This document summarizes four types of transport through cell membranes: diffusion, facilitated diffusion, osmosis, and active transport. Diffusion is the spontaneous movement of molecules from high to low concentration areas. Facilitated diffusion uses transport proteins to assist molecules unable to pass through the membrane. Osmosis is the spontaneous movement of water through a partially permeable membrane from high to low water concentration. Active transport moves molecules against their concentration gradient by using energy in the form of ATP.

1. Transport
Through
Cell Membranes
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2. Transport through cell membranes is
1. DIFFUSION
2. FACILITATED DIFFUSION
3. OSMOSIS
4. ACTIVE TRANSPORT

3. DIFFUSION
Diffusion is the spontaneous
movement of molecules (or ions)
from a region of their high
concentration to a region of their
lower concentration.

4. Diffusion through a membrane
Cell membrane
Inside cell
Outside cell

5. Diffusion through a membrane
Cell membrane
diffusion
Inside cell
Outside cell

6. Diffusion through a membrane
Cell membrane
Inside cell
Outside cell
EQUILIBRIUM

7. What determines the rate of diffusion?
There 4 factors:
1. The steepness of the concentration gradient.
2. Temperature.
3. The surface area.
4. The type of molecule or ion diffusing.

8. The steepness of the concentration
gradient
The bigger the difference between the
two sides of the membrane the quicker
the rate of diffusion.

9. Temperature
Higher temperatures give molecules or
ions more kinetic energy. Molecules move
around faster, so diffusion is faster.

10. The surface area
The greater the surface area the faster
the diffusion can take place. This is
because the more molecules or ions can
cross the membrane at any one moment.

11. The type of molecule or ion diffusing
Large molecules need more energy to get
them to move so they tend to diffuse
more slowly. Non-polar molecules diffuse
more easily than polar molecules because
they are soluble in the non polar
phospholipid tails.

12. FACILIATED DIFFUSION
Facilitated diffusion is a type of Passive
transport that allows substances to
cross membranes with The assistance
of special transport proteins. Some
molecules and ions such as glucose,
sodium ions and chloride ions are
unable to pass through the lipid bilayer
of cell membranes.

13. Facilitated Diffusion through a membrane
Cell membrane
Protein channel
Inside cell
Outside cell

14. Facilitated Diffusion through a membrane
Cell membrane
diffusion
Protein channel
Inside cell
Outside cell

15. Facilitated Diffusion through a membrane
Cell membrane
diffusion
Protein channel
Inside cell
Outside cell
EQUILIBRIUM

16. OSMOSIS
Osmosis is the spontaneous movement
of free water down its concentration
gradient. Water flows across
membranes from regions with higher
water potential (high concentration of
water molecules) to regions with lower
(low concentration of water molecules)
across a partially permeable
membrane.

17. Osmosis
DILUTE SOLUTION
CONCENTRATED SOLUTION
Cell membrane partially
permeable.
Sugar molecule
VERY Low conc.
of water
molecules. High
water potential.
Inside cell
VERY High conc.
of water
molecules. High
water potential.
Outside cell

18. Osmosis
Cell membrane partially
permeable.
OSMOSIS
Inside cell
High conc. of
water molecules.
High water
potential.
Outside cell
Low conc. of
water molecules.
High water
potential.

19. Osmosis
Cell membrane
partially
permeable.
OSMOSIS
Inside cell
Outside cell
AS Biology, Cell membranes and
Transport

20. Active Transport
Active transport is the movement of
all types of molecules across a cell
membrane against its concentration
gradient (from low to high
concentration).