Polysaccharides

Question 1

How are polysaccharides (glycogen, starch and cellulose) formed?

Answer 1

By condensation reactions between many glucose molecules (α-glucose for starch and glycogen, β-glucose for cellulose), this releases a molecule of water each time

Question 2

Describe the structure of a glycogen molecule

Answer 2

A polymer of α-glucose, joined by condensation reactions to make glycosidic bonds. It has a branched structure

Question 3

Describe the structure of a starch molecule

Answer 3

A polymer of α-glucose, joined by condensation reactions to make glycosidic bonds. It has a coiled and branched structure

Question 4

Describe the structure of a cellulose molecule

Answer 4

polymer of β-glucose, joined by condensation reactions to make glycosidic bonds. It has long, straight and unbranched chains.

Question 5

Describe the structure of cellulose

Answer 5

A polymer of β-glucose, joined by glycosidic bonds. It has long, straight and unbranched chains, that can be joined together by Hydrogen bonding to produce microfibrils, and fibres.

Question 6

Explain how the structure of glycogen is related to the function

Answer 6

Glycogen is insoluble, so it doesn’t affect the water potential of the cell. It is a highly branched polymer of α-glucose, so can quickly be hydrolysed by enzymes into glucose to provide a respiratory substrate. It is a large molecule, so cannot pass through the cell surface membrane. It is highly branched so it is compact and many can fit into a small area.

Question 7

Explain how the structure of starch is related to the function

Answer 7

Starch is insoluble, so it doesn’t affect the water potential of the cell. It is a highly branched polymer of α-glucose, so can quickly be hydrolysed by enzymes into glucose to provide a respiratory substrate. It is a large molecule, so cannot pass through the cell surface membrane. It is coiled so it is compact and many can fit into a small area.

Question 8

Explain how the structure of cellulose is related to the function

Answer 8

Cellulose are long, straight, unbranched chains of β-glucose. These polymer chains get joined by hydrogen bonds to form microfibrils and fibres which provide rigidity and strength to the plant cell.

Question 9

. What is the test for starch?

Answer 9

A solution of potassium iodide, add to the test sample. A colour change from orange to blue/black is positive.