Water is the predominant component of all living organisms. It has unique properties due to structural features: water molecules have the form of a dipole and hydrogen bonds form between them. The average water content in the cells of most living organisms is about 70%. Water in the cell is present in two forms: free (95% of all cell water) and bound (4-5% are bound to proteins).
1.Water as a solvent. Many chemical reactions in the cell are ionic; therefore, they occur only in an aqueous medium. Substances that dissolve in water are called hydrophilic (alcohols, sugars, aldehydes, amino acids), insoluble – hydrophobic (fatty acids, cellulose).
2. Water as a reagent. Water is involved in many chemical reactions: polymerization, hydrolysis, in the process of photosynthesis.
3.Transport function. Movement through the body with water of substances dissolved in it to its various parts and removal of unnecessary products from the body.
4. Water as a thermostabilizer and temperature regulator. This function is due to such properties of water as high heat capacity – it softens the effect on the body of significant changes in temperature in the environment; high thermal conductivity – allows the body to maintain the same temperature in its entire volume; high heat of evaporation – used to cool the body during perspiration in mammals and transpiration in plants.
5. Structural function. The cytoplasm of cells contains from 60 to 95% water, and it is it that gives the cells their normal shape. In plants, water supports turgor (elasticity of the endoplasmic membrane), in some animals it serves as a hydrostatic skeleton (jellyfish)
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