1.4 Starch, glycogen and cellulose

Question 1

What is the main role of starch?

Answer 1

Energy storage

Question 2

How is starch suited to its role of energy storage?

Answer 2

• insoluble → doesn’t affect water potential, doesn’t cause osmosis
• large and insoluble → cannot diffuse out of cells
• compact → lots can be stored in a small place
• forms alpha glucose when hydrolysed → easily transported and used in respiration
• can be branched → many ends, large surface area, all ends can be hydrolyses simultaneously, fast release of glucose

Question 3

Where is glycogen found?

Answer 3

Animals and bacteria

Question 4

What is the difference between the structure of glycogen and starch?

Answer 4

Glycogen has shorter chains and is more highly branched.

Question 5

How is glycogen suited to its role of energy storage?

Answer 5

• insoluble → doesn’t affect water potential, doesn’t cause water movement into cells by osmosis, doesn’t diffuse out of cells
• compact → lots stored in a small space
• highly branched → many ends can be acted on simultaneously by enzymes, more rapidly hydrolysed to form glucose used in respiration, this is important because animals have a high metabolic rate

Question 6

Why is it significant that glycogen is more branched than starch?

Answer 6

• more branching → faster hydrolysis
• more ends means more locations for enzymes to hydrolyse simultaneously
• faster rate of glucose production for respiration
• animals have a higher metabolic rate than plants as they are more active

Question 7

How is cellulose different from glycogen and starch?

Answer 7

It is made from beta glucose rather than alpha glucose.

Question 8

What is the monomer of glycogen?

Answer 8

Alpha glucose

Question 9

What is the structure of starch?

Answer 9

Coiled chains, sometimes branched

Question 10

What is the structure of cellulose?

Answer 10

Straight, unbranched chains that run parallel to each other, allowing hydrogen bonds to form cross-linkages between adjacent chains.

Question 11

Why is it significant that cellulose chains runs parallel to each other?

Answer 11

It allows hydrogen bonds to form cross-linkages between the chains.

Question 12

Why are hydrogen bond cross-linkages important for cellulose?

Answer 12

The hydrogen bonds together provide strength, allowing cellulose to have its structural properties.

Question 13

What does cellulose molecules grouped together form?

Answer 13

Microfibrils

Question 14

What do parallel groups of microfibrils form?

Answer 14

Fibres

Question 15

What is the importance of cellulose in a cell wall?

Answer 15

• provides rigidity to the cell

* prevents cell from bursting as water enters via osmosis

Question 16

How is cellulose suited to its function of providing support and rigidity?

Answer 16

• made up of beta glucose, meaning it forms straight, unbranched chains
• cellulose molecular chains run parallel, and are cross-linked by hydrogen bonds providing collective strength
• molecules are grouped to form microfibrils, which in turn are grouped to form fibres, providing more strength