AQA A-Level Biology Paper 3 Predicted Paper 2023 QUESTIONS AND ANSWERS

AQA

A-Level Biology 

Paper 3

Predicted Paper 2023

Name …………………………………………………………………… Date …………………

2 hours allowed.

You may use a scientific calculator and a ruler with millimetre measurements.

Answer all questions in section A. Answer one question from section B.

Grade boundaries

These are VERY rough guesses! Getting a B on this paper does not guarantee you the same mark in the exam.

• A* 65%

• A 55%

• B 45%

• C 40%

• D 35%

• E 30%

SECTION A

Answer all questions in this section.

01

The Hawaiian Islands have the most diverse collection of Drosophilid flies in the world with approximately 800 different species having been identified.

All of the species have been traced back to a single common ancestor from mainland USA that colonised the islands millions of years ago. It is hypothesised that this could have been a single fertilised female blown across in a storm or trapped in a piece of fruit stuck to a bird.

a) What is a gene pool?

[1 mark]

b) Explain how the Hawaiian species of flies could have evolved.

[6 marks]

c) Drosophila are one group of insects which contain polytene chromosomes. These are extra-large chromosomes found in the nuclei of salivary gland cells. They can be removed and stained so their banding patterns can be viewed under a light microscope. Explain how scientists could have used the banding pattern on the chromosomes to establish the evolutionary relationships between flies.

[2 marks]

d) About 100 species of the Hawaiian Drosophila have large, highly patterned wings and are known as the picture-wing Drosophila. In some species, e.g D. truncipenna the males have more detail patterning on their wings than the females.

Suggest how the variety of wing patterns displayed by these flies helps to maintain them as separate species.

[2 marks]

02

Some organisms are able to fix atmospheric nitrogen using a nitrogenase enzyme. Nitrogenase enzymes can be inhibited by high oxygen concentrations. Cyanobacteria are one of the few organisms that photosynthesise but also fix nitrogen.

a) Explain how each of the following adaptations allow cyanobacteria to carry out both processes:

i. Some colonies of cyanobacteria develop heterocysts; specialised cells which only contain photosystem I.

[2 marks]

ii. Some only fix nitrogen at night.

[2 marks]

Some plants make associations with nitrogen fixing bacteria in specialised structures known as root nodules. Genes are activated during root nodule development which code for the protein leghaemoglobin. This is a type of haemoglobin that is very similar to animal haemoglobin, it also binds to oxygen.

b) To investigate its action in nodules scientists used siRNA to silence the leghaemoglobin genes in Lotus japonicus plants. They observed that these plants exhibited less than normal growth. Only after addition of nitrogen fertiliser were the plants able to grow normally. Suggest why.

[3 marks]

c) A company making meat free burgers is using genetically modified yeast to produce large quantities of leghaemoglobin to create more realistic plant-based burgers.

Suggest why adding leghaemoglobin makes the burgers taste more like ones containing meat.

[1 mark]

03

Taxol is a drug used to treat cancer; it was extracted from the bark of the Pacific yew tree. Scientists initially tested this drug on mice that had visible cancerous tumours in their lungs.

Some results are shown in the table below:

Days of Treatment Mean volume of tumour (mm3)

Control mice Mice injected with Taxol in saline

1 1 1

10 8 2

20 23 10

30 52 22

40 117 52

50 342 85

60 652 120

70 744 207

a) Suggest and explain two factors which should be considered when deciding on the number of mice to use in a trial such as this.

[2 marks]

b) The scientists concluded that Taxol did not kill cancer cells. Does the table support this conclusion?

Explain your answer.