Example of Primary active transport-
Ans. is 'c' i.e., Na+-K+ ATPase * Active transport is the method of transport of substance against a concentration or electrochemical gradient (i.e., from low concentration to high concentration), and thus it is called as "uphill movement".* Active transport is mediated by carrier protein and requires energy (ATP), thus transport proteins involved in active transport have ATPase activity incorporated into the carrier protein molecule. The carrier proteins involved in active transport are called ion pumps.* There are two types of active transport: -1) Primary active transport:# In primary active trasnport, the energy is derived directly from hydrolysis (breakdown) of ATP (or related molecule). The most important example is Na+K+ pump (Na+K+ ATPase).2) Secondary active transport:# In secondary active transport, the energy is derived from the store which has been created originally by primary active transport. Secondary active transport represents a combination of primary active transport and facilitated diffusion.# It is exemplified by glucose transport across intestinal mucosal epithelial cells, the Na+K+ pump operates at the basolateral border of the cell and maintains intracellular concentration of Na+ very low. The low intracellular Na+ concentration provides the necessory concentration gradient for Na+ to diffuse in passively at the luminal border through facilitated cotransport with glucose. Thus, the Na+K+ pump (Na+K+ ATPase) indirectly powers the movement of glucose into the cell, and glucose can move in against a concentration gradient so long as Na+ diffuses in along a concentration gradient.# It is important to know that at luminal border, Na+ is transported by facilitated diffusion (as it diffuses along a concentration gradient) while the glucose is transported actively (against a concentration gradient) and the energy is provided by Na+K+ ATPase at basolateral border - So, secondary active transport is a combination of active transport (glucose transport against concentration gradient) and facilitated diffusion (Na+ transport along concentration gradient by carrier protein).
Na+-Glucose contransport
Movement of water across membrane
Na+-K+ ATPase
Na+-H+ antiport
General