AS Biology Definitions (KEY TERMS)


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AS Biology Definitions
Active site ­ the specifically shaped receptor site which messenger molecules with a complimentary
shape bind to, enabling the message to be passed across
Active transport ­ the active movement of a molecule from a low concentration to a high
concentration, requiring energy from ATP, and a carrier protein
Affinity for oxygen ­ the tendency for Haemoglobin to combine with oxygen
Apoplastic pathway ­ a route that water takes when entering a plant's roots, through the cell walls
of the plant cells
Atria ­ the top chambers of the heart, separated from the ventricles by atrioventricular valves.
Atrioventricular Node (AVN) ­ conducts electrical activity/ impulses and directs them to the Bundle of
Bohr Shift ­ the effect that a higher CO2 concentration has on the Haemoglobin dissociation curve,
shifting it down and right
Cardiac Cycle ­ the events that occur in one whole beat of the heart
Carrier protein ­ proteins that transport a specific substance across the cell membrane by either
facilitated diffusion or active transport
Casparian strip ­ a waxy waterproof layer in the endodermis of a plant tissue, which blocks water in
the Apoplastic pathway and forces it to take the Symplastic pathway
Cell cycle ­ the process that all animal cells use to grow and divide
Cell signalling ­ the way that cells can communicate with each other or recognise each other (when a
messenger molecule is released, transported and then binds to the receptor site of the target cell ­
complimentary shape) to provoke a response.
Channel protein ­ a protein that allows a specific substance to diffuse through the channel and
therefore across the cell membrane by facilitated diffusion. If gated, a messenger molecule/
hormone is required.
Closed Circulatory System ­ a Circulatory System in which the blood is contained and transported in
vessels; namely capillaries, veins and arteries. The blood has a much higher pressure.
Cytokinesis ­ the splitting of cytoplasm once cells have divided, often described as the final "pinching
Cytoskeleton ­ a structure inside the cell mainly made up of fibres, which provide mechanical
strength to cells, aid transport within cells and enable cell movement
Diastole ­ relaxation of muscles (e.g. atrial diastole)

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Differentiation ­ the process by which a cell becomes specialised for a particular function, by
changing shape, size, the number or types of organelles, or contents.
Diffusion ­ the passive process of particles moving from a high concentration to a low concentration,
through a partially permeable membrane
Diploid cell ­ cell with normal number of chromosomes; normal body cell
Eukaryotic cells ­ animal and plant cells; they contain a "true" nucleus (double membraned) and also
double membraned organelles, e.g. mitochondria.…read more

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Prokaryotic ­ a bacterial cell identified easily as they do not have a nucleus, but the DNA is free as a
loop in the cytoplasm. The ribosomes are smaller (18nm) and they don't contain any double
membraned organelles (e.g. mitochondria). They often have flagella to propel the cell.
Resolution ­ the ability to distinguish between two very close together points. It is the smallest
distance for which this can be done.
Stem Cells ­ unspecialised cells which can develop into any type of cell.…read more


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