CELLULAR TRANSPORT AND EFFECTS OF OSMOSIS ON CELLS
CELLULAR TRANSPORT
The two main types of transport into and out of cells include passive transport and active transport.
PASSIVE TRANSPORT involves the transport of molecules from regions of high concentration to regions of low concentration. No energy is used in this process.
There are three main types of passive transport:
1. SIMPLE DIFFUSION
Diffusion is the tendency of molecules to spread from regions of high concentration to regions of low concentration. This movement is due to a concentration gradient. This is the difference in concentration between two different regions. An example - when you spray perfume in the corner of a room and eventually you can smell it everywhere.
2. OSMOSIS
Osmosis is the diffusion of water across a selectively permeable membrane from a region of high water concentration to a region of low water concentration.
3. FACILITATED (HELPED) DIFFUSION
Facilitated diffusion is similar to simple diffusion, but it involves molecules diffusion quickly across a cell membrane, through transport proteins. Facilated diffusion only works from high to low concentration. A transport protein binds to the substance on one side of the cell membrane and then releases it on the other side.
ACTIVE TRANSPORT involves the transport of molecules from regions of low concentration to regions of high concentration. Energy is needed for this type of transport.
There are two main types of active transport:
1. TRANSPORT PROTEINS - the same as facilitated diffusion, except a molecule goes from low concentration to high concentration across a cell membrane and it needs energy to take place.
2. MEMBRANE VESICLES - Substances entering the cell become enclosed by an inpocketing of the cell membrane to form a vesicle. This process is called endocytosis.
There are two forms of endocytosis:
a) Pinocytosis - a form of endocytosis that transports liquids into the cell.
b) Phagocytosis - a form of endocytosis that transports solids into the cell.
Exocytosis is the movement of a substance out of a cell via vesicles. Exocytosis is the reverse of endocytosis.