Which of the following organisms have the capacity to concentrate urine?

1.Mammals

2.Fishes

3.Reptile

4.Amphibians

Countercurrent mechanism helps in maintenance of

1.Concentration gradient in the medullary interstitium.

2.Concentration gradient in the cortical interstitium

3.Concentration gradient in the lumen of collecting duct

4.Concentration gradient in the lumen of DCT

Which of the following factors is responsible for the formation of concentrated urine?

The increase in osmolarity from outer to inner medullary interstitium is maintained due to :

(i) Close proximity between Henle's loop and vasa recta

(ii) Counter current mechanism

(iii) Selective secretion of HCO3¯ and hydrogen ions in PCT

(iv) Higher blood pressure in glomerular capillaries

(1) Only(ii)

(2) (iii) and (iv)

(3) (i), (ii) and (iii)

(4) (i) and (ii)