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Key vocabulary terms, definitions, and concepts from the Edexcel GCSE Combined Science course in Chemistry, Biology, and Physics.
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Pure Substance
A substance consisting of only one type of element or compound.
Mixture
A combination of two or more substances that are physically combined.
Filtration
A separation technique used to separate insoluble solids from a liquid.
Crystallisation
A separation technique used to separate a soluble solid from a solution by evaporating the solvent.
Paper Chromatography
A separation technique used to separate different substances based on their different solubilities in a solvent.
Distillation
A separation technique used to separate liquids with different boiling points.
Mobile Phase (Chromatography)
The solvent that moves through the chromatography paper, carrying the substances to be separated.
Rf Value
The ratio of the distance moved by the substance to the distance moved by the solvent in chromatography.
Potable Water
Water that is safe to drink.
Chlorination
The process of adding chlorine to water to kill bacteria and other microorganisms.
Subatomic Particles
Protons, neutrons, and electrons; the particles that make up an atom.
Atomic Number
The number of protons in the nucleus of an atom.
Mass Number
The total number of protons and neutrons in the nucleus of an atom.
Isotope
Atoms of the same element that have the same number of protons but different numbers of neutrons.
Element
A substance made of only one type of atom.
Period
A horizontal row in the periodic table.
Group
A vertical column in the periodic table; elements in the same group have similar chemical properties.
Electronic Configuration
The arrangement of electrons in the different energy levels or shells of an atom.
Ionic Bonding
The electrostatic attraction between oppositely charged ions, formed by the transfer of electrons.
Giant Ionic Lattice
A three-dimensional structure of oppositely charged ions, held together by strong electrostatic forces.
Covalent Bonding
The sharing of electrons between two atoms to form a bond.
Molecule
A group of atoms held together by covalent bonds.
Allotropes
Different forms of the same element in the same physical state (e.g., diamond and graphite are allotropes of carbon).
Acid
A substance with a pH less than 7 that donates protons or accepts electrons.
Alkali
A substance with a pH greater than 7 that accepts protons or donates electrons; a soluble base.
Neutralisation
The reaction between an acid and a base to form a salt and water.
Solubility
The ability of a substance (solute) to dissolve in a solvent.
Strong Acid
An acid that completely ionizes in solution.
Weak Acid
An acid that only partially ionizes in solution.
Relative atomic mass (Ar)
The weighted average mass of the atoms of an element compared to 1/12th of the mass of an atom of carbon-12.
Relative formula mass (Mr)
The sum of the relative atomic masses of all the atoms in a formula unit.
Mole
The amount of substance containing the same number of particles as there are carbon atoms in 12g of carbon-12. One mole contains 6.022 x 10^23 particles.
Avogadro's Constant
The number of particles in one mole of a substance (6.022 x 10^23).
Empirical Formula
The simplest whole number ratio of atoms of each element in a compound.
Electrolysis
The process of using electricity to break down a compound.
Electrolyte
A substance that conducts electricity when molten or dissolved in water.
Anode
The positive electrode in electrolysis.
Cathode
The negative electrode in electrolysis.
Oxidation
Loss of electrons.
Reduction
Gain of electrons.
Ore
A naturally occurring rock containing metal or metal compounds in sufficient concentration to make extraction economically feasible.
Life Cycle Assessment (LCA)
A method to evaluate the environmental impact of a product throughout its entire life cycle.
Alloy
A mixture of two or more metals, or a metal and a non-metal.
Corrosion
The process by which metals are chemically attacked by atmospheric oxygen, water, and other substances.
Reversible Reaction
A reaction that can proceed in both the forward and reverse directions.
Dynamic Equilibrium
A state where the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in concentrations of reactants and products.
Le Chatelier's Principle
When a system at equilibrium is subjected to a change, it will adjust itself to counteract the change and restore a new equilibrium.
Alkali Metals
Elements in Group 1 of the periodic table, known for their high reactivity.
Halogens
Elements in Group 7 of the periodic table, known for their high reactivity as oxidizing agents.
Noble Gases
Elements in Group 0 (or 8) of the periodic table, known for their inertness due to their full outer electron shells.
Transition Metals
Metals located in the d-block of the periodic table, known for forming coloured compounds and often acting as catalysts.
