©tmu_ntt
1. Diffusion, osmosis and active transport (SMALL particles)
©tmu_ntt
A graph showing the change in mass of potato discs in different concentration of sucrose:
(a) Diffusion (~ Equilibrium)
(i)
Definition: The net movement of particles from region of higher concentration
to region of lower concentration.
(ii)
Factors affecting the rate:
(1) S.A
(2) Distance
(3) Concentration gradient
(4) Temperature
(5) Size of molecules
(iii)
NO energy required
(b) Osmosis (apply for water molecules only)
(i)
Definition: The net movement of water molecules from regions of higher
water potential to regions of lower water potential.
(ii)
Factors affecting the rate: (SAME as the above)
(iii)
NO energy required
(iv)
[Solution] ↑, Water potential ↓
(v)
Water potential (ψ) ~ [Water]
(c) Osmosis in cells
Net movement
of water
Change in
animal cells
Change in
plant cell
Hypotonic
ψ > cytoplasm
(e.g diluted solution,
distilled water)
Isotonic
ψ = cytoplasm
Enters the cells
No net movement
(≠ no movement, ~eqm)
Leaves the cells
Swell and finally burst
/
Shrink and become
wrinkled
Become turgid
/
Hypertonic
ψ < cytoplasm
(e.g concentrated
solution)
Become flaccid and
plasmolysed;
vaculoes shrink
(d) Active transport
(i)
Definition: The movement of molecules or ions across a cell membrane
(mainly by the carrier protein) from a region of lower concentration to a
region of higher concentration — against the concentration gradient.
(ii)
Energy REQUIRED (From respiration — ATP)
(iii)
ONLY occurs in living cells
2. Occurrence of phagocytosis in cells (LARGE particles)
(a) Phagocytosis (cell eating)
(i)
Definition: The uptake of large particles into cells by packaging the particles
into vacuoles formed from the cell membrane.
(ii)
Steps:
(1) Pseudopodia are formed to surround the particle to be taken in.
(2) Cell membrane fuses to form a vacuole which encloses the particle.
(3) The vacuole is fused with some other vacuoles which contain
lysosome.
(4) The particle is broken down with the help of the lysosome.
(5) The digested products are absorbed into the cytoplasm.
(iii)
(iv)
(v)
Movement of substances across membrane
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Fluidity of cell membrane allows cell membrane to change shape to form
pseudopodia and fuse with one another to form vacuoles.
Energy REQUIRED (∵ active process)
Example: WBC engulf harmful microorganisms by phagocytosis.
Movement of substances across membrane
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