More biological molecules: Water

Question 1

Explain why water is a polar molecule

Answer 1

• The oxygen has a higher electronegativity than the hydrogen atoms - so the shared pair of electrons from the covalent bond is pulled towards oxygen
• This leaves the oxygen atom with a slightly negative charge (δ-) and hydrogens with slightly positive charges (δ+)

Question 2

Outline benefits for water being a polar molecule

Answer 2

• Hydrogen bonds can occur between the water molecule
• Hydrophilic substances (polar / ionic substances) can be dissolved in water

Question 3

What percentage of cells is made up of water

Answer 3

80%

Question 4

Why is water necessary in metabolic reactions

Answer 4

Because water is a metabolite in lots of important metabolic reactions, such as condensation and hydrolysis

Question 5

State the biological importance of water being a solvent

Answer 5

Some substances dissolve into water, which is useful because most metabolic reactions take place in aqueous solutions

Question 6

State qualities of water that aids in temperature control

Answer 6

• High latent heat of vaporisation
• High specific heat capacity

Question 7

Define latent heat of vaporisation

Answer 7

The amount of heat required to convert a liquid into a gas

Question 8

Define specific heat capacity

Answer 8

The heat required to raise the temperature of the unit mass of a given substance by a given amount

Question 9

State the biological importance of water having a high latent heat of vaporisation

Answer 9

• It provides a cooling effect because a small loss of water through evaporation is enough for organisms to lose a great amount of heat

Question 10

State the biological importance of water having a high specific heat capacity

Answer 10

• Acts as a temperature buffer - resisting changes in temperature

Question 11

What is the cause of high latent heat of vaporisation in water

Answer 11

The hydrogen bonds require a large amount of thermal energy to be broken for water to evaporate

Question 12

Explain why water has a high specific heat capacity

Answer 12

Because a large increase in energy is needed to increase the temperature of water sue to the many hydrogen bonds present

Question 13

State the benefits of water having a high specific heat capacity in living organisms

Answer 13

• Allows for constant temperatures within bodies and cells to be maintained
• Provides suitable habitats (e.g fish bc temperature in water remains relatively stable)

Question 14

How does water cohesion work

Answer 14

The slightly negatively charged oxygen atoms attract the slightly positive charged hydrogen atoms of other water molecules, forming hydrogen bonds

Question 15

State the biological importance of water being cohesive

Answer 15

It allows water to flow making it beneficial transporting substances

Question 16

State quality of water that aids in water transport in plant AND state how

Answer 16

• Water molecules are cohesive
• They stick together which aids transport in plants and other organisms as they can travel up transportation tubes 9e.g xylem against gravity

Question 17

Why is water a buffer

Answer 17

• Water is a buffer because it can resist rapid changes in temperature.
• This is because the hydrogen bonds can absorb a lot of energy, which gives water a high SHC

Question 18

What is water cohesion

Answer 18

Its the attraction of two water molecules.

Question 19

What is adhesion

Answer 19

When two different substances stick together

Question 20

Why can some insects, such as pond skaters ‘walk on water’

Answer 20

Because water has a strong surface tension because of the strong cohesion between the water molecules