Question

The diagrams show vertical sections of kidneys of coypu, brown rat and kangaroo rat, showing the relative size of cortex and medulla. Coypu is found in freshwater and is never of 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. Brown ratCoypuKangaroo rat
• B. Brown rat Kangaroo rat Coypu
• C. Kangaroo ratBrown ratCoypu
• D. Kangaroo ratCoypuBrown rat

Answer 1

Answer: (B)

Brown rat

Kangaroo rat

Coypu

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.

So the correct option is B.