The process of osmosis is the movement of water through a selectively permeable membrane from an area of higher concentration to an area of lower concentration.
If 1% sugar solution is placed in pure water, then there would be a higher concentration of water molecules outside the cell compared to inside the cell. The solution outside the cell would be hypo-tonic (containing fewer solute molecules than inside the cell). Water will move into the cell by inward osmosis and the cell would then swell.
They are like that because they can't always be faulty and may have at least some spark of truth to this theory also as stated earlier a theory in scientific terms is just an observation so it can't really be turned down hence theory.
Proteins that tag pathogens for destruction by immune cells are called Antigens.
