Exam qs + answers

Question 1

Lactose, galactose and glucose are all reducing sugars. After the lactose has been broken down there is a high concentration of reducing sugar. Explain why. (1)

Answer 1

Because 2 sugars are produced.

Question 2

Explain five properties that make water important for organisms. (5)

Answer 2

1. 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 (specific) heat capacity so buffers changes in temperature;
   - For ‘buffer’ accept ‘resist’.
4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
   - Reject latent heat of evaporation
5. Cohesion (between water molecules) so supports columns of water (in plants);
   - For ‘columns of water’ accept ‘transpiration stream’. Do no credit ‘transpiration’ alone but accept description of ‘stream’.
   - For ‘columns of water’ accept ‘cohesion-tension (theory)’.
6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
   - For cohesion accept hydrogen bonding
   - Ignore reference to pH.

Question 3

A polypeptide chain is 128 amino acids long. What is the minimum number of DNA bases that could have coded for this chain? (1)

Answer 3

128 x 3 = 384
(This is because the genetic code for one amino acid is a three-base)

Question 4

Two proteins have the same number and type of amino acids but different tertiary structures. Explain why. (2)

Answer 4

Different sequence of amino acids in primary structure
Forms ionic / hydrogen / disulfide bonds in different places

Question 5

Milk A contains no glucose. Milk B contains glucose. Explain why milk B contains glucose. (1)

Answer 5

Lactase hydrolysed lactose down into galactose and glucose