June 2022

Question 1

1.2. Give 1 similarity & 1 difference between the structure of starch and cellulose. (2)

Answer 1

(1) Similarities:
Both formed from monosaccharide / glucose OR Both contain (1, 4) glycosidic bonds OR both contain (intramolecular) hydrogen bonds within the structure

(2) Differences:
Starch α–glucose and cellulose β–glucose OR Starch coiled (chain) and cellulose straight chain OR Starch (amylopectin) branched and cellulose unbranched OR Starch no H-bonds between chains and cellulose H-bonds between chains

Question 2

3.3. Many insects live on land. Insects living on land have features that reduce water loss. Explain how 2 of the features reduce water loss. (2)

Answer 2

any 2 of:
Spiracles can close so less water diffuses out or so less evaporation (of water)

Hairs around spiracles trap water (vapour) so water potential gradient is reduced

Waterproof covering so less evaporation (of water)

Question 3

4.5. During a penguin’s dive, the oxygen dissociation curve gradually shifts to the right. Explain what causes this shift. (2)

Answer 3

(1) (Respiration) increases carbon dioxide concentration or (respiration) decreases pH

(2) Decreased affinity of haemoglobin for oxygen

Question 4

5.2. What’s the importance of putting the chromatography paper in the tube so that the pigment spot is above the surface of the solvent? (1)

Answer 4

pigment spot is not ‘washed off’ the paper or the solute moves up the paper (with the solvent)

Question 5

6.4. Transcription of a human gene produces pre-mRNA.
The pre-mRNA is processed to produce mRNA.
Explain why a molecule of mRNA has a lower number of bases than a molecule of pre-mRNA. (2)

Answer 5

(1) Pre-mRNA undergoes splicing (to form mRNA)

(2) Introns/non-coding regions removed or only exons left in mRNA

Question 6

7.2. The student measures 100 leaves in total. Give 1 reason why the student uses a large sample size. (1)

Answer 6

To reduce the effect of chance or to collect representative data or to calculate a more valid mean or to reduce the effect of anomalies or to collect enough data for a statistical test

Question 7

9.5. In an immunological test, suggest 1 factor the scientists should control so they can compare the percentage of precipitation from each of the 4 primates tested. (1)

Answer 7

(Same) volume of serum/blood (from rabbit or from primate) or temperature or time