Chemistry for Biology 

Due to the relatively strong hydrogen bonding in water; it contains unique properties that help it support life on Earth.

 

• Cohesiveness: Due to the high intermolecular forces (the bonds between different molecules), the hydrogen bonds are constantly breaking and reforming which causes the H2O molecules to stick together. This leads to water having large surface tension which allows creates such as water striders to stay afloat on the surface and mate there.

 

• Adhesiveness: Water can adhere to the surface of objects. This allows the water to remain attached to cell membranes which can allow it to then be absorbed by the cell through osmosis.

 

• High Specific Heat: Due to the large difference in electronegativity between the hydrogen and oxygen atoms, the bond between the atoms needs more energy to break. This leads to water’s specific heat (the heat energy required to raise the temperature by 1°C). Because of the large amount of energy needed to break the bond, water easily cycle heat to increase and decrease the temperature of surrounding environments.

 

• High Heat of Vaporization: Similar to the reason that water has a high specific heat, it also consumes a higher amount of energy to vaporize into a gas. This leads to making water an effective coolant of the human body with its evaporation of sweat which therefore extends the range of temperatures in which humans can exist.

 

• Freezing and Expansion: If you were to put water in a glass and then left the glass within the freezer overnight, you will find in the morning ice and a frozen glass. This is caused because water expands in volume as it freezes from a liquid to a solid. Water expands due to the hydrogen bonding keeping the molecules in ice farther apart than in the liquid phase however the molecules will be more organized than they were in liquid stage. The farther molecules also helps extend to ice’s lighter density causing it to float and help keep the water beneath it warmer for aquatic life under freezing conditions.

 

• Versatile Solvent: Due to water being polar, it is a unique solvent for any polar or charged molecules. This is particularly helpful because all biological reactions require the reactants to be dissolved in water to become ions. For substances that are not soluble in water such as fats, they act as a container for water like the lipid membrane of a cell.

 

• Medium for Biochemical Reactions: As mentioned before, living cells range from 55% to 95% water since many biochemical reactions occur in aqueous solutions where substances are dissolved into ions to create an ion gradient for diffusion.

 

• Ingredients of Many Biochemical Reactions: Due to water’s unique polarity of containing a particularly strong negative oxygen and positive hydrogens, water can act as an acid or a base by donating or accepting electrons in chemical reactions. An example is in photosynthesis where water is split into its hydrogen and oxygen atoms to generate ATP and NADPH which are then used to fix carbon dioxide and create sugars.

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