Answer
There are two main differences between active trans port and passive transport;
1. Active transport require energy which is supplied by the hydrolysis of ATP. Passive transport does not require energy
2. In active transport, substances are moved up their concentration gradient, while in passive transport substances move down their concentration gradients.
Work Step by Step
In passive transport, substances move down a concentration gradient through the membrane lipid bilayer until an equilibrium is reached. No energy is used in passive processes.
Some examples of passive processes are simple diffusion, facilitated diffusion, and osmosis. In simple diffusion solutes pass down their concentration gradients-- no energy is used and no help from membrane transport proteins is involved. Non-polar, and hydrophobic substances like steroids, fatty acids, oxygen, and carbon dioxide can move by simple diffusion.
Substances that cross the cell membrane by facilitated diffusion utilize the agencies of membrane channels and transport proteins to get through the bilayer. Examples are ions and polar charged molecules like glucose, fructose, Na+, and Cl-..
Osmosis is also a passive process which does not use the energy of ATP. In this process, there is a net flow of solvent molecules (water in the human body) through the selectively permeable membrane from a regions of high water concentration to regions of low water concentration until equilibrium is reached.
In active processes , substances move through a semipermeable membrane against their concentration gradient in activities that require energy from ATP, directly or indirectly, and aided in some cases by trans-membrane protein pumps. Polar charged moities like Na+, K+, and H+ move by primary active transport.
In the secondary form of active transport two processes are coupled using energy supplied by the Na+ and H+ gradients maintained by membrane antiporter and symporter protein pumps.
Transport by vesicles is also an important aspect of active transport: in this process, vesicles form from the plasma membrane and use the energy of ATP to move substance into or out of cells.
In receptor -mediated endocytosis, a receptor-ligand combinations stimulate formation of vesicles that enclose and move substances into a cells: vitamins, hormones, and lipopolysaccharides can be taken into cells in this way. Other forms of active process include phagocytosis, in which pseudopods sent out by the plasma membrane engulf and take
substances and entities into the cytoplasm. Bacteria, viruses, aged and dead cells can be engulfed in these vesicles; they are digested by enzymes when a phagocytic vesicle unites with a lysosome to form a phagosome.
Bulk-endocytosis is a device that uses vesicles to bring extracellutar fluids into the cell. Exocytosis, on the other hand, moves fluid out of the cell. In the latter case, secretory vesicles form, then fuse with the plasma membrane and release substances into the extracellular fluid; neurotransmitters, some hormones and certain digestive enzymes are exported from cells in this manner. Finally, the process of transcytosis is an active process that uses a combination of exocytosis and endocytosis to move substances through the plasma membrane. This process is utilized in the transport of antibodies and other substances from blood plasma into intracelluar fluids of epithelial cells.
