Not 100% sure here but from what I remember I think it is called osmosis... It is if the water is leaving or entering the cell.
The answer would be proper strength since others do not make sense in detailed.
Biological Organisms: Living things that are capable of reacting to stimuli, reproduction, growth, and homeostasis. Organisms are classified by taxonomy into specified groups such as the multicellular animals, plants, and fungi; or unicellular microorganisms such as a protists, bacteria, and archaea.
The immune system.
The immune system acts as a defense system of the body. It fights against bacteria, viruses and any other disease causing pathogens. Some chemicals can weaken the immune system and make them vulnerable.
