14 Homeostasis
Cells function most efficiently if they are kept in near optimum conditions. Cells in multicellular animals are
surrounded by tissue
... [Show More] fluid. The composition of tissue fluid is kept constant by exchanges with the blood as
discussed in the topic on Transport in mammals (Topic 8). 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 topic includes an understanding that waste products are excreted from the body
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.
14.1 Homeostasis in mammals Learning outcomes
Candidates should be able to:
1 explain what is meant by homeostasis and the importance of
homeostasis in mammals
2 explain the principles of homeostasis in terms of internal and
external stimuli, receptors, coordination systems (nervous
system and endocrine system), effectors (muscles and glands)
and negative feedback
3 state that urea is produced in the liver from the deamination of
excess amino acids
4 describe the structure of the human kidney, limited to:
• fibrous capsule
• cortex
• medulla
• renal pelvis
• ureter
• branches of the renal artery and renal vein
5 Identify, in diagrams, photomicrographs and electron
micrographs, the parts of a nephron and its associated blood
vessels and structures, limited to:
• glomerulus
• Bowman’s capsule
• proximal convoluted tubule
• loop of Henle
• distal convoluted tubule
• collecting duct
6 describe and explain the formation of urine in the nephron,
limited to:
• the formation of glomerular filtrate by ultrafiltration in the
Bowman’s capsule
• selective reabsorption in the proximal convoluted tubule
7 relate the detailed structure of the Bowman’s capsule and
proximal convoluted tubule to their functions in the formation
of urine
8 describe the roles of the hypothalamus, posterior pituitary
gland, antidiuretic hormone (ADH), aquaporins and collecting
ducts in osmoregulation
14.1 Homeostasis in mammals
continued
Learning outcomes
Candidates should be able to:
9 describe the principles of cell signalling using the example of the
control of blood glucose concentration by glucagon, limited to:
• binding of hormone to cell surface receptor causing
conformational change
• activation of G-protein leading to stimulation of adenylyl
cyclase
• formation of the second messenger, cyclic AMP (cAMP)
• activation of protein kinase A by cAMP leading to initiation
of an enzyme cascade
• amplification of the signal through the enzyme cascade
as a result of activation of more and more enzymes by
phosphorylation
• cellular response in which the final enzyme in the pathway
is activated, catalysing the breakdown of glycogen
10 explain how negative feedback control mechanisms regulate
blood glucose concentration, with reference to the effects of
insulin on muscle cells and liver cells and the effect of glucagon
on liver cells
11 explain the principles of operation of test strips and biosensors
for measuring the concentration of glucose in blood and urine,
with reference to glucose oxidase and peroxidase enzymes
14.2 Homeostasis in plants Learning outcomes
Candidates should be able to:
1 explain that stomata respond to changes in environmental
conditions by opening and closing and that regulation of
stomatal aperture balances the need for carbon dioxide
uptake by diffusion with the need to minimise water loss by
transpiration
2 explain that stomata have daily rhythms of opening and closing
3 describe the structure and function of guard cells and explain
the mechanism by which they open and close stomata
4 describe the role of abscisic acid in the closure of stomata
during times of water stress, including the role of calcium ions
as a second messenger [Show Less]