Final answer:
Iodine is used by the body for the formation of thyroid hormones, which are involved in various physiological functions. Active transport is necessary to transport iodine into a cell.
Step-by-step explanation:
The body uses iodine for the formation of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). These hormones are involved in various physiological functions such as cellular oxidation, growth, reproduction, and the activity of the central and autonomic nervous systems.
Active transport is necessary to transport iodine into a cell. The follicle cells of the thyroid actively transport iodides (anions of iodine) from the diet into their cytoplasm, resulting in a concentration that is approximately 30 times higher than in blood.