This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
Which of the following transpo processes is passive? 
Select and explain. 
A. Co-transpo of Na+ ion and a molecule into cell, B. Exchange of K+ ion outside the cell for Na+ ion inside the cell, C. Flow of H2O through cell membrane by osmosis, D. Uptake of molecules into cell by endocytosis
C: Flow of H2O through cell membrane by osmosis
Answer: C: Flow of H2O through cell membrane by osmosis 
Explanation: Osmosis is the movement of water molecules across a semi-permeable membrane from a region of Lower solute concentration to an area of higher solute concentration. It is passive in nature. (REF: TEXTBOOK OF MEDICAL PHYSIOLOGY GEETHA N 2 EDITION, PAGE NO - 3)