Question

With reference to the following:

Eric Jaffe’s seminal paper on culture of human umbilical vein endothelial cells (Jaffe et al., 1973) recommends using supplemented M199 culture medium. The basic medium contains common electrolytes at the following millimolar concentrations:

Na+ (164), K+ (5.8), Ca++ (1.26), Mg++ (0.81), Cl- (145), HPO42- (0.78), HCO3- (26.1), SO42- (1.26). It also contains glucose (5.6 mM), amino acids and phenol red (a pH indicator).

The recommended supplements (to be added immediately before use) are foetal calf serum (20% v/v) to provide growth factors, penicillin (200 units ml-1) and streptomycin (200 µgml-1) to prevent bacterial contamination, and L-glutamine (2 mM), a labile amino acid that does not survive storage.

Which two electrolytes will make the biggest contribution to maintaining the pH of the medium at the required value of 7.4?

Group of answer choices

HCO3- and HPO42-

Na+ and Cl-

HCO3- and SO42-

Na+ and K+

Cl- and Mg++

Answer 1

Answer: HCO3- and HPO4 2-

Explanation: the electrolytes work as a buffer which lies in 7 the less than 7 would be acidic and more than 7 would be basic. So they work as a buffer to maintain pH of 7.