CCEA cell physiology
Detailed set of notes covering osmosis and transport across membrane.
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Process in which substances enter the cell. Substances taken out of cell (ie. enzymes,
hormones, antibodies)
Cell surface membrane invaginates enveloping
material outside of cell Vesicle containing the material moves towards the
cell surface and fuses with cell surface membrane
Neck of depression closes and invagination
becomes sealed off to form a vesicle Vesicle opens to exterior and contents are
(membrane bound sac) which pinches off and released (secretory vesicles) which are derived
moves into cell from Golgi Body
Phagocytosis
7 Pinocytosis
Cellular process of engulfing solid particles by cell Uptake of solutes and large molecules (protein) into
membrane to form internal phagosome cell within vesicles
Plasma membrane invaginates to enclose particle Smaller vesicles
Which are digested by enzymes (in lysosome) Highly specific- only allows intake of molecules with
Useful products reabsorbed into cytoplasm corresponding receptor molecule on plasma
Only occurs on white blood cells- ingest harmful membrane
bacteria and amoeba- feeding Widespread across cells
Pinocytosis and phagocytosis are:
Both forms of endocytosis- formation of membrane bound vesicle at cell surface
Pinocytosis involves liquid uptake, phagocytosis involves solid uptake
, Osmosis
Osmosis is the net movement of water molecules from a solution of Water moves from an
less negative water potential to a solution of more negative water area of higher water
potential across a differentially permeable membrane potential (few solutes)
to an area of lower
water potential (many
More concentrated solution = hypertonic
solutes).
Less concentrated solution = hypotonic
Same concentration solution = isotonic Potential of a solution to Water potential increased by
the external pressure
take in water
imposed on it (always +ve)
Measure of the reduction in
water potential due to Pressure exerted on the cell contents
presence of solute molecules by cell wall and cell membrane
Water potential of cell 14 cell / = solute potential 14s ) + pressure potential ( Yp )
Water moves through aquaporins (special channel proteins) through
the d.p.m.
Water molecules collide with the D.P.M. Therefore exerting
pressure on the D.P.M.
The net movement of molecules is a result of pressure
differences on either side of the D.P.M.
Water potential of a solution is regarded as its tendency to take
in water from pure water across a selectively permeable
Hypotonic Hypertonic
membrane and is a measure of “free energy” of water molecules
Cytoplasm contains
solutes so has a -ve Addition of a solute causes water molecules
water potential to form a shell around the solute- water
When cells are placed molecules can’t move so water potential is
reduced A solution will have a water
in water water moves
Presence of a solute reduces the ability of potential less than 0 so Ysol
into cells
molecules to diffuse through solution Will always be -ve.
Only dissolved solutes contribute to y
Insoluble substances are osmotically inert
(don’t cause hydration shells) so no effect on
The water potential of a solution- ability to take in
Some plants store sugars as insoluble starch
water by osmosis from pure water across a
(potatoes) so doesn’t create hydration shells so
selectively permeable membrane
no effect on water potential
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