IB DP Biology Topic 2: Molecular biology 2.3 Carbohydrates and lipids Question Bank HL Paper 1

Question

What distinguishes cellulose from glycogen and starch?

    1. Only cellulose is found in plants.

    2. Only cellulose is made up of glucose monomers.

    3. Cellulose is far more branched than starch and glycogen.

    4. Cellulose has a structural role whereas starch and glycogen function in energy storage.

▶️Answer/Explanation

Ans: D

Starch, cellulose and glycogen are all carbohydrates but they differ in their structure and function. Starch is the main storage carbohydrate source in plants while cellulose is the main structural component of the cell wall of plants and glycogen is the main storage carbohydrate energy source of fungi and animals.
Starch is made up of two types of molecules: amylose and amylopectin. Amylose is a linear molecule while amylopectin is branched. Cellulose is made up of long chains of glucose molecules that are linked together by beta-1,4-glycosidic bonds. The chains are held together by hydrogen bonds between adjacent chains. Glycogen is a highly branched polymer of glucose that is stored in the liver and muscles.

Question

Which of the molecules contain peptide bonds or are sugar molecules?

 

▶️Answer/Explanation

Markscheme

B

  • 3 contains amine bonds which are peptide bonds.
  • 2&4 contains a long chain of  $\rm{CH_2O}$ chain and are hence referred as sugar molecules.

Question

What type of molecule is shown in this diagram?

A. Trans saturated fatty acid

B. Cis unsaturated fatty acid

C. Cis saturated fatty acid

D. Trans unsaturated fatty acid

▶️Answer/Explanation

Markscheme

B

Given structure is cis because both H at 7&8 carbons are at same side, and the chain is unsaturated because it contains double bond.

Question

What type of molecule is shown in this diagram?

A. Trans saturated fatty acid

B. Cis unsaturated fatty acid

C. Cis saturated fatty acid

D. Trans unsaturated fatty acid

▶️Answer/Explanation

Markscheme

B

Given structure is cis because both H at 7&8 carbons are at same side, and the chain is unsaturated because it contains double bond.

Question

Which structure represents a fatty acid?

▶️Answer/Explanation

Markscheme

Ans:A

A fatty acid consists of a straight chain of an even number of carbon atoms, with hydrogen atoms along the length of the chain and at one end of the chain and a carboxyl group (―COOH) at the other end.

Question

What describes the structure of glycogen?

A. Unbranched polymer of alpha-D-glucose linked by 1,4 glycosidic linkages

B. Branched polymer of alpha-D-glucose linked by 1,6 glycosidic linkages with branches linked by 1,4 glycosidic linkages

C. Unbranched polymer of alpha-D-glucose linked by 1,6 glycosidic linkages

D. Branched polymer of alpha-D-glucose linked by 1,4 glycosidic linkages with branches linked by 1,6 glycosidic linkages

▶️Answer/Explanation

Ans:D

Cellulose is made up of long chains of glucose molecules that are linked together by beta-1,4-glycosidic bonds, so option B describes the structure of Cellulose. The chains are held together by hydrogen bonds between adjacent chains. Glycogen is a highly branched polymer of glucose that is stored in the liver and muscles.

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