Given below is a highly simplified diagram of the human kidney cut open longitudinally. Answer the questions that follow.
(a) Define excretion.
(b) Name the functional units of the kidneys.
(c) Why does the cortex of the kidney show a dotted appearance?
(d) Mention two functions of the kidney.
(e) Write two differences in the composition of the blood flowing through the blood vessels, 'A' and 'B'.