Exam-style Questions: Homeostasis

1. The diagram shows the process by which urea is formed from an amino acid.

 

a) (i) Complete the diagram to show the chemical structure of the amino acid.

(ii) Name the cycle of reactions in which urea is produced from ammonia.

b) In a mammalian kidney, the concentration of urea in the filtrate at the beginning of the collecting duct is approximately thirty times that of the urea in the blood plasma. At the end of the collecting duct it is approximately fifty time that of the blood.

Explain what causes the change in urea concentration along the collecting duct.

(Marks available: 4)

Answer

 

Answer outline and marking scheme for question: 1

Give yourself marks for mentioning any of the points below:

a) (i) The diagram is completed with a COOH group.

(ii) Ornithine cycle.

(2 marks)

b) Ammonia is extremely toxic.

Can only be handled by the body if sufficiently dilute.

Large amounts of water are available in the body.

(2 marks)

(Marks available: 4)

2. The diagram shows the main blood vessels going to and from the liver.

 

Exam-Style Questions

 

a) In a healthy person the blood glucose level in the hepatic vein fluctuates much less than that in the hepatic portal vein.

Explain why this is so.

b) Blood sugar level is more or less consistant, even if a person has not eaten for several days.

How does gluconeogenesis help to maintain this constant blood sugar level?

c) Suggest why people suffering from diabetes are advised to eat their carbohydrates in the form of starch rather than sugars.

(Marks available: 6)

Answer

 

Answer outline and marking scheme for question: 2

Give yourself marks for mentioning any of the points below:

a) Blood glucose in hepatic portal vein increases after a meal/variable absorption from gut.

Excess glucose; converted to glycogen in the liver.

Insufficient glucose; liver glycogen broken down.

(3 marks)

b) Glucose produced from molecules other than glycogen.

Produced from lipids/proteins/amino acids.

(1 mark)

c) Starch is broken down/digested.

Therefore slower uptake/no rapid rise in blood sugar.

(2 marks)

(Marks available: 6)

 

3. The photo shows an African elephant.

Exam-Style Questions

a) (i) Explain why a large mammal such as an elephant might be expected to experience difficulties in regulating its body temperature in a hot climate.

ii) There are many blood vessels just below the surface of the skin on the back of an elephant''s ears.

Suggest how this might help an elephant to regulate its body temperature.

b) In many parts of Africa, the year is divided into a wet and a dry season. Elephants often move from one habitat in the dry season to another in the wet season.

Name this type of movement.

(Marks available: 7)

Answer

 

Answer outline and marking scheme for question: 3

Give yourself marks for mentioning any of the points below:

a) (i) Elephants are homiotherms. They generate heat by metabolic processes.

Has small surface area compared to volume/less heat can be lost.

(ii) Large ears increase surface area.

Blood brings heat from core/body/cooler blood is returned.

More heat can be lost by radiation.

Flapping/holding ears out increases flow of air over surface.

(6 marks)

b) Migration

(1 mark)

(Marks available: 7)