Botswana BGCSE Science Double Award (0569) flashcards

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

Cell membrane

A thin partially permeable layer surrounding the cell that controls which substances enter and leave, holding the cell contents together.

Osmosis

The net movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane, without requiring energy.

Enzyme active site

The specific region of an enzyme molecule where the substrate binds; its shape is complementary to the substrate and is destroyed on denaturation.

Alveolus

A tiny air sac in the lungs with thin moist walls and a rich blood supply, providing a large surface area for gas exchange.

Haemoglobin

The red pigment in red blood cells that combines with oxygen in the lungs and releases it in respiring tissues.

Villus

A finger-like projection of the small intestine wall that increases surface area and contains blood vessels for absorbing digested food.

Homeostasis

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

Antibody

A protein produced by lymphocytes that binds specifically to a particular antigen, helping to destroy or neutralise the pathogen.

Vaccination

Introducing weakened or inactive antigens into the body so that memory cells provide rapid immunity on later exposure.

Placenta

The organ through which nutrients, oxygen and waste pass between the mother's blood and the fetus's blood without mixing them.

Ovulation

The release of a mature egg from an ovary, triggered by a surge of luteinising hormone, usually around the middle of the menstrual cycle.

Trophic level

A feeding position in a food chain, such as producer or primary consumer, through which energy passes to the next level.

Decomposer

An organism such as a bacterium or fungus that breaks down dead material, releasing nutrients back into the soil.

Eutrophication

Nutrient enrichment of water causing excessive algal growth, then oxygen depletion by decomposers, killing fish and other animals.

Isotope

An atom of the same element with the same number of protons but a different number of neutrons, giving a different mass number.

Ionic bond

The electrostatic attraction between oppositely charged ions formed when electrons are transferred from a metal to a non-metal.

Covalent bond

A bond formed when two non-metal atoms share a pair of electrons, giving each atom a full outer shell.

Relative atomic mass

The weighted average mass of the atoms of an element compared with one-twelfth the mass of a carbon-12 atom.

Activation energy

The minimum energy colliding particles must possess for a chemical reaction to occur; catalysts lower this value.

Neutralisation

The reaction between an acid and a base or alkali producing a salt and water, bringing the pH towards seven.

Catalyst

A substance that increases the rate of a reaction by providing an alternative pathway with lower activation energy, remaining unchanged itself.

Displacement reaction

A reaction in which a more reactive metal takes the place of a less reactive metal in a compound or solution.

Electrolysis

The decomposition of a molten or dissolved ionic compound by passing an electric current, with oxidation at the anode and reduction at the cathode.

Alloy

A mixture of a metal with other elements; different-sized atoms disrupt the layers, making the material harder and stronger.

Sacrificial protection

Attaching a more reactive metal such as zinc or magnesium to iron so that it corrodes instead of the iron.

Acceleration

The rate of change of velocity, calculated as change in velocity divided by the time taken and measured in metres per second squared.

Principle of moments

For a body in equilibrium, the sum of clockwise moments about a pivot equals the sum of anticlockwise moments.

Kinetic energy

The energy possessed by a moving object, calculated as one half multiplied by mass multiplied by velocity squared.

Refraction

The change in direction of a wave as it passes from one medium to another because its speed changes.

Ohm's law

The current through a conductor is directly proportional to the voltage across it, provided temperature remains constant.

Half-life

The time taken for half of the radioactive nuclei in a sample to decay, or for the activity to halve.

Control variable

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