Question

what happens to tadpoles if iodine is not sufficient in water and why

Answer 1

A hormone released by the thyroid gland is a signal for metamorphosis in many amphibians like frogs.
This hormone requires the presence of iodine in water for its production.
If the water in which tadpoles are growing is deficient in iodine , the tadpoles fail to grow and cannot become adult frogs.

thanks