UPMSP High School Science key terms

A starting substance present before a chemical change occurs, written on the left side of a chemical equation and consumed as the reaction proceeds to form new substances.

A new substance formed when reactants undergo a chemical change, written on the right side of a chemical equation and possessing properties different from the starting materials.

A symbolic representation of a reaction in which the number of atoms of each element is equal on both sides, satisfying the law of conservation of mass.

A chemical change in which a substance gains oxygen or loses hydrogen or electrons, such as burning magnesium in air to form magnesium oxide.

A chemical change in which a substance loses oxygen or gains hydrogen or electrons, for example the removal of oxygen from copper oxide by heating with hydrogen.

A reaction in which oxidation and reduction take place simultaneously, one substance losing electrons or gaining oxygen while another gains electrons or loses oxygen.

A substance that changes colour in acidic or basic solutions, such as litmus, methyl orange or phenolphthalein, allowing the nature of a solution to be identified.

A number from 0 to 14 expressing the concentration of hydrogen ions in a solution; values below 7 are acidic, 7 is neutral and above 7 is basic.

A reaction between an acid and a base that produces a salt and water, for example hydrochloric acid reacting with sodium hydroxide to give sodium chloride.

An ionic compound formed when the hydrogen of an acid is replaced by a metal or ammonium ion, commonly produced in an acid-base reaction along with water.

A metal oxide that reacts with both acids and bases to form salts, such as aluminium oxide or zinc oxide, showing both acidic and basic behaviour.

The gradual eating away of a metal surface by moisture, air or chemicals, as when iron rusts to form a reddish-brown flaky coating of hydrated iron oxide.

A method of protecting iron from rusting by coating it with a thin layer of zinc, which corrodes in preference to the iron beneath it.

A homogeneous mixture of a metal with one or more other elements, made to improve properties such as hardness, strength or resistance to corrosion.

A bond formed by the sharing of one or more pairs of electrons between atoms, typical of carbon compounds and of molecules such as water and ammonia.

The ability of an element, especially carbon, to link its own atoms into long chains or rings, giving rise to the very large number of carbon compounds.

A family of organic compounds with the same functional group and similar chemical properties, in which successive members differ by one carbon and two hydrogen atoms.

An atom or group of atoms attached to a carbon chain that determines the characteristic chemical properties of a compound, such as hydroxyl, carboxyl or aldehyde groups.

One of two or more compounds having the same molecular formula but different arrangements of atoms, and therefore different physical or chemical properties.

The process by which green plants use sunlight, carbon dioxide and water to make glucose and oxygen in chloroplasts containing the pigment chlorophyll.

Tiny pores on the surface of leaves through which carbon dioxide enters and oxygen and water vapour escape, opened and closed by guard cells.

The loss of water vapour from the aerial parts of a plant, mainly through stomata, which helps pull water and minerals upward through the xylem.

Vascular tissue that carries water and dissolved minerals from the roots upward to the stem and leaves, made of dead, hollow conducting cells.

Vascular tissue that transports food made in the leaves to other parts of the plant, including growing tips, roots, fruits and storage organs.

A rapid, automatic response to a stimulus in which a message travels through a reflex arc without waiting for conscious decision-making by the brain.

The structural and functional unit of the nervous system, a cell with dendrites, a cell body and an axon that carries electrical impulses.

The tiny gap between two nerve cells across which a chemical messenger diffuses so that an impulse can pass from one neuron to the next.

A chemical messenger secreted by an endocrine gland into the blood, which carries it to target organs where it regulates growth, metabolism or reproduction.

The transfer of pollen grains from the anther of a flower to the stigma, brought about by wind, water or animals and followed by fertilisation.

The fusion of a male gamete with a female gamete to form a zygote, which is the first cell of a new individual in sexual reproduction.

A form of asexual reproduction in plants in which new individuals arise from roots, stems or leaves, producing offspring genetically identical to the parent.

A characteristic that appears in the offspring when an organism carries at least one copy of the allele responsible for it, masking the recessive form.

A characteristic that is expressed only when both copies of the inherited allele are of the recessive type, remaining hidden when a dominant allele is present.

The genetic makeup of an organism, that is, the particular combination of alleles it carries for a trait, which may be homozygous or heterozygous.

The observable characteristics of an organism, such as seed shape or eye colour, resulting from its genotype together with the influence of the environment.

The distance between the optical centre of a lens or the pole of a mirror and its principal focus, determining how strongly it converges or diverges light.

The ratio of the speed of light in a vacuum to its speed in a given medium, expressing how much a ray bends on entering that medium.

The ratio of the height of an image to the height of the object, indicating how many times larger or smaller the image appears than the object.

Short-sightedness, a defect in which a person sees near objects clearly but distant objects blurred because the image forms in front of the retina.

Long-sightedness, a defect in which distant objects are seen clearly but nearby objects appear blurred because the image falls behind the retina.

The splitting of white light into its constituent colours when it passes through a refracting medium such as a glass prism, because each colour bends differently.

The redirection of light in many directions by tiny particles in a medium; it makes the sky appear blue and sunsets appear red.

The statement that the current through a conductor is directly proportional to the potential difference across it, provided its temperature remains constant.

The property of a conductor that opposes the flow of electric current, measured in ohms and depending on length, area, material and temperature.

A circuit in which components are connected one after another so that the same current flows through each and the total resistance is their sum.

A circuit in which components are connected across the same two points, so each receives the full supply voltage and the total current divides among them.

The rate at which electrical energy is transferred or consumed in a circuit, equal to the product of voltage and current and measured in watts.

The region around a magnet or current-carrying conductor in which its magnetic force can be detected, represented by field lines from north to south.

A coil of insulated wire wound in the shape of a cylinder; when current flows it behaves like a bar magnet with north and south poles.

The production of an electric current in a coil when the magnetic field linked with it changes, as when a magnet is moved near the coil.

A natural source that is replenished by natural processes within a short time, such as sunlight, wind, flowing water, biomass or geothermal heat.

A device that converts sunlight directly into electrical energy using a semiconductor material, commonly silicon, without any moving parts or fuel.

A mixture of gases, mainly methane and carbon dioxide, produced by the anaerobic decomposition of animal dung and plant waste in a biogas plant.