An ecological factor that makes up part of the non-biological environment of an organism, e.g. temperature, pH, rainfall and humidity
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Acetylcholine
A group of chemicals called neurotransmitters, released by neurones. It diffuses across the synapse between adjacent neurones and passes an impulse from one neurone to the next
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Action Potential
Change that occurs in the electrical charge across the membrane of an axon when it is stimulated and a nerve impulse passes
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Actin
Filamentous protein which is involved in contraction within cells, specifically muscle cells.
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Activation Energy
Energy required to bring about a reaction
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Active Immunity
Resistance to disease resulting from the activities of an individual's own immune system whereby an antigen induces plasma cells to produce antibodies
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Active Site
A group of amino acids that makes up the region of an enzyme into which the substrate fits in order to catalyse a reaction
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Active Transport
Movement of a substance from a region where it is in a low concentration to a region where it is in a high concentration. The process requires the expenditure of metabolic energy
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Adenosine Triphosphate (ATP)
An activated nucleotide found in all living cells that acts as an energy carrier. The hydrolysis of ATP leads to the formation of ADP and inorganic phosphate, with the release of energy.
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Adrenaline
A hormone produced by the adrenal glands in times of stress that prepares the body for an emergency
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Aerobic
Connected with the presence of free oxygen. Aerobic respiration requires free oxygen to release energy from glucose
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Alelle
One of a number of alternative forms of a gene.
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For example, the gene for the shape of pea seeds has two alleles: one for 'round' and one for 'wrinkled'
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Allergen
A normally harmless substance that causes the immune system to produce an immune response.
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Allergy
The response of the immune system to an allergen
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Examples include hay fever and asthma
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Anaerobic
Connected with the absence of oxygen. Anaerobic respiration releases energy from glucose or other foods without the presence of oxygen
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Antibiotic
A substance produced by living organisms that can destroy or inhibit the growth of microorganisms
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Antibiotic Resistance
The development in microorganisms of mechanisms that prevent antibiotics from killing them
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Antibody
A protein produced by lymphocytes in response to the presence of the appropriate antigen
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Anticodon
A sequence of three adjacent nucleotides on a molecule of transfer RNA that is complementary to a particular codon on a messenger RNA molecule
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Antidiuretic Hormone (ADH)
A hormone produced by the hypothalamus that passes to the posterior pituitary gland from where it is secreted. Reduces the volume of water in urine by increasing water reabsorption in the kidneys
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Antigen
A molecule that triggers an immune response by lymphocytes
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Antioxidant
Chemical which reduces or prevents oxidation. Often used as an additive to prolong the shelf-life of certain foods
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Apoplastic Pathway
Route through the cell walls and intercellular spaces of plants by which water and dissolved substances are transported
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Artificial Selection
Breeding of organisms by human selection of parents/gametes in order to perpetuate certain characteristics and/or to eliminate others
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Asthma
A chronic illness in which there is resistance to air flow to the alveoli of the lungs as a result of the airways becoming inflamed due to an allergic response to an allergen
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Atheroma
Fatty deposits in the walls of arteries, often associated with high cholesterol levels in the blood
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Autonomic Nervous System
Part of the nervous system that controls the muscles and glands but is not under voluntary control
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Autosomes
A chromosome which is not a sex chromosome
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Axon
A process extending from a neurone that conducts action potentials away from the cell body
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B Cell (B Lymphocyte)
Type of white blood cell that is produced and matures within the bone marrow. B lymphocytes produce antibodies as part of their role in immunity
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Benedict's Test
A simple biochemical reaction to detect the presence of reducing sugars
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Biodiversity
The range and variety of genes, species and habitats within a particular region
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Biomass
The total mass of living material, normally measured in a specific area over a given period of time
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Biotic
An ecological factor that makes up part of the living environment of an organism. e.g. food availability, competition and predation
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Biosensor
A device that uses biological molecules to measure the level of certain chemicals
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Biuret Test
A simple biochemical reaction to detect the presence of protein
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Body Mass Index (BMI)
A person's body mass in kilograms divided by the square of their height in metres
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Cancer
A disease, resulting from cells that break away from an original tumour to form secondary tumours elsewhere in the body
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Carcinogen
A chemical, a form of radiation, or other agent that causes cancer
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Cardiac Cycle
A continuous series of events which make up a single heart beat
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Cardiac Output
The total volume of blood that the heart can pump each minute (stroke volume x heart rate)
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Carrier Molecule (Carrier Protein)
A protein on the surface of a cell that helps to transport molecules and ions across plasma membranes
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Casparian Strip
A distinctive band of suberin around the endodermal cells of a plant root that
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prevents water passing into xylem via the cell walls. The water is forced through the living part (protoplast) of the endodermal cells
