1.4 Starch, glycogen and cellulose

Question 1

How are glycogen and starch formed?

Answer 1

Condensation of α-glucose

Question 2

What are the function of glycogen and starch?

Answer 2

Energy source

Question 3

How are cellulose formed?

Answer 3

Condensation of β-glucose

Question 4

What is the function of cellulose?

Answer 4

Structural support to plant cells

Question 5

What are the features of starch? Explain each of them.

Answer 5

1. insoluble - so it doesn’t affect water potential > water isn’t drawn into cells by osmosis + so it doesn’t diffuse out of the cell
2. compact (緊湊) - so a lot of it can be stored in a small place
3. when hydrolysed it forms α-glucose - so it’s easily transported and readily used in respiration
4. the branched form has many ends - so each of it can be acted on by enzymes simultaneously, meaning that glucose monomers can be released very rapidly

Question 6

Is starch never been found in animal, plant or bacterial cells?

Answer 6

Animal cells

Question 7

Is glycogen never been found in animal, plant or bacterial cells?

Answer 7

Plant cells

Question 8

What is the main carbohydrate storage product of animals?

Answer 8

Glycogen

Question 9

What is the difference between glycogen and starch?

Answer 9

Glycogen: shorter chains, more highly branched
Starch: longer chains, less highly branched

Question 10

What are the features of glycogen? Explain each of them.

Answer 10

1. insoluble - so it doesn’t tend to draw water into the cell by osmosis + so it doesn’t diffuse out of the cell
2. compact (緊湊) - so a lot of it can be stored in a small place
3. more highly branched than starch - so it has more ends that can be acted on simultaneously by enzymes > more rapidly broken down into glucose

Question 11

How is glycogen stored in animals?

Answer 11

In muscles and liver as small granules (小顆粒)

Question 12

What is the difference between cellulose and glycogen & starch?

Answer 12

Cellulose: made of β-glucose
Glycogen & starch: made of α-glucose

Question 13

What are the features of cellulose? Explain each of them.

Answer 13

1. made of β-glucose - so forms long, straight, unbranched chains
2. the chains run parallel to each other and are crossed linked by hydrogen bonds - so it adds collective strength
3. grouped to form microfibrils then fibres - so can provide more strength

Question 14

What are the functions of cellulose

Answer 14

1. to provide rigidity of cells
2. prevents the cell from bursting as water enters in by osmosis

Question 15

Does cellulose has branched chains or unbranched chains? Why?

Answer 15

Unbranched, so hydrogen bonds can form cross-linkages between adjacent chains.

Question 16

Why are living plant cells are turgid and push against each other?

Answer 16

To maintain stems and leaves in a turgid state, so that they can provide the maximum surface area for photosynthesis.

Question 17

What is used to test for starch?

Answer 17

Iodine/potassium iodide

Question 18

How will the colour of the food sample change?

Answer 18

yellow-brown > blue-black