Page 10 - 02 Cells Biology Notes
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#17 Diffusion
Diffusion is the net movement of molecules from a region of
its higher concentration to a region of its lower concentration. Molecules
move down a concentration gradient, as a result of their random
movement.
For living cells, the principle of the movement down a concentration
gradient is the same, but there is one problem:
The cell is surrounded by a cell membrane, which can restrict the free
movement of the molecules à This is a selective permeable
membrane: the composition of the membrane (lipid and protein) allows
some molecules to cross with ease, but others with difficulty or not at all.
The simplest sort of selection is based on the size of the molecules.
