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cell membranes
7-13
7
Biology
Undergraduate 1
09/26/2006

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Term
Hypotonic
Definition
the solution outside the cell is hypotonic, means that the
concentration of solute is higher inside the cell, therefore water enters the cell and the cell
swells.
Term
Hypertonic
Definition
the solution outside the cell is hypertonic, means that the
concentration of solutes is lower inside the cell, therefore water leaves the cell and the
cell shrinks.
Term
Facilitated diffusion
Definition
The process of crossing a membrane DOWN a concentration gradient with the aid of a carrier protein,
eg glucose, amino acids and iron. Does NOT require energy input.
Term
Active Transport
Definition
process of crossing a membrane AGAINST a concentration gradient with the aid of a carrier
protein. DOES require energy input.
This is necessary when the cell needs more of a nutrient it already has quite a lot of; or
when the cell wants to get rid of something that there is already more of outside the cell.
Term
Exocytosis:
Definition
Transports large particles out of cells.
Vesicles move to the cell membrane, fuse with it and then release contents out of the cell.
Term
Endocytosis:
Definition
Transports large particles into the cell.
The cell membrane enfolds and pinches off a vesicle into the cell, bringing particles from outside
with it.
Term
Receptor-mediated Endocytosis
Definition
A receptor protein on the cell surface is bound by a particular biochemical called a ligand. The cell
membrane then indents and endocytoses the ligand-bound receptor. Receptor-mediated endocytosis enables
liver cells to bind and take in dietary cholesterol from the blood.
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