Homeostasis

Question 1

What is meant by homeostasis? (1)

Answer 1

maintaining a constant internal environment

Question 2

Giving one example, explain why homeostasis is important in mammals (2)

Answer 2

• temperature

- affects enzyme activity if too high or low

Question 3

Give the location of osmoreceptors in the body of a mammal (1)

Answer 3

Hypothalamus

Question 4

When a person is dehydrated, the cell volume of an osmoreceptor decreases. Explain why (2)

Answer 4

• Water potential of blood will decrease;

- Water moves from osmoreceptor into blood by osmosis

Question 5

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 (4)

Answer 5

• Water potential of blood will decrease;
• Water moves from osmoreceptor into blood by osmosis.
• Permeability of cells (to water) is increased;
• More water absorbed from collecting duct
• Urine becomes more concentrated.

Question 6

Describe how urea is removed from the blood (2)

Answer 6

• Hydrostatic pressure

- Causes ultrafiltration at Bowman’s capsule

Question 7

Explain how urea is concentrated in the filtrate (3)

Answer 7

• Reabsorption of water by osmosis
• At the PCT
• Active transport of ions / glucose creates gradient

Question 8

Describe how ultrafiltration produces glomerular filtrate (5)

Answer 8

• high blood pressure
• forces small molecules
• to pass through to the Bowmans capsule to form glomerular filtrate
• larger molecules like proteins cant pass through so they stay in the blood
• podocytes

Question 9

Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin (4)

Answer 9

• High concentration of glucose in blood;
• Reabsorbed by facilitated diffusion
• Requires proteins
• Not all glucose is reabsorbed / some is lost in urine;

Question 10

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 (6)

Answer 10

• More water (from filtrate) reabsorbed
• By osmosis;
• From collecting duct
• Due to longer loop of Henle
• Large amounts of ADH means they act on collecting duct
• Makes cells more permeable

Question 11

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.
(3)

Answer 11

In Diabetic person:

• Lack of insulin
• Reduced uptake of glucose by cells / liver / muscles;
• Reduced conversion of glucose to glycogen;

Question 12

The urine of a non-diabetic person does not contain glucose. Explain why. (2)

Answer 12

• Leaves the blood at kidney;

- Taken back into blood / reabsorbed (from kidney tubule);

Question 13

A high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. Suggest how (2)

Answer 13

• Large amount of glucose in filtrate;

- Cannot all be reabsorbed

Question 14

If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why (3)

Answer 14

• Glucose in filtrate lowers water potential;
• Lower Ψ gradient
• Less water reabsorbed by osmosis;

Question 15

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 (3)

Answer 15

• Glomerulus / Bowman’s capsule / renal capsule;
• Basement membrane;
• proteins can only pass through if filter damaged;