In frog, cutaneous respiration takes place in
A. Only in water, when pulmonary respiration does not take place
B. Only in water, but along with pulmonary respiration
C. Only on land
D. Always

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Hint: Cutaneous respiration is a mode of respiration in which gaseous exchange takes place across the skin (integument) of an organism rather than gills or lungs. It occurs in a wide variety of organisms, including insects, amphibians, fish, turtles, etc.

Complete answer:
Due to the amphibious nature of life, frogs show different modes of respiration. In frogs, respiration takes place in following four ways:
> Gill respiration (in tadpole stage only)
> Cutaneous respiration
> Bucco-pharyngeal respiration
> Pulmonary respiration
While completely submerged, all the respiration in the frog takes place through the skin. The skin comprises thin membranous tissue that is quite permeable to water and comprises a large network of blood vessels. The thin membranous skin permits the respiratory gases to readily diffuse directly down between the blood vessels and the surroundings. When the frog is out of the water, mucus glands present in the skin keep the frog moist, which helps absorb dissolved oxygen from the air.
Cutaneous gas exchange mostly meets for most of the breathing needs of a frog, but it still has lungs to supplement his oxygen demands. If the cutaneous and buccopharyngeal respiration cannot supply a sufficient amount of oxygen, then the frog respires by lungs to fulfil their demand. Frog’s lungs have comparatively thin walls that can act like balloons. When a frog fills its lungs with air, it can hold the air to help it remain buoyant while swimming in water.

So the correct answer is option D.

Note: Although frogs have two developed lungs, they do most of their respiration through their moist skin, completely bypassing their lungs. Their moist skin contains thin blood vessels near the body surface to help diffuse oxygen in and carbon dioxide out, even when the frogs are underwater or hibernating.