Water

Question 1

Functions of water

Answer 1

• Water is reactant in many chemical reactions such as hydrolysis.
• It’s a polar molecule due to uneven distribution of charge.
• Water is a solvent therefore substances can dissolve in it to form solutions where most biological reactions occur in.
• It transports substances such as glucose and oxygen around plants and animals. This is due to strong cohesion.
• It helps with minimising temperature fluctuations and thus acts as a buffer due to its high specific heat cap.
• As it becomes less dense when frozen, ice floats to top and creates insulating layer. This increases the chance of survival of organisms in large bodies of water.

Question 2

Polarity of water

Answer 2

• A molecule of water has one oxygen joined to two hydrogen atoms by shared electrons.
• As the shared electrons are pulled more to the oxygen atom, the hydrogen atoms have a slightly positive charge and oxygen has a slightly negative charge.
• This makes water a polar molecule.

Question 3

Hydrogen bonding in water

Answer 3

• Hydrogen bonds are formed between the oxygen of one water molecule and the hydrogen of another.
• Because of this, water molecules have an attraction for each other known as cohesion.

Question 4

High specific heat capacity and High latent heat of evaporation

Answer 4

• Hydrogen bonds give water a high specific heat capacity.
• Hydrogen bonds require more energy to break.
• This means water doesn’t experience rapid temperature changes. Making it a good habitat.

Question 5

Very cohesive

Answer 5

• Cohesion is the attraction between molecules of the same type.
• Water molecules are very cohesive because they are polar.
• This helps the water flow - making it good for transportation of substances. E.g up plant stems in transpiration.

Question 6

Low density when solid

Answer 6

• Water molecules are further apart in ice because it is in a lattice shape making it less dense.
• In cold temps ice forms an insulating layer on top of the water so the water below doesn’t freeze.
• So organisms like fish can survive.

Question 7

Good solvent

Answer 7

• Many important substances in reactions are ions.
• Water is polar as the slightly positive end attracts anions and slightly neg end will attract cations.
• This means ions will become surrounded by water molecules so they dissolve.
• This is useful because water can transport dissolved substances such as in the blood.