Practise negative feedback, kidney function, osmoregulation, glucose and temperature control by identifying receptors, coordinators and effectors in data and mechanisms.
Explain what is meant by homeostasis in a mammal and explain why it is important to maintain body temperature, blood glucose concentration and the water potential of blood.
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.
Glucagon-like peptide-1 (GLP-1) is a hormone consisting of 31 amino acids. It is secreted by specialised intestinal epithelial cells known as L cells.
Fig. 6.1 outlines the secretion of GLP-1 and its effects on the pancreas, brain and stomach.
GLP-1 inhibits the secretion of glucagon by cells in the pancreas.
Describe two processes in the liver that are stimulated by glucagon.
GLP-1 inhibits the emptying of the stomach. This is an example of negative feedback.
Explain what is meant by negative feedback.
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