transport throught the cell membrane
TRANSCRIPT
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
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.
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.