TRANSPORT ACROSS THE CELL MEMBRANE

Done by : 1-Zain Ali 2-Ghufran Taher 3-Hala Fuade 4-Ola Hussein

TRANSPORT ACROSS THE CELL MEMBRANE

There are 4 basic mechanisms:

1-DIFFUSION

2-OSMOSIS

3-FACILITATED TRANSPORT

4-ACTIVE TRANSPORT

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

• 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

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

OSMOSIS

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 

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

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

• 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.

GlucoseTransport protein

Concentrationgradient

FACILITATED DIFFUSION

ACTIVE TRANSPORT

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

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.

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.

Endocytosis

Exocytosis