69 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
A very large molecule made of thousands or more atoms, such as a polysaccharide, protein or nucleic acid; most macromolecules are polymers.
A large phagocyte found in tissues that engulfs pathogens and presents their antigens on its surface to helper T-lymphocytes.
A large piece of plastic debris, larger than 5 mm, such as a bag, bottle, packaging or fishing net, which can entangle or be swallowed by animals.
The number of times larger an image is than the real object; magnification = image size ÷ actual size, with both sizes in the same units.
A cancerous tumour whose cells divide rapidly, invade neighbouring tissue and can spread to other parts of the body by metastasis.
An event in which a large proportion of the Earth's species, usually 75% or more, become extinct in a geologically short time.
The largest harvest that can be taken from a population year after year without reducing its size, obtained by keeping the population at about half its carrying capacity, where growth rate is greatest.
The average of a set of values, calculated by adding the values and dividing by the number of values.
The range within which the true value of a measurement is expected to lie, set by the precision of the instrument and how it is read; written as ± a value with the same unit.
Irreversible inhibition in which an inhibitor in the active site is chemically changed by the enzyme and forms a covalent bond that permanently inactivates it, as penicillin does.
The middle value of a set of data arranged in order; for an even number of values, the mean of the two middle values.
The lowest part of the brainstem, joining the brain to the spinal cord, containing the cardiovascular and respiratory centres that control heart rate and ventilation.
Division of a diploid nucleus into four haploid nuclei by two successive divisions, producing nuclei that are genetically different from one another.
A hormone secreted by the pineal gland, mainly during darkness, that helps to set the timing of the sleep–wake cycle and other circadian rhythms.
The ease with which phospholipids and proteins move within a membrane; it depends on temperature, the proportion of unsaturated fatty acids and, in animal cells, cholesterol.
The difference in electrical charge (potential difference) across a plasma membrane, measured in millivolts, with the inside usually negative compared with the outside.
A long-lived lymphocyte produced during an immune response that remains in the body and responds rapidly if the same antigen is met again.
The monthly cycle of changes in the ovaries (the ovarian cycle) and the endometrium (the uterine cycle), controlled by FSH, LH, oestradiol and progesterone.
A region of undifferentiated plant cells that divide repeatedly by mitosis, producing new cells for growth.
A 1958 experiment that grew E. coli on heavy nitrogen (¹⁵N) and then light nitrogen (¹⁴N) and separated their DNA by density, showing that DNA replication is semi-conservative.
A small experimental ecosystem, enclosed in a container such as a sealed glass vessel, set up to investigate the effects of variables on a community under controlled conditions.
A sequence of enzyme-catalysed reactions in which the product of each reaction is the substrate of the next.
Water produced inside an organism by aerobic cell respiration of food, an important water source for desert animals such as kangaroo rats.
The complex network of interdependent and interacting chemical reactions that take place in a living organism.
The phase of mitosis in which chromosomes, attached to spindle microtubules from both poles, line up on the equator of the cell.
The spread of cancer cells from a primary tumour to other parts of the body, through blood or lymph, where they form secondary tumours.
A greenhouse gas (CH₄) produced by anaerobic decomposition by methanogens, for example in ruminants, rice paddies, wetlands and landfill; per molecule it absorbs infrared radiation far more strongly than CO₂.
A bundle of parallel cellulose molecules held together by hydrogen bonds; microfibrils give plant cell walls their high tensile strength.
A thin solid filament made of the protein actin, part of the cytoskeleton; microfilaments change cell shape and are involved in cell movement and division of the cytoplasm.
A photograph or digital image taken through a microscope; an electron micrograph is taken with an electron microscope and a light micrograph with a light microscope.
A piece of plastic smaller than 5 mm, either manufactured at that size or formed by the breakdown of larger plastic items.
A hollow cylinder made of the protein tubulin, part of the cytoskeleton; microtubules form the spindle in cell division and the core of cilia and flagella.
A tiny finger-like fold of the plasma membrane on the surface of some animal cells, such as those lining the small intestine, that increases the surface area for absorption.
The regular, usually seasonal, movement of animals from one region to another and back, for example between breeding and feeding areas.
