polysaccharides

Question 1

Starch and cellulose are two important plant polysaccharides.

The following diagram shows part of a starch molecule and part of a cellulose molecule.

(a) Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.

Answer 1

Starch formed from α-glucose but cellulose formed from β-glucose;

2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.

Question 2

Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.

Explain one way in which starch molecules are adapted for their function in plant cells.

Answer 2

Insoluble;

2. Don’t affect water potential;

OR

5. Large molecule;
6. Cannot leave cell.

Question 3

Explain how cellulose molecules are adapted for their function in plant cells.

Answer 3

Long and straight chains;

2. Become linked together by many hydrogen bonds to form fibrils;
3. Provide strength (to cell wall).

Question 4

Give one feature of starch and explain how this feature enables it to act as a storage substance.

Answer 4

Branched chains;

8. (So) easy to remove glucose;

Question 5

Name the monomers that form a cellulose molecule.

Answer 5

beta glucose

Question 6

Complete the table to show two ways in which the structure of cellulose is different from the structure of starch

Answer 6

Starch

Cellulose

1. (1,4 and) 1,6
   bonds / contains 1,6
   bonds / branching
2. 1,4 bonds / no 1,6
   bonds /
   unbranched /
   straight;
3. All glucoses /
   monomers same
   way up
4. Alternate
   glucoses / monomers
   upside down;
5. Helix / coiled / compact
6. Straight;
7. Alpha glucose
8. Beta glucose;
9. No (micro / macro)
   fibrils / fibres
10. Micro / macro
    fibrils / fibres;

Question 7

Explain one way in which the structure of cellulose is linked to its function.

Answer 7

H-bonds / micro / macro fibrils / fibres;

Reject strong hydrogen bonds

2. Strength / rigidity / inelasticity;

‘Strong hydrogen bonds’ = 0 but ‘Strong hydrogen bonds give strength (to the molecule)’ = 1

Question 8

Hydrogen bonds are important in cellulose molecules. Explain why.

Answer 8

forms cross links between chains / cellulose molecules / forms microfibrils, providing strength / rigidity (to cellulose / cell wall);

Hydrogen bonds strong in large numbers providing strength or any factor above

Question 9

The structure of cellulose is related to its role in plant cell walls. Explain how.

Answer 9

Long / straight / unbranched chains (of glucose joined by) hydrogen bonds;

Form (micro)fibrils / (macro)fibrils;

Provide rigidity / strength / support;

Allow suitable descriptions for last point e.g. ‘prevents bursting’;

Question 10

The cell walls of potato cells contain cellulose. Cellulose and starch are both carbohydrates. Describe two ways in which molecules of cellulose are similar to molecules of starch.

Answer 10

Both are polymers / made of monomers;

Joined by condensation / molecules can be broken down by hydrolysis;

Both have 1-4 links;

Contain C(arbon), H(ydrogen) and O(xygen) / both made up of glucose;

Both insoluble;

Both contain glycosidic bonds;

Question 11

Cotton is a plant fibre used to make cloth. Explain how cellulose gives cotton its strength.

Answer 11

(long) straight / unbranched chains;
(idea of more than 1) chains lie side by side / form (micro)fibrils;
idea of H bonds holding chains together;