IB Biology HL 3.1.20 Auxin efflux carriers Question Bank
Practise IB Biology HL 3.1.20 by applying auxin efflux carriers concepts to exam-style questions.
- Syllabus
- First assessment 2025
- Course
- Biology HL
- Level
- HL
Exam points
- identify the relevant biological structure, process or evidence
- apply the correct biological mechanism to the question
- evaluate the result using data, adaptation or ecological reasoning
C3.1.20 (HL)—Auxin efflux carriers question 1
Auxin can be used to promote the development of roots from stem and leafy cuttings in some plants. In a study into the distribution of auxin in the development of these roots, scientists measured the amount of auxin in different leaves of a shoot tip of Petunia hybrida.
The figure indicates the numbering of leaves on the shoot, from L1 as the youngest and smallest to L6 as the largest and oldest leaf. The developmental stage of L5 and L6 was very similar, so L5 was not analysed. The stem base is the lowest part of the cutting where roots may form.
The graph shows the auxin concentration in the different leaves.
Question (a)
(a)
N-1-naphthylphthalamic acid (NPA) is an inhibitor used to block auxin transport. NPA was sprayed onto the leaves of a set of cuttings for 14 days. Development of the roots in control (non-treated) and NPA-treated cuttings was measured 14 days after taking the cuttings. The table shows the influence of NPA on rooting.
Analyse the effect of NPA on the formation of roots.
[ 2 ]
Question (b)
(b)
The scientists also measured the changes in auxin concentration in L6 and the stem base during the early period of root formation. They recorded the concentration in the control and NPA-treated cuttings for 24 hours after taking the cuttings.
[ 4 ]
Question (i)
(i)
Compare and contrast the changes in auxin concentration in the stem base over time for the control and NPA-treated cuttings.
[ 2 ]
Question (ii)
(ii)
Deduce the effect of NPA on auxin transport between L6 and the stem base.
[ 2 ]
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