CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET ANSWERS The questions and example answers that appear in this digital material were written by the authors. Worksheet answers – Chapter B3 B3.1A: Classifying carbohydrates Question Answer 1 A 2a glucose – in ‘sugars’ starch – in ‘polysaccharides’ 2bi storage (of food / carbohydrate / chemical energy) 2 b ii used in respiration to release energy / used as a source of (chemical) energy 3 indication that the bonds (lines joining the hexagons) are broken by a digestive enzyme / amylase / carbohydrase 4a cooking time 4b temperature, mass of sweet potato, variety of sweet potato, age of sweet potato, cooking method 4c Benedict’s test crush a small known mass of sweet potato in a known volume of water add Benedict’s reagent heat to over 65 °C or boil observe the colour B3.1B: Classifying carbohydrates Question Answer 1 C 2a cellulose and glycogen – in ‘polysaccharides’ sucrose, maltose – in ‘disaccharides’ 2b starch – underlined once glycogen – underlined twice sucrose – circled once glucose – circled twice cellulose – in a box (continued) © Cambridge University Press & Assessment 2023 1 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET ANSWERS Question Answer use Figure 3.2 from question 3 in the help sheet for WS B3.1 with indication that the bonds (lines joining the hexagons) are broken by a digestive enzyme / amylase / carbohydrase 3 4 dependent variable – cooking time factors to be kept constant – temperature, mass of sweet potato, variety of sweet potato, age of sweet potato, cooking method test – Benedict’s test crush a small known mass of sweet potato in a known volume of water add Benedict’s reagent heat to over 65 °C or boil observe the colour B3.1C: Classifying carbohydrates Question Answer 1 For the reducing sugar: crush a small mass of eggplant in water add Benedict’s reagent heat to over 65 °C or boil would see no colour change / reagent would stay blue. For the starch: cut a piece of eggplant to expose the inner part to be tested add a few drops of iodine solution would see colour change from brown to blue–black. 2a Polysaccharides may include: cellulose, glycogen Monosaccharides may include: fructose Disaccharides may include: sucrose 2b Any two from: cellulose – making plant cell walls / fibre in animal diets starch – food storage in plants / energy source in animal diets sucrose – form of carbohydrate that is transported in plants / energy source in animal diets fructose – found in fruits / energy source in animal diets (continued) © Cambridge University Press & Assessment 2023 2 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET ANSWERS Question Answer use Figure 3.2 from question 3 in the help sheet for WS B3.1 with indication that the bonds (lines joining the hexagons) are broken by a digestive enzyme / amylase / carbohydrase 3 4 dependent variable – cooking time factors to be kept constant – temperature, mass of sweet potato, variety of sweet potato, age of sweet potato, cooking method test – Benedict’s test crush a small known mass of sweet potato in a known volume of water add Benedict’s reagent heat to over 65 °C or boil observe the colour B3.2A: Proteins and fats Question Answer 1 carbon, hydrogen, oxygen, nitrogen 2 carbon, hydrogen, oxygen 3 add some milk to a test-tube add a few drops of biuret solution or biuret reagent colour change from blue to violet or purple if protein is present 4 add some butter to a test-tube add ethanol dissolve the butter in the ethanol add water and shake the mixture will go cloudy or milky if fat is present 5 proteins are made from one type of molecule amino acids fats are made from two types of molecules fatty acids and glycerol © Cambridge University Press & Assessment 2023 3 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET ANSWERS B3.2B: Proteins and fats Question Answer 1a carbon, hydrogen, oxygen, nitrogen 1b sulfur 2 carbon, hydrogen, oxygen 3 add some milk to a test-tube add a few drops of biuret solution or biuret reagent colour change from blue to violet or purple if protein is present 4 add some butter to a test-tube add ethanol dissolve the butter in the ethanol add water and shake the mixture will go cloudy or milky if fat is present 5i Molecule a is a fatty acid and is used to make fats or oils. 5 ii Molecule b is an amino acid and is used to make proteins. B3.2C: Proteins and fats Question Answer 1 proteins and fats both contain carbon, hydrogen and oxygen proteins contain nitrogen but fats do not some proteins contain sulfur but fats do not 2 idea that mass of each sample (hazelnut or peanut) is the same grind each nut into a fine powder method for grinding, e.g. pestle and mortar or crush between two hard objects suspend each in water in a test-tube equal volume of water used to suspend each add biuret reagent equal number of drops or equal volume added to each compare the colour change colour change is blue to violet or purple the one with more protein should go purple sooner or a stronger shade of purple method of comparing, such as holding them against a white background 3 Proteins in the diet are broken down into amino acids which are taken into cells or tissues and re-assembled to make different proteins. 4 i ii Molecule a is a fatty acid and is used to make fats or oils. Molecule b is an amino acid and is used to make proteins. © Cambridge University Press & Assessment 2023 4
