Biological molecules Banker

1. (a) A student adds biuret solution to a sample of liquid egg white and shakes the tube. What colour shows that protein is present?A blue-blackB brick redC purpleD cloudy white [1]

1. (a) Which food test must be carried out in a hot water bath?A Benedict's test for reducing sugarB biuret test for proteinC ethanol emulsion test for fatD iodine test for starch [1]

1. (a) Name the reagent used to test a food for starch. [1]
2. (b) State the colour of the reagent before the test and the colour seen if starch is present. [2]
3. (c) A potato slice gives a positive result. Suggest why a slice of ripe mango gives only a weak result. [1]

1. (a) Describe how you would test a sample of ground peanuts for fat using the ethanol emulsion test. [3]
2. (b) State why the test tube and sample must be kept away from a Bunsen flame. [1]

1. (a) Name the food substance detected by each of these tests.Test 1: iodine solutionTest 2: Benedict's solutionTest 3: biuret solutionTest 4: ethanol emulsion [4]
2. (b) Which test needs heating? [1]

Four food samples, P, Q, R and S, were tested. Results:P: iodine blue-black; Benedict's blue; biuret purple; emulsion clearQ: iodine orange-brown; Benedict's brick red; biuret blue; emulsion cloudy whiteR: iodine orange-brown; Benedict's blue; biuret blue; emulsion cloudy whiteS: iodine blue-black; Benedict's green; biuret blue; emulsion clear

1. (a) State the substances present in sample P and in sample Q. [2]
2. (b) Which sample could be a mixture of fruit juice and coconut milk? Give a reason. [2]
3. (c) State one variable that should be kept the same when doing each test on the four samples. [1]

1. (a) Name the food test that uses copper(II) sulfate and sodium hydroxide. [1]
2. (b) Name the food test that turns brick red. [1]
3. (c) Give one example of a food that gives a positive ethanol emulsion test. [1]

Benedict's test was done on four samples heated for 4 minutes at 80 °C.Tube 1 (sugarcane juice, diluted): yellowTube 2 (milk): greenTube 3 (apple juice): brick redTube 4 (distilled water): blue

1. (a) State which tube shows the most reducing sugar. [1]
2. (b) State the control tube. [1]
3. (c) Suggest why all tubes were heated for exactly the same time. [1]

1. (a) A crushed sample of a food gave these results.A boiled riceB grape juiceC cooking oilD boiled egg white [1]

1. (a) Describe how to carry out the Benedict's test on a sample of honey dissolved in water. Include the safety precaution you would take. [3]
2. (b) State the colour change seen if a large amount of reducing sugar is present. [1]
3. (c) Explain why a negative result with Benedict's solution does not prove that a food contains no sugar at all. [1]

1. (a) A food technologist in Faisalabad tests a new flavoured milk drink. It gives a purple colour with biuret solution and a green colour with Benedict's solution. State what these results show. [2]
2. (b) Biuret solution can be made by mixing two solutions. Name the two solutions. [2]
3. (c) The technologist also tests plain water in the same way. Explain why. [1]

1. (a) A student says: "Chapati gave a blue-black colour with iodine, so chapati contains only starch." Explain why the student is wrong. [2]
2. (b) Suggest how the student could find out whether the chapati also contains protein. [2]

A student heated 2 cm³ of each of four drinks, A to D, with 2 cm³ Benedict's solution in a water bath at 80 °C. She recorded the time for the first appearance of green.A: 85 sB: 240 sC: 40 sD: 130 s

1. (a) Use the results to put the drinks in order of reducing sugar content, highest first. [1]
2. (b) Explain how the time taken links to the reducing sugar concentration. [1]
3. (c) Calculate a relative rate of colour change for drink A as 1000/time (arbitrary units), giving your answer to 1 decimal place. [1]
4. (d) Suggest one way to make the end point of the test more reliable. [1]

A student crushed 2 g each of lentils (daal), boiled rice, chicken and banana with 10 cm³ water and tested them with biuret solution.lentils: deep purpleboiled rice: very pale lilacchicken: purplebanana: blue

1. (a) Suggest why each crushed sample was mixed with the same volume of water. [1]
2. (b) Which food contained the most protein? Explain how you decided. [2]
3. (c) Describe one hazard in this test and how to reduce it. [1]
4. (d) Suggest an improvement so that the colours could be compared more objectively. [1]

Four unlabelled tubes, W, X, Y and Z, contain glucose solution, starch suspension, albumin (protein) solution and an oil-in-water mixture, in some order.W: iodine orange-brown; Benedict's blue; biuret blueX: iodine orange-brown; Benedict's brick red; biuret blueY: iodine blue-black; Benedict's blue; biuret blueZ: iodine orange-brown; Benedict's blue; biuret purple

