A consumer that feeds on producers; it occupies the second trophic level.
130 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
The parental generation in a series of genetic crosses: the two individuals (often pure-breeding) crossed first.
The peptidyl site of a ribosome, which holds the tRNA carrying the growing polypeptide chain.
The layer of tall, closely packed cells below the upper epidermis of a leaf, containing many chloroplasts; the main site of photosynthesis.
An epidemic that spreads across many countries or continents, affecting a large number of people.
A fundamental change in the accepted framework of ideas in a field of science, when evidence accumulates that the existing framework cannot explain.
A group that contains a common ancestor and some, but not all, of its descendants, such as the traditional reptiles, which exclude birds.
An interspecific relationship in which a parasite lives on or in a host and obtains food from it, harming the host but usually not killing it quickly.
The principle that, of all possible cladograms for a group of organisms, the one requiring the fewest evolutionary changes is the most likely to be correct.
A charge smaller than that of an electron or proton, written δ+ or δ−, found on atoms at the ends of a polar covalent bond because electrons are shared unequally.
The pressure exerted by one gas in a mixture of gases, proportional to its concentration; pO₂ is used as a measure of oxygen concentration, in kilopascals (kPa).
A membrane that allows some particles to pass through it but not others; in cells, small non-polar molecules cross the bilayer while ions and large polar molecules need membrane proteins.
Short-term protection from antibodies made by another organism, such as antibodies passed from mother to baby or given by injection; no memory cells are formed.
Movement of particles across a membrane down their concentration gradient using only their own kinetic energy, without energy from ATP; includes simple diffusion, facilitated diffusion and osmosis.
An organism or virus that causes disease in another organism (its host); most human pathogens are viruses, bacteria, fungi or protists.
Partly decomposed plant matter that accumulates in waterlogged, acidic, oxygen-poor conditions where decomposition is very slow; peatlands are long-term carbon sinks.
A diagram that shows the occurrence of a characteristic in the members of a family over several generations, used to deduce its pattern of inheritance.
A limb with one upper bone, two lower bones, a group of wrist or ankle bones and up to five digits, found in amphibians, reptiles, birds and mammals and inherited from a common ancestor.
A sugar with five carbon atoms; the pentose in DNA is deoxyribose and in RNA is ribose.
The covalent C–N bond between the carboxyl carbon of one amino acid and the amine nitrogen of the next, formed by a condensation reaction.
The polymer of sugars cross-linked by short chains of amino acids that forms the cell walls of bacteria; it is thick in Gram-positive bacteria.
The change in a quantity between two times expressed as a percentage of its original value: (new value − original value) ÷ original value × 100.
The difference between two comparable values measured at the same time, expressed as a percentage of their mean: |a − b| ÷ ((a + b) ÷ 2) × 100.
A membrane protein attached to one surface of the membrane, to phospholipid heads or to an integral protein, without entering the hydrophobic core of the bilayer.
Waves of contraction of the circular and longitudinal muscle in the wall of the gut that push food along in one direction.
Ground, including soil and rock, that has remained frozen for at least two consecutive years; in the Arctic it often contains large stores of undecomposed organic matter.
Medical care in which the prevention, diagnosis or treatment of disease is tailored to an individual, using information such as their genome sequence.
A white blood cell, such as a neutrophil or macrophage, that engulfs pathogens by endocytosis and digests them with enzymes from lysosomes.
A membrane-bound vacuole formed around a particle, such as a bacterium, taken into a cell by phagocytosis; it fuses with lysosomes so that the particle is digested.
A type of endocytosis in which a cell takes in large solid particles, such as bacteria, by enclosing them in a vesicle formed from the plasma membrane.
A loss of synchrony between the timing of life-cycle events in interacting species, such as a consumer's breeding and the peak of its food supply, often because they respond to different cues.
The study of the timing of recurring biological events, such as flowering, budburst, bud set, migration and breeding, and of how they are influenced by variables such as photoperiod and temperature.