Theoretical Yield
The maximum amount of product that can be obtained in a chemical reaction, assuming complete conversion of reactants.
Actual Yield
The amount of product actually obtained from a chemical reaction.
Atom Economy
A measure of how many of the atoms in the reactants end up in the desired product.
Avogadro's Law
Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.
Light Microscope
An optical instrument that uses visible light and lenses to magnify small objects.
Electron Microscope
A microscope that uses beams of electrons to magnify objects, providing higher resolution and magnification than light microscopes.
Organelle
A specialized subunit within a cell that has a specific function.
Cell Wall
A rigid outer layer found in plant cells, providing support and protection.
Chloroplast
An organelle found in plant cells where photosynthesis occurs.
Vacuole
A membrane-bound organelle in plant and animal cells that stores water, nutrients, and waste products.
Enzyme
A biological catalyst that speeds up chemical reactions in living organisms.
Prokaryotic Cell
A type of cell that does not have a nucleus or other membrane-bound organelles.
Diffusion
The net movement of particles from an area of high concentration to an area of low concentration.
Osmosis
The net movement of water molecules across a semi-permeable membrane from a region of high water potential to a region of low water potential.
Active Transport
The movement of molecules across a cell membrane against their concentration gradient, requiring energy (ATP).
Mitosis
A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
Stem Cell
An undifferentiated cell that can differentiate into specialized cells and can divide (self-renew) to produce more stem cells.
Meristems
Regions of plant tissue, found chiefly at the growing tips of roots and shoots and in the cambium, consisting of actively dividing cells forming new tissue.
Cell Differentiation
The process by which a cell becomes specialized for a specific structure or function.
Cancer
A disease caused by uncontrolled division of abnormal cells in a part of the body.
Cerebrum
The principal and most anterior part of the brain in vertebrates, located in the front area of the skull and consisting of two hemispheres, left and right.
Cerebellum
The part of the brain at the back of the skull in vertebrates. Its function is to coordinate and regulate muscular activity.
Medulla Oblongata
The continuation of the spinal cord within the skull, forming the lowest part of the brainstem and containing control centers for the heart and lungs.
Hypothalamus
A region of the forebrain below the thalamus that coordinates both the autonomic nervous system and the activity of the pituitary, controlling body temperature, thirst, hunger, and other homeostatic systems, and involved in sleep and emotional activity.
Synapse
A junction between nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.
Reflex Arc
The nerve pathway involved in a reflex action including at its simplest a sensory nerve and a motor nerve with a synapse between.
sexual reproduction
Type of reproduction in which cells from two parents unite to form the first cell of a new organism.
asexual reproduction
Process of reproduction involving a single parent that results in offspring that are genetically identical to the parent.
meiosis
Cell division that produces reproductive cells in sexually reproducing organisms; results in cells with half the chromosome number of the original cell and leads to genetic variation.
DNA
Deoxyribonucleic acid, a self-replicating material present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information.
gene
A unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring.
chromosome
A threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
nucleotide
A compound consisting of a nucleoside linked to a phosphate group. Nucleotides form the basic structural unit of nucleic acids such as DNA.
allele
One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
genotype
The genetic constitution of an individual organism.
phenotype
The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
gene mutation
A change in the sequence of nucleotides in DNA. That change can alter the amino acids that make up a protein, causing it to function improperly or not at all.
non-communicable diseases
A disease not capable of being spread from one person to another.
pathogen
A bacterium, virus, or other microorganism that can cause disease.
antibiotic
A medicine that inhibits the growth of or destroys microorganisms.
vaccine
A substance used to stimulate the production of antibodies and provide immunity against one or several diseases.
Ecosystem
A community of living organisms in conjunction with the nonliving components of their environment (things like air, water, and mineral soil), interacting as a system.
Community
A group of interdependent organisms of different species growing or living together in a specified region or habitat.
Population
A group of organisms of one species that interbreed and live in the same place at the same time.
habitat
The natural home or environment of an animal, plant, or other organism.
niche
The role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces.
food security
The state of having reliable access to a sufficient quantity of affordable, nutritious food.
Abiotic factors
Non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems.
Biotic factors
The living components of an ecosystem which directly or indirectly affect an environment.