CAIE A-Level Biology 15 Control and Coordination Question Bank

Practise nervous and endocrine signalling, action potentials, synapses, muscle contraction and plant responses through membrane traces, pathways and structure-function evidence.

[Maximum number: 5]

There are more than 600 plant species in the genus Ipomoea. Many species are grown for their attractive flowers, and some species are used as crop plants.

(a)

Scientists are researching whether abscisic acid can be used in crop treatment to increase yield. Evidence suggests that abscisic acid modifies the effect of auxin on elongation growth in plants.

[ 5 ]

(i)

Scientists investigated the effect of different concentrations of abscisic acid on root elongation in seedlings of thale cress, Arabidopsis thaliana.

The seedlings were divided into four groups:
- a control group ( $0.0 \mu \mathrm{~mol}$ abscisic acid)
- three experimental groups, each treated with a different concentration of abscisic acid: $0.1 \mu \mathrm{~mol}, 1.0 \mu \mathrm{~mol}$ , or $10.0 \mu \mathrm{~mol}$ .

For each group of seedlings, root length was measured for six days during treatment. The rate of root elongation was calculated each day.

The results are shown in Fig. 3.3.

Key
- control (no abscisic acid)
- $0.1 \mu \mathrm{~mol}$ of abscisic acid
$\times 1.0 \mu \mathrm{~mol}$ of abscisic acid
△ $10.0 \mu \mathrm{~mol}$ of abscisic acid

Fig. 3.3

With reference to Fig. 3.3, describe the effect of treatment with abscisic acid on the rate of root elongation.

[ 3 ]

any two from:

1 0.1, ( $\mu \mathrm{mol}$ ) increases / gives higher, rate (compared to control / normal) ;

2 1(.0) and 10(.0), ( $\mu \mathrm{mol}$ ) decrease / give lower, rate (compared to control / normal) ;

$310(.0)(\mu \mathrm{mol})$ rate, stays (approx.) constant / plateaus / does not increase, over, time / (6) days ;

4 data quote comparing rate at two concentrations on one day

or

data quote comparing rate on two different days for $10 \mu \mathrm{~mol}$ ;

(ii)

The passage outlines the role of auxin in elongation growth in plants.

Complete the passage by using the most appropriate scientific terms.

The binding of auxin to receptors causes to be pumped into cell walls.

This activates proteins called expansins, which disrupt the links between microfibrils. The cell walls are then able to expand.

[ 2 ]

1 protons / $\mathrm{H}^{+}$ (ions) ;

2 cellulose ;

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Covered syllabus points

15. Control and Coordination question 1

Question (a)

Question (i)

Question (ii)