Biol 5 - Homeostasis

Question 0

How an injection of glucagon rapidly increases the concentration of glucose (6)

Answer 0

~Amplification effect
~More than 1 cAMP formed per glucagon
~Each cAMP activates more than 1 enzyme
~Each enzyme causes breakdown of more than 1 glycogen
~Each glycogen produces more than 1 glucose
~Glucose diffuses into the blood from high to low conc.

Question 1

How blood glucose is controlled by hormones (in a non-diabetic) (7)

Answer 1

~Insulin (produced at high conc.) and Glucagon (low conc.) secreted by pancreas
~Hormone receptors on membranes of target cells
~Insulin stimulates conversion of glucose to glycogen
~Which involves the activation of enzymes within the cell
~Insulin also stimulates the uptake of glucose by cells
~Glucagon stimulates conversion of glycogen to glucose
~Also conversion of non-carbohydrates to glucose

Question 2

How glucose returns to its normal value after a meal/after injecting glucagon (3)

Answer 2

~High glucose conc. detected by pancreas (Islets of Langerhans)
~Insulin is released
~Insulin causes glucose uptake by liver and muscle cells producing glycogen (glycogenesis)

Question 3

How high conc. of blood glucose is controlled by negative feedback. (3)

Answer 3

~High glucose causes high insulin conc.
~Insulin reduces glucose conc. back to within normal levels
~This results in decrease in insulin levels

Question 4

Homeostatic mechanisms that restore body temperature after exercise (7)

Answer 4

~Receptors in hypothalamus detect increase in core temperature (of blood)
~Heat loss centre stimulated
~Vasodilation
~More blood flows to skin surface via capillaries
~Heat loss by radiation
~Heat loss by evaporation of sweat
~Remove clothing / cold drink

Question 5

How normal body temperature is maintained when a person moves into a cold room (7)

Answer 5

~Sensors in skin and hypothalamus detect temperature decrease
~Heat loss center inhibited
~Vasoconstriction
~Less blood to skin surface
~Therefore less heat loss by radiation
~Increased heat gain by increased metabolic rate
~Put on my clothes/hug the person next to you

Question 6

Advantage of endothermy over ectothermy (3)

Answer 6

~Enzymes at optimum temperature
~Metabolic reactions proceed more quickly
~Better able to survive in different environments/independent of environment