2.3.d Explain how hydrogen bonding occurs between water molecules and relate the properties of water to its roles in living organisms (limited to solvent action, specific heat capacity and latent heat of vapourisation). 

• Life as we know it would not be possible without water. 
• Water has extraordinary properties that make it an essential part of life. 

• A water molecule contains two hydrogen atoms and one oxygen atom held together by hydrogen bonds.  
• Hydrogen bonds make it difficult to separate water molecules.
• Therefore, to change liquid to gas, lots of energy is required to break the hydrogen bonds. 

• Water is an effective solvent for ions and polar molecules, as it separates them. 
• Non-polar molecules are pushed together, as they are insoluble, which affects protein structure (due to hydrophobic interactions). 
• Water is the transport medium in blood and the solvent properties are essential.

• Specific Heat Capacity is defined as the amount of heat energy required to raise the temperature of 1kg of water by 1°C. 
• Hydrogen bonds that tend to make water molecules stick to each other, therefore, more energy needed to raise water temperature to break hydrogen bonds. 
• Water has a high specific heat capacity.
• Because larger bodies of water require more time to heat up, and therefore there is a slower change in temperature, aquatic habitats are relatively more stable.

• Latent Heat of Vaporisation is a measure of the heat energy needed to vaporise a liquid. 
• Water has a high Latent Heat of Vaporisation because the hydrogen bonds need to be broken before water can vaporise. 
• As explained above, more energy is needed to break hydrogen bonds. 
• Energy transfer to water molecules during vaporisation causes loss of energy from surrounding, therefore cooling down occurs.
• Therefore, sweating is a good cooling mechanism. 
• But careful if too much energy is lost for little amount of water, dehydration can occur.

See you next time for 'shore' 🙃

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Written by Aayushi | GCE CIE Biology Specialist @ TUTTEE

References:

Jones, M., & Parkin, M. (2018). Cambridge International AS and A Level Biology. Cambridge: Cambridge University Press.