Water's ability to form weak H-bonds to other polar molecules allows the anion and the cation of a polar-bonded molecule to separate from one another, and go into solution. Evene large molecules such as proteins can form enough H-bonds with water to become soluble, also the catalytic activity totally depends upon the soluble nature of the enzyme molecules. Water, takes up a large space in cells, which are the single components of the human body. This is a physical demonstration, of how water is essential for life to be happening. The structure of the cells themeselves is highly dependant upon the solvent properties of water. The cytoplasm is a mixture of water soluble molecules, but some of them, knows as phospholipids are unable to dissolve totally in water. The partial attraction and partial repulsion of the phospholipids to and from water cause them to form interfaces, or membranes, separating the cytoplasm from the external enviroment, and hence defining the cell.
Humans themselves are made up of a 70% of water, they are considered the most-solid looking organisms. Without this high water content, waste heat generated from metabolic reactions would soon denature cellular enzymes. The high specific heat capacity, and the high thermal conductivity, of the water in cytoplasm dissipates heat from cellular reactions, preventing thermal damage from occuring.
As water warms , some of the molecules gain sufficient energy to detach from liquid water and become vapour. Each water molecule requires a considerable amount of energy for this to occur (i.e water has a high latent heat of vaporisation), due to the need to break H-bonds to free individual molecules. So, as water evaporates from a surface, it carries with it relatively large amounts of heat energy, cooling the surface from which it vaporises
Water also demonstrates strange properties when it cools> water attains its maximum density, not as a solid like most molecules, but as a liquid at 4 degress C. This is the reason why ice is able to float on water, benefitting living organisms by forming an insulating layer on the surface of freezing ponds and lakes. Freezing however, can cause considerable damage to organisms exposed to sub-zero temperatures, because of the expansion of water when ice crystals form within their cells. Many polar ectothermic species possess natural anti-freeze compunds (e.g glycerol) which prevent their body fluids freezing, even at temperatures well below zero.
Hydrogen bonds between water molecules are responsible for the cohesive and adhesive properties of liquid water. Cohesion means a tendency for "like to stick to like", and results in water having a high surface tension. The skin of large surfaces of water provides a habitat for small invertebrates, such as pond skaters, which glide across the water without penetrating the surface.
Adhesion is the tendency to adhere to dissimiliar molecules- in the case of water, to other polar molecules. This adhesive property of water causes capillarity, the ability of water to resist gravitational pull and rise up thin tubes, or form a thin layer around soil particles. Adhesion and cohesion, coupled with the "transpirational pull" generated by evaporation of water from leaves which acts upon the continuos column of water in xylem tissue, allow water and dissolved minerals to be supplied to plant tissues up to 100 metres above the ground.
Another property of water is its transparency to visible light. light can penetrate water to a considerable depth, provided the water is free of suspended, particulate matter. Different wavelengths of light penetrate to different depths. Red and yellow light only travel to a maximum of 50 metres depth, whilst blue and violet light can reach 100 metres. This allows large volumes of water to serve as habitats for photosynthetic organisms. On land, light can easily penetrate plant leaf epidermal tissues, which are 90 % water, to reach the underlying photosynthetic cells.
