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Assertion: PCT, DCT and collecting duct ...

Assertion: PCT, DCT and collecting duct helps in the maintenance of pH and ionic balance of blood by the selective secretion of `H^(+)` and `K^(+)` ions.
Reason: PCT and DCT, both are capable of reabsorbing `HCO_(3)^(-)`ion

A

if both assertion and reason are true and the reason is correct explanation of the assertion

B

if both assertion and reason are true but reason is not a correct explantion of the assertion

C

If assertion is true but reason is false

D

If both assertion and reason are false.

Text Solution

Verified by Experts

The correct Answer is:
B
PCT, DCT and collecting duct helps in the maintenance of pH and ionic balance of blood by the selective secretion of `H^(+)` and `K^(+)` ions
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Assertion: PCT, DCT and collecting duct helps in the maintenance of pH and ionic balance of blood by the selective secretion of H^(+) and K^(+) ions. Reason: PCT and DCT, both are capable of reabsorbing HCO_(3)^(-) ion

Assertion: DCT and collecting duct maintain the pH and ionic balance of blood. Reason: DCTs of many nephrons open into a collecting duct.

Which of the following statements is/are incorrect regarding the collecting duct? (i). It extends from the cortex to medulla. (ii). Large amount of water could be reabsorbed by it to produce concentrated urine. (iii). Small amount of urea diffuses into it from the medulla to keep up the osmolarity. (iv). it plays a role in maintaining pH and ionic balance of blood by the selective secretion of H^(+) and K^(+) ions.

Assertion :- Conditional reabsorption of Na^(o+) and water takes place in DCT. Reason :- DCT is also capacble of selective secretion of hydrogen and potassium ions.

Which of the following statements is false regarding the collecting duct? I. Collecting duct is a straight duct II. It extends from the cortex to medulla III. Large amount of water could be reabsorbed from it to produce concentrated urine IV. Small amount of urea diffuses out from it into the medulla to keep up the osmolarity V. It plays a role to maintain pH and ionic balance of blood by the selective secretion of H^(+)andK^(+) ions

Consider a solution of CH_3COONH_4 which is a salt weak acid and weak base. The equilibrium involved in the solutions are : CH_3COO^(-)+H_2OhArrCH_3COOH+OH^(-) " ........"(i) NH_(4)^(+)+H_(2)hArrNH_(4)OH+H^(+)" ........"(ii) H^(+)+OH^(-)hArrH_(2)O" ........"(iii) If we add these reactions, then the net reaction is : CH_(3)COO^(-)+H_(2)^(+)+H_(2)OhArrCH_(3)COOH+NH_(4)OH" ........"(iv) Both CH_(3)COO^(-) and NH_(4)^(+) get hydrolysed independently and their hydrolysis depends on : (a) their initial concentration (b) The value of K_(h) which is (K_(w))/(K_(a)) for CH_(3)COO^(-) and (K_(w))/(K_(b)) for NH_(4)^(+) . Since both of the ions were produced form the salt, their initial concertration are same. Therefore, unless and until the value of (K_(w))/(K_(a)) or K_(a) and K_(b) is same, the degree of hydrogen of ions can't be same. To explain why we assume that degree of hydrolysis of cation and anion is same, we needed to now look at the third reaction i.e.,combination of H^(+) and OH^(-) ions. It is obvious that this reaction happens only because one reaction produced H^(+) ion and the other prodcued OH^(-) ions. We can also note that this reaction causes both the hydrolysis reaction to occur more since their product ions are being consumed. Keep this in mind that the equilibrium which has smaller value of the equilibrium constant is affected more by the common ion effect. For the same reason if for any reson a reaction is made to occur to a greater extent by the consumption of any of the prodcut ion, the reaction with the smaller value of equilibrium constant tends to get affected more. Therefore, we conclude that firstly the hydroylsis of both the ions occurs more in the presence of each other (due to consumption of the product ions) than in each other's absence. Secondly,the hydroylsis of the ion which occurs to a lesser extent (due to smaller value of K_(h)) is affected more than the one whole K_(h) is greater. Hence we can see that the degree of hydroylsis of both the ions would be close to each other when they are getting hyderolysed in the presence of each other. In the hydrolysis of salt weak acid and weak base :

Consider a solution of CH_3COONH_4 which is a salt weak acid and weak base. The equilibrium involved in the solutions are : CH_3COO^(-)+H_2OhArrCH_3COOH+OH^(-) " ........"(i) NH_(4)^(+)+H_(2)hArrNH_(4)OH+H^(+)" ........"(ii) H^(+)+OH^(-)hArrH_(2)O" ........"(iii) If we add these reactions, then the net reaction is : CH_(3)COO^(-)+H_(2)^(+)+H_(2)OhArrCH_(3)COOH+NH_(4)OH" ........"(iv) Both CH_(3)COO^(-) and NH_(4)^(+) get hydrolysed independently and their hydrolysis depends on : (a) their initial concentration (b) The value of K_(h) which is (K_(w))/(K_(a)) for CH_(3)COO^(-) and (K_(w))/(K_(b)) for NH_(4)^(+) . Since both of the ions were produced form the salt, their initial concertration are same. Therefore, unless and until the value of (K_(w))/(K_(a)) or K_(a) and K_(b) is same, the degree of hydrogen of ions can't be same. To explain why we assume that degree of hydrolysis of cation and anion is same, we needed to now look at the third reaction i.e.,combination of H^(+) and OH^(-) ions. It is obvious that this reaction happens only because one reaction produced H^(+) ion and the other prodcued OH^(-) ions. We can also note that this reaction causes both the hydrolysis reaction to occur more since their product ions are being consumed. Keep this in mind that the equilibrium which has smaller value of the equilibrium constant is affected more by the common ion effect. For the same reason if for any reson a reaction is made to occur to a greater extent by the consumption of any of the prodcut ion, the reaction with the smaller value of equilibrium constant tends to get affected more. Therefore, we conclude that firstly the hydroylsis of both the ions occurs more in the presence of each other (due to consumption of the product ions) than in each other's absence. Secondly,the hydroylsis of the ion which occurs to a lesser extent (due to smaller value of K_(h)) is affected more than the one whole K_(h) is greater. Hence we can see that the degree of hydroylsis of both the ions would be close to each other when they are getting hyderolysed in the presence of each other. For 0.1 M CH_3COONH_(4) salt solution given, K_(a)(CH_(3)COOH)=K_(b)(NH_(4)OH)=2xx10^(-5) . In the case : degree of hydrolysis of cation and anion are :

Which of the following statements are correct? (i). Reabsorption of water occurs passively in the initial segment of nephron. (ii). Nitrogenous wastes are absorbed by passive transport. (iii). Conditional reabsorption of Na^(+) and water takes palce in DCT. (iv). DCT reabsorbs HCO_(3)^(-) (v). DCT is capable of selective secretion of H^(+),K^(+) and NH_(3) to maintain pH and Na^(+)-K^(+) balance in blood. (vi). Substance like glucose, amino acids, Na^(+) , etc,. it the filtrate are reabsorbed actively.

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