WASSCE key terms

The process by which green plants use sunlight, water, and carbon dioxide to make glucose and release oxygen. Chlorophyll in the chloroplasts captures the light energy that drives the reaction.

The breakdown of food substances such as glucose to release energy in living cells. Aerobic respiration uses oxygen and gives carbon dioxide and water; anaerobic respiration occurs without oxygen.

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

A biological catalyst, usually a protein, that speeds up chemical reactions in living things without being used up. Each enzyme works best at a particular temperature and pH.

The movement of water molecules through a semi-permeable membrane from a region of higher water concentration to a region of lower water concentration. It explains water uptake by plant roots.

The net movement of particles from a region of higher concentration to a region of lower concentration, caused by random motion. It does not need a membrane or energy from the cell.

The movement of substances across a cell membrane against a concentration gradient, using energy from respiration. It allows cells to absorb mineral ions even when they are scarce outside.

The shrinking of a plant cell's cytoplasm away from the cell wall when the cell loses water by osmosis. It happens in a strong sugar or salt solution and can make the plant wilt.

Cell division that produces two daughter cells with the same number of chromosomes as the parent cell. It is used for growth, repair, and asexual reproduction.

Cell division that produces four daughter cells, each with half the chromosome number of the parent cell. It forms gametes and creates genetic variation through crossing over and independent assortment.

The genetic makeup of an organism for a particular characteristic, such as the pair of alleles it carries. It is often written with letters, for example AA, Aa, or aa.

The observable characteristics of an organism that result from its genotype and its environment. Examples include eye colour, plant height, and blood group.

One of two or more alternative forms of a gene that can occupy the same position on a chromosome. A dominant allele shows in the phenotype even when only one copy is present.

A community of living organisms interacting with one another and with their non-living surroundings, such as soil, water, and air. Energy flows through it and nutrients are recycled.

A sequence of organisms in which each one feeds on the one before it, showing the direction of energy flow. It usually begins with a producer and ends with a top consumer.

An organism such as a bacterium or fungus that breaks down dead plants and animals and returns nutrients to the soil. Decomposers keep nutrients cycling within an ecosystem.

The amount of a substance that contains the same number of particles as there are atoms in 12 g of carbon-12, that is 6.02 x 10^23 particles. It links mass, particles, and gas volume.

The mass of one mole of a substance, expressed in grams per mole. It is found by adding the relative atomic masses of all the atoms in the formula.

The number of particles in one mole of a substance, approximately 6.02 x 10^23 per mole. It allows chemists to count atoms and molecules by weighing them.

The average mass of the atoms of an element compared with one-twelfth the mass of a carbon-12 atom. It takes the natural abundances of the element's isotopes into account.

One of two or more atoms of the same element with the same number of protons but different numbers of neutrons. Isotopes have identical chemical properties but different masses.

The strong electrostatic attraction between oppositely charged ions formed when electrons are transferred from a metal atom to a non-metal atom. Ionic compounds usually form crystals and conduct when molten or dissolved.

A bond formed when two atoms share one or more pairs of electrons. Covalent compounds are usually simple molecules with low melting points and do not conduct electricity.

The decomposition of an ionic compound, in molten form or in solution, by passing a direct electric current through it. Positive ions move to the cathode and negative ions to the anode.

A reaction in which a substance loses electrons, gains oxygen, or loses hydrogen. In terms of electron transfer it is the opposite of reduction and always occurs alongside it.

A reaction in which a substance gains electrons, loses oxygen, or gains hydrogen. It is the partner process to oxidation in every redox reaction.

A substance that releases hydrogen ions when dissolved in water, turning blue litmus red and reacting with bases to form salts. Examples include hydrochloric acid and sulphuric acid.

A substance that reacts with an acid to form a salt and water only, often by accepting hydrogen ions. Soluble bases such as sodium hydroxide are called alkalis.

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

The rate of change of displacement with time, expressed as a vector with both size and direction. It differs from speed, which has size only and ignores direction.

The rate of change of velocity with time. A body accelerates when its speed changes, its direction changes, or both change, and it is measured in metres per second squared.

The straight-line distance moved from a starting point in a stated direction. It is a vector quantity, so a round trip back to the start has zero displacement.

The law stating that the acceleration of a body is directly proportional to the resultant force on it and inversely proportional to its mass, written as F = ma.

The product of a body's mass and its velocity, measured in kilogram metres per second. In a closed system the total momentum before a collision equals the total after it.

The product of a force and the distance moved in the direction of that force, measured in joules. No work is done when the force is perpendicular to the motion.

The rate at which work is done or energy is transferred, measured in watts. One watt equals one joule of energy transferred each second.

The capacity of a body or system to do work, measured in joules. It exists in forms such as kinetic, potential, chemical, and electrical, and is conserved in a closed system.

The law stating that the current through a conductor is directly proportional to the potential difference across it, provided its temperature stays constant. It gives V = IR.

The opposition of a component to the flow of electric current, measured in ohms. It equals the potential difference across the component divided by the current through it.