1.7 Water

Question 1

Why is water a polar molecule

Answer 1

• It has an uneven distribution of charge within the molecule (the oxygen atoms attracts electrons more strongly than the hydrogen atoms).
• The unequal sharing of electrons gives water delta negative regions (near the oxygen atom) and delta positive regions (near the hydrogen atoms).
• The opposite charges cause water molecules to be attracted to each other, so hydrogen bonds are formed.

Question 2

Why does water have a very high specific heat capacity and how does this link to its function

Answer 2

• A large amount of energy is needed to change the temperature of water.
• This is because when water is heated, the heat energy goes towards weakening/ breaking the hydrogen bonds, rather than increasing the kinetic energy of the water molecules.
• This allows water to act as a buffer against rapid temperature changes (the temperature of water doesn’t usually change rapidly), allowing water to act as a habitat for aquatic organisms.

Question 3

How does ice being less dense than water link to its function

Answer 3

• Ice acts as a habitat for lots of organisms and insulates the water below to prevent it from freezing.
• This allows organisms to continue to live in the water under the ice

Question 4

Why does water have a very high latent heat of vaporisation and how does this link to its function

Answer 4

• Large amount of heat energy needed to evaporate water.
• This allows organisms to cool themselves without losing lots of water.
• E.g. sweating - heat energy is used to evaporate water from the surface of the skin which transfers heat from the organism to the environment, so it can cool down.

Question 5

What is a metabolite and why is it important that water is one

Answer 5

• A metabolite is a molecule that takes part in a metabolic reaction.
• Water is a key metabolite in condensation and hydrolysis reactions.
• Water is an important metabolite as it is often a reactant necessary to start metabolic reactions or a byproduct of a reaction.

Question 6

What is a solvent and why is it important that water is one

Answer 6

• Many biological molecules are either polar or ionic molecules which need ti be dissolved in a polar solvent in order to function.
• Water’s polarity makes it a very good solvent.
• E.g. Calcium chloride - the positive Ca2+ ions will be attracted to the delta negative regions of water (the oxygen) and the negative Cl- ions will be attracted to the delta positive regions of water (the hydrogens).

Question 7

Why is water cohesive and why is this important

Answer 7

• Cohesion is the attraction between the same type of molecule.
• Water molecules are very cohesive which allows water to flow and be transported (necessary in the xylem of plants).
• The cohesion enables water to move up against the force of gravity.
• Cohesion also produces surface tension where water meets air. This property is used by small organisms to walk on water.