A - 3 - Polysaccharides

Question 1

What is a polysaccharide?

Answer 1

Carbohydrates that are formed when more than two monosaccharides are joined together by condensation reactions

Question 2

Name the two polysaccharides starch is made from

Answer 2

Amylose

Amylopectin

Question 3

What is the function of starch?

Answer 3

Plants store excess glucose as starch

It is an energy storage molecule

Question 4

Describe the structure of Amylose

Answer 4

• A long unbranched chain of a-glucose

- It has a coiled structure which makes it compact

Question 5

How does the structure of Amylose relate to its function?

Answer 5

Its coiled structure makes it compact so its good for storage as you can fit more into a small space

Question 6

Describe the structure of Amylopectin

Answer 6

• A long branched chain of a-glucose

- Has lots of side branches

Question 7

How does the structure of Amylopectin relate to its function?

Answer 7

Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily so glucose can be released quickly

Question 8

What makes starch good for storage?

Answer 8

It is insoluble in water and doesn’t affect water potential, so it doesn’t cause water to enter cells via osmosis, which would make them swell

Question 9

What is the function of Glycogen?

Answer 9

Animals use glycogen to store excess glucose

Question 10

How does the structure of glycogen relate to its function?

Answer 10

• Has lots of side branches which means the glucose stored can be released quickly which is important for energy release in animals
• Compact so good for storage

Question 11

What is the function of cellulose?

Answer 11

Provides structural support for cells (Eg. In plant cell walls)

Question 12

Describe the structure of cellulose and how this relates to its function

Answer 12

• Made of long unbranched chains of beta-glucose
• When beta-glucose molecules bond, they form straight cellulose chains
• These chains are linked by hydrogen bonds to form strong fibres called microfibrils
• The strong fired mean cellulose provides structural support for cell walls

Question 13

How would you test a substance to see if starches are present?

Answer 13

The iodine test

Question 14

Describe how you would carry out the iodine test

Answer 14

• Add iodine dissolved in potassium iodide solution to the test sample
• If a starch Is present, the sample chains from browny-orange to a dark blue-black colour

Question 15

How are glycogen and starches formed?

Answer 15

They are formed by the condensation of a-glucose molecules

Question 16

How is cellulose formed?

Answer 16

Cellulose is formed by the condensation of beta-glucose