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Centrifugation
Process of separating out particles of different sizes and densities by spinning them at high speed in a centrifuge
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Cholesterol
Lipid that is an important component of cell-surface membranes. Excess in blood can lead to atheroma
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Chromatid
One of the two strands of a chromosome that are joined together by a single centromere prior to cell division
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Chromatin
The material that makes up chromosomes. It consists of DNA and the protein histone
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Chromosome
A thread-like structure made of protein and DNA by which hereditary information is physically passed from one generation to the next
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Climax Community
The organisms that make up the final stage of ecological succession
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Clone
A group of genetically identical cells or organisms formed from a single parent as the result of asexual reproduction or by artificial means
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Codon
A sequence of three adjacent nucleotides in mRNA that codes for one amino acid
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Cohesion
Attraction between molecules of the same type. It is important in the movement of water up a plant
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Collagen
Fibrous protein that is the main constituent of connective tissues such as tendons, cartilage and bone
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Community
All the living organisms present in an ecosystem at a given time
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Complementary DNA
DNA that is made from messenger RNA in a process that is the reverse of
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normal transcription
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Condensation
Chemical process in which two molecules combine to form a more complex one with the elimination of a simple substance, usually water
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Consumer
Any organism that obtains energy by 'eating' another.
Variation in which organisms do not fall into distinct categories but show
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gradations from one extreme to the other
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Coronary Arteries
Arteries that supply blood to the cardiac muscle of the heart
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Coronary Heart Disease (CHD)
Any condition, for example, atheroma and thrombosis, affecting the coronary arteries that supply heart muscle
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Correlation
When a change in one variable is reflected by a change in the second variable
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Countercurrent System
A mechanism by which the efficiency of exchange between two substances is increased by having them flowing in opposite directions
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Co-transport
The transport of one substance coupled with the transport of another substance across a plasma membrane in the same direction through the same protein carrier
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Crossing over
The process whereby a chromatid breaks during meiosis and rejoins to the
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chromatid of its homologous chromosome so that their alleles are exchanged
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Covalent bond
Type of chemical bond in which two atoms share a pair of electrons, one from each atom
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Cuticle
Exposed non-cellular outer layer of certain animals and the leaves of plants.
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Waxy, impermeable to water = reduces water loss
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Deciduous
Term applied to plants that shed all their leaves together at one season
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Denaturation
Permanent changes due to the unravelling of the three-dimensional structure of a protein as a result of factors such as changes in temperature or pH
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Depolarisation
Temporary reversal of charges on the cell-surface membrane of a neurone that takes place when a nerve impulse is transmitted
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Diastole
The stage in the cardiac cycle when the heart muscle relaxes
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Differentiation
The process by which cells become specialised for different functions
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Diffusion
The movement of molecules or ions from a region where they are in high concentration to one where their concentration is lower
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Dipolar
Having a pair of equal and opposite electrical charges
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Diploid
A term applied to cells in which the nucleus contains two sets of chromosomes
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Dominant Allele
An allele that is always epressed in the phenotype of an organism, even in the heterozygous
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Ecological Niche
Describes how an organism fits into its environment. It describes what a
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species is like, where it occurs, how it behaves, its interactions with other species and how it responds to its environment
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Ecosystem
All the living and non-living components of a particular area
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Effector
An organ that responds to stimulation by a nerve impulse resulting in a
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change or response
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Electron
Negatively charged subatomic particle that orbits the positively charged nucleus of all atoms
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Emphysema
A disease in which the walls of the alveoli break down, reducing the surface area for gaseous exchange, thereby causing breathlessness in the patient
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Enzyme
A protein or RNA that acts as a catalyst and so alters the speed of a biochemical reaction
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Epidemiology
The study of the spread of disease and the factors that affect this spread
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Eukaryotic Cell
Cell that has a membrane-bound nucleus and chromosomes. The cell also possesses a variety of other membranous organelles, such as mitochondria and endoplasmic
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reticulum
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Exocytosis
The outward bulk transport of materials through the cell-surface membrane
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Facilitated diffusion
Diffusion involving the presence of protein carrier molecules to allow the
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passive movement of substances across plasma membranes
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Gamete
Reproductive cell that fuses with another gamete during fertilisation
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Gene
Section of DNA on a chromosome coding for one or more polypeptides
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Gene Marker
A section of DNA that is used to indicate the location of a gene or other section of DNA