whose product restrains the cell cycle, repairs DNA or triggers the death of damaged cells; mutations that inactivate it allow uncontrolled division.
A treeless biome with very low temperatures for most of the year, low precipitation and permanently frozen subsoil (permafrost), with mosses, lichens and dwarf shrubs.
The pressure exerted by the contents of a plant cell against its cell wall, which builds up as water enters by osmosis; the wall pushes back with an equal pressure.
A form of diabetes in which the beta cells of the islets of Langerhans are destroyed by the body's own immune system, so little or no insulin is secreted.
A form of diabetes in which target cells become less sensitive to insulin (insulin resistance), so blood glucose is not lowered effectively even though insulin is secreted.
An extremely thin, flattened cell that forms most of the alveolar wall, keeping the diffusion distance for gas exchange very short.
A rounded cell in the alveolar epithelium that secretes surfactant from lamellar bodies, reducing surface tension, and can divide to replace type I pneumocytes.
An enzyme that phosphorylates tyrosine residues in proteins; the insulin receptor has tyrosine kinase activity in its region inside the cell.