MECEE-BL Nepal key terms

The control of water and dissolved-solute balance inside an organism so that cells neither swell nor shrink. In humans the kidneys adjust how much water is reabsorbed, guided mainly by ADH.

The microscopic filtering unit of the kidney. Each one filters blood at the glomerulus, then reabsorbs useful substances and secretes wastes along its tubule to produce urine.

The tendency of a living system to keep internal conditions such as temperature, pH, and blood glucose within narrow limits despite changes outside. It relies on negative feedback loops.

A control mechanism in which a change triggers a response that opposes the change, restoring the original level. Examples include insulin lowering high blood glucose and sweating cooling an overheated body.

The net movement of water across a partially permeable membrane from a region of higher water potential to one of lower water potential. It needs no energy input from the cell.

A measure of the tendency of water to move from one place to another, usually written in pressure units. Pure water at atmospheric pressure has the highest value, set at zero.

The shrinking of a plant cell's protoplast away from its cell wall when the cell loses water by osmosis in a strongly hypertonic solution. It shows the wall is freely permeable.

Nuclear division that produces two genetically identical daughter nuclei with the same chromosome number as the parent. It underlies growth, repair, and asexual reproduction in eukaryotes.

Two successive nuclear divisions that halve the chromosome number and generate genetic variation through crossing over and independent assortment. It produces gametes in animals and spores in plants.

The exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis. It breaks linkage and creates new allele combinations.

The tendency of genes located close together on the same chromosome to be inherited together, so their alleles appear in offspring less often in independent ratios than free assortment predicts.

A model stating that allele and genotype frequencies in a large, randomly mating population stay constant across generations when there is no mutation, migration, or selection. It predicts p squared plus 2pq plus q squared equals one.

The proportion of all copies of a gene in a population that are of one particular allele. It is usually expressed as a decimal or percentage and changes under selection or drift.

The light-driven formation of ATP in chloroplast thylakoid membranes, using energy from electron transport and a proton gradient. It occurs in cyclic and non-cyclic forms during photosynthesis.

ATP synthesis driven by protons flowing back through ATP synthase down an electrochemical gradient across a membrane. It operates in mitochondria, chloroplasts, and aerobic bacteria.

The number of moles of solute dissolved in one litre of solution, with units mol per litre. It depends on total solution volume, not on the volume of solvent alone.

The number of moles of solute per kilogram of solvent. Unlike molarity it does not change with temperature, because it is based on mass rather than volume.

A procedure in which a solution of known concentration is added gradually to a measured volume of unknown solution until the reaction is just complete, usually signalled by an indicator.

The stage in a titration when the amount of titrant added exactly matches the stoichiometric requirement of the analyte. It is detected by an indicator or instrumental change, not necessarily at pH 7.

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.

A relationship giving the pH of a buffer as the acid's dissociation constant plus the logarithm of the ratio of conjugate base concentration to weak acid concentration. It is used to design buffers.

A logarithmic scale of hydrogen ion activity, defined as the negative logarithm to base ten of hydrogen ion concentration in dilute aqueous solution. Lower values mean greater acidity.

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts in the direction that partly opposes the disturbance until a new equilibrium is reached.

The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric power, at equilibrium for a given temperature. Its size indicates whether products or reactants dominate.

The property of a molecule that cannot be superimposed on its mirror image, usually because a carbon atom carries four different groups. Such molecules rotate plane-polarised light and exist as enantiomers.

Isomerism in which molecules have the same molecular and structural formula but different spatial arrangements of atoms. It includes geometric (cis-trans) and optical forms such as enantiomers.

A species that is electron-poor and accepts an electron pair from a nucleophile to form a new bond. Common examples are the proton, carbocations, and the positively charged end of a polarised carbonyl group.

A species with a lone pair or a negative charge that donates electrons to an electron-poor centre, forming a new covalent bond. Examples include hydroxide ion, ammonia, and water.

The induced electromotive force in a circuit equals the negative rate of change of magnetic flux through it. The minus sign expresses Lenz's law, which opposes the change.

