Question

1. Explain the different forms of membrane transport: Passive, Facilitated, Active.
2. Describe the bulk transport mechanisms of Endocytosis and Exocytosis.

Answer 1

Passive transport :

It is the movement of ions and atomic substances across cell membrane from an area of high concentration to an area of lower concentration without using energy input.It depends on the permeability of the cell membrane and structure of lipids in the membrane .

There are four types of passive transport,they are simple diffusion,facilitated diffusion, filtration and osmosis.

Simple diffusion : Movement of solute(small molecules like oxygen) from higher concentration to a lower concentration until the solute become equal.

Facilitated diffusion(carrier mediated osmosis): It is also known as facilitated transport or passive mediated transport.It is the spontaneous movement of large molecules through special transmembrane integral proteins .Example: sucrose, potassium and glucose ions. They pass across the cell membrane using carrier proteins and energy along with concentration gradient.

Filtration: movement of water and solute across the membrane due to hydrostatic pressure .Only solutes of particular size can pass through the membrane pores depending on its size.In kidneys , the membrane pores of Bowman's capsule is small so smaller size albumin can pass through it .

Osmosis: Movement of water from higher concentration to lower concentration until there is equal concentration of water and solute.

Active transport: Movement of ions or molecules from the area of lower concentration to higher concentration with the use of energy and enzymes against concentration gradient.Example : uptake of glucose in intestine.

There are two types of active transport.They are primary active transport(direct active transport) that uses ATP (adenosine triphosphate) as energy and secondary active transport that uses electrochemical gradient for energy.

In primary active transport, charged particles such as Na+,Ca2+ need ion pumps or ion channels to cross cell membrane and get distributed across the body.

Secondary active transport is also known as coupled transport or cotransport.It depends on the electrochemical differences produced by pumping ions in and out of the cell.