MDCAT key terms

The ability of a living organism to keep its internal conditions, such as temperature and blood glucose, within a narrow, stable range despite changes in the outside environment.

The movement of water across a partially permeable membrane from a region where water is more abundant to one where it is less abundant, driven by the difference in water potential.

A protein, or sometimes an RNA molecule, that speeds up a specific biochemical reaction by lowering its activation energy without being consumed or permanently changed by the reaction.

Adenosine triphosphate, the small molecule cells use as their immediate energy currency; breaking its terminal phosphate bond releases energy that powers movement, transport, and synthesis.

The type of cell division that produces two genetically identical daughter cells from one parent cell, used for growth, repair, and asexual reproduction in many organisms.

One of the alternative versions of a gene at a particular position on a chromosome; different alleles may produce different traits, and an individual inherits one from each parent.

The process in which individuals with inherited traits that suit their environment tend to survive and reproduce more, so those traits become more common in later generations.

The microscopic functional unit of the kidney, consisting of a filtering capsule and a tubule; it removes wastes from blood and reabsorbs useful water, salts, and glucose.

A chemical messenger released by a gland or cell into the blood, which travels to target cells and alters their activity, helping to regulate growth, metabolism, and reproduction.

The amount of a substance that contains the same number of particles as there are carbon atoms in exactly twelve grams of carbon-12; used to count atoms and molecules in bulk.

The number of particles in one mole of a substance, approximately 6.02 × 10^23 per mole; it connects particle counts to measurable masses in chemistry calculations.

A measure of solution concentration equal to the number of moles of solute dissolved in one litre of solution; often written as mol/dm³.

An atom of the same element that has a different number of neutrons, and therefore a different mass number, but the same number of protons and the same chemical behaviour.

The state of a reversible reaction in which the forward and reverse rates are equal, so the concentrations of reactants and products stay constant even though both reactions continue.

A scale from about 0 to 14 that expresses how acidic or alkaline a solution is, calculated from the concentration of hydrogen ions present.

A reaction in which an atom, ion, or molecule loses electrons, and usually also loses hydrogen or gains oxygen; it is always accompanied by reduction.

A fairly strong attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom and a lone pair of electrons on a nearby electronegative atom.

The use of a direct electric current, passed through an electrolyte using inert or reactive electrodes, to drive a non-spontaneous chemical change such as decomposing a compound.

The principle that whenever one body exerts a force on a second, the second exerts an equal force on the first in the opposite direction; the two forces act on different bodies.

The energy transferred to or from an object when a force acts on it while it moves, calculated as force multiplied by displacement in the direction of the force.

The rule that, for a conductor kept at constant temperature, the current through it is directly proportional to the potential difference across it, with resistance as the constant of proportionality.

The ratio of the speed of light in a vacuum to its speed in a given medium; it measures how much the medium bends light and is always greater than one.

The time taken for half the atoms of a radioactive sample to decay, or for the concentration of a substance to fall to half its initial value; it does not change with sample size.

The large increase in the amplitude of vibration of a system when it is driven at a frequency close to its own natural frequency; it can be useful or destructive.

A region around a charged object where another charge would experience a force; its strength at a point is the force per unit charge placed there.

The energy absorbed or released when a substance changes state at constant temperature, without any change in its kinetic energy, for example when ice melts.

The steady speed reached by a falling object when the upward drag force, plus any buoyancy, has become equal in size to its weight, so its acceleration is zero.

A word that has the same, or very nearly the same, meaning as another word; for example, begin and start are synonyms.

The feelings or ideas a word suggests beyond its literal dictionary meaning, such as the emotional tone that makes slender sound more positive than skinny.

A conclusion drawn from stated evidence by reasoning rather than direct statement; the reader combines clues in the text with general knowledge to reach it.

A sentence construction in which the subject performs the action, as in the student answered the question, rather than receiving it.

A descriptive phrase that does not clearly connect to the word it is meant to describe, so that the sentence seems to say something absurd or unintended.

The practice of expressing items in a list or comparison in the same grammatical form, which makes writing clearer, more balanced, and easier to read.

The central point a passage is written to convey; it is usually broad enough to cover all the supporting details but narrow enough to say something specific.

A statement in an argument offered as a reason or evidence for accepting another statement; it is what the arguer expects the reader to accept as true.

The statement an argument is trying to establish; it is the claim supported by the premises and is usually signalled by words like therefore or so.

An unstated belief that an argument depends on, which must be true for the premises to support the conclusion; spotting it helps reveal hidden weaknesses in reasoning.

A common pattern of faulty reasoning that makes an argument look convincing when it is not, such as attacking a person instead of their argument.

A deductive argument made of two premises and a conclusion, in which statements about groups are combined, as in all A are B, all B are C, so all A are C.

A relationship in which two variables tend to change together; on its own it does not prove that one variable causes the other, because a third factor may be responsible.