An induced current flows in a direction whose magnetic effect opposes the change in flux that produced it. It follows from conservation of energy and gives the sign in Faraday's law.

The product of magnetic flux density and the area of a surface measured perpendicular to the field, with unit weber. It measures how many field lines pass through the surface.

A condition in which an oscillating system is driven at its natural frequency, so it absorbs energy efficiently and its amplitude reaches a maximum, as in a tuned radio circuit.

The frequency at which a system oscillates freely after being disturbed, determined by its mass and stiffness or capacitance and inductance. Driving it at this rate produces resonance.

The emission of electrons from a metal surface when light of sufficiently high frequency falls on it. The kinetic energy of escaping electrons depends on frequency, not on intensity.

The minimum energy needed to remove an electron from the surface of a particular metal. Light must supply at least this energy per photon for photoemission to occur.

The change in observed frequency of a wave when the source, the observer, or both move relative to the medium, heard as a higher pitch from an approaching siren.

The value that a function approaches as its input approaches a given point, whether or not the function is defined there. Limits underpin continuity, derivatives, and integrals.

A property of a function at a point when its limit there exists, the function is defined there, and the two are equal. Informally, the graph has no break or hole.

The instantaneous rate at which a function's value changes with respect to its variable, equal to the limit of a difference quotient. Geometrically it gives the slope of the tangent.

The limit of a sum of areas of thin rectangles under a curve between two limits, interpreted as signed area. It is computed using the fundamental theorem of calculus.

The maximum number of linearly independent rows, or equivalently columns, of a matrix. It equals the number of non-zero rows in its reduced row-echelon form.

A single number computed from a square matrix that tells whether the matrix is invertible. A zero determinant means the rows are linearly dependent and no inverse exists.

An arrangement of a set of items in which order matters, so choosing and ordering r items from n distinct items gives n factorial divided by n minus r factorial.

A selection of items from a larger set in which order is irrelevant. The number of ways to choose r items from n is n factorial divided by r factorial times n minus r factorial.

A rule for updating a probability when new evidence arrives, expressing the probability of a hypothesis given evidence in terms of the hypothesis's prior probability and the likelihood of the evidence.

The probability that an event occurs given that another event is known to have occurred, written as the probability of both events divided by the probability of the given event.

A measure of how far values in a data set typically lie from their mean, equal to the square root of the variance. It carries the same units as the original data.

The average of the squared deviations of data values from their mean. Squaring makes it sensitive to outliers and gives it squared units, so its square root is often preferred.

A sequence of numbers following a hidden rule, such as a constant difference, a ratio, or alternating operations. The task is to identify the rule and predict the missing term.

A reasoning task in which words or letters are converted into a code by a rule such as shifting letters or reversing order, and the candidate must apply or reverse that rule.

A form of deductive reasoning with premises that lead to a conclusion, tested by asking which conclusions necessarily follow. Only conclusions forced by the premises are valid.

A reasoning problem that describes family links in words or symbols and asks how two people are related. Drawing a family tree with gender and generation marked helps avoid errors.

A question format giving a problem plus two statements, where the candidate decides whether the statements supply enough information to answer, without actually computing the answer.

The process of sorting patients by urgency so that limited care goes first to those who will benefit most. It is used in emergencies, disasters, and crowded hospital departments.

Basic measurements that indicate whether the body is functioning normally: body temperature, pulse rate, breathing rate, and blood pressure. Abnormal values prompt further assessment.

A screening measure calculated as weight in kilograms divided by the square of height in metres. It classifies underweight, normal, overweight, and obesity but ignores body composition.

Indirect protection of unvaccinated people that arises when a large enough share of a population is immune, so a pathogen cannot easily spread from person to person.

The deliberate exposure of a person to a harmless form or component of a pathogen so that the immune system develops memory and can respond quickly to later real infection.

The ability of bacteria to survive and grow despite exposure to antibiotics that would normally kill or inhibit them, often arising from mutation or transfer of resistance genes.

A mixture of clean water, salts, and glucose given by mouth to replace fluid and electrolytes lost through diarrhoea or vomiting. Glucose helps sodium and water be absorbed.