Water, carbohydrates and lipidsEdexcel A-Level Biology A: Subtopic test

1. 1
   Blood plasma in a mammal is mostly water. It carries dissolved glucose, amino acids and mineral ions around the body between the gut, the liver and the tissues.

   (a)

   Which statement explains why water is described as a polar molecule?

   [1 mark]

   • AWater contains ionic bonds between hydrogen and oxygen
   • BThe oxygen atom carries a slight negative charge and each hydrogen atom a slight positive charge, because the electrons in the O–H bonds are shared unequally
   • CWater has a net positive charge overall
   • DHydrogen atoms in water have a full outer shell of eight electrons

   (b)

   Which substance would dissolve most readily in blood plasma so that it can be transported?

   [1 mark]

   • AA triglyceride
   • BCellulose
   • CGlucose
   • DWax

   (c)

   Explain why an ionic compound such as sodium chloride dissolves in water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Glycogen is stored in the liver and muscle cells of mammals. Starch is stored in the tubers of potato plants. Both are made by joining sugar molecules together.

   (a)

   Sucrose is formed when two monosaccharides join. Which two monosaccharides form sucrose?

   [1 mark]

   • AGlucose and fructose
   • BGlucose and glucose
   • CGlucose and galactose
   • DFructose and galactose

   (b)

   What is released when two monosaccharides join to form a disaccharide?

   [1 mark]

   • AA molecule of carbon dioxide
   • BA molecule of water
   • CA molecule of oxygen
   • DA molecule of ATP

   (c)

   Describe how maltose is broken down into glucose.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A marathon runner stores glycogen in her muscles and liver and relies on it during the race. A potato plant stores starch in its tubers over winter. Both stores are made from the same monomer.

   (a)

   Explain how the structure of glycogen makes it suitable as an energy store in the runner's muscles.

   [3 marks]

   (b)

   Compare the structures of starch and glycogen.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student is investigating how a mammalian cell obtains and stores energy from the carbohydrates and lipids in food. The lipids in the diet are mainly triglycerides, found in butter (rich in saturated fatty acids) and olive oil (rich in unsaturated fatty acids).

   (a)

   Describe how a triglyceride is synthesised and explain how saturated and unsaturated triglycerides differ.

   [6 marks]

   (b)

   Discuss how the structures of glucose, sucrose and the polysaccharides starch and glycogen relate to their roles in providing and storing energy.

   [6 marks]

   Total for question 4: 12 marks

End of questions