1. (a) Identify the solution in each tube. [3]
2. (b) State what tube W must contain, and explain how you can tell from these results. [1]
3. (c) Suggest a further test to confirm that W is the oil-in-water mixture, and state the expected result. [1]

1. (a) A student in Lahore tests milk for fat by shaking it with ethanol and pouring into water. The result is cloudy. Explain why this result might be unreliable unless a control is used. [2]
2. (b) State why fats form a cloudy emulsion in this test. [1]

1. (a) Four glucose solutions of different concentrations were each heated with the same volume of Benedict's solution for 5 minutes. Which final colour shows the highest concentration of glucose?A blueB greenC yellowD brick red [1]

1. (a) A doctor suspects that a patient has diabetes. Explain how a Benedict's test on the patient's urine could support this diagnosis. [2]
2. (b) Suggest why the Benedict's test is not used to measure exact blood glucose concentration in a hospital. [2]

1. (a) A seed is cut in half and one half is crushed with water, then filtered. Explain why the seed must be crushed before testing it for starch and protein. [2]
2. (b) The filtrate gives a blue-black colour with iodine but the solid residue on the filter paper gives an even darker colour. Suggest why. [2]
3. (c) State the result you would expect with Benedict's solution if the seed has just started to germinate, and explain your answer. [2]

A student had a 10 % glucose stock solution and distilled water. She wanted to make 10 cm³ each of 2 %, 4 %, 6 % and 8 % glucose standards to compare with an unknown sample using Benedict's solution.

1. (a) Calculate the volume of the stock solution and of distilled water needed to make 10 cm³ of each standard. Give the volumes for 2 %, 4 % and 6 %. [3]
2. (b) The unknown sample went the same colour as the 4 % standard after the same heating time. State the glucose concentration of the unknown, and suggest how to make the estimate more precise. [2]
3. (c) State two variables that must be kept constant. [2]

Starch solution and amylase were mixed at 35 °C. Every 2 minutes a drop of the mixture was added to a drop of iodine solution on a spotting tile.0 min: blue-black2 min: blue-black4 min: dark brown6 min: orange-brown8 min: orange-brown

1. (a) State the time when all the starch had been digested. [1]
2. (b) Explain why the colour of the iodine changed during the experiment. [2]
3. (c) Describe a test you could do on the mixture at 8 minutes to show a product of the reaction, and state the expected result. [2]
4. (d) Calculate the rate of starch digestion as 1/time in min⁻¹, to 2 decimal places. [1]

1. (a) Plan an investigation to compare the reducing sugar content of three brands of orange juice using Benedict's solution. Include the variables you would control and how you would record results. [6]

1. (a) A solution of the enzyme amylase is tested with biuret solution and with Benedict's solution. Predict both results and explain them. [2]
2. (b) The amylase solution is mixed with starch suspension and left at 37 °C for 15 minutes. Predict the results of the iodine, Benedict's and biuret tests on the mixture. Explain each prediction. [3]

1. (a) Which molecules are joined together to form a protein?A amino acidsB fatty acidsC glucoseD glycerol [1]

1. (a) Name the smaller molecules that make up:(i) starch(ii) fats and oils [3]
2. (b) Name the chemical elements found in all carbohydrates. [1]

1. (a) Name the polysaccharide stored in the liver and muscles of humans. [1]
2. (b) Name the polysaccharide that forms plant cell walls. [1]
3. (c) Starch, glycogen and cellulose are all made of the same smaller molecule. Name it, and state one reason why starch is a good storage molecule. [2]

1. (a) Sucrose is the sugar in sugarcane. Name the two simple sugars that make one sucrose molecule. [2]
2. (b) Maltose is made when starch is digested. State the simple sugar it is made of. [1]
3. (c) State which one of these carbohydrates is insoluble in water: glucose, cellulose, maltose. [1]

1. (a) State one element found in proteins that is not found in carbohydrates or fats. [1]
2. (b) Different enzymes have different shapes even though they are all made of amino acids. Explain why. [2]
3. (c) Explain why a person whose diet lacks protein may not be able to make some enzymes. [1]

1. (a) Which property of water makes it important for transporting substances in blood plasma and phloem?A It is a solvent for many substances.B It contains nitrogen.C It is a source of energy.D It is an enzyme. [1]

1. (a) Explain why water is important as a solvent in living organisms. Give two examples. [3]
2. (b) A student says fats contain the same elements as carbohydrates. State whether this is correct and give one difference in their composition. [1]