BGCSE Science Single Award 0568 flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Independent variable

The single factor that the investigator deliberately changes in an experiment, so that its effect on the measured dependent variable can be observed.

Control variable

A factor kept constant throughout an experiment to ensure any change in the dependent variable is caused only by the independent variable.

Accuracy vs precision

Accuracy is how close a measurement is to the true value; precision is how close repeated measurements are to each other under the same conditions.

Anomalous result

A reading that lies clearly outside the general trend of the other data, usually caused by a measurement or recording error, and excluded with a stated reason.

Meniscus reading

The curved surface of a liquid in a measuring cylinder. Read the bottom of the curve with the eye level with the mark to avoid parallax error.

Line of best fit

A straight or smooth line drawn through the centre of plotted data points to show the overall trend, ignoring clear outliers.

Magnification formula

Magnification equals image size divided by actual size. Convert both measurements to the same unit before dividing.

Osmosis

The net movement of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution, down a water potential gradient.

Active transport

Movement of substances across a cell membrane against a concentration gradient, using energy released by respiration and carrier proteins.

Enzyme denaturation

Above the optimum temperature, bonds holding an enzyme's active site break, changing its shape so the substrate no longer fits and activity falls.

Double circulation

A circulatory system in which blood passes through the heart twice per complete circuit, once to the lungs and once to the body.

Reflex arc

The pathway of a reflex response: receptor, sensory neurone, relay neurone in the spinal cord, motor neurone and effector muscle or gland.

Homeostasis

The maintenance of a stable internal environment, such as constant body temperature and blood glucose concentration, despite external changes.

Meiosis

Cell division producing four genetically different haploid gametes, halving the chromosome number and creating variation by crossing over and independent assortment.

Genotype and phenotype

Genotype is the combination of alleles an organism carries; phenotype is the observable characteristic produced by that genotype and the environment.

Dominant allele

An allele that is expressed in the phenotype even when only one copy is present, masking the effect of a recessive allele.

Discontinuous variation

Differences in a characteristic that fall into distinct categories with no intermediate values, usually controlled by one or a few genes.

Mass number

The total number of protons and neutrons in the nucleus of an atom, written as a superscript before the chemical symbol.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons, so they have different mass numbers.

Ionic bonding

Electrostatic attraction between oppositely charged ions formed when a metal atom transfers electrons to a non-metal atom.

Covalent bonding

A bond formed when two non-metal atoms share one or more pairs of electrons, so both achieve a full outer shell.

Activation energy

The minimum energy colliding particles need for a reaction to occur; a catalyst lowers it, increasing the proportion of successful collisions.

Exothermic reaction

A reaction that transfers energy to the surroundings, usually shown by a temperature rise, because the products have less stored energy than the reactants.

Conservation of mass

In a closed system the total mass of reactants equals the total mass of products, because atoms are rearranged, not created or destroyed.

Neutralisation

The reaction between an acid and a base or alkali to form a salt and water, bringing the pH towards 7.

Strong acid

An acid that ionises completely in water, releasing all its hydrogen ions, so it has a low pH and conducts electricity well.

Resultant force

The single force equivalent to all forces acting on an object; a non-zero resultant causes acceleration in its direction.

Kinetic energy formula

Kinetic energy equals one half multiplied by mass multiplied by speed squared, measured in joules when mass is in kilograms and speed in metres per second.

Refraction

The change in direction of a wave as it crosses a boundary between media, caused by a change in wave speed.

Wave equation

Wave speed equals frequency multiplied by wavelength; speed in metres per second, frequency in hertz, wavelength in metres.

Ohm's law

For a fixed resistance at constant temperature, current through a conductor is directly proportional to the potential difference across it.

Parallel circuit

A circuit in which components are connected across the same potential difference; branch currents add and total resistance is less than any single branch.

Trophic level

The position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer, defined by its feeding relationship.

Energy loss in food chains

Only about ten per cent of energy passes to the next trophic level; the rest is lost as heat through respiration, movement and undigested waste.