Tadpoles of frog can be made to grow as giant sized tadpoles, if they are

• administered antithyroid substance like thiourea

• administered large amounts of thyroxine

• reared on a diet rich in egg yolk

• reared on a diet rich in both egg yolk and glucose.

A.

administered antithyroid substance like thiourea

Thyroxine, the principal hormone, of thyroid gland, is required for tissue differentiation and metamorphosis (the rapid transformation from the larval to the adult form) in amphibians. Thyroxine triggers a response from the hypothalamus, (probably by a genetic mechanism) followed by the production and release of TSH (Thyroid stimulating hormone), thus metamorphosis begins and tadpoles metamorphose into frogs. Thiourea is an organic compound of carbon, nitrogen, sulphur and hydrogen, with the formula CSN₂H₄, or (NH₂)₂CS. It is similar to urea, except that oxygen atom is replaced by a sulphur atom.