Question

How can a tadpole be prevented from changing into a frog for a long time?
(a)By giving very less food
(b)By giving fat-rich food
(c)By adding a lot of thyroxine to the water in which they are kept
(d)Provide them an antithyroid substance like thiourea.

Answer 1

Hint: The metamorphic changes of frog development are accompanied by the secretion of the hormones thyroxine and triiodothyronine from the thyroid during metamorphosis. Blocking the ${{T}_{3}}$ activity can paralysis the limbs.

Complete answer:
The changes in amphibian metamorphosis are initiated by thyroid hormones ${{T}_{3}}$ and ${{T}_{4}}$. During metamorphosis, the liver begins to synthesis the urea cycle enzyme necessary to make urea from $CO_2$ and ammonia. ${{T}_{3}}$ regulates this alteration by inducing a transcription factor that activates the urea cycle gene and suppressing the gene for ammonia synthesis. ${{T}_{3}}$ causes degeneration of tail and gills that were important for larval movement and respiration but not for an adult. Two organs most sensitive to thyroxine are the thyroid itself and therefore the pituitary, which regulates hormone production.

Additional Information:
-Metamorphosis may be a transition in multicellular organisms amphibians, from larval to a juvenile or adult stage, amid morphological, physiological, and ecological changes.
-Amphibian metamorphosis is related to morphological changes that prepare an aquatic organism for terrestrial existence.
-${{T}_{3}}$ induces the subsequent changes:
The emergence of limbs on metamorphosing tadpoles.
In the eyes, eyelids and nictitating membranes emerge.
Proliferation and differentiation of latest neurons-to form limb musculature.

So, the right answer is, ‘provide them an antithyroid substance like thiourea.’

Note: -The thyroid hormones that can control metamorphosis were demonstrated by Gudernatsch by discovering that metamorphosed prematurely when fed powered sheep thyroid.
-Bennet Allen found that when he removed or destroyed the thyroid rudiment from early tadpoles the larvae never metamorphosed, instead of becoming giant tadpoles.