Water has importance inside cells and outside. This may be because of its chemical and physical properties; it can be found naturally in all three of its states. At room temperature water is in a liquid state, It boils at 100ºC and freezes at 0ºC.
However its molecules are bonded together by hydrogen bonds, this raises it’s melting and boiling points, e.g. its boiling point would be -120ºC rather than 100ºC.
Water can also be used as a solvent because of it polarity. Many things will dissolve in it, and more reactions take place while in solution with water. Often in organisms substances must be in solution and water is the solvent.
Plants can only obtain mineral salts in solution so require water to live. Also human digestion will only dissolve soluble foods, meaning large starch molecules must be broken down into soluble sugars. Also many organisms living in water spend most of their lives underwater, yet they require oxygen to live and respire, and as water is such a good solvent the required oxygen gas is dissolved in the water and the organisms can use it.
Water is the most abundant component in any organism, proving its importance, the lowest is 20% in seeds, while jellyfish are about 99% water. Around 60% of the human body consists of water.
It plays roles in the metabolism of all cells and for plants in photosynthesis. It is a main reactant in the photosynthesis reaction:
CO2 + H2O →→→→ C6H12O6 + H20
In all cells, water is used for hydrolysis, which is the breakdown of a substance by water, like polysaccharides to monosaccharides, forming a glycosidic bond. Water is used as a medium for chemical reactions, due to its properties as a solvent; the diffusion and osmosis of substances, e.g. gaseous exchange, which need to be moist as the exchange takes place in solution, therefore there is water in the lungs or in mesophyll cells in the ‘spongy’ part of leaf cells.
It is also used on a much larger scale for transport. Blood plasma is mostly water, and is used to transport food, hormones, waste products like ammonia and urea and also oxygen in haemoglobin, similarly in plants, sap is used to transport food and other substances.
These substances all easily dissolve in water and they can be transported. Water is also used during fertilization when sperm must reach the ovum, the sperm is transported in semen, which is mostly water.
Water is also in they eye in the aqueous and vitreous humour of the eye help maintain its shape. Amniotic fluid protects and supports a fetus when it is growing aswell.
Water can also be used for support. As plant cells have cell walls as well as cell membranes, when the plant cell becomes full of water (osmosis) it wont burst but the cell wall exerts a force equal to the osmotic force, the cell becomes turgid and this is important in the support of leaves and prevents wilting, as too little water makes the cells become flaccid which causes the plant to wilt.
Temperature of water remains constant (due it to its high specific heat capacity) so few temperature controls are needed. So a high temperature is required to heat a small amount due to the overall strong bonds between molecules. Water has a high latent heat of vapourisation, which is the energy required to change a certain amount of of water in liquid form, into a gas, as water vapour. Water is used in perspiration to help regulate body temperature as it uses the heat from the body to vapourise the sweat taking away the heat and cooling the skin.
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