Water

Question 1

State and explain the property of water that can help to buffer changes in temperature.

Answer 1

water has a relatively) high (specific) heat capacity;

Ignore numbers relating to heat capacity

2. Can gain / lose a lot of heat / energy without changing temperature;

OR

Takes a lot of heat / energy to change temperature;

Question 2

Water and inorganic ions have important biological functions within cells.

(a) Give two properties of water that are important in the cytoplasm of cells.

For each property of water, explain its importance in the cytoplasm/ cells

Answer 2

Polar molecule;

2. Acts as a (universal) solvent;

OR

3. (Universal) solvent;
4. (Metabolic) reactions occur faster in solution;

OR

5. Reactive;
6. Takes place in hydrolysis / condensation / named reaction;

Question 3

Compare and contrast the processes by which water and inorganic ions enter cells.

Answer 3

Comparison: both move down concentration gradient;

2. Comparison: both move through (protein) channels in membrane;

Accept aquaporins (for water) and ion channels

3. Contrast: ions can move against a concentration gradient by active transport

Question 4

Give three properties of water that are important in biology.

Answer 4

Is a metabolite

*   Is a solvent

*   Has a (relatively) high heat capacity

*   Has a (relatively) large latent heat of vaporisation / evaporation

*   Has cohesion / hydrogen bonds between molecules

Question 5

Explain five properties that make water important for organisms.

Answer 5

A metabolite in condensation/hydrolysis/ photosynthesis/respiration;

2.   A solvent so (metabolic) reactions can occur

OR

A solvent so allowing transport of substances;

3.   High heat capacity so buffers changes in temperature;

For ‘buffer’ accept ‘resist’.

4.   Large latent heat of vaporisation so provides a cooling effect (through evaporation);

5.   Cohesion (between water molecules) so supports columns of water (in plants);

For ‘columns of water’ accept ‘transpiration stream’.

Do not credit ‘transpiration’ alone but accept description of ‘stream’.

For ‘columns of water’ accept ‘cohesion-tension (theory)’.

For cohesion accept hydrogen bonding

6.   Cohesion (between water molecules) so produces surface tension supporting (small) organisms;