14. Homeostasis

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.

  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

  1. 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

  1. 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

  1. relate the detailed structure of the Bowman’s capsule and proximal convoluted tubule to their functions in the formation of urine

  2. describe the roles of the hypothalamus, posterior pituitary gland, antidiuretic hormone (ADH), aquaporins and collecting ducts in osmoregulation

  3. 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

  1. 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

  2. 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

The endocrine system

Negative feedback

Thermoregulation

The kidney

Selective reabsorption

ADH and reabsorption

The kidney webclass

Osmoregulation support

14.2 Homeostasis in plants

  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