The observable characteristics of an organism, resulting from its genotype and the effects of the environment.
The capacity of an organism to develop traits suited to its environment by changing patterns of gene expression, without any change in its genotype.
An inherited disease caused by a recessive allele of the gene for phenylalanine hydroxylase, so phenylalanine cannot be converted to tyrosine and builds up in the blood.
The vascular tissue that transports organic compounds, mainly sucrose, in solution from where they are made or stored to where they are used, through living sieve tubes.
The negatively charged group in a nucleotide, attached to carbon 5′ of the pentose, that links to the next sugar in the sugar–phosphate backbone.
The covalent bond, formed by a condensation reaction, linking the phosphate of one nucleotide to carbon 3′ of the pentose of the next in a nucleic acid strand.
A lipid made of glycerol linked to two fatty acids and a phosphate group; it is amphipathic, with a hydrophilic phosphate head and two hydrophobic tails.
A double layer of phospholipids in which the hydrophilic heads face the water on each side and the hydrophobic tails form the core; the basis of all cell membranes.
The addition of a phosphate group to a molecule, which usually makes it less stable and more reactive, as when glucose is phosphorylated at the start of glycolysis.
An autotroph that uses light as its external energy source to make carbon compounds by photosynthesis, such as plants, algae and cyanobacteria.
The splitting of water molecules using energy from light, which releases electrons, protons (H⁺) and oxygen; in photosynthesis the oxygen released comes from this reaction.
The length of the period of light in each 24-hour day, which organisms use as a cue to time seasonal events such as flowering, migration and breeding.
The production of carbon compounds in cells using light energy, with carbon dioxide and water as the raw materials and oxygen released as a by-product.
A coloured molecule, such as chlorophyll or a carotenoid, that absorbs specific wavelengths of light and uses the energy in photosynthesis.
A complex of proteins and an array of pigment molecules in a thylakoid membrane that absorbs light and passes the energy to a reaction centre, which emits an excited electron.
The photosystem (PSI, reaction centre P700) that re-excites electrons arriving from the electron transport chain and passes them to NADP reductase, or back to the chain in cyclic flow.
The photosystem (PSII, reaction centre P680) that emits excited electrons to the electron transport chain and replaces them by the photolysis of water, releasing oxygen.
A directional growth response to light from one side; shoots show positive phototropism, growing towards the light.
A branching diagram of the evolutionary relationships of a group of organisms; when drawn to scale, branch lengths represent time since divergence or amount of genetic change.
A signalling chemical produced by plant cells that controls growth, development or responses to stimuli, often in tissues away from where it is made.
A small endocrine gland near the centre of the brain that secretes melatonin, mainly at night, under the control of the suprachiasmatic nucleus.
A type of endocytosis in which a cell takes in small droplets of the surrounding fluid, with the solutes dissolved in it, in small vesicles.
The first organisms to colonise bare ground in primary succession; they tolerate harsh conditions and begin soil formation, for example lichens and mosses on bare rock.
A small endocrine gland below the hypothalamus whose anterior and posterior lobes secrete hormones, many of which control other endocrine glands.
The organ formed from fetal and maternal tissue in the uterus, through which substances are exchanged between the blood of the mother and the fetus without the two bloods mixing.
A diagram showing the outlines and positions of the tissues in an organ, without individual cells, drawn with clear, continuous lines and no shading.
An activated B-lymphocyte that has differentiated to secrete large amounts of one specific antibody.
The partially permeable membrane of phospholipids and proteins that surrounds the cytoplasm of every cell and controls what enters and leaves; also called the cell membrane.
A small, circular DNA molecule in many prokaryotes, separate from the main loop of DNA; plasmids carry a few genes, such as antibiotic resistance, and are not essential.
A narrow channel of cytoplasm through the cell walls of adjacent plant cells, allowing substances to pass directly between them, for example between companion cells and sieve tube elements.
The shrinking of the protoplast of a plant cell away from its cell wall when the cell loses water by osmosis in a hypertonic solution.
