homeostasis

Question 1

Explain how insulin reduces the blood glucose concentration.

Answer 1

• (More) insulin binds to receptors;
• (Stimulates) uptake of glucose by channel/transport proteins
• Activates enzymes which convert glucose to glycogen;

Question 2

Explain the action of Glucagon.

Answer 2

• Binds to receptors on target cells and activates/stimulates enzymes;
• Hydrolysis of glycogen to glucose / glycogenolysis;
• Conversion of glycerol and amino acids to glucose / gluconeogenesis;

Question 3

Explain the effect of sweating or panting on temperature control.

Answer 3

• Evaporation (of water from lining of mouth or skin);
• Heat transferred from blood;

Question 4

Describe how a change in blood pH or blood pressure can cause a change in heart rate.

Answer 4

• (Carbon dioxide) detected by chemoreceptors / (pressure) detected by baroreceptors;
• Medulla/cardiac centre involved;
• More impulses to SAN/along sympathetic nerve;
• (Decrease) pH detected by chemoreceptors in carotid artery /aorta;
• Sends (more) impulses to medulla (oblongata);
• More Nerve impulses sent by sympathetic nervous system to SAN;

Question 5

Less CO2 in the blood leads to a reduction in heart rate.

Describe how.

Answer 5

• (less CO2 in blood) Detected by chemoreceptors;
• (Chemoreceptors) located in aorta / carotid artery;
• Fewer impulses to cardiac centre / medulla (oblongata);
• (More) impulses along parasympathetic nerve OR less impulses along sympathetic nerve;
• (To) SAN;

Question 6

Describe the secondary messenger model.

Answer 6

• Adenylate cyclase activated;
• cAMP produced / second messenger produced;
• Activates protein kinase enzyme(s) (in cell);
• (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited;

Question 7

Describe the role of glycogen formation and its role in lowering blood glucose levels.

Answer 7

• Glucose concentration in cell/liver falls;
• Below that in blood (plasma)/ higher in blood;
• Creates/maintains glucose concentration/diffusion gradient;
• Glucose enters cell/leaves blood by facilitated diffusion/via carrier(protein)/channel (protein);

Question 8

Describe how blood glucose levels can be increased using hormones.

Answer 8

• Release of glucagon;
• Leads to formation of glucose in liver (cells);
• From non-carbohydrates/amino acids/fatty acids;

Question 9

Describe how ultrafiltration occurs in a glomerulus.

Answer 9

• High blood/hydrostatic pressure;
• Two named small substances pass out eg water, glucose, ions, urea;
• (Through small) gaps/pores/fenestrations in (capillary) endothelium;
• (And) through (capillary) basement membrane;

Question 10

Explain why a thicker medulla leads to more concentrated urine.

Answer 10

• Thicker medulla means a longer loop of Henle;
• (The longer the loop of Henle means) increase in sodium ion concentration (in medulla) so sodium ion gradient maintained for longer (in medulla);
• (Therefore) water potential gradient maintained (for longer), so more water (re)absorbed (from loop and collecting duct) by osmosis;

Question 11

Describe the action of ADH in the kidney.

Answer 11

• Permeability of membrane/cells (to water) is increased;
• More water absorbed from/leaves distal tubule/collecting duct;
• Smaller volume of urine;
• Urine becomes more concentrated;

Question 12

Explain why glucose is found in the urine of a person with untreated diabetes.

Answer 12

• High concentration of glucose in blood/filtrate;
• Not all the glucose is (re)absorbed at the proximal convoluted tubule;
• Carrier/co-transport proteins are working at maximum rate OR carrier/co-transport proteins are saturated;