Transportation is an essential activity in our day to day life. It is needed for moving oneself or one’s goods from one place to another. Amazingly, certain substance move in and out of the cell through its membrane in a process known as cell transport.
See also Cell membrane
Cell transports are of two types
- The passive transport
- The active transport
Passive Cell Transport
Passive transport deals with the diffusion of substances across the cell membrane. These substances diffuse easily from a region of higher concentration from the surrounding through the semi-permeable structure of the cell membrane into the cell cytoplasm are relatively small. No energy is required to facilitate the transport of these substances into the cytoplasm through the cell membrane. This can be likened a bicycle amount riding down the hill and requiring almost no energy to power the movement of the bicycle down the hill. Molecules often transported through this type of transport include gases such as oxygen and carbon (iv) oxide
Active cell transport
This is the complete opposite of passive transport, substance moves from the region of lower concentration to a region of higher concentration in a process known as osmosis. A specialized protein pump such as Sodium-Potassium pump, Calcium pump and Proton pump. Molecules transported through this process are usually too big to cross the cell membrane on their own and therefore need the help of a transport pump. Energy in form of ATP is expended to transport molecules in active transport.
An important example of active cell transport is vesicle-mediated cell transport; this is a type of cell transport in which transported molecules are transported in membrane-bound vesicles such as vacuole and cell membrane
Examples of vesicle-mediated cell transport include:
- Endocytosis
- Exocytosis
Endocytosis
Endocytosis is the process of cellular absorption by which a cell membrane folds inward to take in a substance that is bound to its surface into the cell membrane.
Endocytosis includes:
- Pinocytosis
- Phagocytosis
Pinocytosis
This is the inward folding of the cell membrane to take in portions of fluid and forms a vesicle which later uses with cellular vesicles such as endosome and lysosome.
Phagocytosis
This pertains to the engulfing and taking in of food substances from outside of the cell into the cell. This mechanism of food intake is usually used by protists such as Amoeba to feed on bacteria and small organic matters, Plasmodium falciparum to feed on red blood cells and immune cells to remove pathogens and cell debris. The recognition of food substances by protists and immune cells is based on the ligand-receptor mechanism
Exocytosis
This type of active cell transport pertains to movement of certain molecules such as Ca2+, Na+ K+ particles into the cell through specialized pumps such as Sodium and potassium pumps and Calcium pumps.
