Control of blood glucose concentrationAQA A-Level Biology: Subtopic test

1. 1
   A healthy adult eats no food for 14 hours. During this time the concentration of glucose in her blood stays at about 4.5 mmol dm⁻³, even though no glucose is being absorbed from her gut. Her liver cells are responsible for much of this regulation.

   (a)

   In the first few hours of the fast, which process in the liver is mainly responsible for releasing glucose into the blood?

   [1 mark]

   • AGlycogenolysis, the hydrolysis of glycogen to glucose
   • BGlycogenesis, the conversion of glucose to glycogen
   • CGluconeogenesis, the conversion of glucose to fatty acids
   • DGlycolysis, the conversion of glycogen to pyruvate

   (b)

   After many hours without food the liver's glycogen stores are low. Which substances can the liver convert into glucose by gluconeogenesis?

   [1 mark]

   • AStarch and cellulose
   • BLactose and sucrose
   • CFatty acids and cholesterol
   • DGlycerol and amino acids

   (c)

   Glucagon is released when blood glucose concentration falls. State two ways in which glucagon increases the concentration of glucose in the blood.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A researcher adds insulin to cultured muscle cells. Within minutes, the uptake of glucose by the cells increases, and the number of glucose channel proteins in the cell surface membrane is found to be greater than before. The concentration of glucose in the surrounding solution is the same throughout.

   (a)

   What is the most likely explanation for the increased uptake of glucose by the muscle cells?

   [1 mark]

   • AInsulin enters the cells and binds to glucose molecules, so they diffuse in more easily
   • BInsulin forms channels through which glucose enters the cells
   • CInsulin binds to receptors on the cell surface, leading to more glucose channel proteins in the surface membrane
   • DInsulin makes the phospholipid bilayer more permeable to glucose by dissolving it

   (b)

   By what process does glucose enter the muscle cells through these channel proteins?

   [1 mark]

   • AActive transport against a concentration gradient using ATP
   • BFacilitated diffusion down a concentration gradient that is kept steep by conversion of glucose to glycogen
   • CSimple diffusion directly through the phospholipid bilayer
   • DOsmosis through the channel proteins

   (c)

   Insulin also activates enzymes inside the muscle cells. Explain how this helps to increase the uptake of glucose.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A clinic is testing the urine of two patients with diabetes: patient 1 has type I diabetes and patient 2 has type II diabetes. The clinic estimates glucose concentration using Benedict's reagent and a colorimeter with a red filter. Standard glucose solutions of 0.0, 0.2, 0.4, 0.6 and 0.8 mmol dm⁻³ gave absorbances of 0.90, 0.72, 0.54, 0.36 and 0.18, because less blue copper(II) remains as glucose concentration increases. A urine sample from patient 2 was diluted by mixing 1 cm³ of urine with 9 cm³ of distilled water, and the diluted sample gave an absorbance of 0.45.

   (a)

   Explain why patient 1 needs insulin injections, but patient 2 may be able to control their blood glucose concentration by changing their diet.

   [3 marks]

   (b)

   Calculate the concentration of glucose in the undiluted urine of patient 2. Show your working.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Information A: glucagon is a protein hormone that cannot cross the surface membrane of a liver cell, yet it causes the cell to release glucose. Information B: the number of people with type II diabetes in one country has risen sharply. Health advisers say that sugar intake must be cut, by taxing sugary drinks and requiring clear labelling. A food manufacturers' association says that diabetes risk depends on total energy intake, exercise and genes, not on a single ingredient, and that its members are already reducing the sugar in their products.

   (a)

   Explain how glucagon, although it cannot enter the cell, causes a liver cell to release glucose.

   [6 marks]

   (b)

   Evaluate the positions of the health advisers and the food industry in relation to the increased incidence of type II diabetes.

   [6 marks]

   Total for question 4: 12 marks

End of questions