ESSLCE key terms

The process by which green plants, algae and some bacteria use light energy to convert carbon dioxide and water into glucose, releasing oxygen as a by-product. It occurs mainly in chloroplasts containing chlorophyll.

The controlled release of energy from glucose inside cells. Aerobic respiration uses oxygen and yields much more energy than anaerobic respiration, which produces lactic acid or ethanol instead.

The net movement of water molecules through a partially permeable membrane from a region of higher water concentration to one of lower water concentration. It is passive and requires no energy input.

A protein that speeds up a specific biochemical reaction by lowering its activation energy. Each enzyme has an active site whose shape fits particular substrate molecules, and activity is affected by temperature and pH.

The genetic makeup of an organism for a particular characteristic, described by the alleles it carries, such as homozygous dominant, heterozygous or homozygous recessive. It interacts with the environment to produce the phenotype.

One of two or more alternative versions of the same gene occupying the same position on homologous chromosomes. Alleles may be dominant or recessive and determine the variation seen in inherited traits.

The observable characteristics of an organism, such as eye colour, height or blood group. It results from the genotype being expressed under particular environmental conditions.

The spontaneous spreading of particles from a region of higher concentration to a region of lower concentration, driven by random molecular motion. It is faster at higher temperatures and over shorter distances.

The green pigment found in chloroplasts that absorbs mainly red and blue light for photosynthesis and reflects green light. It is the reason most leaves appear green.

The amount of substance containing exactly 6.02 × 10^23 elementary particles, equal to the Avogadro constant. It links mass in grams to numbers of atoms, molecules or ions in calculations.

The mass of one mole of a substance, expressed in grams per mole and numerically equal to its relative molecular mass. It is used to convert between mass and amount of substance.

The ratio of the amounts of reactants and products shown by the coefficients in a balanced chemical equation. It allows the quantity of one substance to be calculated from a known quantity of another.

The reactant that is completely used up first in a reaction and therefore determines the maximum amount of product formed. The other reactants are said to be in excess.

A process in which a substance loses electrons, gains oxygen or loses hydrogen, and its oxidation number increases. It always occurs together with reduction in a redox reaction.

A process in which a substance gains electrons, loses oxygen or gains hydrogen, and its oxidation number decreases. It is the partner process to oxidation in every redox reaction.

The decomposition of an ionic compound, either molten or in solution, by passing a direct electric current through it using inert or reactive electrodes. Products depend on the ions present and their discharge potentials.

A logarithmic measure of the hydrogen ion concentration of a solution, defined as the negative logarithm to base ten of that concentration. Values below 7 are acidic and above 7 are alkaline.

One of two or more compounds with the same molecular formula but different arrangements of atoms, giving different physical or chemical properties. Examples include structural isomers and stereoisomers.

The resultant force on a body equals the product of its mass and its acceleration, written as F = ma. The acceleration is always in the direction of the resultant force.

The rate of change of velocity with respect to time, a vector quantity measured in metres per second squared. It occurs whenever speed, direction or both change.

The product of a body's mass and its velocity, a vector quantity measured in kilogram metres per second. In a closed system with no external force, total momentum is conserved.

The current through a metallic conductor is directly proportional to the potential difference across it, provided temperature stays constant, giving V = IR. Resistance is measured in ohms.

The rate at which energy is transferred or work is done, measured in watts, where one watt is one joule per second. In circuits it can be calculated as the product of voltage and current.

The change in direction of a wave as it passes from one medium into another of different optical density, caused by a change in speed. It is described by Snell's law.

An equation of the form ax² + bx + c = 0 where a is not zero. It can be solved by factorisation, completing the square or the quadratic formula, and has at most two real roots.

The expression b² − 4ac taken from a quadratic equation. Its sign shows whether the equation has two distinct real roots, one repeated real root or no real roots.

A rule that assigns to each element of a set exactly one element of another set. It may be written as f(x) and can be represented by a formula, table or graph.

The instantaneous rate of change of a function with respect to its variable, interpreted as the gradient of the tangent to its curve. It is found using differentiation rules from first principles or standard results.

A sequence in which the difference between consecutive terms is constant, called the common difference. Its nth term is a + (n − 1)d and its sum can be calculated by a standard formula.

A sequence in which each term after the first is obtained by multiplying the previous term by a fixed number called the common ratio. It may converge to a limit when the ratio is between minus one and one.

A number between zero and one expressing how likely an event is, calculated for equally likely outcomes as the number of favourable outcomes divided by the total number of possible outcomes.

A political idea holding that a people sharing language, culture or history should form a nation and control its own state. It drove both independence movements and unification struggles in modern history.

The practice by which a powerful state takes political control of another territory, settles it and exploits its resources and people. In Africa it shaped borders, economies and administration well beyond independence.

The supreme authority of a state to govern itself without external interference, including over its territory and citizens. It is a core principle of international relations and of the United Nations system.

A system of government in which power is divided between a central authority and constituent regional units, each with powers protected by a constitution. It contrasts with a unitary state.

The principle that everyone, including government officials, is subject to the same publicly known laws, applied equally and fairly by independent courts. It protects citizens against arbitrary power.

A conclusion drawn from evidence and reasoning rather than stated directly. In reading comprehension, an inference must be supported by details in the passage even though it is not written word for word.

The central point that a paragraph or whole passage is written to convey, usually stated in a topic sentence or implied through supporting details. Identifying it is essential for summarising a text.

The quality of a text that makes it easy to follow because ideas are logically connected and organised. It is achieved through linking words, consistent pronouns and clear paragraph structure.

A comparison that explains an unfamiliar idea by showing how it is similar to a familiar one, often in the form A is to B as C is to D. It tests the ability to recognise relationships between words or concepts.