homeostasis

Question 1

Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours.

Answer 1

Release of glucagon;

Leads to formation of glucose in liver (cells);
Reject: glucagon breaks down glycogen, or any other biological molecule

From non-carbohydrates / amino acids / fatty acids.

Question 2

Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose concentration.

Answer 2

Glucose concentration in cell / liver falls below that in blood (plasma) which creates / maintains glucose concentration / diffusion gradient;

Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) / channel (protein);

Question 3

Glycogen to glucose / glycogenolysis by activating enzymes;
If name incorrect this disqualifies.
Gluconeogenesis;Diabetic people who do not control their blood glucose concentration may become unconscious and go into a coma. A doctor may inject a diabetic person who is in a coma with glucagon. Explain how the glucagon would affect the person’s blood glucose concentration.

Answer 3

Glycogen to glucose / glycogenolysis by activating enzymes;

Gluconeogenesis;

Question 4

Give the location of osmoreceptors in the body of a mammal.

Answer 4

Hypothalamus.

Question 5

When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why.

Answer 5

Water potential of blood will decrease;

Water moves from osmoreceptor into blood by osmosis.

Question 6

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys.

Answer 6

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 7

Describe how urea is removed from the blood.

Answer 7

Hydrostatic pressure
Causes ultrafiltration at Bowman’s capsule
Through basement membrane; Enabled by small size urea molecule;

Question 8

Explain how urea is concentrated in the filtrate.

Answer 8

Reabsorption of water / by osmosis;
At the PCT / descending LoH;
At the DCT / CD;
Active transport of ions / glucose creates gradient (in context);

Question 9

Describe how ultrafiltration produces glomerular filtrate.

Answer 9

Blood pressure / hydrostatic pressure;
Small molecules / named example;
Pass through basement membrane / basement membrane acts as filter; Protein too large to go through / large so stays behind;
Presence of pores in capillaries / presence of podocytes;

Question 10

Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin.

Answer 10

High concentration of glucose in blood;
High concentration in tubule / in filtrate;
Reabsorbed by facilitated diffusion / active transport; Requires proteins / carriers;
These are working at maximum rate / are saturated; Not all glucose is reabsorbed / some is lost in urine;

Question 11

Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH). Explain how these two features are adaptations to living in desert conditions.

Answer 11

1. More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
2. By osmosis;
3. From collecting duct / from end of second convoluted tubule;
4. Due to longer loop of Henle;
5. Sodium / chloride ions absorbed from filtrate in ascending limb;
6. Gradient established in medulla / concentration of ions increases down
   medulla;
7. Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
8. Makes cells more permeable / inserts aquaporins in plasma membranes;

Question 12

The urine of a non-diabetic person does not contain glucose. Explain why.

Answer 12

Leaves the blood at kidney;
Taken back into blood / reabsorbed (from kidney tubule);
Reject some reabsorption
(Reabsorbed)in1st convolutedtubule;

Question 13

A high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. Suggest how.

Answer 13

Large amount / high concentration of glucose in filtrate;

Cannot all be reabsorbed / 1st convoluted tube too short to reabsorb all of glucose / saturation of carriers;

Question 14

A test for glucose in urine uses immobilised enzymes on a plastic test strip. One of these enzymes is glucose oxidase. Explain why the test strip detects glucose and no other substance.
(2)

Answer 14

Enzyme has specific shape to active site / active site has specific tertiary structure;
Only glucose fits / has complementary structure / can form ES complex;

Question 15

If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why.

Answer 15

Glucose in filtrate lowers water potential;
Ignore ‘urine’. Accept
increase solute potential

Lower Ψ gradient / less difference in Ψ filtrate − Ψ plasma;
Ignore ‘concentration’

Less water reabsorbed by osmosis;

Question 16

In some forms of kidney disease, proteins from the blood plasma are found in the urine. Which part of the nephron would have been damaged by the disease to cause proteins from blood plasma to be present in the urine? Explain your answer.

Answer 16

Glomerulus / Bowman’s capsule / renal capsule;
Basement membrane;
Proteins are large (molecules) / proteins cannot normally pass through filter / proteins
can only pass through if filter damaged;

Question 17

The kangaroo rat is a small desert mammal. It takes in very little water in its food and it rarely drinks. Its core body temperature is 38 °C.
The kangaroo rat takes in some water by feeding and drinking. Describe another method by which the kangaroo rat could obtain water.

Answer 17

metabolic water / from respiration;
allow condensation reactions.

aerobic / use of oxygen;

Question 18

A diabetic person and a non-diabetic person each ate the same amount of glucose. One hour later, the glucose concentration in the blood of the diabetic person was higher than that of the non-diabetic person. Explain why.

Answer 18

In Diabetic person:
Lack of insulin / reduced sensitivity of cells to insulin;
Reduced uptake of glucose by cells / liver / muscles;
Reduced conversion of glucose to glycogen;