Extended only
More than 40 years ago, botanists studied the leaves of broad bean plants and discovered that guard cells control the opening and closing of stomata. They found that stomata were open when the guard cells were turgid.
Table 1 shows some of their measurements.
Table 1
| closed stomata | open stomata |
ion concentration in guard cells /pmol | 0.3 | 2.5 |
guard cell volume/μm3 | 4000.0 | 6500.0 |
turgor pressure in the guard cells /MPa | 2.0 | 4.8 |
width of stomatal opening/μm | 0.0 | 8.0 |
(i)
Ions move into guard cells by active transport.
Describe how the ions move into the guard cells.
[2]
(ii)
Describe and explain how the change in ion concentration causes the guard cell volume to change.
Use the information in Table 1 in your answer.
[6]
(iii)
The botanists left the broad bean plants unattended for three days. During this time the broad bean plants wilted.
Suggest two environmental factors that can cause plants to wilt.
[2]