1. the sodium-iodide symporter plays a role in the accumulation of iodide in the thyroid gland. here, one iodide gets converted to one iodine, which is utilized for the formation of either of the two types of thyroid hormones, t3 and t4. t3 and t4 are named after the number of iodines found in each of these hormones. to produce a single molecule of t3, a total of sodium ions must move down their concentration gradients by secondary active transport. the movement of iodide ions occurs in the direction as sodium ions.

(1) 6 sodium ions

(2)The movement of iodide ions occurs in the same direction as the sodium ions.

Explanation: Sodium-iodide symporter actively transports 2 sodium ions together with one iodide ions across the basement membrane into the thyroid follicular cells.(therefore for production of a single molecule of T3 3×2=6 sodium ions)This system utilises the concentration of sodium ions so that iodide ions can move against its concentration gradient.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.