The 1953 experiment in which methane, ammonia, hydrogen and water vapour were exposed to electrical sparks in a closed apparatus, producing amino acids and showing that carbon compounds can form from inorganic molecules.
A base substitution that changes a codon into one for a different amino acid, so one amino acid in the polypeptide is replaced.
The fluid inside the inner membrane of a mitochondrion, containing enzymes of the Krebs cycle and link reaction, 70S ribosomes and naked circular DNA.
A double-membrane organelle in which aerobic cell respiration produces ATP; the inner membrane is folded into cristae around a fluid matrix, which holds 70S ribosomes and circular DNA.
Division of the nucleus into two genetically identical daughter nuclei, each with the same number of chromosomes as the parent nucleus.
The ratio of the number of cells in mitosis to the total number of cells in a sample of tissue, used as a measure of how fast cells are dividing.
An organism that combines autotrophic nutrition (photosynthesis) with heterotrophic nutrition, such as Euglena; mixotrophs may be obligate or facultative.
The most frequent value, or class, in a set of data.
The way in which an organism obtains its energy and carbon compounds, such as photosynthesis, holozoic, mixotrophic or saprotrophic nutrition.
A species studied in depth because it is easy to keep, breed and manipulate, so that discoveries about it can be applied to other organisms.
Using the number of differences between base or amino acid sequences of two species to estimate the time since they diverged, assuming differences accumulate at a roughly constant rate.
An antibody produced by a clone of identical cells derived from a single B-lymphocyte, so all its molecules bind to the same site on one specific antigen.
A genetic cross that follows the inheritance of a single gene.
A small molecule that can be joined to other similar molecules by condensation reactions to form a polymer, for example glucose, an amino acid or a nucleotide.
A single sugar unit, such as glucose, fructose or ribose; the monomer from which disaccharides and polysaccharides are built by condensation.
A fatty acid with one carbon–carbon double bond in its hydrocarbon chain, which puts a kink in the chain and lowers its melting point.
Twins that develop from a single fertilised egg that splits into two embryos, so they have identical genomes.
A signalling chemical that forms a concentration gradient across an embryo and causes cells to develop differently according to the concentration they receive.
The definition of a species as a group of organisms that share the same set of observable structural features (morphology).
Describes an organism that can move from place to place by itself, such as most animals; motile animals are sampled by capture–mark–release–recapture.
A neuron that carries impulses from the central nervous system to an effector, such as a muscle, stimulating it to contract.
A single motor neuron together with all the skeletal muscle fibres it stimulates through neuromuscular junctions; all the fibres of the unit contract together.
Messenger RNA: RNA transcribed from a gene that carries its base sequence, as codons, to the ribosomes for translation.
A thin layer of tissue lining the openings and internal passages of the body that secretes mucus, which traps pathogens and particles.
The condition of an organism made of many cells that stay together, communicate and are specialised for different functions; it has evolved independently many times.
The existence of more than two alleles of a gene in the gene pool of a population; each individual still has only two of them.
Describes a stem cell that can differentiate into a limited range of cell types, usually within one tissue, such as blood stem cells in bone marrow.
An agent that increases the rate of mutation, such as benzo[a]pyrene, nitrosamines, mustard gas, UV light, X-rays and gamma rays.
A close interspecific relationship between two species in which both species benefit.
A mutualistic association between a fungus and the roots of a plant, in which fungal hyphae supply water and mineral ions to the plant and receive carbon compounds in return.
An insulating layer around an axon, made of many layers of plasma membrane wrapped round by Schwann cells, with small gaps at intervals, that increases the speed of nerve impulses.
The death of part of the heart muscle because its blood supply has been blocked, usually by a thrombus in a coronary artery; commonly called a heart attack.
A long cylindrical bundle of actin and myosin filaments inside a muscle fibre, divided along its length into repeating sarcomeres.
Describes contraction that starts in the muscle tissue itself, without a nervous stimulus; the heartbeat is myogenic because each beat starts in the sinoatrial node.
A motor protein forming the thick filaments of a sarcomere; its heads bind to actin, hydrolyse ATP and perform the power stroke that slides the filaments.