Structure - water is made up of two hydrogen atoms covalently bonded to one oxygen atom. The single electron of each hydrogen atom is shared with one off the six outer electrons from the oxygen resulting in the oxygen having two non-bonding pairs of electrons.
The oxygen is slightly negatively charged and hydrogen is
slightly positively charged. Therefore tiny charges make water molecules attracted to each other.
So positively hydrogen atoms attracted to negatively charged oxygen atoms to form hydrogen bonds
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Structure relating to medium of life (solvent)
The tiny charges on the water molecules attract other molecules or ions that have charges on them. This makes the molecules/ions spread in between water molecules (dissolve)
Examples - sodium chloride is an ionic compound that dissolve in water and glucose is a covalent compound that dissolve in water.
Most metabolic reactions take place in solution only because this make it possible for ions or molecules to come in contact with each other.
Cytoplasm contains many dissolved substances and water can flow so therefore carrying the dissolved substances from one place to another.
Example : urea dissolves in water as urine
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Properties of water
- solvent - water is a solvent within cells and solvent in transport medium such as blood. - solvent in nutrients and gases such as carbon dioxide
- High heat capacity - it requires 4.2J to rise the temperature of 1g of water by 1 degree Celsius. so this keeps the temperature of organisms and the environment fairly constant
- high latent heat of fusion - much thermal energy is required to change ice to water and much is transferred from water when it forms ice. This keep the water in cells as liquid so membranes of the cell are not damaged by ice crystals
- high latent of vaporization - much thermal energy is need to change water to vapour. so lots of energy is needed to evaporate small quantities of water and this is helpful in cooling of organisms by sweating and transpiration. This is also useful because water in shallow aquatic habitats do not evaporate quickly
- density - ice is less dense than water. so ice floats on water and act as insulation for aquatic organisms.
- reactive - water splits to form hydrogen ions and hydroxyl ions. This makes water a raw material for photosynthesis and water is used in hydrolysis reactions
- high cohesion - hydrogen bonds hold water molecules together. This supports columns of water in xylem and provides surface tension for organisms that love on the surface of water
- transparent - pure water is transparent to visible wavelength of light. This allows aquatic photosynthetic organisms to obtain enough light fr photosynthesis.
