2023 AQA AS BIOLOGY 7401/2 Paper 2 Question Paper & Mark scheme (Merged) June 2023 [VERIFIED]

2023 AQA AS BIOLOGY 7401/2 Paper 2 Question Paper
& Mark scheme (Merged) June 2023 [VERIFIED]

The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in the
nucleus.
[3 marks] - ans -In chloroplasts
-DNA shorter;
-Fewer genes;
-DNA circular not linear;
-Not associated with protein/histones, unlike nuclear DNA;
-Introns absent but present in nuclear DNA;

Some DNA nucleotides have the organic base thymine, but RNA nucleotides do
not have thymine. RNA nucleotides have uracil instead of thymine.
Give one other difference between the structure of a DNA nucleotide and the
structure of an RNA nucleotide.
[1 mark] - ans -Deoxyribose in DNA and Ribose in RNA

Not all mutations in the nucleotide sequence of a gene cause a change in the
structure of a polypeptide.
Give two reasons why.
[2 marks] - ans -1. Triplets code for same amino acid2. Occurs in introns /non-
coding sequence;

What is a monoclonal antibody?
[1 mark] - ans -(Antibodies with the) same tertiary structure
OR
(Antibody produced from) identical/cloned plasma cells/B cells/B lymphocytes;

After a disease is diagnosed, monoclonal antibodies are used in some medical
treatments.
Give one example of using monoclonal antibodies in a medical treatment.
[1 mark] - ans -Accept any one suitable use, eg Targets/binds/carries
drug/medicine to specific
cells/antigens/receptors
OR

,Block antigens/receptors on cells;

Describe the role of antibodies in producing a positive result in an ELISA test.
[4 marks] - ans -1. (First) antibody binds/attaches /complementary (in shape) to
antigen;
2. (Second) antibody with enzyme attached is added;
3. (Second) antibody attaches to antigen;4. (Substrate/solution added) and colour
changes;

Write the chemical group in each glucose molecule used to form a glycosidic
bond.
[1 mark] - ans -OH, HO

A precipitate is produced in a positive result for reducing sugar in a Benedict's
test. A precipitate is solid matter suspended in solution.
A student carried out the Benedict's test. Suggest a method, other than using a
colorimeter, that this student could use to measure the quantity of reducing sugar
in a
solution.
[2 marks] - ans -1. Filter and dry (the precipitate);
2. Find mass/weight;

In an investigation, a student wanted to identify the solutions in two beakers, A
and B. She knew one beaker contained maltose solution and the other beaker
contained glucose solution. Both solutions had the same concentration.
She did two separate biochemical tests on a sample from each beaker.
Test 1 - used Benedict's solution to test for reducing sugar.
Test 2 - added the enzyme maltase, heated the mixture at 30 °C for 5 minutes,
and then used Benedict's solution to test for reducing sugar.
Maltose is hydrolysed by maltase.The student's results are shown in Table 1:
Beaker A- Red (Test 1), Red (Test 2)
Beaker B- Red (Test 1), Dark red (Test 2)
Explain the results for beakers A and B in Table 1.
[2 marks] - ans -A = glucose and B = maltose;
Because more sugar/precipitate after hydrolysis/maltase action;

, Use of a colorimeter in this investigation would improve the repeatability of the
student's results.
Give one reason why.
[1 mark] - ans -1. Quantitative
OR
(Colour change is) subjective; 2. Standardises (the) method;

Explain why it is more useful to calculate an index of diversity than to record
species
richness.
[2 marks] - ans -1. (Index of diversity also) measures abundance / number /
population (size) of each species;
2. (So useful because) may be many of some species
OR
(So useful because) may be few of other species;

Suggest how the scientist measured the rate of water flow in the river.
[1 mark] - ans -1. Movement of (floating) object over known distance and over
given timeORTime to fill container of known volume OR
Use of data logging device;

explain a reason for the
difference in the numbers of Slate Drake mayfly at these sites in this river.
[2 marks]
Hint: Site 1 has less mayfly than Site 2 - ans -1. Less food/prey at site 1; 2. (So
more) mayfly starve;
OR
3. Less oxygen at site 1;4. (So) less respiration/ATP/energy (for mayflies);
OR
5. More predators/Anglers' Curse at site 1; 6. (So more) mayfly
killed/eaten/removed;
OR
7. More competition at site 1; 8. (So more) mayfly starve;

It was important that the sampling procedure was standardised when collecting
the Slate Drake mayflies from the two sites.
Give one way in which the sampling procedure could be standardised.