June 2020 QP - Paper 1 AQA Biology AS-level.PDF

Question 1

A biochemical test for reducing sugar produces a negative result with raffinose
solution.
Describe a biochemical test to show that raffinose solution contains a non-reducing
sugar.

Answer 1

01.3 1. Heat with acid and neutralise;
2. Heat with Benedict’s (solution);
3. Red precipitate/colour

Question 2

0 2 box . 1 Explain the arrangement of phospholipids in a cell-surface membrane.

Answer 2

1. Bilayer
   OR
   Water is present inside and outside a cell;
2. Hydrophobic (fatty acid) tails point away/are
   repelled from water
   OR
   Hydrophilic (phosphate) heads point to/are in/are
   attracted to water;

Question 3

0 2 . 2 Describe how an ester bond is formed in a phospholipid molecule.

Answer 3

1. Condensation (reaction)
   OR
   Loss of water;
2. Between of glycerol and fatty acid;

Question 4

State and explain the property of water that helps to prevent temperature increase in a
cell.
[2 marks]
Property
Explanation

Answer 4

1. High (specific) heat capacity;
2. Buffers changes in temperature;

Question 5

0 6 box . 1 Describe how mRNA is produced from an exposed template strand of DNA.
Do not include DNA helicase or splicing in your answer.

Answer 5

1. (Free RNA) nucleotides form complementary
   base pairs;
2. Phosphodiester bonds form;
3. By (action of) RNA polymerase;

Question 6

0 6 . 2 Define the term exon.

Answer 6

Base/nucleotide/triplet sequence coding for
polypeptide/sequence of amino acids/primary
structure;

Question 7

A mutation in the nucleotide sequence shown in Figure 6 resulted in the following
amino acid sequence.
Serine Glycine Glycine Proline
A student concluded that the mutation involved the addition of one nucleotide within
the sequence shown in Figure 6. Does information in this question support the
student’s conclusion? Give reasons for your answer.

Answer 7

(No)
1. G to C (in the second codon/for Glycine)
OR
CGT to CCT (in second codon/for Glycine);
2. (So), substitution (not addition mutation);
OR
3. (If addition) frameshift / all triplets moved;
4. (So), affects more than one amino acid;

Question 8

Channel proteins called aquaporins enable water to be transported across box
membranes. Aquaporins are produced in cells when genes coding for the proteins
are expressed. One aquaporin gene is called PIP1b. The expression of PIP1b in
tobacco plant cells produces an aquaporin located in their cell membranes.
Scientists have produced genetically modified tobacco plants. The scientists
inserted a gene from a different species into the DNA of tobacco plant cells. This
gene causes an increase in the rate of transcription of the PIP1b gene.
The scientists found that the stomatal density of leaves from tobacco plants with
the inserted gene was greater than that of unmodified control plants.
In a different investigation, scientists measured the movement of potassium ions
and water molecules through cell-surface membranes and vacuole membranes.
They found 6 potassium ions moved for every 150 water molecules across vacuole
membranes. They found 3 potassium ions moved for every 1500 water molecules
across cell-surface membranes.
Use information from the passage and your own understanding to answer the
questions.
5
10
0 9 . 1 Explain how the proteome of a cell from a genetically modified tobacco plant
(lines 5–7) differs from that of a cell from an unmodified control tobacco plant.
[2 m

Answer 8

1. Expression of gene from different species;
2. (So) a new/one more protein (in set/range of
   proteins);

Question 9

Explain how an increase in the rate of transcription of the PIP1b gene (lines 6–7) will
affect the permeability of tobacco plant cell membranes to water.

Answer 9

1. More/increased aquaporin/channel protein
   (made)
2. Increased (water) permeability;

Question 10

Suggest and explain one advantage and one disadvantage of increased stomatal
density on the growth of tobacco plant leaves (lines 8–9).

Answer 10

Advantage
1. More carbon dioxide uptake;
2. More photosynthesis so faster/more growth;
Disadvantage
3. More water loss/transpiration
4. Less photosynthesis so slower/less growth;