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Centre Number Candidate Number
Pearson Edexcel Level 3 GCE
Wednesday 19 June 2024
Morning (Time: 2 hours) Paper
reference 9BN0/03
Biology A (Salters Nuffield)
Advanced
PAPER 3: General and Practical Applications in Biology
You must have: Ruler, HB pencil, scientific calculator and a copy Total Marks
of the scientific article adapted from the New Scientist and the
Brazilian Journal of Medical and Biological Research (enclosed)
Instructions
•• Use black ink or ball-point pen.
Fill in the boxes at the top of this page with your name,
centre number and candidate number.
• Answer all questions.
• Show all your working out in calculations and include units where appropriate.
• Answer the questions in the spaces provided
– there may be more space than you need.
Information
• The total mark for this paper is 100.
• The marks for each question are shown in brackets
– use this as a guide as to how much time to spend on each question.
• structure
In questions marked with an asterisk (*), marks will be awarded for your ability to
your answer logically, showing how the points that you make are related or
follow on from each other where appropriate.
Advice
• Read each question carefully before you start to answer it.
• Try to answer every question.
• Check your answers if you have time at the end. Turn over
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1 One of the first plant species to colonise some habitats is thale cress
(Arabidopsis thaliana).
The plant hormone IAA (auxin) is produced in the growing tips of plants such as
thale cress.
(Source: Nigel Cattlin / Alamy Stock Photo)
(a) State what is meant by the term colonisation of a habitat.
(1)
, (b) One role of IAA is to stimulate the phototropic response of shoots.
Describe how IAA causes a phototropic response in the shoots of a plant.
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(c) Another role of IAA is to stimulate the growth of lateral roots.
The diagram shows the roots of thale cress.
lateral roots
main root
3
*P74458RA0336* Turn over
, One type of receptor for IAA is coded for by the tir1 gene.
Scientists have investigated the effect of IAA on the growth of lateral roots in
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thale cress.
Plants homozygous for a normal tir1 gene and plants homozygous for a mutation
in the tir1 gene were used in this investigation.
The plants were treated with different concentrations of IAA.
The mean number of lateral roots produced per mm of main root was recorded.
The graph shows the results of this investigation.
Key
1.6 Thale cress
homozygous for:
1.4
1.2 normal
tir1 gene
Mean number of 1.0
lateral roots per mm mutant
0.8 tir1 gene
0.6
0.4
0.2
0.0
0.00 0.01 0.10 1.00
IAA concentration / μmol dm –3
(i) Explain why the scientists used plants homozygous for the normal and the
mutant tir1 gene in this investigation.
(2)
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