Mechanisms of Transport

Passive Transport

Passive transport is a method of cell transport in which no energy is required.
The most common types of passive transport are diffusion, osmosis and facilitated diffusion.
Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, until equilibrium is reached.
When diffusion involves water, it is called osmosis. Water moves across a semi-permeable membrane from an area with more water to one with less water.
In facilitated diffusion, carrier proteins aid in the movement of molecules across the plasma membrane from high to low concentration.

Active Transport

Active transport involves moving molecules across the cell membrane from an area of low concentration to an area of high concentration.
It requires energy, often in the form of adenosine triphosphate (ATP), because it is against the concentration gradient.
The most common types of active transport are protein pumps, endocytosis, and exocytosis.
Protein pumps use energy to change their shape and pump small molecules and ions across the cell membrane.
Endocytosis involves the engulfing of large substances by the cell membrane to form a vesicle or vacuole.
In exocytosis, the opposite happens: Cells use vesicles to expel large materials out of the cell.

Bulk Transport

Bulk transport is used to move large molecules, or large amounts of molecules, across the plasma membrane.
It includes two types of transport: endocytosis and exocytosis.
Endocytosis is a process by which the cell membrane can pinch off a vesicle to bring outside substances into the cell.
Exocytosis is the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.

Understanding these mechanisms of transport allows a deep comprehension of how substances move in and out of cells, maintaining the necessary balance for cells to function properly.