SRMHCAT key terms

The straight-line distance and direction from a starting point to an ending point, regardless of the path taken. It is a vector quantity measured in metres and can be zero even when distance travelled is not.

The rate at which displacement changes with time, including its direction. Average velocity divides total displacement by total time, while instantaneous velocity describes motion at a single moment.

The rate at which velocity changes with time, whether speeding up, slowing down, or changing direction. It is a vector measured in metres per second squared and can be negative during deceleration.

Scalars are quantities described fully by magnitude alone, such as mass, time, and temperature. Vectors need both magnitude and direction, such as force, velocity, and displacement, and combine by geometric rules rather than simple addition.

The net force on a body equals its mass multiplied by the acceleration produced, written F = ma. It links force, mass, and motion, and explains why heavier objects need larger forces for the same acceleration.

The single force that produces the same effect as all individual forces acting on a body combined. When it is zero, the body stays at rest or moves with constant velocity; otherwise the body accelerates.

The net work done on an object equals the change in its kinetic energy. It connects force applied over a distance with changes in speed and is often used instead of force analysis to solve motion problems.

The energy a body possesses because of its motion, calculated as one-half mass times velocity squared. It is always positive or zero and increases fourfold when speed doubles.

In the absence of friction and other non-conservative forces, the total of kinetic and potential energy in a system stays constant. Energy shifts between forms but is neither created nor destroyed.

The bending of light as it passes from one transparent medium into another of different optical density, caused by a change in speed. It explains why a stick appears bent in water.

A number expressing how much slower light travels in a medium compared with a vacuum, equal to the ratio of those speeds. Higher values mean greater bending of light at the boundary.

The complete reflection of light back into a denser medium when it strikes the boundary beyond the critical angle. It requires travel from denser to rarer medium and underlies optical fibres.

For a conductor at constant temperature, current through it is directly proportional to the potential difference across it, giving V = IR. Resistance is the constant of proportionality, measured in ohms.

The opposition a component offers to the flow of electric current, equal to voltage divided by current. It depends on material, length, cross-sectional area, and temperature, and dissipates energy as heat.

In series, components share one path, so current is the same and voltages add. In parallel, components share the same voltage while currents add, and total resistance is lower than the smallest branch.

A mole is the amount of substance containing Avogadro's number of particles, roughly 6.022 times ten to the twenty-third. It links the mass of a sample to the number of atoms or molecules it contains.

The number of particles in one mole of any substance, approximately 6.022 times ten to the twenty-third per mole. It allows conversion between particle counts and amounts in moles.

The mass of one mole of a substance in grams per mole, numerically equal to its formula mass in atomic mass units. It converts between mass and moles in calculations.

The quantitative relationship between reactants and products in a balanced chemical equation. Coefficients give mole ratios used to predict masses or volumes consumed and formed.

The reactant that is fully consumed first and therefore determines the maximum amount of product formed. Excess reagents remain after the reaction stops.

A logarithmic scale from 0 to 14 measuring hydrogen ion concentration, where pH equals the negative logarithm of that concentration. Values below 7 are acidic, above 7 basic, and 7 neutral at room temperature.

Acids donate protons or accept electron pairs, while bases accept protons or donate electron pairs. Their reaction, neutralisation, produces salt and water and is central to titration problems.

A solution that resists large pH changes when small amounts of acid or base are added, usually containing a weak acid with its conjugate base. Blood is a familiar natural example.

Oxidation is loss of electrons and increase in oxidation number; reduction is gain of electrons and decrease in oxidation number. The two always occur together in redox reactions.

A bookkeeping value showing the apparent charge an atom would have if bonding electrons were assigned to the more electronegative atom. It helps identify which species are oxidised or reduced.

A device converting chemical energy into electrical energy, or the reverse, through redox reactions at two electrodes. Electrons flow through an external circuit while ions move through the electrolyte.

