BGCSE Science Single Award 0568 key terms

A testable statement predicting what will happen in an investigation, based on prior knowledge. It must be possible to show it is wrong by collecting evidence.

Any factor in an investigation that can change or be changed. Investigators identify which one they alter, which they measure, and which they keep constant.

An investigation in which only the independent variable is changed while all other relevant factors are held constant, so any effect measured can be attributed to that change.

The extent to which repeated measurements or repeated trials give consistent results. Reliability is improved by taking repeats and calculating a mean.

How close a measured value is to the true value. Accuracy depends on using suitable instruments correctly and reading scales carefully, not on repeating the measurement.

How closely repeated measurements agree with each other, or how fine the scale divisions of an instrument are. Precise readings can still be inaccurate if there is a systematic error.

The smallest unit of living material able to carry out all the processes of life. Some organisms consist of one cell; others are built from many specialised cells.

A specialised structure inside a cell that performs a particular job, such as the nucleus, mitochondrion or chloroplast. Different organelles are suited to different functions.

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

The diffusion of water molecules across a partially permeable membrane from a dilute solution to a more concentrated solution. It is a passive process important in plant and animal cells.

A protein that speeds up a specific chemical reaction in living things without being used up. Each enzyme has an active site whose shape must fit its substrate.

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

The controlled release of energy from glucose in living cells. Aerobic respiration uses oxygen and releases carbon dioxide and water; anaerobic respiration releases less energy.

The breakdown of large insoluble food molecules into smaller soluble molecules that can be absorbed into the blood. It involves mechanical action and chemical action by enzymes.

The movement of digested food molecules through the wall of the small intestine into the blood. The lining has villi that increase surface area for efficient uptake.

The continuous movement of blood around the body, driven by the heart, delivering oxygen and nutrients to cells and removing carbon dioxide and other waste products.

The maintenance of a stable internal environment, such as constant body temperature and blood glucose concentration, despite changes outside the body. It relies on automatic control systems.

A rapid, automatic response to a stimulus that does not involve conscious thought, protecting the body from harm. The message passes through a reflex arc in the spinal cord.

A nerve cell specialised to carry electrical impulses quickly between parts of the body. It has a long fibre and branches that connect with other neurons or effectors.

A chemical messenger produced by a gland and carried in the blood to a target organ, where it alters the organ's activity. Hormones act more slowly than nerve impulses.

The fusion of a male gamete nucleus with a female gamete nucleus to form a zygote. In humans it happens in the oviduct; in flowering plants it occurs in the ovule.

A reproductive cell containing half the normal number of chromosomes, able to fuse with another gamete at fertilisation. Sperm and egg cells are human gametes.

Cell division that produces gametes with half the chromosome number of the parent cell. It creates genetic variation because the resulting cells differ from each other.

One of the alternative forms of a gene that can occupy the same position on a chromosome. Different combinations of alleles produce different characteristics.

Describing an allele whose effect appears in the phenotype even when only one copy is present. A recessive allele's effect shows only when two copies are inherited.

The observable characteristics of an organism, resulting from the interaction of its genotype with the environment. Two organisms with the same genotype may differ in phenotype.

The smallest particle of an element that can take part in a chemical reaction. It consists of a nucleus of protons and neutrons surrounded by electrons.

A pure substance made of only one kind of atom, which cannot be broken down into simpler substances by chemical means. Elements are listed in the periodic table.

A substance formed when two or more elements are chemically combined in fixed proportions, with properties different from those of the elements. Water and carbon dioxide are examples.

Two or more substances together in no fixed proportion, which can be separated by physical means because no chemical bonds join them. Air and salt solution are mixtures.

An atom or group of atoms that has gained or lost electrons, giving it a positive or negative electrical charge. Oppositely charged ions attract to form ionic compounds.

How quickly reactants are used up or products are formed in a chemical reaction. It increases with higher temperature, higher concentration, greater surface area or a catalyst.

A substance that speeds up a chemical reaction without being used up itself. It provides an alternative pathway of lower activation energy for the reaction.

A substance that releases hydrogen ions when dissolved in water, giving a solution with a pH below 7. Acids react with bases to form a salt and water.

A substance that can neutralise an acid, often by accepting hydrogen ions. A soluble base is called an alkali and gives a solution with a pH above 7.

The reaction between an acid and a base that produces a salt and water, bringing the pH towards 7. It is used to treat indigestion and to reduce soil acidity.

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

A force that opposes motion when two surfaces slide or tend to slide past each other, converting kinetic energy into heat. It can be reduced with lubricants or streamlined shapes.

The capacity to do work or cause change, measured in joules. Energy is conserved overall but is transferred between stores and often dissipated as heat.

The distance between two consecutive corresponding points on a wave, such as from one crest to the next. It is measured in metres and relates to frequency and wave speed.

The number of complete waves passing a point each second, measured in hertz. A higher frequency means a shorter wavelength for a wave of the same speed.

The change in direction of a wave when it crosses a boundary between materials at which its speed changes. It explains why a stick looks bent in water.

The rate of flow of electric charge around a circuit, measured in amperes. Current is the same at every point in a series circuit.

The energy transferred per unit charge as charge passes through a component, measured in volts. It is also called potential difference.

A measure of how difficult it is for current to flow through a component, measured in ohms. For a fixed voltage, a higher resistance allows a smaller current.

A sequence showing the transfer of energy from one organism to the next, beginning with a producer. Arrows point in the direction of energy flow.

An organism that makes its own food by photosynthesis, usually a green plant or alga, forming the first level of a food chain. It supplies energy to all other organisms in the chain.

An organism that obtains its energy by feeding on other organisms rather than making its own food. Herbivores, carnivores and decomposers are all consumers.