The average $pH$ of human urine is

The given figure shows the human excretory system with parts labeled $A$ to $D$. Select the option that correctly identifies these parts and describes their characteristics or functions.

The blood leaving the kidney is significantly lower in:

Match the items in Column-$I$ with those in Column-$II$.

Column-$I$	Column-$II$
$(a)$ Podocytes	$(i)$ Crystallised oxalates
$(b)$ Protonephridia	$(ii)$ Annelids
$(c)$ Nephridia	$(iii)$ Amphioxus
$(d)$ Renal calculi	$(iv)$ Filtration slits

Select the correct option from the following:

Why do we urinate more frequently during cold and humid weather?

Which of the following statements is/are true?
$I.$ Urine is hypertonic while entering distal convoluted tubule.
$II.$ When the urine moves in the collecting tubule,it becomes hypertonic.
$III.$ Urine is isotonic in proximal convoluted tubule.
$IV.$ Urine becomes more and more hypotonic as it passes through the descending Henle's loop.