Water

Question 1

What are the functions of water?

Answer 1

• a metabolite in many important metabolic reactions including condensation and hydrolysis
• a solvent (some substances dissolve in it) and most metabolic reactions take place in solution
• helps with temp control (has high specific heat capacity and latent heat of vaporisation)
• very cohesive which helps transport in plants and other organisms

Question 2

What is the structure of water?

Answer 2

a molecule of water is one atom of oxygen joined by two atoms of hydrogen by shared electrons

Question 3

What bonds hold water together?

Answer 3

hydrogen bonds form between water molecules because the slightly negative charged oxygen atoms attract the slightly positive charged hydrogen atoms - its the hydrogen bonds that give water its properties

Question 4

What are the properties of water?

Answer 4

Polar/ Dipolar
Important metabolite
Very cohesive
Good solvent
High latent heat of vaporisation
High specific heat capacity

Question 5

What makes water polar/dipolar?

Answer 5

the shared electrons are slightly pulled towards the oxygen atom which causes the other side of the hydrogen atom to have a slightly positive charge (S+) and the unshared negative electrons on the oxygen atom gives it a slightly negative charge (S-)
This makes water a polar molecule as it has a slightly negative charge on one side and slightly positive charge on the other

Question 6

Why is water a important metabolite?

Answer 6

• many metabolic reactions involve a condensation or hydrolysis reaction
• H = require water molecule to break a bond
• C = releases a water molecule as a new bond is formed

Question 7

Why are water molecules cohesive and why is it good?

Answer 7

Cohesion = the attraction between molecules of the same type
- water molecules are very cohesive because they’re polar
- strong cohesion helps water to flow which makes it good for transporting substances e.g. xylem
- strong cohesion means water has a high surface tension when it comes into contact with air - why sweat forms droplets.

Question 8

Why is water a good solvent?

Answer 8

Ionic substances = made from 1 positively charged molecule and 1 negatively charge molecule
- as water is polar the slightly positive charged atom will be attracted to the negative ion and the slightly negative charged end of the water molecule will be attracted to the positive ion
- the ion will be surrounded by water molecules - will dissolve so dissolves substances can be transported

Question 9

What does it mean that water has a high latent heat of vaporisation?

Answer 9

water evaporates/vaporises when the hydrogen bonds holding water molecules together break
- takes lots of energy to break so lots of energy is used when water evaporates
- lots of heat is used to change from liquid to gas so organisms can cool down without losing too much water
- helps to lower the temp

Question 10

What does it mean that water has a high specific heat capactiy?

Answer 10

when water is heated a lot of the heat energy is used to break hydrogen bonds which means there is less heat energy available to increase the temp of the water
- this is useful to buffer (resist) changes in the temp