Q.25 Hormone responsible for metamorphosis in frog is :-

(1) Ecdysone

(2) Juvenile hormone

(3) Growth hormone

(4) Thyroid hormone

Frog Metamorphosis Hormone: Thyroid Hormone Explained

Thyroid hormone drives metamorphosis in frogs, transforming tadpoles into adults through tail resorption and organ remodeling. The correct answer is option (4) Thyroid hormone.

Correct Answer

Thyroid hormone (Option 4). Thyroxine (T4) and triiodothyronine (T3) from the tadpole thyroid gland peak during metamorphosis, inducing apoptosis in tail tissues, leg development, and gastrointestinal restructuring via gene expression changes.

Option Explanations

Ecdysone (Option 1)

Ecdysone, an ecdysteroid from insects’ prothoracic glands, regulates molting and pupal transitions in arthropods. It plays no role in amphibian metamorphosis.

Juvenile hormone (Option 2)

Juvenile hormone in insects maintains larval state and prevents premature metamorphosis. It opposes ecdysone and is absent in frog physiology.

Growth hormone (Option 3)

Growth hormone (somatotropin) promotes somatic growth across vertebrates but lacks specificity for metamorphic tissue remodeling in frogs.

Thyroid hormone (Option 4)

Thyroid hormone orchestrates frog life stages: prometamorphosis (low levels), climax (high surge for rapid changes), and post-metamorphosis. Its absence halts development.

Metamorphosis Stages

Frog transformation spans 12-15 weeks: external gills → internal gills → limb buds → tail loss, all thyroid-dependent.