The mineral element whose deficiency causes goiter in humans is ...... .

Read the given statements $:$
$(A)$ Hypothyroidism during pregnancy causes defective development and maturation of the growing baby.
$(B)$ Thyroxine does not require a secondary messenger.
$(C)$ Thyroxine plays a major role in the regulation of Basal Metabolic Rate $(BMR)$.
$(D)$ Hypersecretion of thyroxine could cause immunodeficiency.
How many of the above statements are correct?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A):$ During pregnancy,the level of thyroxine is increased in the maternal blood.
Reason $(R):$ Pregnancy is characterised by metabolic changes in the mother.
In the light of the above statements,choose the most appropriate answer from the options given below:

Assertion: The thyroid gland is composed of follicles and stromal tissue.
Reason: Iodine is essential for the normal rate of hormone synthesis in the thyroid.

Metamorphosis in frog can be promoted by

Write a short note on the disorders/diseases of the thyroid gland.