Mammals/humans can excrete hyperosmotic urine or hypo-osmotic urine depending on the availability of water in the body. The regulation of kidney functioning is under both neural and hormonal control.
(a) Where are the osmoreceptors located in our body?
(b) Mention any two factors that activate the osmoreceptors
(c) Name the hormone secreted under water scarcity. Mention the two ways in which it acts.

The renal tubule consists of Bowman's capsule, proximal convoluted tubule, Henle's loop, distal convoluted tubule and the collecting tubule. 70-80o/o of the glomerular filtrate is reabsorbed in the PCT.
(a) How is the structure of PCT suited for this absorption?
(b) Why is glomerular filtration considered as ultra filtration?
(c) How does the descending limb of Henle's loop differ from the ascending limb in its permeability to substances?

The kidneys have built-in mechanisms for the regulation of glomerular filtration rate. One such mechanism carried out by the juxta glomerular apparatus is shown in the following flow chart. Fill in the blanks A, B. C, D, E and F in the flow chart.
The (A) cells release Renin when there is a fall in (B)
\(\downarrow\) 
Renin converts (C) in the in blood into (D)
\(\downarrow\) 
D activates the adrenal cortex to release (E)
\(\downarrow\)
E raises the reabsorption of Na⁺ and water and raises the (F)

A diagram of a Malpighian body (also called Renal corpuscle) is given above. Answer the following questions
(a) Name the parts labelled as A, B, C and D.
(b) What does the Malpighian body continue as?
(c) What are peritubular capillaries?

Nephrons are the structural and functional of human kidneys; they are the complex tubular structures.
(a) What are the two major parts of a nephron?
(b) What is renal corpuscle?
(c) Name the two types of nephrons in human kidneys.

A survey of the animal kingdom shows that different groups of animals have different types of excretory structures. They depend on their habitats and the nature of the excretory products.
(a) Human kidneys perform not only excretion of nitrogenous wastes, but also another function. Name that function.
(b) Name the excretory structures of
(i) Amphioxus
(ii) Crustaceans (iii) Insects
(iv) Platyhelminths
(v) Annelids.

Animals accumulate nitrogenous wastes, carbon dioxide, water and some inorganic ions as metabolic wastes, which have to be eliminated totally or partially.
(a) Name the most toxic and the least toxic nitrogenous wastes.
(b) Kidneys do not play any significant role in the elimination of Ammonia. How is ammonia eliminated by animals?
(c) What term is given to the animals which excrete urea as their major nitrogenous waste?
(d) How is carbon dioxide eliminated by human beings?