Which of the following animals can live for the longest duration without drinking water?

The correct answer is D, the kangaroo rat. This small nocturnal rodent of the North American deserts (genus Dipodomys) can live its whole life without drinking water. It gets all the moisture it needs from the metabolic water produced when it oxidises the dry seeds it eats. Its kidneys produce highly concentrated urine, its nasal passages recover water from exhaled air, and its burrows keep it out of the daytime heat.

• Camel (B): It conserves water very well and can go weeks or even months without drinking, but it does need to drink. Its hump stores fat, not water, which is a common mix-up.
• Giraffe (A): It gets some water from the leaves it browses, but it needs to drink regularly from water sources.
• Kangaroo (C): Red kangaroos can go long periods without drinking by getting moisture from plants, but they still drink when water is available. They are not in the same class as the kangaroo rat.

The core concept is xerophily, or adaptation to arid conditions through water conservation and metabolic water production. This links to the Environment and Ecology syllabus on desert ecosystems and adaptation, and to Mains questions on desertification and how species respond to climate change.

Trap: Aspirants usually pick the camel because of its fame in deserts. The question asks for the longest possible survival without any drinking at all, and that points to the kangaroo rat.