Question

10a. What is active membrane transport. (2.5 pts)

b. What is passive membrane transport. (2.5 pts)

c. What is an antiporter? (2.5 pts)

d. What is a symporter. ? (2.5 pts)

Answer 1

10..Answer

(a) Plasma membrane is a selective permeable membrane ,it forms a barrier that blocks the free exchange of molecules,ions,chemicals between the cytoplasm and external environment of the cells.Plasma membrane is made of phospholipids bilayer, which are permeable for nonpolar and uncharged polar molecules diffusion but impermeable for charged molecules.It require transport proteins ( carrier or channel) for passage of polar molecules such as ions,sugar,amino acids etc.. So transport across plasma membrane can occur either through lipid bilayer or through transport proteins.

The transport of molecules when occur against the concentration gradient means from low concentrations to high concentration, mediated by carrier proteins are called Active transport. In active transport metabolic energy will be used to move ions or molecules against the concentration gradient.It is of two types : primary and secondary active transport. Primary transport also called direct active transport ,which is coupled with a metabolic source of energy such as ATP hydrolysis .Eg.. Transport of Na ion and K ion by carrier protein.Secondary transport occurs when endergonic transport of one solute is coupled with exergonic flow of other solutes ( that was originally pumped endergonic by primary active transport).Eg ..symport of Na ions and glucose ....

(b)Passive transport occurs along the concentration gradient means movement of molecules from high concentration to low concentrations and without the use of metabolic energy. It is of two types simple diffusion and facilitated diffusion.In simple diffusion ,molecules simply diffuse across the plasma membrane without involvement of carrier proteins from high to low concentrations.eg. diffusion of gases Oxygen, carbodioxide, hydrophobic molecules ( benzene), Water,Ethanol etc...In facilitated diffusion movement of molecules also occur along the concentration gradient but it requires carrier or channel protein for diffusion.Eg.. diffusion of carbohydrates,amino acids,nucleotides,ions etc...

(C)Antiporter is a transport carrier proteins responsible for selective transport of molecules.It is co transporter mediated coupled transport ,in which transport of one solute is occur in the opposite direction of other solute transport.It is an example of active transport which means it requires use of metabolic energy .So, as name suggests one molecules transported anti direction to other solutes which means if a solutes moves from cytoplasm to outside then other will move outside to cytoplasm simultaneously.

(d)Symporter is also a transport carrier proteins,which is coupled mediated co transporter responsible for transport of two molecule in the same direction simultaneously either from cytoplasm to outside or from outside to cytoplasm. It also requires metabolic energy because it is also active transport.Eg..Sodium ion and glucose transport...

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