Jan 2019

Question 1

1.5. Explain how a change in the primary structure of a protein may result in a different 3-D structure. (3)

Answer 1

(1) Sequence / order of amino acid changes
(2) Tertiary structure changes / folds / coils in a different way / bonds form in different positions
(3) Named bond affected e.g. hydrogen / ionic / disulphide / hydrophobic

Question 2

3.4. There’s less oxygen at high altitudes than at sea level. People living at 4000 metres above sea level have more red blood cells than people living at sea level.
Explain why having more RBCs at 4000 metres is an advantage. (2)

Answer 2

(1) (More red blood cells means) More haemoglobin
(2) So (haemoglobin) can load / pick up / bind more oxygen (in the lungs) or so haemoglobin can carry / transport more oxygen (to cells / tissues)

Question 3

3.5. Explain the advantage to the people living at 4000 metres above sea level of having their oxygen dissociation curve to the right of the people living at 1000 metres above sea level. (4)

Answer 3

(1) (Haemoglobin) has lower affinity for oxygen
(2) At the same partial pressure (of oxygen)
(3) (Haemoglobin) releases / dissociates more oxygen Or (Haemoglobin) releases / dissociates oxygen (more) easily
(4) To (aerobically) respiring cells / tissues

Question 4

6.3. A species may be defined as a group of organisms capable of interbreeding and producing fertile offspring. Suggest the difficulty with using this definition. (2)

Answer 4

(1) Considerable variation within a species
(2) Interbreeding may not be possible

Question 5

7.4. An mRNA strand had the base sequence GCC, which coded for the AA alanine. A different mRNA strand didn’t have the base sequence GCC, but the protein it translated contained the AA alanine. Explain how this is possible. (2)

Answer 5

(1) (Genetic) Code is degenerate / amino acids coded for by more than one triplet
(2) Different codon but same amino acid / different codon but still alanine

Question 6

7.6. A chemical called oligomycin prevents respiration. Protein synthesis doesn’t happen in cells treated with oligomycin. Suggest why. (3)

Answer 6

(1) (No respiration so) no ATP produced
(2) ATP needed to form peptide bond
(3) ATP needed to activate the amino acid / ATP needed to attach amino acid to tRNA

Question 7

8.1. Define resolution. (1)

Answer 7

(Idea of) minimum distance between two objects for them to appear as separate objects

Question 8

8.4. Optical microscopes use lenses to focus light rays. What is used to focus on the specimen in an electron microscope? (1)

Answer 8

(electro)magnets

Question 9

8.6. What is the meaning of artefacts? (1)

Answer 9

(Structures that are) not part of the natural specimen / produced as a result of specimen preparation