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xxTerwin: Osmosis and Cell Activities


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Selective Permeability

In Cell membranes, biological feature that allows some substances to pass through membrane quicker than others.

Yes: small hydrophobic molecules: O2, H2o, CO2.
No: Larger molecules & ions.

Tendency of molecules to spread out into available space.
Any substance will diffuse down concentration gradient spontaneously, reducing free energy.

Results from intrinsic kinetic energy (thermal motion).

Diffusion of water across selectively permeable membrane (a special case of passive transport).
Depends on total solute concentration

Not to be confused with “Ozzmosis”, the Ozzy Osbourne album…

Solution with higher concentration of solutes

Solution with lower concentration of solutes.
More unbound water molecules letting them move across membrane.
Osmoregulation & Paramecium

Paramecium doesn’t explode because it lives in hypotonic pond water that constantly enters cell, but is offset by osmoregulation.

Cell membrane is less permeable to water.
Contractile vacuole works to ‘bail out’ cell.

Removal of waste or secretory proteins from cells.

Cells take in macromolecules & particulates by forming new vesicles.
Cell cycle
Mitosis & Cytokinesis.

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