exam questions

• Justify how loss of heat when sweating is related to the dipole nature of water molecules (3)

  -       The water has an uneven distribution of charge making it a dipole

  -       So, water forms hydrogen bonds with other water molecules

  -       And it requires a lot of heat energy to break these bonds

  -       And allow water to evaporate taking the heat energy with it- latent heat of evaporation

   
• Explain how the properties of water make it an ideal transport medium (3)

  -       Water is a solvent- allowing polar/ ions to dissolve

  -       Because water molecules surround polar molecules/ ions

  -       Hydrogen bonds form between water molecules and the solute molecules

  -       Water is also liquid so can flow- cohesion between water molecules
• Explain the role of hydrogen bonding and its importance in transporting water

  -       Allows water molecules to stick together as form hydrogen bonds with each other/cohesion of water molecules

  -       Hydrogen bonds form between other molecules and water/ adhesion to sides/lining of transport vessels
• With references to covalent bonding, explain the dipolar nature of water molecules (3) 

  -       Covalent bonding occurs between an oxygen atom and 2 hydrogen atoms 

  -       Electrons are shared unequally between an oxygen atom and hydrogen atom

  -       Oxygen has a greater electronegative charge than hydrogen

  -       Thus, oxygen attracts/pulls electrons from hydrogen towards its nucleus 

  -       Therefore, oxygen is slightly negative, and hydrogen is slightly positive 

  -       Water is therefore a polar molecule
• Describe what is meant by mass transport system (1) 

  -       A bulk movement of gases or liquids in one direction, usually via a system of vessels and tubes 
• Using named example, explain the benefits of the circulatory system as a mass transport system (3)

  -       The lungs and the circulatory system

  -       Brings oxygen quickly from the lungs/alveoli to the cells (for respiration) faster transport of oxygen from the lungs/alveoli

  -       Removes carbon dioxide quickly (from the respiring cells) to the lungs/alveoli --faster removal of carbon dioxide (from the respiring cells) to the lungs/alveoli

  -       Maintains diffusion/concentration gradients (of oxygen and carbon dioxide) at the alveoli and (respiring)cells.

   
• Explain how the dipolar nature of water is essential for living organisms (2)

  -       Idea that water can form hydrogen bonds

  -       Water is a solvent- ions and polar molecules can dissolve/be transported in water

  -       Hydrogen bonding holds water together as a liquid so that it a move in mass flow systems