Question

The diagrams show vertical sections of kidneys of coypu, brown rat and kangaroo rat, showing the relative size of cortex and medulla. Coypu are found in freshwater and are never short of water to drink. Brown rats are able to go some days without drinking. Kangaroo rats are able to live in deserts without drinking at all. Which kidney belongs to which animal?

	$A$	$B$	$C$
(a)	Brown rat	Coypu	Kangaroo rat
(b)	Brown rat	Kangaroo rat	Coypu
(c)	Kangaroo rat	Brown rat	Coypu
(d)	Kangaroo rat	Coypu	Brown rat

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (B)

The loop of Henle has a key role in water conservation. Based on lengths of the loop of Henle, there are two types of nephrons: (i) Cortical nephrons: they have short loops of Henle which only just extend into the medulla which function most importantly when the water supply is normal to excessive, (ii) Juxtamedullary nephrons: they have long loops of Henle that extend deep into the medulla which function most importantly when water is in short supply. The lengths of loops of Henle and of the collecting ducts, and the general thickness of the medulla region of the kidneys, increase progressively in animals best adapted to the drier habitats