Chemistry A-Level Dictionary

Active siteThe site where the reactants bind to the enzyme.
Active transportThe movement of substances against a concentration gradient using energy.
AdaptationsSpecial features which make an organism particularly well suited to its habitat.
AllelesDifferent versions of a particular gene.
AntigensThe unique proteins on the surface of a cell, that are recognised by the immune system as ‘self’ or ‘non-self’.
BiogasGas made through the action of microorganisms on the remains of living organisms.
Cell membraneThe membrane around a cell which controls what moves in and out of the cell.
Central nervous system (CNS)The central nervous system is made up of the brain and spinal cord where information is processed.
ChlorophyllThe green pigment contained in the chloroplast that absorbs sunlight.
ChloroplastsThe organelles where photosynthesis takes place.
ChromosomesThread-like structures made of DNA that carry the genetic information found in the nucleus of a cell.
ClonesOffspring produced by asexual reproduction which are genetically identical to their parent organism.
Concentration gradientThe gradient between an area where a substance is at a high concentration and an area where it the substance is at a low concentration.
CytoplasmThe water-based gel where the organelles of all living cells are suspended.
DecomposersMicroorganisms that break down waste products and dead matter.
DenaturedEnzymes that are denatured have unfolded protein structures and can no longer catalyse a reaction.
DiffusionThe net movement of particles of a gas or a solute from an area of high concentration to an area of low concentration (along or down a concentration gradient).
DNADeoxyribose nucleic acid, the material that makes up chromosomes.
EcosystemThe total of the animals and plants living in an area, along with things which affect them such as the soil and the weather.
EnzymeProtein molecules which function as biological catalysts. They change the rate of chemical reactions without being affected themselves at the end of the reaction.
EvolutionThe slow change in living organisms over long periods of time as those best fitted to survive breed successfully.
GeneA short section of DNA carrying genetic information (codes fora single protein or characteristic).
Genetic engineering / genetic modificationA modern technique for changing the genetic information of a cell.
HemoglobinThe red pigment which carries oxygen around the body, found in red blood cells.
HomeostasisThe maintenance of constant internal body conditions such as temperature and blood pH.
HormonesChemical messages secreted by special glands and carried around the body in the blood, e.g. insulin and adrenaline.
Limiting factorsFactors which limit the rate of a reaction, e.g. light intensity for photosynthesis.
MeiosisA two-stage process of cell division which halves the chromosome number of the daughter cells. It is involved in making the gametes for sexual reproduction.
Menstrual cycleThe reproductive cycle in women regulated by hormones.
Metabolic rateThe rate at which all the reactions of your body take place, particularly cellular respiration.
MicroorganismBacteria, viruses and other small organisms which can only be seen using a microscope.
MitochondriaOrganelles responsible for aerobic cellular respiration in cells.
MitosisAsexual cell division where two genetically identical daughter cells are formed.
MutationAny change in the genetic material of an organism.
Natural selectionThe process by which evolution takes place. Organisms produce more offspring than the environment can support so only those which are most suited to their environment will survive to breed and pass on their useful characteristics.
NeuronesBasic cells of the nervous system that carry minute electrical impulses around the body.
Nucleus (of a cell)An organelle found in many living cells that contain the genetic information.
OrganellesMembrane-bound structures in a cell which carry out particular functions.
OsmosisThe passive movement of water from an area of high concentration (of water) to an area of low concentration (of water) along a concentration gradient.
Partially permeableAllowing only particular substances to pass through.
PathogensMicroorganisms which can cause disease in humans and other organisms.
PhotosynthesisThe process by which plants produce their own food using carbon dioxide, water and light energy.
RespirationThe process by which food molecules are broken down to release energy for living cells.
RibosomesThe site of protein synthesis in a cell, found in the cytoplasm.
SpecialisedAdapted for a particular biological function.
Stem cellsUndifferentiated cells that have the potential to form a wide variety of different cell types.
StomataOpenings in the leaves of plants that allow gases to enter and leave the leaf. They are opened and closed by the guard cells.
SynapsesThe gaps between neurones where the transmission of information is passed chemically rather than electrically.
TranspirationThe loss of water vapour from the leaves of plants through the stomata when they are opened to facilitate gas exchange for photosynthesis.
VilliThe finger-like projections from the lining of the small intestines which increases the surface area for the absorption of nutrients into the blood.
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