3.1.7 Water

Question 1

water is a d____ molecule

Answer 1

dipolar

Question 2

why does water form hydrogen bonds?

Answer 2

• water has unevenly distributed charges as the oxygen atom is slightly negative and the hydrogen atoms are slightly positive
• the opposite charges mean that water molecules are attracted to each other
• these forces of attraction are called hydrogen bonds

Question 3

what are the five key properties of water?

Answer 3

• it is a metabolite
• an important solvent in reactions
• has a relatively high heat capacity
• has a relatively large latent heat of vaporisation
• has strong cohesion between water molecules

Question 4

what is the significance of water as a metabolite?

Answer 4

it is involved in many metabolic reactions such as photosynthesis, hydrolysis and condensation reactions

Question 5

what is the significance of water being a good solvent?

Answer 5

• polar/charged molecules dissolve readily in water since it is dipolar
• slight positive charge on hydrogen atoms will attract any negative ions in solutes
• slight negative charge on oxygen atoms will attract any positive ions in solutes
• many essential polar substances dissolve in water, allowing them to be transported easily in the blood/xylem

Question 6

what is the significance of water having a high specific heat capacity?

Answer 6

• can gain/lose a lot of heat/energy without changing temperature
• therefore acts as a buffer to changes in temperature
• the internal temperature of organisms remains relatively stable
• aquatic organisms are provided with a stable environment

Question 7

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

Answer 7

• a lot of energy is required to convert water in its liquid state to a gaseous state
• means that water provides a significant cooling effect
• when sweating, a large amount of heat energy from the skin is transferred to the water to evaporate it, this removes a lot of heat and cools the organism

Question 8

what is the significance of water having a strong cohesion?

Answer 8

• water molecules ‘stick’ together by hydrogen bonds
• water moves up the xylem in plants due to transpiration as a continuous column of water
• provides surface tension which enables small invertebrates to move and live on the surface

Question 9

explain 5 properties that make water important for organisms (5 mark qs)

Answer 9

• a metabolite in condensation/hydrolysis/photosynthesis/respiration
• a solvent so metabolic reactions can occur and allows transport of substances
• high specific heat capacity so buffers changes in temperature
• large latent heat of vaporisation so provides a cooling effect through evaporation
• cohesion between water molecules so supports columns of water in plants and produces surface tension supporting small organisms

Question 10

what properties of water make it important in the cytoplasm of cells?

Answer 10

• polar molecule so acts as a solvent
• solvent so reactions occur faster
• reactive so it takes place in hydrolysis/condensation reactions