BJC General Science key terms

A testable statement predicting what will happen in an experiment, based on prior observation or reasoning. It must be worded so that evidence could show it to be wrong.

Any factor in an experiment that can change or be changed, such as temperature, time, or amount of a substance. Investigators adjust one and measure another.

A standard setup or group in an experiment where the tested factor is not applied, giving a baseline for comparison so the effect of the treatment can be judged.

A laboratory gas burner producing an adjustable flame, used for heating. The air hole controls the mix of gas and air, changing the flame from yellow and sooty to blue and hot.

The curved upper surface of a liquid in a narrow tube. It is read at eye level, taking the bottom of the curve for most liquids, to obtain an accurate volume.

The amount of three-dimensional space a substance or object occupies. It is measured in cubic units or litres, often with a measuring cylinder or by displacement.

The mass of a substance per unit of its volume, usually found by dividing mass by volume. Denser materials sink below less dense ones when placed together.

The quantity of matter in an object, measured in grams or kilograms with a balance. Unlike weight, it does not change when the object is taken to another place.

The force of gravity acting on an object's mass, measured in newtons with a spring balance. It changes with the strength of gravity, so it differs on the Moon.

A pure substance made of only one kind of atom, which cannot be split into simpler substances by chemical means. Examples include oxygen, iron, and carbon.

A pure substance formed when two or more different elements are chemically joined in fixed proportions, such as water or carbon dioxide. Its properties differ from its elements.

Two or more substances combined without chemical bonding, in any proportion. Each part keeps its own properties and the parts can usually be separated by physical means.

A separation method that pours a mixture through a filter to trap solid particles while liquid passes through. It separates an insoluble solid from a liquid.

A change of state in which a liquid gains energy and becomes a gas. In separation work it can recover a dissolved solid by boiling away the solvent.

A separation technique in which a liquid is boiled, its vapour is condensed and collected. It separates a solvent from dissolved solids or liquids with different boiling points.

A thin, flexible layer surrounding the cytoplasm of a cell. It controls which substances enter and leave, holding the cell together and allowing selective movement of materials.

The net movement of particles from a region of higher concentration to one of lower concentration, caused by random motion. It needs no energy input from the cell.

The movement of water across a partially permeable membrane from a dilute solution to a more concentrated one. It explains water uptake by plant roots and cell shape changes.

The process by which green plants use light energy to combine carbon dioxide and water into glucose, releasing oxygen. Chlorophyll in chloroplasts absorbs the light needed.

The green pigment found in chloroplasts that absorbs light energy for photosynthesis. It absorbs mainly red and blue light and reflects green, making leaves look green.

A protein that speeds up a specific chemical reaction in living things without being used up. Each enzyme works best at a particular temperature and pH.

The breakdown of large food molecules into small soluble ones that can be absorbed into the blood. It happens mechanically in the mouth and chemically by enzymes along the gut.

Tiny finger-like projections covering the inner wall of the small intestine. They greatly increase the surface area for absorbing digested nutrients into the bloodstream.

One of many tiny air sacs in the lungs where gas exchange occurs. Thin walls and a rich blood supply let oxygen enter the blood and carbon dioxide leave it.

Introducing a weakened or inactive form of a pathogen, or its antigens, so the body makes antibodies and memory cells. This gives protection against later infection.

A protein produced by certain white blood cells in response to a specific antigen. It binds to the invading organism or toxin and helps destroy or neutralise it.

A sex cell such as a sperm or egg, containing half the normal number of chromosomes. Two gametes join at fertilisation to form a new individual.

The joining of a male and a female gamete so that their nuclei fuse. The resulting cell has a full set of chromosomes and develops into a new organism.

A section of a chromosome that carries the instructions for a particular characteristic or protein. Genes are passed from parents to offspring and exist in different forms called alleles.

One of the alternative forms of a gene, such as the tall or short form for plant height. An individual inherits two alleles, one from each parent.

Describing an allele whose effect appears in the offspring even when only one copy is present. The masked allele is described as recessive.

A sequence showing how energy passes from one organism to another through feeding, beginning with a producer. Arrows point in the direction the energy travels.

An organism that makes its own food from simple substances, usually by photosynthesis, forming the base of a food chain. Green plants and algae are common examples.

An organism such as a bacterium or fungus that breaks down dead material and waste, releasing nutrients back into the soil. Decomposers recycle matter through ecosystems.

A push or a pull acting on an object, measured in newtons. A resultant force can change an object's speed, direction, or shape.

A force that opposes motion when two surfaces slide or rub against each other, converting kinetic energy into heat. It can be reduced with lubricants or smooth surfaces.

The rate of flow of electric charge around a circuit, measured in amperes. It flows only in a complete circuit and is the same at every point in a series loop.

The energy transferred per unit charge as charge moves between two points in a circuit, measured in volts. It is provided by a cell or battery and drives the current.

A measure of how strongly a component opposes the flow of electric current, measured in ohms. It depends on the material, its length, thickness, and temperature.

The reaction between an acid and a base that produces a salt and water. The products are usually closer to neutral pH than either reactant.

A scale from 0 to 14 expressing how acidic or alkaline a solution is. Values below 7 are acidic, 7 is neutral, and values above 7 are alkaline.

A substance that changes colour to show whether a solution is acidic or alkaline. Universal indicator gives a range of colours matching different pH values.