UPCATET key terms

The planned sequence of different crops on the same field across seasons, used to interrupt pest and disease cycles, balance soil nutrients, and maintain organic matter and soil structure.

Growing a leafy crop such as sunhemp or dhaincha and ploughing it into the soil while still green, so that its nitrogen and organic matter enrich the field before the next crop.

A plant of the pea family that forms root nodules with Rhizobium bacteria and fixes atmospheric nitrogen, leaving extra nitrogen in the soil for the following crop.

The stage of crop growth during which weeds must be controlled to prevent the largest yield loss, usually early in the season when the crop is small and slow growing.

The property by which a herbicide kills target weeds at a dose that the crop can tolerate, depending on crop species, growth stage, formulation, dose, and method of application.

The total number of negatively charged sites on soil particles that hold exchangeable cations such as calcium, magnesium, potassium, and ammonium; a measure of the soil's ability to retain nutrients.

The percentage of the soil's cation exchange capacity occupied by basic cations (calcium, magnesium, potassium, sodium) rather than acidic ones such as hydrogen and aluminium.

A logarithmic measure of the hydrogen ion activity in the soil solution, indicating acidity or alkalinity and governing nutrient availability, microbial activity, and choice of crop and amendment.

The removal of anthers from a flower before they shed pollen, done in plant breeding so that the flower can be pollinated only with pollen chosen by the breeder.

A genetic mechanism in which a plant's own pollen fails to fertilise its ovules, promoting cross-pollination and requiring breeders to use different parental lines in hybrid seed production.

The superior growth, yield, or vigour of an F1 hybrid compared with its parents, exploited commercially in crops such as maize, sorghum, and many vegetables.

Seed formation without fertilisation, so that offspring are genetically identical to the mother plant; useful for fixing hybrid vigour in a crop over successive generations.

Air spaces or cavities in plant tissue, such as the large air chambers in the stem and root cortex of aquatic plants that provide buoyancy and internal ventilation.

A spongy plant tissue with large interconnected air spaces that allows oxygen to move from aerial parts to submerged roots, typical of wetland and aquatic species.

The loss of water vapour from aerial plant surfaces, mainly through stomata, which drives the upward movement of water and minerals and cools the leaf.

Small pores in the leaf epidermis bounded by guard cells, through which carbon dioxide enters and water vapour and oxygen leave; opening is regulated by turgor and light.

The control of several apparently unrelated traits by a single gene, as when one mutation affects both flower colour and stem height in a plant.

Interaction between genes at different loci in which one gene masks or modifies the expression of another, altering the expected Mendelian ratios in the offspring.

The tendency of genes located close together on the same chromosome to be inherited together, so that their alleles do not assort independently.

The feeding position an organism occupies in a food chain, such as producer, primary consumer, or secondary consumer; energy available falls at each higher level.

A graphical representation of numbers, biomass, or energy at successive trophic levels in an ecosystem, showing the progressive reduction of energy up the chain.

The maximum population size of a species that a given habitat can sustain indefinitely with the resources available, beyond which mortality or emigration increases.

The concentration of a solution expressed as moles of solute per litre of solution; it changes slightly with temperature because solution volume expands or contracts.

The concentration expressed as moles of solute per kilogram of solvent; unlike molarity it is independent of temperature and is preferred for colligative property calculations.

A concentration measure equal to the number of gram equivalents of solute per litre of solution, used in acid-base and redox titrations where equivalent weights matter.

A solution that resists a change in pH when small amounts of acid or base are added, usually made from a weak acid with its conjugate base or a weak base with its conjugate acid.

The negative logarithm to base ten of the hydrogen ion concentration in a solution; values below seven are acidic, above seven alkaline, and seven is neutral at room temperature.

The existence of molecules with the same structural formula but non-superimposable mirror images, which differ in the direction they rotate plane-polarised light.

The geometric property of an object that cannot be superimposed on its mirror image; in molecules it usually arises from a carbon atom bonded to four different groups.

The motion of an object launched into the air and moving under gravity alone, with constant horizontal velocity and constant vertical acceleration when air resistance is ignored.

The rotational analogue of mass, measuring how strongly an object resists angular acceleration; it depends on the object's mass and on how that mass is distributed about the axis.

The energy an object possesses because of its motion, equal to half the mass times the square of its speed for translation, and to half the moment of inertia times angular speed squared for rotation.

The upward movement of a liquid in a narrow tube or soil pore caused by surface tension and the relative strength of adhesive and cohesive forces between liquid and wall.

The force per unit length acting along the surface of a liquid, arising because surface molecules have unbalanced attractive forces; it makes drops spherical and supports small objects.

An arrangement of a set of objects in a definite order; the number of permutations of n distinct objects taken r at a time is n factorial divided by (n minus r) factorial.

A selection of objects from a group in which order does not matter; the number of combinations of n objects taken r at a time equals n factorial divided by r factorial times (n minus r) factorial.

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

A measure of the spread of data around the mean, equal to the positive square root of the variance; a small value means observations cluster near the mean.

A form of deductive reasoning with two premises and a conclusion, in which the conclusion follows necessarily from the premises if the argument is valid.

A reasoning puzzle type in which relationships among family members are described in coded or indirect statements, and the candidate must deduce how two named people are related.

A reasoning item presenting a pair of related words or numbers and asking the candidate to complete a second pair that shares the same logical relationship.

A word that expresses a meaning opposite to that of another word, such as 'scarce' for 'abundant'; tested in English vocabulary sections of competitive examinations.

A word that has the same or nearly the same meaning as another word in a given context, such as 'begin' and 'commence'; commonly tested in English usage questions.

A fixed expression whose meaning cannot be worked out from the literal meanings of its individual words, such as 'to bite the bullet' meaning to endure something difficult.

An English usage item requiring a single word that replaces a whole phrase, such as 'philanthropist' for a person who gives generously to good causes.