15.2 Control & Coordination in Plants

Electrical activity occurs in living organisms as the result of the movement of charged particles, or ions, across cell membranes. The reversal of electrical charge across a cell membrane is known as depolarisation.

Outline how the cell surface membrane of an animal neurone is depolarised.

Plant cells can also be depolarised. The cells of the sensitive Mimosa plant, Mimosa pudica, can become depolarised in response to a touch stimulus. Fig. 2.1 shows the first two stages of depolarisation in M. pudica.

Fig. 1

Suggest how the cells of M. pudica become depolarised in the next stage of the process shown in Fig. 1.

[2]

Suggest how the cells of M. pudica might become repolarised to return to a resting state.

[2]

Touch stimulation of the leaves of M. pudica leads to the sequence of events shown in Fig. 1 and results in the physiological response shown in Fig. 2.

Fig. 2

The response shown in Fig. 2 comes about due to a reduction in cell volume of certain stem and leaf cells.

Suggest how the process described in part b) could lead to a reduction in leaf volume.

Suggest the advantage to M. pudica of the response shown in Fig. 2.

Plant roots are particularly sensitive to the effects of auxin (IAA). Fig. 1 shows the results of an investigation that was done to determine the effect of increasing auxin concentration on the growth of young roots.

Fig. 1

Calculate the difference in the root growth per hour between the roots that were not exposed to auxins and those exposed to an auxin concentration of 1.0 µM.

Show your working.

A pot plant was accidentally knocked over.

Based on the information in Fig. 1, suggest and explain how the growth of the root could be affected by this.

An investigation was carried out to determine the effect of increasing auxin (IAA) concentration on the growth of plant shoots. Fig. 2 shows the results of this investigation. The investigation was then repeated with shoots that were treated with a respiratory inhibitor.

Fig. 2

Use the axes in Fig. 2 to sketch a graph of the plant growth that would be observed in the shoots treated with the respiratory inhibitor.

Suggest a reason for your answer at part (c).

Fig. 1 shows a drawing of a barley seed.

Fig. 1

Identify structures A-C in Fig.1.

Fig. 2 shows the effect of increasing gibberellin concentration on the percentage of barley seeds that germinate. The smaller bars show standard deviations.

Fig. 2

Calculate the percentage increase in the seeds germinated at a gibberellin concentration of 100 parts per million in comparison to the seeds germinated at 50 parts per million.

A student viewed Fig. 2 and concluded that adding gibberellin increases barley seed germination.

Using only information from Fig. 2, evaluate the student's conclusion.

Explain the results shown in Fig. 2.

Fig. 1 shows part of a cell in a growing region of a plant.

Fig. 1

(i)

State the type of protein represented by A.

(ii)

Proteins B, C and D are transport proteins.

Identify proteins B, C and D.

Describe the effects on the cell wall of many hydrogen ions moving into the cell wall.

Explain the consequences of an influx of potassium ions into the cell.