39 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
The three-carbon compound produced by anaerobic respiration of glucose in human cells such as muscle fibres; its formation releases no carbon dioxide, and at HL it is the step that regenerates NAD.
The new DNA strand built discontinuously, away from the replication fork, as a series of Okazaki fragments that are later joined.
The hypothesis, proposed by Lamarck, that characteristics acquired by an organism during its lifetime through use or disuse are inherited by its offspring.
Sea ice that is attached to the coast, the sea floor in shallow water or an ice shelf, so that it does not drift with winds and currents.
The most recent population of organisms from which all organisms living today are descended; it was already a cell with DNA, ribosomes and the genetic code.
The loss of soluble mineral ions, such as nitrate, from soil as water drains through it, carrying them below the reach of plant roots and into groundwater and rivers.
The new DNA strand built continuously in the same direction as the replication fork moves, from a single RNA primer.
Carbon that has accumulated in the soil and biomass of an ecosystem over many years, decades or centuries, which can be released rapidly by fire or decomposition.
One of the four scales at which biology is studied: molecules, cells, organisms and ecosystems; each level is built from the one before it.
A rigid bar that turns about a fixed point (the fulcrum) so that an effort applied at one point moves a load at another; in animals, bones act as levers at joints.
A woody climbing plant rooted in the soil that uses trees for support to reach light in the canopy.
A tough band of fibrous connective tissue that joins bone to bone, holding a joint together and limiting its movement.
A signalling chemical that binds specifically to a receptor protein, causing a conformational change in the receptor that passes on the signal.
An ion channel that opens when a specific signalling molecule (ligand), such as a neurotransmitter, binds to it.
A microscope that uses visible light focused by glass lenses to form a magnified image; its resolution is limited to about 0.2 µm, but it can be used to view living cells in colour.
The reactions of photosynthesis on the thylakoid membranes that use light energy to split water, release oxygen and produce ATP and reduced NADP.
The reactions of photosynthesis in the stroma, also called the Calvin cycle, in which CO₂ is fixed by Rubisco, GP is reduced to triose phosphate using ATP and reduced NADP, and RuBP is regenerated.
A hard, waterproof polymer deposited in the cell walls of xylem vessels and other plant tissues, which strengthens them and stops them collapsing under tension.
The environmental factor that is furthest from its optimum value and so restricts the growth, survival, distribution or abundance of a species, or the rate of a process.
An estimate of population size from capture–mark–release–recapture data: , where M is the number marked in the first sample, n the total in the second sample and m the number recaptured.
The oxidation and decarboxylation of pyruvate in the mitochondrial matrix, producing CO₂, reduced NAD and an acetyl group carried by coenzyme A as acetyl-CoA.
The short stretch of DNA that connects one nucleosome to the next.
A member of a diverse group of carbon compounds that dissolve in non-polar solvents but are only sparingly soluble in aqueous solvents; includes fats, oils, waxes and steroids.
The movement of ions, mainly Na⁺ diffusing along the inside of an axon, from a depolarised region to the adjacent resting region, which depolarises that region to the threshold potential.
An early model of enzyme action in which the active site is a rigid shape that exactly fits the substrate, as a key fits a lock; replaced by the induced-fit model.
The movement of a whole organism from one place to another, for example by walking, swimming, flying or crawling.
The particular position of a gene on a chromosome.
A scale on which each equal interval represents multiplication by the same factor (for example 1, 10, 100, 1000), so that exponential change appears as a straight line.
The hairpin part of the nephron in the medulla; its water-impermeable ascending limb actively transports sodium ions out, making the medulla concentrated so water can be reabsorbed from collecting ducts.
The space inside a tubular structure such as a blood vessel, xylem vessel or gut, through which material flows.
A hormone (LH) secreted by the anterior pituitary; a surge of LH triggers ovulation and the formation of the corpus luteum.
Excess tissue fluid that has entered the lymphatic vessels, which carry it through lymph nodes and return it to the blood in the subclavian veins.
A small organ along the lymphatic vessels that filters lymph and contains large numbers of lymphocytes, which multiply there during an infection.
A thin-walled vessel of the lymphatic system with gaps that let tissue fluid in and valves that keep lymph flowing towards the subclavian veins.
A type of white blood cell with a large nucleus that is part of the adaptive immune system; B-lymphocytes produce antibodies and T-lymphocytes help control the response.
The bursting of a cell when its plasma membrane breaks, for example when an animal cell takes in water by osmosis in a hypotonic solution; in red blood cells it is called haemolysis.
The cycle in which phage DNA is integrated into the host chromosome as a prophage and replicated with it at every cell division, without making new virions, until induction triggers the lytic cycle.
A small membrane-bound vesicle in animal cells containing hydrolytic (digestive) enzymes, which break down food, worn-out organelles and engulfed bacteria.
The cycle in which a virus enters a host cell, uses the cell's machinery to replicate its genome and make viral proteins, assembles new virions and releases them by lysis, killing the cell.