Starch, Cellulose and Plant Fibres

Question 1

Name the two-types of starch.

Answer 1

Amylose and Amylopectin

Question 2

Describe the structure of amylose.

Answer 2

1. Long, unbranched chains of alpha-glucose molecules
2. Angles of glycosidic bonds give it its coiled structure
3. Coiled structure makes it compact so it is good for storage.

Question 3

Describe the structure of amylopectin.

Answer 3

1. Long, branched chains of alpha-glucose molecules
2. Side branches allow enzymes to access glycosidic bonds easily. This increases the rate that alpha-glucose is broken down
3. Therefore, glucose can be released quickly.

Question 4

Describe the structure of cellulose.

Answer 4

1. Long, unbranched chains of beta-glucose joined by 1,4 glycosidic bonds
2. Glycosidic bonds are straight so cellulose is straight
3. Cellulose chains are linked together by the weak hydrogen bonds.
4. Large number of hydrogen bonds form strong threads called microfibrils
5. The microfibrils mean cellulose provides structural support for cells

Question 5

Why are plant fibres strong?

Answer 5

1. Cell walls contain cellulose. The microfibrils in cellulose are laid out in a net-like structure. The strength and arrangement of the microfibrils makes plant fibres strong
2. Secondary thickening

Question 6

What is secondary thickening?

Answer 6

Structural plant cells produce secondary cell walls between the original cell wall and the cell membrane. The secondary cell wall is thicker and contains more lignin than the normal cell wall. This makes plant fibres stronger.