Blood and an IV solution need to be isotonic or the cells will be damaged because water will either flow into cells or out of cells:
An isotonic solution is one that has the same osmolarity, or solute concentration, as another solution. If these two solutions are separated by a semipermeable membrane, water will flow in equal parts out of each solution and into the other.
Based on this answer try to think of additional examples.
Jade S.
I see. Thank you for the help!12/20/20