exam questions

• Name the monomer that makes up cellulose (1) 

  -       B glucose
• How are these monomers held together in a cellulose molecule (1) 

  -       By glycosidic bonds in an unbranched chain
• Cellulose molecules are held together in bundles called microfibrils. 

  These microfibrils are embedded in a matrix containing calcium pectate. Calcium pectate can be found in the… (1)

  -       Middle lamella
• Compare and contrast the structure of chitin with that of a cellulose molecule (3)

  -       Both are polysaccharides/polymers of glucose

  -       Both have 1,4 glycosidic bonds 

  -       Both have every other monomer rotated 

  -       However, the monomers of chitin have 8 carbon atoms whereas in cellulose there are 6 carbon atoms
• Compare and contrast the structure of cellulose and amylopectin (3) 

  -       Cellulose has b glucose monomers whereas amylopectin has a glucose molecule 

  -       Both have glycosidic bonds formed via condensation reactions 

  -       Amylopectin is branched (1,6 glycosidic bonds) whereas cellulose is not
• Name the bond between adjacent cellulose molecules in a cellulose myofibril (1)

  -       Hydrogen bond
• Describe the structure of starch (3) 

  -       Starch is a polysaccharide made from alpha glucose 

  -       Monomers in the chains are joined by 1,4 glycosidic bonds

  -       Starch contains unbranched amylose and branched chains amylopectin 

  -       Branches are joined to chains by 1,6 glycosidic bonds
• Explain why starch must be broken down before it can be used by the cells of the growing plant (2) 

  -       To produce glucose 

  -       Which is soluble and can be transported, used in respiration  
• Explain how the structure and properties of starch are related to its function as a storage molecule (3) 

  -       Contains glucose needed for respiration to produce energy 

  -       Insoluble so has no osmotic effect 

  -       Amylose is coiled making starch compact, so more can be stored 

  -       Amylopectin is branched so is rapidly hydrolysed for a quick release of energy 
• Describe the arrangement of glucose monomers in a cellulose molecule (2) 

  -       B glucose monomers are connected by 1,4 glycosidic links 

  -       Alternate monomers are inverted
• Explain the relationship between the composition of the starch and the rate of hydrolysis by enzymes (4) 

  -       Starch contains amylose and amylopectin 

  -       When amylose content increases the content of amylopectin decreases

  -       So, when amylose content increases the percentage of starch hydrolysed decreases 

  -       Because amylopectin is branched meaning it can be rapidly hydrolysed however amylose is not branched so takes longer.
• Explain how the structures of amylopectin and glycogen make them suitable for storing energy (3) 

  -       Both are insoluble thus have no osmotic effect

  -       Branched therefore can be rapidly hydrolysed to release glucose 

  -       Compact so more glucose can be stored 

  -       Molecules too large to diffuse across the cell surface membrane
• State the role of cellulose in plant cell walls and explain how its structure is related to this role (3) 

  -       Provides tensile strength/ support

  -       They are long unbranched straight chains of glucose joined by hydrogen bonds 

  -       Formation of microfibrils 
• Explain how the structure of amylopectin allows it to be hydrolysed quickly to supply cells with glucose for respiration (3) 

  -       It contains 1,6 glycosidic bonds 

  -       Which gives a highly branched structure 

  -       There are lot of terminal end glucose monomers

  -       That can be hydrolysed simultaneously, so glucose is produced faster
• Describe 2 similarities and 2 differences between the structures of cellulose and starch (4) 

  -       Both are polysaccharide chains/monomers of glucose 

  -       Both have 1,4 glycosidic bonds 

  -       Both are insoluble

  -       However, cellulose has B glucose whereas starch has A glucose 

  -       Amylopectin is branched so has 1,6 glycosidic bonds whereas starch does not

  -       Starch has a helical/coiled/compact structure whereas cellulose has a straight structure 
• Describe the structure of cellulose microfibril (4) 

  -       Cellulose contains beta glucose 

  -       Joined by condensation reactions 

  -       To form 1,4 glycosidic bonds 

  -       Inversion of every other glucose molecule 

  -       Forming an unbranched, straight chain 

  -       Microfibril composed of many cellulose molecules 

  -       Cellulose chains held together by hydrogen bonds