A lipid-soluble electron carrier in the thylakoid membrane that accepts electrons from photosystem II and carries protons from the stroma into the thylakoid space.
A small cell fragment without a nucleus, found in blood, that sticks to damaged vessel walls and releases clotting factors.
Describes a stem cell that can differentiate into any type of cell in the body, but not extra-embryonic cells, so cannot form a whole organism alone.
A specialised root that grows vertically upwards out of waterlogged mud, allowing gas exchange with the air through lenticels, as in Avicennia mangroves.
A change to a single base in the base sequence of DNA, such as the substitution of one base for another.
A small haploid cell, with very little cytoplasm, formed by the unequal division of the cytoplasm in meiosis I and meiosis II of oogenesis; it usually degenerates.
A covalent bond in which the electrons are shared unequally because one atom is more electronegative, giving one end a partial negative charge and the other a partial positive charge.
A molecule with an uneven distribution of electrical charge, so that one part carries a partial negative charge and another part a partial positive charge.
A small structure produced in the anther of a flower, with a tough outer wall, that contains the male gametes.
A tube that grows from a pollen grain on the stigma, through the style to an ovule, and carries the male gametes to the egg cell.
The transfer of pollen from an anther to a stigma.
A chain of adenine nucleotides added to the 3′ end of eukaryotic pre-mRNA, which protects the mRNA from breakdown.
The inheritance of a characteristic that is controlled by two or more genes, each with a small additive effect, which gives continuous variation.
A large molecule made of many similar subunits (monomers) linked together by covalent bonds, such as a polysaccharide, polypeptide or nucleic acid.
A technique that amplifies a chosen DNA sequence by repeated cycles of denaturation, primer annealing and extension, doubling the number of copies in each cycle.
An unbranched chain of many amino acids joined by peptide bonds, made on ribosomes; one or more polypeptides fold to form a protein.
Describes a group whose members evolved from more than one ancestral source, so they do not share a single most recent common ancestor; viruses are thought to be polyphyletic.
The condition of having more than two complete sets of chromosomes in each cell, such as three sets (triploid) or four sets (tetraploid).
A polymer of many monosaccharides joined by glycosidic bonds, such as starch, glycogen or cellulose.
The fertilisation of an egg by more than one sperm, which produces an embryo with too many sets of chromosomes.
A fatty acid with two or more carbon–carbon double bonds in its hydrocarbon chain, giving several kinks and a low melting point.
A group of organisms of the same species that live in the same area at the same time and normally interbreed.
A control mechanism in which a change in a variable triggers a response that increases the change still further, so that a process speeds up until it is completed.
Changes made to a eukaryotic pre-mRNA before translation: removal of introns and splicing of exons, and addition of a 5′ cap and a 3′ poly-A tail.
Changes made to a polypeptide after translation, such as removal of amino acids, cutting of the chain, glycosylation or forming disulfide bonds, that make it functional.
A mechanism acting after a hybrid zygote has formed, such as hybrid inviability, hybrid sterility or hybrid breakdown, so that alleles do not pass between species.
The neuron (or effector cell) on the receiving side of a synapse, whose membrane carries receptors for the neurotransmitter.
The tilting of a myosin head bound to actin, releasing ADP and phosphate, which pulls the actin filament towards the centre of the sarcomere.
A mechanism that prevents mating or fertilisation between individuals of different species, so that no hybrid zygote is formed.
How close repeated measurements of the same quantity are to each other; precise measurements show little spread, though they may still be inaccurate.
An interaction in which one animal, the predator, kills and eats another animal, the prey.
An animal that kills and eats other animals (its prey).
The movement of water and small solutes out of a capillary through gaps in its wall, driven by the high hydrostatic pressure of the blood, while cells and large proteins are held back.
The component of water potential due to hydrostatic pressure on water; positive under pressure, as in a turgid plant cell, and negative under tension, as in xylem (symbol Ψp).
