25/09/2001Draft
In some circumstances, passive transport (osmosis and diffusion) may not fulfill sufficient amount for proper metabolism. Active transport absorbs substances on purpose for the cell requirements. Substances (solutes and water) are transported against the concentration gradient.
Typical examples of active transport;
Absorption of
minerals from soil water into root system;
Absorption of minerals from alimentary canal into blood in fresh water fishes;
Excretions of
minerals from blood into alimentary canal in marine fishes;
Excretion of water from cytoplasm to the environment in fresh water organism,
Concentrating waste products from blood to urine;
Active transport is an active process, which requires energy, i.e. it could only be carried out in living organism. And active transport could be stop by poison.