Question

Axolotl larva of Ambystoma/tadpole of frog normally fails to metamorphose due to

• A. Lack of Ca and Mg in water
• B. Absence of phosphorus in water
• C. High concentration of iodine in water
• D. Lack of iodine in water

Answer 1

The correct option is D Lack of iodine in water

Gudernatsch discovered that metamorphosis in frog's tadpole begins only when adequate amount of thyroxine is secreted by the thyroid of the tadpole. It was also found that hyposecretion of thyroxine retards and hypersecretion enhances the rate of metamorphosis. In the hilly tracts of North America from whose soil all iodine has been washed away by rainwater, the tadpoles of Ambystoma probably never metamorphose. Therefore, these tadpoles grow to a large size and attain sexual maturity,i.e., these become paedogenetic larvae. This phenomenon is called paedogenesis. The paedogenetic larvae of Ambystoma are called Axolotl larvae. Addition of thyroxine or iodine in pond water naturally induces and enhances metamorphosis in the tadpoles.

So, the correct answer is 'Lack of iodine in water'.