1. The Structure & Storage Polysaccharides

2. Learning Objectives Recap how polysaccharides are formed
Describe the roles of cellulose, starch and glycogen in plants and animals
Explain how the structure of these polysaccharides relates to their function in plants and animals

3. Starter Questions Which polysaccharide makes up plant cell walls?
Which monosaccharide makes up this polysaccharide?
Is this polysaccharide branched or unbranched?

4. Cellulose Main structural sugar in plants
Structural component of plant cell walls
Very strong
Also permeable to numerous substances
About 33% of plant matter
Most common organic compound on Earth

7. Why can’t humans digest cellulose?
We don’t produce Cellulase
Ruminants, like cows, have symbiotic bacteria in their stomachs

8. Starch Amylose (α helix) – 20% of starch
Amylopectin (branched starch) – 80%

9. Amylopectin

10. Amylopectin Highly branched
Can be hydrolysed more quickly than amylose
α-glucose molecules joined by α1-4 glycosidic bonds with α1-6 branches every monomers
Plants store it then hydrolyse it
when they need a supply
of energy

11. Glycogen Same subunits as amylopectin but much more branched
The storage sugar found in animals
Made mostly by the liver & muscles
Stored as granules in the cytoplasm
of cells.
Can be quickly hydrolysed when
energy supply needed.

12. Questions
Compare and contrast the structures of glycogen and cellulose, showing how each molecule’s structure is linked to its function.
[10 marks]
2. Compare and Contrast the structures of starch and cellulose, describing how each molecule’s structure is linked to its function [12 marks]

13. Mark Scheme
[1] Gycogen is a chain of α-glucose molecules [2] Cellulose – chain of β-glucose molecules [3] Glycogen’s chain is compact but very branched, whereas [4] Cellulose’s chain is very long, straight and unbranched [5] and these chains in cellulose are bonded to form fibres [6] Glycogen’s structure is very compact which makes it a good food store in animals [7] The branches allow enzymes to access the glycosidic bonds [8] to break the stored glucose down quickly , which is important for energy release in animals [9] Cellulose chains are linked together by hydrogen bonds to form fibres called microfibrils. [10] Theses strong fibres provide structural support for cells (e.g. plant cell walls)

14. [2] Cellulose – chain of β-glucose molecules
Mark Scheme
[1] Starch made up of α-glucose molecules whereas
[2] Cellulose – chain of β-glucose molecules
[3] Cellulose is a single chain polysaccharide, whereas starch is made of two polysaccharides (amylose and amylopectin)
[4]Amylose in starch is unbranched and coiled and
[5] Amylopectin is branched. In contrast
[6] Cellulose is straight and unbranched and
[7] Cellulose chains are linked together by hydrogen bonds to form strong fibres /microfibrils.
[8] Starch’s structure makes it a good energy storage material in plants
[9] The branches allow enzymes access to break the glycosidic bonds and release glucose quickly to break the stored glucose down quickly
[10] Starch is insoluble, so it can be stored in cells without causing water to enter by osmosis, which could cause them to swell
[11] Cellulose’s structure makes it a good supporting structure in plant cell walls
[12] The fibres provide strength