Water, carbohydrates and lipids

Sample questions

Original practice questions written in the style of the exam.

1. Question 13 marks

   Describe how a triglyceride molecule is formed.

   Mark scheme

   • One glycerol molecule and three fatty acid molecules (1)
   • Joined by condensation reactions, releasing three molecules of water (1)
   • Forming three ester bonds (1)
2. Question 24 marks

   Glycogen is the main carbohydrate store in mammalian liver and muscle cells.

   Explain how the structure of glycogen makes it suitable as an energy store.

   Mark scheme

   • Highly branched with many $\alpha$-1,6 bonds, so there are many ends where enzymes can hydrolyse it (1)
   • So glucose can be released rapidly when it is needed for respiration (1)
   • Insoluble, so it does not lower the water potential of the cell / has no osmotic effect (1)
   • Compact / coiled, so a lot of glucose is stored in a small space (1)