HOMEOSTASIS

Question 1

Homeostasis

Answer 1

• maintenance of a stable internal environment
• ensuring a constant internal environment including ph, temperature, water potential and blood glucose level is maintained despite changes in external environment of organisms.

Question 2

temperature and enzymes

Answer 2

body temperature too high - enzymes become denatured - enzyme molecules vibrate too much - breaking the hydrogen bonds that hold them together in a 3d shape - shape of active site is changed - metabolic reactions are less efficient.

Question 3

glucose concentration

Answer 3

too high glucose conc in blood - reduces water potential - water molecules diffuse out of cells by osmosis - causing cells to shrivel up and die

too low glucose concentration - cells are unable to carry out normal activities - not enough glucose for respiration to provide energy.

Question 4

negative feedback

Answer 4

mechanism that restores the levels back to optimum condition is called a negative feedback. eg if blood glucose levels are falling, hormones are released to convert glycogen into glucose.

Question 5

homeostatic system

Answer 5

involves receptors and effectors.
- receptors detect when a level is too high or low and the info is communicated via the nervous system or hormonal system to effectors.
- effectors then respond to counteract the change - bringing level back to normal.

Question 6

positive feedback

Answer 6

• increases change in original conditions
• effectors respond to further away from the normal level.
• not involved in homeostasis as it doesnt keep your internal environment stable.
  eg dilation of cervix during child birth

Question 7

blood glucose control

Answer 7

• pancreas detects blood glucose levels
• clusters of cells in pancreas called islets of langerhans releases hormone insulin and glucagon to bring blood glucose level back to normal.

Question 8

adrenaline

Answer 8

• released by adrenal glands, results in more glucose being released from stores of glycogen in liver

Question 9

insulin and glucagon

Answer 9

alpha cells secrete glucagon and beta cells secrete insulin.

Question 10

insulin

Answer 10

• insulin lowers the blood glucose concentration
• when blood glucose concentration increases, it is detected by beta cells in islets of langerhans and beta cells releases insulin.
• insulin binds to specific receptor on cell membranes of liver cell and muscle cell.
• insulin increases the permeability of muscle cell membrane to glucose which involves inc no of channel proteins.
• insulin also activates enzymes in liver and muscle cells to convert glucose into glycogen.
• cells are now then able to store glycogen in their cytoplasm

Question 11

glucagon

Answer 11

• glucagon raises blood glucose concentration
• low blood glucose conc is detected by alpha cells in islets of langerhans and alpha cells releases glucagon.
• glucagon then binds to specific receptors on liver cells and activates enzymes in liver cells that break down glycogen into glucose which is known as glycogenolysis.
• glucagon also activates enzymes involved in formation of glucose from amino acids and glycerol which are non carbohydrates. this is called gluconeogenesis.

Question 12

processes in blood glucose concentration

Answer 12

glycogenesis, glycogenolysis, gluconeogenesis

Question 13

glycogenesis

Answer 13

process of forming glycogen from glucose is called glycogenesis

Question 14

glycogenolysis

Answer 14

process of breaking down glycogen into glucose is called glycogenolysis

Question 15

gluconeogenesis

Answer 15

process of forming glucose from non carbohydrate proteins eg amino acids. this happens when all glycogen is hydrolysed and the body needs more glucose.

Question 16

action of insulin

Answer 16

• when the blood glucose concentration is too high, it is detected by beta cells in the islets of langerhans which secretes hormone insulin
• insulin then binds to specific receptors on the membrane of target cells which changes the tertiary structure of channel proteins resulting in more glucose being absorbed from the blood into the cells by facilitated diffusion.
• more protein carriers are incorporated into the cell membrane resulting in more glucose being absorbed into the cell
• insulin also activates the enzyme involved in the conversion of glucose to glycogen resulting in glycogenesis in the liver.

Question 17

GLUT4

Answer 17

• GLUT4 is a channel protein and a glucose transporter found in skeletal and cardiac muscles. it is stored in vesicles in cytoplasm in cells when insulin level is low
• when insulin binds to receptors on cell surface membrane it triggers the movement of GLUT4 to membrane.
• glucose can then be transported into the cell through the protein GLUT4 by facilitated diffusion.

Question 18

action of glucagon

Answer 18

• low levels of glucose detected by alpha cells in islets of langerhans which then secretes hormone glucagon.
• glucagon then binds to specific receptors on target cells membrane ( liver cells)
• when glucagon binds, it causes a protein to be activated into adenylate cyclase and to convert ATP into a molecule of cyclic AMP ( cAMP).
• cAMP activates an enzyme protein kinase which is involved in the hydrolysis of glycogen into glucose which is what we call glycogenolysis
• activating enzymes are also involved in the conversion of glycerol and amino acids into glucose.

Question 19

glucagon action summarised

Answer 19

1. glucagon binds to specific receptors in cell membrane of liver cells
2. once bound it causes a change in shape of protein to an enzyme adenyl cyclase
3. activated adenyl cyclase converts atp into a molecule of cyclic amp
4. camp activates enzyme protein kinase for the hydrolysis of glucagon back to glucose
5. camp is called the second messenger model.

Question 20

role of adrenaline ( second messenger model)

Answer 20

• if blood glucose level is too low, adrenal glands will secrete adrenaline
• adrenaline attatches to receptors on surface of target cell membrane, causing a protein called g protein to be activated to convert atp into camp
• camp then activates an enzyme that can hydrolyse glycogen to glucose
• this is known as second messenger model of adrenaline and glucagon action because this results in the formation of camp which is the second messenger model.