AQA Biology GCSE Student Required Practical 4 PDF

B3.3 Student required practical 4 Name..................................................................... Class................. Date..................... Food tests – Aiming for grade 8 Specification references:  Required practical 4: Use qualitative reagents t...

B3.3 Student required practical 4 Name..................................................................... Class................. Date..................... Food tests – Aiming for grade 8 Specification references:  Required practical 4: Use qualitative reagents to test for a range of carbohydrates, lipids, and proteins. To include: Benedict’s test for sugars; iodine test for starch; and Biuret reagent for protein.  B2.2.1 The human digestive system  AT 2 Safe use of a Bunsen burner and a boiling water bath  AT 8 Use of qualitative reagents to identify biological molecules  WS 2.4 Aims In this practical you will test foods to investigate if they contain carbohydrates (simple sugars or starch), lipids (fats), or proteins. Learning outcomes After completing this practical, you should be able to:  write down the methods used to test if a food contains starch, sugars, lipids (fats), or proteins, including descriptions of the positive results  safely carry out each type of food test in an organised manner  design a results table to clearly record results from food tests  suggest what an item of food contains using results from food tests, evaluating the data collected. Safety  Do not eat any of the food  Some people may have food allergies  Wear chemical splash-proof eye protection  Biuret reagent: IRRITANT  Sodium hydroxide: IRRITANT  Ethanol: HIGHLY FLAMMABLE, keep away from naked flames  Iodine solution: HARMFUL, avoid contact with skin  Water in the water bath will be HOT Equipment and materials  a range of small pieces of different foods (e.g., cheese, crisps, pasta, ham, bread, boiled sweets)  test tubes  test-tube rack  spotting tile © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original. 1  B3.3 Student required practical 4 Name..................................................................... Class................. Date.....................  iodine solution  Benedict’s solution  Biuret reagent or dilute sodium hydroxide solution and copper sulfate solution  disposable pipettes  filter paper  water bath or beakers and a supply of hot water  sticky labels or waterproof pen. Setting the scene Food packaging includes nutritional information on the contents of the food. In this practical you will carry out tests to identify some of these nutrients. Method Test for starch: 1 Place a small amount of food on the spotting tile. 2 Add a few drops of iodine solution to the food on the spotting tile. 3 Yellow–red iodine solution turns blue–black if starch is present. 4 Repeat steps 1–3 for other types of food. 5 Record all your results in a results table. Test for sugar: 1 Place a small amount of food in a test tube. 2 Add enough Benedict’s solution to cover the food. 3 Place the test tube in a warm water bath for 10 minutes. 4 Blue Benedict’s solution turns brick red on heating if a sugar such as glucose is present. 5 Repeat steps 1–4 for other types of food. 6 Record all your results in a results table. Test for lipids (fats): 1 Place a small amount of food into a test tube. 2 Add a few drops of ethanol to the test tube. 3 Shake the test tube and leave for one minute. 4 Pour the solution into a test tube of water. 5 Ethanol added to a solution gives a cloudy white layer if a lipid is present. 6 Repeat steps 1–5 for other types of food. 7 Record all your results in a results table. Test for protein: 1 Place a small amount of food in a test tube. 2 Add 1 cm3 of Biuret reagent. Alternatively add 1 cm3 of sodium hydroxide solution and then add a few drops of copper sulfate solution. © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original. 2  B3.3 Student required practical 4 Name..................................................................... Class................. Date..................... 3 Blue Biuret reagent turns purple if protein is present. 4 Repeat steps 1–3 for other types of food. 5 Record all your results in a results table. Results table Design a table to record all your results. Questions 1 Look at your results table. a Which food(s) gave a positive result for protein? (1 mark) b Which food(s) gave a negative result for lipid? (1 mark) c Do the foods that contain sugar also contain starch? Use your results to justify your answer. (1 mark) 2 Complete the table. Food group Colour before Colour change if food Reagent tested for adding to food group is present colourless starch Benedict’s solution purple (4 marks) © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original. 3  B3.3 Student required practical 4 Name..................................................................... Class................. Date..................... 3 Your teacher carried out a risk assessment before you started this practical. Complete the following risk assessment for testing a food for the presence of proteins. Hazard Risk Control test tubes Biuret reagent (2 marks) 4 The more lipids there are in an item of food, the more cloudy the positive result is. Suggest how you could use this information to help you to measure the amount of lipids present in different items of food. (2 marks) Student follow-up 1 A student carried out some food tests. She designed the following results table to show her observations and conclusions. Food Sugar Lipid Protein Starch A  X X  B X X  X C  X X X D X   X E X X X  The table does not fully show observations and conclusions. Describe two ways she could improve the design of the results table. (2 marks) © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original. 4  B3.3 Student required practical 4 Name..................................................................... Class................. Date..................... 2 A student carried out some food tests and presented the results in the following table.   food present X  food not present blank  not tested Is sugar Is lipid Is protein Is starch Food tested present? present? present? present? A  X  B X  X C  X X D   X E X X X  He concludes that food B contains only protein. Evaluate his conclusion. (2 marks) 3 A student uses Benedict’s solution to test different foods for sugar. Each food is tested under the same conditions and the results are presented in the following table. Food tested Final colour of Benedict’s solution A blue B brick-red C green D yellow Suggest an explanation for these results. (2 marks) © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements This resource sheet may have been changed from the original. 5