Jan 2022

Question 1

1.4. Describe a biochemical test that a student could use to show that sucrose is a non-reducing sugar. (3)

Answer 1

(1) Heat with Benedict’s solution to confirm a negative result / sucrose is not a reducing sugar

(2) Boil/heat (sucrose) with an acid then neutralise with alkali

(3) Heat with Benedict’s solution and red/orange colour indicates
sucrose is a non-reducing sugar

Question 2

2.3. Describe 2 structural differences between the DNA in the mitochondria and the DNA in the nucleus. (2)

Answer 2

(1) mitochondrial DNA = circular & nucleus DNA = linear
(2) DNA in mitochondria is not associated with proteins Or DNA in the nucleus is associated with proteins/histones

Question 3

2.4. Describe the process of semi-conservative replication of DNA. (5)

Answer 3

(1) (DNA) helicase breaks hydrogen bonds (between DNA strands) or (DNA) helicase separates the DNA strands (between 2 DNA strands)
(2) Both strands act as templates or each strand acts as a template
(3) (Free) nucleotides attach by complementary / specific base
pairing / AT and GC
(4) DNA polymerase joins nucleotides (to the new DNA strand)
(5) Reference to condensation reactions / formation of phosphodiester bonds (between nucleotides)

Question 4

3.2. Describe what happens in meiosis 1 and meiosis 2 to produce 4 haploid cells. (2)

Answer 4

(Meiosis 1)
1. Homologous chromosomes separate/are pulled/move apart (to opposite poles)

(Meiosis 2)
2. (Sister) chromatids separate/are pulled/move apart (to opposite poles)

Question 5

4.4. Explain why the temp. was kept at 37 degrees during the experiment investigating active transport in human epithelial cells. (2)

Answer 5

(1) Temperature affects the rate of enzyme reactions / metabolism or 37ºC is optimal temperature for enzymes or (So) temperature is not a limiting factor/enough kinetic energy for
enzymes to work efficiently or Too high a temperature would denature enzymes / transport proteins

(2) Enzymes are needed for respiration / to generate ATP or Enzyme needed to hydrolyse ATP (to release energy)

Question 6

5.2. Explain why bacteria doesn’t need a specialised gas exchange system. (2)

Answer 6

(1) Bacteria have a large surface area to volume ratio

(2) Idea that bacteria can just use diffusion (through cell membranes to exchange gases)
or
Idea of bacteria having a short diffusion distance

Question 7

5.3. Explain how human lungs maximise the rate of diffusion of oxygen into the blood. (3)

Answer 7

(1) Many alveoli / capillaries so provide a large surface area

(2) Thin epithelium / wall / surface of alveoli / capillaries so short diffusion distance / pathway

(3) Constant ventilation / breathing / circulation so maintains concentration gradient

Question 8

6.3. After polypeptides are formed, they are folded. Describe what happens during folding. (3)

Answer 8

(1) Named bonds form eg hydrogen / ionic / disulfide / hydrophobic

(2) Chaperone proteins assist in the folding (of polypeptides)

(3) The polypeptide folds into the secondary / tertiary structure

Question 9

IF ANY QUESTION INVOLVES ENZYMES, ALWAYS MENTION THE E-S COMPLEXES.

Answer 9

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Question 10

8.4. Scientists say that classifying the penguins as four separate species gives conservationists a better chance of protecting their diversity. Why? (1)

Answer 10

All four species would more likely be protected (as the population sizes would be smaller) rather that treating them as one large population
Or
Specific conservation plans could be put into place for each
population
Or
Some populations may be more at risk than others so can monitor certain populations more carefully

Question 11

8.2. Give 3 ways that genetic diversity between the separate colonies of gentoo penguins could be compared. (3)

Answer 11

(1) The (base) sequence of DNA or of mRNA
(2) The frequency of specific base sequences or alleles
(3) The amino acid sequence of a particular protein e.g. haemoglobin