2 Learning Objectives Recap how polysaccharides are formed Describe the roles of cellulose, starch and glycogen in plants and animalsExplain 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 wallsVery strongAlso permeable to numerous substancesAbout 33% of plant matterMost common organic compound on Earth
10 Amylopectin Highly branched Can be hydrolysed more quickly than amyloseα-glucose molecules joined by α1-4 glycosidic bonds with α1-6 branches every monomersPlants store it then hydrolyse itwhen they need a supplyof energy
11 Glycogen Same subunits as amylopectin but much more branched The storage sugar found in animalsMade mostly by the liver & musclesStored as granules in the cytoplasmof cells.Can be quickly hydrolysed whenenergy supply needed.
12 QuestionsCompare 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 Gycogen is a chain of α-glucose molecules  Cellulose – chain of β-glucose molecules  Glycogen’s chain is compact but very branched, whereas  Cellulose’s chain is very long, straight and unbranched  and these chains in cellulose are bonded to form fibres  Glycogen’s structure is very compact which makes it a good food store in animals  The branches allow enzymes to access the glycosidic bonds  to break the stored glucose down quickly , which is important for energy release in animals  Cellulose chains are linked together by hydrogen bonds to form fibres called microfibrils.  Theses strong fibres provide structural support for cells (e.g. plant cell walls)
14  Cellulose – chain of β-glucose molecules Mark Scheme Starch made up of α-glucose molecules whereas Cellulose – chain of β-glucose molecules Cellulose is a single chain polysaccharide, whereas starch is made of two polysaccharides (amylose and amylopectin)Amylose in starch is unbranched and coiled and Amylopectin is branched. In contrast Cellulose is straight and unbranched and Cellulose chains are linked together by hydrogen bonds to form strong fibres /microfibrils. Starch’s structure makes it a good energy storage material in plants The branches allow enzymes access to break the glycosidic bonds and release glucose quickly to break the stored glucose down quickly Starch is insoluble, so it can be stored in cells without causing water to enter by osmosis, which could cause them to swell Cellulose’s structure makes it a good supporting structure in plant cell walls The fibres provide strength