The mixing of atomic orbitals to form new equivalent orbitals that explain molecular geometry, such as sp, sp2, and sp3. It predicts bond angles and shapes in molecules like methane and ethene.

The existence of compounds with the same molecular formula but different arrangements of atoms, giving different properties. Types include structural, geometric, and optical isomerism.

A specific group of atoms within a molecule that determines its characteristic chemical reactions, such as hydroxyl, carboxyl, or amino groups. It defines families of organic compounds.

A chemical bond formed when two atoms share one or more pairs of electrons. It is typically strong and directional, and occurs mainly between non-metals.

A specialised structure inside a cell performing a particular function, such as mitochondria for energy release or ribosomes for protein synthesis. Each has a membrane or distinct composition suited to its role.

A double-membraned organelle where aerobic respiration produces most of the cell's ATP. Its inner membrane is folded into cristae to increase the surface area for reactions.

A selectively permeable barrier of phospholipids and proteins surrounding the cell, controlling what enters and leaves. Its fluid mosaic structure allows transport, signalling, and recognition.

The movement of water across a semi-permeable membrane from a region of higher water potential to lower water potential. It is passive and drives water uptake in plant roots.

The process by which green plants, algae, and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen. It occurs in chloroplasts and underpins most food chains.

A green organelle containing chlorophyll where photosynthesis takes place. Its stacked thylakoid membranes capture light, while the surrounding stroma hosts sugar synthesis.

The stepwise breakdown of glucose to release usable energy as ATP, with or without oxygen. Aerobic respiration yields far more ATP than anaerobic pathways such as fermentation.

Patterns of inheritance described by Gregor Mendel, where alleles segregate and assort independently during gamete formation. Dominant and recessive alleles explain predictable ratios in offspring.

Genotype is the genetic makeup of an organism at particular loci, while phenotype is its observable traits. Environment and gene interactions shape how genotype produces phenotype.

A grid used to predict the possible genotypes of offspring from the alleles of two parents. It displays combinations of gametes and the resulting ratios.

The semi-conservative process by which a DNA molecule is copied before cell division. Each new double helix contains one original strand and one newly synthesised strand.

Transcription copies a DNA sequence into messenger RNA in the nucleus; translation reads that RNA at ribosomes to assemble a chain of amino acids into protein. Together they express genes.

A permanent change in the DNA sequence, caused by copying errors, radiation, or chemicals. Effects range from harmless to harmful or occasionally beneficial, and may be inherited.

A ratio compares two quantities by division, while a proportion states that two ratios are equal. Cross-multiplication solves for unknown terms in proportional relationships.

A fraction expressed out of one hundred, used to compare quantities and express change. Percentage increase or decrease is the change divided by the original value, multiplied by one hundred.

The sum of a set of values divided by the number of values, also called the arithmetic mean. It summarises a group but can be distorted by extreme values.

The relationship that distance equals speed multiplied by time, used to solve travel problems. Variations include relative speed for objects moving towards or away from each other.

Permutations count arrangements where order matters, while combinations count selections where order does not. Factorials and the nCr formula are used to compute them.

A number between zero and one expressing how likely an event is, calculated as favourable outcomes divided by total equally likely outcomes. Complementary events sum to one.

A form of logical reasoning with two premises leading to a conclusion, often tested with statements about categories. Validity depends on structure, not on real-world truth.

Reasoning from general statements to a necessary conclusion, where true premises guarantee a true conclusion if the form is valid. It contrasts with inductive reasoning, which generalises from examples.

A relationship question asking you to identify how one pair of items is connected and apply the same relationship to a second pair. Recognising the rule type is the key step.

A sequence of numbers following a hidden rule, such as arithmetic differences, squares, or alternating operations. The task is to find the pattern and predict the next or missing term.

A reasoning task where words or letters are transformed by a rule, and you must either apply the rule to new input or infer it from examples. Common rules shift letters or reverse order.