The Biological Importance of Water as a Solvent and as a Medium for Living Organisms, including Change of State and Specific Heat Capacity

        Not only is water a habitat for life but it is also vital for the structure of many organisms, i.e. in plants and humans. Plants need water to make their cells rigid in order to support the plant- especially the stem and it does this due to the fact that water is incompressible. Moreover, a plant needs water to grow. It uses a process called active uptake to take water up through it’s roots against the concentration gradient in order for the plant to absorb water and ions from the soil. Plants also use water for keeping a constant temperature by a process called transpiration. Water has properties which allows plants to pull up water through xylem vessels from the roots to the leaves.  Also plants need water for photosynthesis (carbon dioxide + water = glucose + oxygen) for it’s source of hydrogen atoms needed to produce glucose. This demonstrates the fact that all life is dependant on water as photosynthesis produces glucose (food) which is consumed by all plants and animals releasing energy allowing them to move and live and this energy moves down the food chain to every other organism. Water is also vital in condensation reactions where water is removed from molecules to bond them together which usually happens with sugars such as glucose and carbohydrates.

        Water can change it’s state from a solid to a liquid or a gas. It has a boiling point of 100degrees celcius and a melting point of 0degrees celcius, which is unusual for a molecule this size as other molecules similar in size like CO2 or NH4 are all gaseous molecules at room temperature and pressure. Because a large number of bonds hold the water molecules together, it takes 2KJ per gram of water hence a lot of energy needed to separate bonds and turn the liquid to vapour. Furthermore water needs 300Joules per gram of ice to melt it. However it’s freezing point is lowered by solutes because the soluble molecules disrupt the hydrogen making the water freeze at a lower temperature hence it’s easier to melt the ice. Ice is less dense than water and this is proven as ice floats on the surface of the water. The particle arranged in ice are slightly further apart than particles in water as energy is required to freeze it making the particles move slightly hence ice expands.

        The specific heat capacity of water is high, this results in 4.2J of energy needed to raise one gram of water by 1degree, therefore a lot of heat energy is required to raise the temperature of water significantly, but once warm it cools down slowly.