Question

Which gland plays a key role in the metamorphosis of a frog?
(a) Adrenal
(b) Thyroid
(c) Pituitary
(d) Pancreas

Answer 1

Hint: Frogs depend on water for external fertilization. The male and female frogs produce a large number of male and female gametes respectively. They are released into water where fertilization occurs. In frogs, indirect development takes place. This means larval stages are present during the life cycle of a frog. The tadpole larva changes into an adult frog by the process of metamorphosis.

Complete answer:
Class Amphibia includes animals that can live in both terrestrial and aquatic habitats. Amphibians have three chambered hearts and are cold blooded. Indirect development occurs in them. They lay eggs (oviparous). They can respire through lungs, gills and moist skin. Frog, tree frog, salamander are some examples of Amphibians.
The tadpoles of the frog are fully aquatic. They look like fish and respire through gills. They have tails for the movement in water. During the process of development, they lose their tails.
Metamorphosis is an important phenomenon in the life cycle of amphibians. When the gill-breathing larva changes or develops into lung-breathing adults, this process is called metamorphosis. It provides an evolutionary advantage to amphibians over other animals. During metamorphosis, a number of physiological and morphological changes take place.
Metamorphosis is under the control of hormones.
The thyroid gland plays an important role in the metamorphosis process in frogs. The hypothalamus secretes the thyroid stimulating hormone (TSH) which in turn stimulates the thyroid gland to secrete thyroxine hormone (TH). The thyroid hormone promotes the growth and development and also affects the tissues directly by causing the degeneration and death of some cells.

Thus the answer of the above question is option (B) thyroid gland.

Note: Frogs can respire through gills, lungs and moist skin. When they are present in water, they respire through moist skin while on land; they respire through lungs and buccal cavity. The mucus makes the skin moist and slippery. Eyes have nictitating membrane that protects their eyes in water. Tympanum membrane of the ear helps them in hearing.