ACTIVE AND PASSIVE TRANSPORT

As we all know, cells need nutrients and need to get rid of waste. Therefore, materials need to be transported in and out of the cells. Transport occurs across the plasma membrane. They are divided into passive transport and active transport.

Passive transport involves the transfer of materials down the concentration gradient. It is further divided into simple diffusion, osmosis and facilitated diffusion. In simple diffusion, small, uncharged molecules pass through the phospholipid bilayer. Osmosis involves the movement of water. Next, charged or polar molecules which undergo facilitated diffusion need the help of carrier protein to pass through the plasma membrane.

Active transport needs energy in the form of ATP whereas passive transport does not need it. This is because substance is transported against the concentration gradient. An example of active transport is the uptake of iodine by the thyroid gland. Endocytosis and exocytosis are also under active transport. Endocytosis is the uptake of large molecules by the pinching of plasma membrane to form vesicle. Uptake of solid is known as phagocytosis whereas uptake of liquid is known as pinocytosis. Cells remove large molecules by exocytosis in which the vesicle fuses with the plasma membrane releasing the content out of the cell.