Question

What is the effect on metamorphosis of tadpoles of frogs when there is less amount of iodine in water?
A. Accelerated
B. Delayed
C. Stopped
D. Not affected

Answer 1

Hint: Frogs belong to class Amphibia of phylum chordata. They can survive both on land and in water (freshwater). Frogs are poikilotherms or cold blooded, that is they cannot regulate their own temperature, it varies with the temperature of the environment. They show camouflage which is the ability to change colour to protect themselves from enemies. Frogs are not seen during peak summers and winters as they undergo aestivation and hibernation respectively to protect themselves from scorching heat and freezing cold. Aestivation is when organisms undergo rest during summers and hibernation is when organisms undergo rest during winters.

Complete Step by Step Answer:
In certain organisms, direct development cannot happen. They undergo an intermediate larval stage. Such development is called indirect development. The larval stage in case of frogs is tadpole. Changes occur in tadpoles that give rise to an adult. Metamorphosis is the process by which tadpoles develop into a fully matured adult frog. Thyroxine produced by the thyroid gland is essential for the process of metamorphosis. And for the production of thyroxine, iodine is essential. More iodine in water will ensure more secretion of thyroxine and hence fastens the process of metamorphosis. Thus if iodine level is low in water, tadpoles will not be able to grow into a fully matured frog.
Hence, the correct option is C.

Note: Iodine cannot be substituted with any other substance such as bromine, even if fed in large quantities as bromine is physiologically inert. Iodine is an active constituent of the thyroid gland. It stimulates intracellular oxidation and hence is specific in action.