Due to the polarity of the molecules and the ability to form hydrogen bonds, water easily dissolves ionic compounds (salts, acids, bases). Some non-ionic but polar compounds are also well soluble in water, i.e., in the molecule of which there are charged (polar) groups, for example, sugars, simple alcohols, amino acids. Substances that are readily soluble in water are called hydrophilic (from the Greek. Hygros – wet and philia – friendship, addiction). When a substance goes into solution, its molecules or ions can move more freely and, therefore, the reactivity of the substance increases. This explains why water is the main medium in which most chemical reactions take place, and all hydrolysis reactions and numerous redox reactions occur with the direct participation of water.
Substances that are poorly or completely insoluble in water are called hydrophobic (from the Greek. Phobos – fear). These include fats, nucleic acids, some proteins and polysaccharides. Such substances can form interfaces with water, on which many chemical reactions proceed. Therefore, the fact that water does not dissolve non-polar substances is also very important for living organisms. Among the physiologically important properties of water is its ability to dissolve gases (O2, CO2, etc.).
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