water

Question 1

describe the structure of a water molecule?

Answer 1

• O has a slightly negative charge
• H atoms have a slight positive charge
• water is a dipolar molecule

Question 2

how is water different to molecules of a similar size? (E.g CO2, O2, N2)

Answer 2

water is a liquid at room temperature because of its dipolar structure

Question 3

what are the properties of a water molecule?

Answer 3

• water is a solvent
• water has cohesion between molecules
• water has a high specific heat capacity
• water has a large latent heat of vaporisation
• water is a metabolite

Question 4

describe how water can be a solvent?

Answer 4

since water is polar it readily dissolves other polar or charged substances

Question 5

what is the biological significance of water being a solvent?

Answer 5

• allows dissolved substances to be transported
• allows reactions to take place in aqueous solution which is faster

Question 6

describe how water can have cohesion between molecules?

Answer 6

water molecules stick together due to hydrogen bonding between them

Question 7

what is the biological significance of water having cohesion between molecules?

Answer 7

• cohesive forces allow water to be pulled up the xylem vessels in plants in a continuous column without breaking during transpiration
• surface tension water molecules at the surface where they meet air tend to be drawn back into the body of water rather than escaping, the water surface can support small organisms (eg pond skaters)

Question 8

describe how water can have a high specific heat capacity?

Answer 8

• it takes a lot of energy to change the temperature of water
• this is because the thermal energy adsorbed is used to break hydrogen bonds

Question 9

whats the biological significance of water having a high specific heat capacity?

Answer 9

water resists changes in temperature, large bodies of water maintain a much more stable temperature compared to the air. this makes water a stable habitat (ponds, lakes, seas)

Question 10

describe how water can have a large latent heat of vaporisation?

Answer 10

• it takes a lot of energy to evaporate water
• this is because it takes a lot of energy to break the hydrogen bonds between water molecules

Question 11

what is the biological significance of water having a large latent heat of vaporisation?

Answer 11

• evaporation of water in the form of sweating, panting is an effective mean of cooling with little loss of water since body heat is used to evaporate water
• plants are also cooled when water evaporates from their leaves

Question 12

describe how water can be a metabolite/reactive?

Answer 12

• condensation and hydrolysis reactions
• a reactant in photosynthesis

Question 13

whats the biological significance of water being a metabolite/reactant?

Answer 13

hydrolysis reactions are important in digestion of large molecules. also important for releasing energy via ATP.
condensation reactions are important in synthesis of important molecules eg. proteins, lipids, polysaccharides in living organisms.

Question 14

what are some other useful properties of water?

Answer 14

• transparent, light can penetrate allowing plants to photosynthesise
• floats when freezes (due to hydrogen bonding), allows organisms to survive under the ice + provide insulating layer
• contains dissolved gases, oxygen/carbon dioxide can be used for photosynthesis/respiration