carbohydrates

• Relate the structure of tryglycerides to their properties (4) ➤ source of energy - high ratio of energy storing C-H bonds to C atoms ➤ storage - low mass to energy ratio; much energy in a small volume ➤ insoluble in water - large non polar molecules dont affect water potential ➤ water source - high ratio of H to O atoms release water when oxidised
• Describe the process of using Benedict’s test to test for reducing sugars: All monosaccharides (e.g. glucose) and some disaccharides (e.g. maltose and lactose).Add blue Benedict’s reagent to the sample.Heat the solution using a water bath.A coloured precipitate will form if the test is positive.The higher the concentration of sugar the further the colour change Alternatively the solution can be
• How do you test for starch? (3 marks) Use the iodine test Add iodine dissolved in potassium iodide solution Starch present will cause the brown/orange to change to a black/blue colour
• Define "monosaccharides""" The monomers from which larger carbohydrates are made
• Examples of common monosaccharides

  Glucose

  galactose fructose
• Define "glycosidic bond""" The bond formed by the condensation reaction between two monosaccharides
• How are disaccharides formed? The condensation of two monosaccharides
• Disaccharide formed by condensation of 2 glucose molecules Maltose
• Disaccharide formed by condensation of a glucose molecule and a fructose molecule Sucrose
• Disaccharide formed by condensation of a glucose molecule and a galactose molecule Lactose
• How are polysaccharides formed? The condensation of many glucose units
• What polysaccharides are formed by the condensation of α-glucose? Glycogen + starch
• What polysaccharide is formed by the condensation of β-glucose? Cellulose
• Define "condensation reaction""" A chemical reaction between 2 molecules where there is the elimination of water (or another simple molecule)
• Define "hydrolysis reaction""" A chemical reaction where water is used to break a bond within a substance
• How are polymers and disaccharides broken down into monomers? Hydrolysis reaction
• What is starch? Storage polysaccharide found in plants
• Where are large amounts of starch found? Seeds storage organs e.g. potato tubers
• What are the 2 molecules that make up starch & their proportions? Amylose ~25% Amylopectin ~75%
• What monomer makes up starch? Alpha glucose
• What type of bond joins the glucose monomers in amylose? alpha 1 4 glycosidic linkages
• Amylose structure - Long linear unbranched chain - Helical 3D structure coiled like a spring - 6 glucose monomers per turn
• Why is amylose an excellent storage molecule? Its coiled structure makes it highly compact
• What types of bonds join the glucose monomers in amylopectin? alpha 1 4 glycosidic bonds with occasional alpha 1 6 glycosidic bonds
• Amylopectin structure Long branched chain
• What is the benefit of amylopectin chains being branched? The branches provide many exposed ends so many enzymes can act on them simultaneously so it is hydrolysed faster so glucose can be released more quickly
• How is starch adapted for storage? "- Insoluble so doesn't affect water potential of surrounding cells - Large and insoluble so doesn't diffuse out of cells - Compact - When hydrolysed forms alpha glucose which is easily transported and readily used in respiration - Amylopectin branched"
• What is glycogen? Energy (glucose) storage polysaccharide in animals
• What monomer makes up glycogen? alpha glucose
• What bonds join the monosaccharides in glycogen? Alpha-1. 4 and alpha-1 6 (more 1 6 than in amylopectin)
• What is the benefit of glycogen being branched? More branching = more ends that can be acted on simultaneously by enzymes so more easily broken down into glucose monomers for higher rate of respiration in animals
• How is glycogen structurally adapted for storage? - Insoluble so does not affect water potential of surrounding cells - Insoluble so does not diffuse out of cells - Compact - More highly branched than starch
• What is cellulose? Polysaccharide found in plant cell walls
• Function of cellulose - Strengthens plant cell walls to provide rigidity to plant cell - Prevents cell from bursting as water enters it by osmosis
• How does cellulose prevent cells bursting from osmotic pressure? It exerts an inward pressure that prevents any further influx of water so the living plant cells are turgid and push against one another making non-woody parts of the plant semi-rigid
• Why is it important that stems and leaves maintain a turgid state? To provide maximum surface area for photosynthesis
• What monomer makes up cellulose? beta glucose
• What bonds join the glucose monomers in cellulose? beta-1 4 glycosidic bonds
• Structure of cellulose Straight unbranched chains adjacent parallel chains crosslinked by hydrogen bonds
• Why are adjacent glucose molecules in cellulose rotated by 180? Allows hydrogen bonds to form between -OH groups on adjacent parallel chains