The neuron that releases neurotransmitter into the synaptic cleft at a synapse.
A consumer that feeds on producers; it occupies the second trophic level.
The barriers that prevent pathogens from entering the body, mainly the skin and mucous membranes and their secretions.
The first response of the adaptive immune system to an antigen; it is slow to start and produces a relatively small amount of antibody, but forms memory cells.
The region of the cerebral cortex, in a strip across the top of each cerebral hemisphere, that initiates voluntary contractions of skeletal muscles.
The accumulation of carbon compounds in biomass by autotrophs, measured as mass of carbon (or dry biomass) per unit area per unit time, usually g m⁻² yr⁻¹.
The sequence of amino acids in a polypeptide, linked by peptide bonds; it determines the higher levels of structure and therefore the conformation of the protein.
Succession that begins in an area with no soil and no previous community, such as bare rock, a new volcanic island or ground exposed by a retreating glacier.
The tumour that forms first, at the site in the body where a cancer began.
A short single strand of nucleic acid that pairs with a complementary sequence on a template and provides a 3′ end from which DNA polymerase can start building a new strand.
An autotroph that makes carbon compounds from inorganic substances using light or chemical energy; producers form the first trophic level.
A steroid hormone secreted by the corpus luteum and later the placenta that maintains the endometrium and inhibits FSH and LH secretion.
The hypothesis that viruses arose from pieces of genetic material that escaped from cells and gained a protein capsid; also called the escape hypothesis.
An organism whose cells have no nucleus and no membrane-bound organelles; its DNA is a naked loop in the cytoplasm. Bacteria and archaea are prokaryotes.
A base sequence of DNA just upstream of a gene, where RNA polymerase binds, with transcription factors, to start transcription.
Checking of a new DNA strand by DNA polymerase III, which removes a nucleotide with a mismatched base from the 3′ end and replaces it with a correctly paired one.
Phage DNA that has been inserted into the chromosome of a host bacterium and is replicated with it, without producing new virions.
The first phase of mitosis, in which chromosomes condense, the spindle forms and the nuclear membrane breaks down.
A non-polypeptide component permanently bound to a protein and needed for its function, such as the haem group of haemoglobin.
A large protein complex that breaks down unneeded or damaged proteins, tagged with ubiquitin, into short peptides, allowing their amino acids to be reused.
A large molecule made of one or more polypeptides folded into a specific three-dimensional shape that determines its function.
An enzyme that adds phosphate groups from ATP to specific proteins, changing their activity; chains of protein kinases form the cascades of signal transduction pathways.
The complete set of proteins produced by a cell, tissue or organism at a particular time.
A normal gene whose product stimulates cell division, such as a growth factor receptor; a mutation can convert it into an oncogene.
A hypothetical early stage in the origin of cells: a vesicle enclosing self-replicating molecules such as RNA, able to grow and divide.
A difference in proton (H⁺) concentration across a membrane, built up by electron transport, which stores potential energy used by ATP synthase.
The coiled part of the nephron after Bowman's capsule, lined with cells with microvilli and many mitochondria, where all glucose and amino acids and most ions and water are reabsorbed.
The period of development during which the reproductive organs mature and secondary sexual characteristics appear, caused by rising secretion of GnRH, LH, FSH and the steroid sex hormones.
The rhythmic expansion and recoil of an artery wall caused by the pressure wave that each heartbeat sends through the arteries.
An integral membrane protein that uses energy from ATP to move specific particles across a membrane against their concentration gradient by changing shape.
A table that shows all the possible combinations of gametes from two parents, used to predict the genotypes and phenotypes of their offspring and their expected ratios.
A nitrogenous base with a double-ring structure; adenine and guanine are purines, and each pairs with a pyrimidine.
A nitrogenous base with a single-ring structure; cytosine, thymine and uracil are pyrimidines, and each pairs with a purine.
The three-carbon end product of glycolysis; it enters the link reaction when oxygen is available or is converted to lactate or ethanol when it is not.