Practise plant control and coordination by tracing Venus flytrap responses, auxin-driven cell-wall loosening and gibberellin's role in barley seed germination.
The Venus fly trap is a plant that is able to capture and digest insects. It has modified leaves, which have sensory hairs that respond to touch. When an insect comes into contact with the hairs, receptor potentials are generated.
Name the ion that moves into the cells at the base of the sensory hairs to generate receptor potentials.
If two or more of these hairs are stimulated within a period of 20-35 seconds, action potentials are generated, causing the leaf to close quickly and trap the insect.
Suggest why it is beneficial to the plant for stimulation of two or more hairs to be necessary before the leaf will close.
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.
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.
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.
An investigation was carried out to study the effect of different intensities of blue light on the percentage germination of barley seeds. Barley seeds were exposed to blue light for a period of seven days. All other variables were kept constant.
The results are shown in Table 9.1.
Table 9.1
The effect of blue light on the concentration of abscisic acid (ABA) was also investigated. ABA concentration was measured at intervals over seven days in barley seeds exposed to blue light at an intensity of 57 arbitrary units.
The results are shown in Table 9.2.
Table 9.2
For comparison, in the dark the concentration of ABA in barley seeds fell from 100 au at the start (day 0 ) to 45 au on day 1 and did not increase from day 1 to day 7.
ABA is thought to affect gibberellin synthesis or activity.
Using the information in Table 9.1 and Table 9.2, describe the effect of blue light on the germination of barley seeds and suggest an explanation for this effect.
(b) After germination, auxin is important in the growth of barley plants.
Describe and explain the role of auxin in cell elongation.