This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
The intake of Iodine in to the Thyroid Gland is an example of which of the followings means of molecular transpo? 
Select and explain. 
A. Primary active transpo, B. Secondary active transpo, C. Facilitated diffusion, D. Endocytosis
B: Secondary active transpo
Answer: B: Secondary active transpo 
Explanation: Secondary active transpo or co-transpo, uses energy to transpo molecules across a membrane against a concentration/electrochemical gradient.In contrast to primary active transpo, there is no direct coupling of ATP; instead, the electrochemical potential difference created by pumping ions out of the cell is used. Primary active transpo, also called direct active transpo, directly uses energy to transpo molecules across a membrane. Facilitated diffusion is a type of passive transpo that allows substances to cross membranes with the assistance of special transpo proteins. Endocytosis is a process by which cells absorb molecules (such as proteins) by engulfing them.