water + ions

Question 1

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.

Property 1__________________________________________________________

Biological importance within cells________________________________________

___________________________________________________________________

___________________________________________________________________

Property 2__________________________________________________________

Biological importance within cells

Answer 1

1. 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 2

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

Answer 2

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 3

Explain five properties that make water important for organisms.

Answer 3

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’.

but accept description of ‘stream’.

For cohesion accept hydrogen bonding

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

Question 4

(a) Describe the roles of iron ions,

Answer 4

Haemoglobin binds/associates with oxygen

OR

Haemoglobin transports/loads oxygen

Question 5

(a) Describe the roles of , sodium ions,d

Answer 5

   Co-transport of glucose/amino acids (into cells);

3.   (Because) sodium moved out by active transport/Na – K pump;

4.   Creates a sodium concentration/diffusion gradient;

5.   Affects osmosis/water potential;

Question 6

describe the roles of a phosphate ion

Answer 6

  Affects osmosis/water potential;

Accept 5. OR 6. – not both

7.   Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;

8.   Used in/to produce ATP;

Reject ‘energy produced’

9.   Phosphorylates other compounds (usually) making them more reactive;