This document discusses four mechanisms of transport across cell membranes: diffusion, osmosis, facilitated transport, and active transport. Diffusion is the passive movement of molecules from an area of high concentration to low concentration. Osmosis is a type of diffusion where water moves through a semi-permeable membrane from high to low concentration. Facilitated transport uses carrier proteins to transport molecules along a concentration gradient. Active transport transports molecules against a concentration gradient and requires energy from ATP.

1. TRANSPORT ACROSS THE CELL MEMBRANE
 Done by :
 1-Zain Ali
 2-Ghufran Taher
 3-Hala Fuade
 4-Ola Hussein

2. TRANSPORT ACROSS THE CELL MEMBRANE
There are 4 basic mechanisms:
1-DIFFUSION
2-OSMOSIS
3-FACILITATED TRANSPORT
4-ACTIVE TRANSPORT

3. MEMBRANE PERMEABILITY
• Biological membranes are physical
barriers, but which allow small uncharged
molecules to pass.
• They are described as semi-permeable
Because;
• Lipid soluble molecules and small
molecules pass through
• Macromolecules and charged ions do NOT
pass through

4. • Movement generated by random motion of
particles.
• Movement always from region of high
concentration to regions of low
concentration.
• Increased water pressure is caused by
water moving to decrease a concentration
gradient or concentration difference
between two areas.
DIFFUSION

6. OSMOSIS
 Osmosis is a special type of diffusion.
 Osmosis is the diffusion of water.
Osmosis is the movement of
water molecules from a high
concentration of water to a low
concentration of water through
a partially-permeable membrane

7. OSMOSIS

8. TYPE OF SOLUTIONS
• Hypotonic Solutions:
• contain a low concentration of solute
(more water)
• When a cell is placed in a hypotonic
solution, the water diffuses into the cell,
causing the cell to swell

9.  Hypertonic Solutions:
 contain a high concentration
of solute (less water)
 When a cell is placed in a
hypertonic solution, the
water diffuses out of the cell,
causing the cell to shrivel

10. Isotonic Solutions:
 contain the same concentration of
solute( equal amounts of water)
 When a cell is placed in an
isotonic solution, the water
diffuses into and out of the cell at
the same rate
 The fluid that surrounds the body
cells is isotonic

11. • It is passive – does not require energy but:
• It uses carrier proteins
• Here the solute molecules “combine” with
carrier proteins in the membrane. These
carrier molecules speed (or facilitate) the
passage of the solute molecules across the
membrane.
FACILITATED DIFFUSION
• Movement is along a concentration
gradient (i.e. From higher to lower)
• Each type of transport protein will carry
only one type of molecule.

12. GlucoseTransport protein
Concentration
gradient
FACILITATED DIFFUSION

13. ACTIVE TRANSPORT
Active transport:is the transport of
molecules or ions across a
membrane by carrier proteins
against a concentration gradient.

14. Key facts
1-It requires energy from respiration
2-Factors that reduce respiration will also
reduce active transport: e.g. lower
temperature; lack of oxygen; metabolic and
respiratory inhibitors.
3-Active transport involves carrier proteins in
the membrane.
4-The hydrolysis of ATP releases the energy
required for active transport.
5-Cells involved in active transport have a LARGE
NUMBER of MITOCHONDRIA to provide the ATP
required via AEROBIC RESPIRATION.

15. Endocytosis and Exocytosis
1-Endocytosis is the transport of large particles
into the cell in vesicles formed by invagination
of the cell surface membrane.
2-Exocytosis is the reverse process and is
used to secrete proteins, e.g digestive
enzymes, out of the cells.

16. Endocytosis
Exocytosis