Key Questions

• What is a monomer?

  Smaller units from which large molecules are made.
• What is a polymer?

  Molecules made from many monomers joined together.
• Name examples of monomers.

  Monosaccharide; amino acid; nucleotide.
• What reaction joins monomers together?

  A condensation reaction.
• What happens in a condensation reaction?

  Two monomers are bonded together, water is formed as a by product.
• What reaction takes place when biological molecules are separated?

  A hydrolysis reaction.
• What happens in a hydrolysis reaction?

  Two monomers are separated by breaking a bond. Water is used up in this reaction.
• Which monomers make up a polysaccharide?

  Monosaccharides
• What are the common monosaccharides?

  Glucose, fructose, and galactose.
• What reaction forms the bond between two monosaccharides?

  A condensation reaction.
• What bond forms when monosaccharides join?

  A glycosidic bond.
• What is a disaccharide?

  A molecule made from 2 monosaccharides.
• How is a disaccharide formed?

  A condensation reaction between 2 monosaccharides.
• What is maltose and what is it formed from?

  A disaccharide formed from the condensation reaction between 2 glucose molecules.
• What is sucrose and what is it formed from?

  Sucrose is a disaccharide composed of glucose and fructose.
• What is lactose and what is it formed from?

  A disaccharide formed from the condensation reaction between glucose and galactose.
• What is an isomer?

  Molecules where the molecular formula stays the same, but the structural formula is different.
• What are the isomers of glucose?

  Alpha and beta glucose.
• What is the difference between alpha and beta glucose?

  The OH group on carbon 1 of alpha glucose is below the ring, on beta glucose it is above.
• What is a polysaccharide?

  A complex carbohydrate formed from the condensation reaction of many monosaccharides.
• What is glycogen and what is it made of?

  A complex carbohydrate, a polysaccharide made from multiple alpha glucose molecules.
• What is starch and what is it formed from?

  A complex carbohydrate, a polysaccharide made form multiple alpha glucose molecules.
• What is cellulose?

  A complex carbohydrate, a polysaccharide made from multiple beta glucose molecules.
• What is the purpose of glycogen?

  It is an insoluble store of glucose in animals.
• What is the purpose of starch?

  It is an insoluble store of glucose in plants.
• What is the purpose of cellulose?

  It is an insoluble structural molecule for plants, found in plant cell walls.
• What are the two molecules that together make up starch?

  Amylose - a helical molecule.

  Amylopectin - a branched molecule.
• What is the structure of glycogen?

  Heavily branched polymer of alpha glucose molecules. Linked at alpha-1,4-glycosidic bonds. Branched with alpha-1,6-glycosidic bonds.
• How is glycogen's structure related to its function?

  Insoluble so does not affect water potential and osmosis.

  Insoluble so does not diffuse out of cells.

  Compact due to helical structure so lots of glucose can be stored in small spaces.

  Highly branched so many ends can be simultaneously hydrolysed by enzymes.
• What is the structure of starch?

  Lightly branched polymer of alpha glucose molecules. Linked at 1,4-glycosidic bonds. Branched with 1,6-glycosidic bonds.
• How is starch's structure related to its function?

  Insoluble so doesn't affect water potential and osmosis.

  Large and insoluble so doesn't diffuse out of cells.

  Compact due to helical structure so lots of glucose stored in small space.

  Hydrolysed to form alpha glucose so easily transported and used for respiration.

  Branched so more enzymes can hydrolyse bonds simultaneously.
• What is the basic structure of cellulose?

  Straight chains of beta-glucose molecules. Bonded with 1,4 glycosidic bonds.
• How are the monosaccharides in cellulose arranged?

  Alternative beta-glucose molecules are turned upside down.
• How is cellulose's structure related to its function?

  Made up of beta-glucose so form long, straight unbranched chains/chains run parallel to each other and are crossed linked by hydrogen bonds which add collective strength/molecules are grouped to form microfibrils which are also grouped to form fibres which provides more strength.
• Based on the arrangement of cellulose molecules, explain why cell walls provide strength and support to plant cells.

  Cellulose molecules form hydrogen bonds with each other to make micro fibrils.

  -microfibrils join to make macrofibrils

  -macrofibrils join to make fibres

  -fibres are insoluble and tough
• What are examples of reducing sugars?

  All monosaccharides - glucose, galactose, fructose. Also some disaccharides - e.g. lactose and maltose.
• What is an example of a non-reducing sugar?

  Sucrose.
• What does the Benedict's test test for?

  Reducing Sugar
• What is the test for reducing sugars?

  -Add equal volumes of the sample and Benedict's reagent, then gently heat for 5 minutes and if reducing sugar is present, then colour change from blue to red/green/orange.
• What is the test for non-reducing sugars?

  If the reducing sugar test presents no colour change:

  -add another sample to equal volume of HCl

  -then slowly add sodium hydrogen carbonate and re-test with Benedict's reagent while gently heating for 5 minutes.

  -If sugar is present, then colour will change from blue to yellow/green/orange/brick-red.