(a) Deficiency of iodine causes goitre. This disorder is commonly prevalent in northern hilly areas. It causes enlargement of thyroid gland which results in swelling of neck region.
(b) Thyroid gland secretes iodine containing hormone called thyroxine. Thyroxine controls basal metabolic rate. It regulates carbohydrates, protein and fat metabolism in the body. The hormone also controls physical development, mental development, muscular activity, nervous activity and sexual activity.