Practise plant homeostasis by interpreting stomatal responses and daily opening rhythms, then tracing how guard-cell turgor and ABA signalling change pore size.
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 investigated the response of stomata to changing carbon dioxide ( ) concentrations in the beach morning glory, I. pes-caprae.
The scientists placed I. pes-caprae plants in chambers. They measured the width of open stomata (stomatal apertures) after the plants had been exposed to different concentrations for 40 minutes. Light intensity and temperature were kept constant.
The relationship between concentration and the mean width of stomatal apertures is shown in Fig. 3.2.
Fig. 3.2
In 2016, a study measured the atmospheric concentration as .
In the future, climate change may reduce water availability and increase atmospheric concentrations in some habitats.
Suggest how the stomatal response shown in Fig. 3.2 would allow I. pes-caprae to survive the effects of climate change.
Under certain conditions, the closure of stomata is controlled by abscisic acid.
Describe how abscisic acid causes the closure of stomata.
Guard cells are located in the epidermis of the leaves of most plants. When environmental conditions change, this causes changes in guard cells that control the opening and closing of stomata.
Describe the structure of guard cells.
Stomata have daily rhythms of opening and closing.
Fig. 6.1 shows the percentage of stomata open at different times of the day, over a period of three days, in the thale cress plant, Arabidopsis thaliana.
Fig. 6.1
With reference to Fig. 6.1, describe the rhythm of stomatal opening and closing.
Suggest other environmental factors, apart from the time of day, that can contribute to stomatal closure.
Table 6.1 shows some of the events occurring during the closure of a stoma.
The events are not listed in the correct order.
Table 6.1
Complete Table 6.2 to show the correct order of the events shown in Table 6.1.
Three of the events have been completed for you.
Table 6.2
Stomata in leaves respond to changes in environmental conditions by opening and closing. This regulates carbon dioxide uptake and water loss.
Describe the mechanism by which stomata open in sunlight.
Stomatal conductance is a measure of the rate of water vapour loss from the intercellular air spaces of leaves to the atmosphere through the stomata.
A student investigated the effect of different concentrations of abscisic acid (ABA) on stomatal conductance in Helianthus annuus, the common sunflower.
The student treated the roots of 15 sunflower plants with different concentrations of ABA solution. The plants were left in standardised conditions for 24 hours.
After 24 hours, the student measured:
- the concentration of ABA in the xylem sap of each plant
- the stomatal conductance of the leaves of each plant.
The results are shown in Fig. 3.1.
Fig. 3.1
With reference to Fig. 3.1, describe the relationship between the concentration of A B A in the xylem sap and stomatal conductance.
Suggest explanations for the results shown in Fig. 3.1.