Biology HL
Carbohydrate and Lipid Structure
- 1.
An unbranched carbohydrate is made by joining 80 glucose molecules into one chain using condensation. Calculate how many water molecules are released, explain why hydrolysis needs water, and explain one advantage of storing glucose as a large relatively insoluble polymer.
[4 marks] · no calculator - 2.
Compare cellulose with starch as glucose polymers. Explain how monomer orientation and interactions between chains suit cellulose to plant cell walls, whereas starch is suited to storage.
[4 marks] · no calculator - 3.
Contrast a triglyceride with a phospholipid in composition and behaviour in water. Explain why phospholipids assemble into bilayers but triglycerides are better described as hydrophobic energy stores.
[4 marks] · no calculator - 4.
Compare a triglyceride with a phospholipid in terms of fatty-acid attachment and interaction with water. Explain why phospholipids can form bilayers whereas triglycerides are more suited to bulk energy storage than to forming the main membrane bilayer.
[4 marks] · no calculator - 5.
A linear chain is assembled from 25 glucose molecules by condensation, with one glycosidic linkage between each successive pair. Calculate the number of glycosidic linkages and water molecules released. Explain what hydrolysis would require to separate the chain completely back into glucose molecules.
[3 marks] · no calculator - 6.
Two fatty acids each contain 18 carbon atoms. X has no carbon-carbon double bonds; Y has one cis carbon-carbon double bond. Classify X and Y as saturated or unsaturated. Explain why the cis bond can make Y-containing lipid chains pack less closely than otherwise comparable X-containing chains, and predict which of two pure triglycerides would usually have the lower melting temperature if one contains only X chains and the other only Y chains. All other structural features are matched; do not generalize this comparison to every natural mixture of fats.
[4 marks] · no calculator - 7.
A hypothetical pure sample contains 0.20 mmol of triglyceride molecules. Each has one glycerol joined to three fatty acids by three ester bonds. Assume complete hydrolysis without side reactions. Name the products, calculate the amounts of glycerol and fatty acids formed and the amount of water consumed, and explain why melting the same sample would not produce those chemical products.
[5 marks]