1.7 - Water

Question 1

1) ) Draw a molecules of water and indicate which parts are partially charged

Answer 1

Check notes

Question 2

1) What does it mean to say that water is a ‘metabolite’?

Answer 2

It means that water is either a reactant or a product in metabolic reactions in living organisms
e.g. it is required for hydrolysis reactions to take place and it is produced in condensation reactions

Question 3

1) What is a solvent? Why can water act as a solvent? How is this beneficial in terms of chemical reactions?

Answer 3

● A solvent is a substance in which other substances can dissolve in

● Water is polar, so it can form hydrogen bonds

● This means that polar and ionic substances are able to dissolve in water
(due to the attraction of opposite charges, allowing them to be completely surrounded by the polar water molecules)
This is useful because many metabolic reactions occur when substances are dissolved in water.

Question 4

1) Explain why there is surface tension in water

Answer 4

Because water molecules are polar, so can form H-bonds with other water molecules

This causes cohesion between water molecules, holding them together

(this allows pond skater to walk on water without falling in!)

Question 5

1) Explain how the properties of water help water to move up the xylem vessel of a plant

Answer 5

● Water is polar, so it can form hydrogen bonds between other water molecules
● Therefore, there is COHESION between water molecules due to H-bonds
● There is also ADHESION between the water molecules and the wall of the xylem
Therefore the column of water molecules in the xylem does not break.

Question 6

1) (i) What does it mean that water has a high specific heat capacity?
(ii) Why does water have a high specific heat capacity?
(iii) How is this property beneficial
(iv) How is it useful to a) aquatic organisms b) humans?

Answer 6

(i) High specific heat capacity means that a lot of energy is required to raise the temperature of water by 1°C
(ii) Because there are lots of Hydrogen bonds between water molecules and they can absorb lots of energy. OR water can gain / lose a lot of heat / energy without changing temperature;
(iii) This makes it good at BUFFERING CHANGES IN TEMPERATURE
(iv) (a) it makes water a good habitat because the temperature underwater is likely to be more stable than on land (so the temperature changes are not as big)
(b) Water INSIDE organisms remain at a fairly stable temperature therefore helping to maintain a constant internal body temperature

Question 7

1) (i) What does it mean when we say that ‘Water has a large latent heat of vaporization’?
(ii) How is this property beneficial to organisms living in hot countries?

Answer 7

(i) This means a lot of energy is required to convert liquid water into water vapour
(ii) It allows water to provide a cooling effect with little loss of water through evaporation
This is because it takes a lot of energy to break the hydrogen bonds between the water molecules for evaporation to take place
This is why organisms sweat or cover themselves in mud!

Question 8

1) Water is a metabolite in many reactions. Which ones do you know of?

Answer 8

Condensation/hydrolysis/photosynthesis/respiration

Question 9

1) Give five properties of water that are important in biology. Explain the importance of each property you identify. [5]

Answer 9

1. Metabolite
2. Solvent
3. High specific heat capacity
4. High specific latent heat of vaporisation
5. Cohesion between water molecules, to support columns of water in plants.
6. Cohesion between water molecules to produce surface tension as this helps to support small organisms.