48 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
The light band of a sarcomere, containing thin actin filaments only and divided by a Z-line; it shortens during contraction.
A cylinder of ice drilled from an ice sheet or glacier, containing trapped bubbles of ancient air and other evidence from which past atmospheric gas concentrations and temperatures are measured.
The ability to eliminate an infectious disease from the body, due to memory cells that can rapidly produce the specific antibody against its pathogen.
A light microscopy technique in which antibodies carrying a fluorescent marker bind to one specific protein, showing where that protein is located in a cell or tissue.
The embedding of the blastocyst in the endometrium of the uterus, about 6–7 days after fertilisation.
The conservation of species in their natural habitat, for example by protecting and managing ecosystems in nature reserves and national parks.
Fertilisation of eggs by sperm outside the body, in a laboratory dish, after which one or more embryos are transferred to the uterus.
Reproduction between closely related individuals, or self-fertilisation, which increases homozygosity and decreases genetic diversity and vigour.
The point at which the plasma membrane of a plant cell is just beginning to pull away from the cell wall as the cell loses water; turgor pressure has fallen to zero.
A pattern of inheritance in which a heterozygote has a phenotype intermediate between those of the two homozygotes, for example pink flowers from red and white parents.
The random and independent distribution of the alleles of different genes into gametes, caused by the random orientation of pairs of homologous chromosomes in meiosis I.
The variable that is deliberately changed by the experimenter in an investigation, such as temperature in an enzyme experiment.
Movement of a substance against its concentration gradient using energy from another substance moving down a concentration gradient that a pump has set up using ATP.
A model of enzyme action in which binding of the substrate changes the shape of both the active site and the substrate, so they fit closely and bonds in the substrate are stressed.
Reasoning from many specific observations to a general statement or theory, such as concluding that all organisms are made of cells after observing cells in many different organisms.
A disease caused by a pathogen that can be passed from one host to another, such as measles, tuberculosis or malaria.
The taking of food into the body, for example through the mouth into the gut, or into a food vacuole by phagocytosis.
A hyperpolarisation of the postsynaptic membrane, caused by an inhibitory neurotransmitter such as GABA opening Cl⁻ or K⁺ channels, which makes an action potential less likely.
The part of the immune system that responds in the same, non-specific way to broad categories of pathogen and does not change during an organism's life.
A gene mutation in which one or more nucleotides are added to the base sequence of DNA.
Breathing in: contraction of the diaphragm and external intercostal muscles increases the volume of the thorax, lowering pressure so that air flows into the lungs.
The extra volume of air that can be breathed in with maximum effort after a normal inspiration.
A globular protein hormone secreted by β cells of the pancreas that lowers blood glucose; it has two polypeptides (21 and 30 amino acids) linked by disulfide bonds.
Reduced sensitivity of target cells, such as liver, muscle and adipose cells, to insulin, so they take up less glucose; the physiological change underlying type 2 diabetes.
A membrane protein embedded in one or both layers of the phospholipid bilayer, held there by a hydrophobic region in the core; many span the whole membrane.
The coordination of the component parts of a system so that, together, they carry out the overall function of the system.
A specialised junction joining cardiac muscle cells end to end, containing gap junctions that allow electrical impulses to pass between cells and strong junctions that hold them together.
Muscles between the ribs: the external intercostals raise the ribs in inspiration and the internal intercostals lower them in forced expiration; they form an antagonistic pair.
The dependence of the parts of a biological system on one another, so that a change in one part, such as a molecule, cell, organ or species, affects the others.
The narrow space between the outer and inner membranes of a mitochondrion (or chloroplast) into which protons are pumped, building up a proton gradient.
An attraction between separate molecules, such as a hydrogen bond, which is much weaker than the covalent bonds holding atoms together within a molecule.
A neuron within the central nervous system that passes impulses from one neuron to another, for example from a sensory neuron to a motor neuron in a reflex arc.
The part of the cell cycle between divisions, in which the cell grows, synthesises proteins, replicates its DNA and carries out its normal functions.
The difference between the upper quartile and the lower quartile, which measures the spread of the middle 50% of the data.
Competition between individuals of different species for the same limited resource, such as food, light or space.
An enzyme that catalyses reactions inside the cell that produced it, in the cytoplasm or within an organelle, such as the enzymes of glycolysis.
A receptor protein in the cytoplasm or nucleus that binds a hydrophobic ligand, such as a steroid hormone, that has crossed the plasma membrane; the complex usually regulates transcription.
Competition between individuals of the same species for resources that are in limited supply, such as food, water, territory, light or mates.
A species moved by humans, deliberately or accidentally, to an area outside its natural range.
A non-coding sequence within a eukaryotic gene that is transcribed but removed from the pre-mRNA by splicing before translation.
An inward folding of a membrane or layer of cells, which increases surface area; in some cells the plasma membrane folds deeply into the cytoplasm.
An introduced species that spreads rapidly in its new range and harms endemic species or ecosystems, often by outcompeting them for resources.
An atom or group of atoms with an overall electrical charge because it has gained or lost electrons, such as Na⁺ (a cation) or Cl⁻ (an anion).
An attraction between oppositely charged ions or groups; in proteins, between positively charged (–NH₃⁺) and negatively charged (–COO⁻) R-groups.
An inadequate blood supply to a tissue, which deprives its cells of oxygen and nutrients.
Groups of endocrine cells in the pancreas; their beta cells secrete insulin and their alpha cells secrete glucagon in response to changes in blood glucose concentration.
Describes a solution with the same concentration of solutes as another solution, such as the cytoplasm of a cell, so that there is no net movement of water between them by osmosis.
The International Union for Conservation of Nature's assessment of species' risk of extinction, placing each in a category from Least Concern to Extinct using standard criteria.