14.1 Homeostasis in mammals
14.2 Homeostasis in plants
Cells function most efficiently if they are kept in near constant conditions. Cells in multicellular animals are surrounded by tissue fluid. The composition, pH and temperature of tissue fluid are kept constant by exchanges with the blood as discussed in the section on Transport in mammals. In mammals, core temperature, blood glucose concentration and blood water potential are maintained within narrow limits to ensure the efficient operation of cells. Prior knowledge for this section includes an understanding that waste products are excreted from the body – a role that is fulfilled by the kidneys – and an outline of the structure and function of the nervous and endocrine systems. In plants, guard cells respond to fluctuations in environmental conditions and open and close stomata as appropriate for photosynthesis and conserving water.
Candidates will be expected to use the knowledge gained in this section to solve problems in familiar and unfamiliar contexts.
Learning outcomes
Candidates should be able to:
14.1 Homeostasis in mammals
Homeostasis in mammals requires complex systems to maintain internal conditions near constant.
The kidneys remove wastes from the blood and are the effectors for controlling the water potential of the blood.
a) discuss the importance of homeostasis in mammals and explain the principles of homeostasis in terms of internal and external stimuli, receptors, central control, co-ordination systems, effectors (muscles and glands)
b) define the term negative feedback and explain how it is involved in homeostatic mechanisms
c) outline the roles of the nervous system and endocrine system in co-ordinating homeostatic mechanisms, including thermoregulation, osmoregulation and the control of blood glucose concentration
d) describe the deamination of amino acids and outline the formation of urea in the urea cycle (biochemical detail of the urea cycle is not required)
e) describe the gross structure of the kidney and the detailed structure of the nephron with its associated blood vessels using photomicrographs and electron micrographs
f) describe how the processes of ultrafiltration and selective reabsorption are involved with the formation of urine in the nephron
g) describe the roles of the hypothalamus, posterior pituitary, ADH and collecting ducts in osmoregulation
h) explain how the blood glucose concentration is regulated by negative feedback control mechanisms, with reference to insulin and glucagon
i) outline the role of cyclic AMP as a second messenger with reference to the stimulation of liver cells by adrenaline and glucagon
j) describe the three main stages of cell signalling in the control of blood glucose by adrenaline as follows:
• hormone-receptor interaction at the cell surface
• formation of cyclic AMP which binds to kinase proteins
• an enzyme cascade involving activation of enzymes by phosphorylation to amplify the signal
k) explain the principles of operation of dip sticks containing glucose oxidase and peroxidase enzymes, and biosensors that can be used for quantitative measurements of glucose in blood and urine
l) explain how urine analysis is used in diagnosis with reference to glucose, protein and ketones
14.2 Homeostasis in plants
Stomatal aperture is regulated in response to the requirements for uptake of carbon dioxide for photosynthesis and conserving water.
a) explain that stomata have daily rhythms of opening and closing and also respond to changes in environmental conditions to allow diffusion of carbon dioxide and regulate water loss by transpiration
b) describe the structure and function of guard cells and explain the mechanism by which they open and close stomata
c) describe the role of abscisic acid in the closure of stomata during times of water stress (the role of calcium ions as a second messenger should be emphasised)
14.2 Homeostasis in plants
Cells function most efficiently if they are kept in near constant conditions. Cells in multicellular animals are surrounded by tissue fluid. The composition, pH and temperature of tissue fluid are kept constant by exchanges with the blood as discussed in the section on Transport in mammals. In mammals, core temperature, blood glucose concentration and blood water potential are maintained within narrow limits to ensure the efficient operation of cells. Prior knowledge for this section includes an understanding that waste products are excreted from the body – a role that is fulfilled by the kidneys – and an outline of the structure and function of the nervous and endocrine systems. In plants, guard cells respond to fluctuations in environmental conditions and open and close stomata as appropriate for photosynthesis and conserving water.
Candidates will be expected to use the knowledge gained in this section to solve problems in familiar and unfamiliar contexts.
Learning outcomes
Candidates should be able to:
14.1 Homeostasis in mammals
Homeostasis in mammals requires complex systems to maintain internal conditions near constant.
The kidneys remove wastes from the blood and are the effectors for controlling the water potential of the blood.
a) discuss the importance of homeostasis in mammals and explain the principles of homeostasis in terms of internal and external stimuli, receptors, central control, co-ordination systems, effectors (muscles and glands)
b) define the term negative feedback and explain how it is involved in homeostatic mechanisms
c) outline the roles of the nervous system and endocrine system in co-ordinating homeostatic mechanisms, including thermoregulation, osmoregulation and the control of blood glucose concentration
d) describe the deamination of amino acids and outline the formation of urea in the urea cycle (biochemical detail of the urea cycle is not required)
e) describe the gross structure of the kidney and the detailed structure of the nephron with its associated blood vessels using photomicrographs and electron micrographs
f) describe how the processes of ultrafiltration and selective reabsorption are involved with the formation of urine in the nephron
g) describe the roles of the hypothalamus, posterior pituitary, ADH and collecting ducts in osmoregulation
h) explain how the blood glucose concentration is regulated by negative feedback control mechanisms, with reference to insulin and glucagon
i) outline the role of cyclic AMP as a second messenger with reference to the stimulation of liver cells by adrenaline and glucagon
j) describe the three main stages of cell signalling in the control of blood glucose by adrenaline as follows:
• hormone-receptor interaction at the cell surface
• formation of cyclic AMP which binds to kinase proteins
• an enzyme cascade involving activation of enzymes by phosphorylation to amplify the signal
k) explain the principles of operation of dip sticks containing glucose oxidase and peroxidase enzymes, and biosensors that can be used for quantitative measurements of glucose in blood and urine
l) explain how urine analysis is used in diagnosis with reference to glucose, protein and ketones
14.2 Homeostasis in plants
Stomatal aperture is regulated in response to the requirements for uptake of carbon dioxide for photosynthesis and conserving water.
a) explain that stomata have daily rhythms of opening and closing and also respond to changes in environmental conditions to allow diffusion of carbon dioxide and regulate water loss by transpiration
b) describe the structure and function of guard cells and explain the mechanism by which they open and close stomata
c) describe the role of abscisic acid in the closure of stomata during times of water stress (the role of calcium ions as a second messenger should be emphasised)
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