G.T. College G10 Term One Biology Form Test 2

Transcription

1 G.T. College G10 Term One Biology Form Test 2 Total marks: 40 marks Time allowed: 35 minutes Date: Name: Class: ( ) Section A: Multiple choice questions (10 marks@ 1 mark each) 1. Given a solution containing starch, amylase and lipase, which of the following tests will give a negative result with this solution? A. iodine test B. Benedict s test C. use of an Albustix paper D. grease spot test 2. Which of the following statements about enzymes is correct? A. The function of boiled enzyme can be restored at lower temperature. B. It can provide an alternative pathway with lower activation energy for reactions. C. All enzymes work best at ph of nearly 7. D. Enzymes are not reusable. 3. Which of the following combinations about the industrial applications of enzymes is incorrect? Application Enzyme used A. meat tenderiser protease B. fruit juice extraction pectinase C. production of lactose free milk amylase D. contact lens cleaner protease

2 4. Some blue green algae can tolerate temperature up to 72ºC because A. their enzymes are not protein in nature. B. the denatured enzymes can be replenished quickly. C. their enzymes are not denatured at high temperatures. D. they can survive with denatured enzymes. 5. A rise in temperature can speed up the rate of an enzyme reaction because at high temperature (1) substrate and enzyme molecules can collide with one another more frequently. (2) the activation energy of the reaction is higher. (3) less enzyme is denatured. A. (1) only B. (1) and (2) C. (1) and (3) D. (2) and (3) Directions: Questions 6 and 7 refer to a biochemical reaction illustrated by the diagram below. 6. Which molecule can be reused at the end of reaction? A. P B. Q C. R D. S

3 7. If molecule S is a lactose molecule, what may be molecules P and R? P R A glucose fructose B. fructose galactose C. glucose galactose D. maltose glucose 8. The graph below shows the activity of an enzyme at different temperatures. Enzyme activity Temperature (ºC) Which of the following the statements can correctly explain the graph? (1) The enzyme is inactive at 0ºC. (2) The enzyme works best at 40ºC. (3) The enzyme is inactive at 60ºC. A. (1) and (2) only B. (1) and (3) only C. (2) and (3) D. (1), (2) and (3)

4 Directions: Questions 9 to 10 refer to the experimental set up below. Sucrase is an enzyme which can digest sucrose and is used in this experiment. 9. glass tube initial liquid level dialysis tubing 10% sucrose solution 0.5% sucrase solution Benedict s test was carried out to test the liquid in the dialysis tubing an hour later. What will you observe in the mixture of Benedict s solution and the liquid? A. A brick red precipitate is formed in the mixture. B. The mixture is blue in colour. C. The mixture is blue black in colour. D. A blue black precipitate is formed in the mixture. 10. Which of the following is the correct explanation for the observation in Q.9? A. Sucrose molecules are too large to pass through the dialysis tubing. B. Sucrose solution is broken down into reducing sugars when it is heated during Benedict s test. C. Sucrose is a non reducing sugar. D. Reducing sugar is formed as a result of the action of sucrase on sucrose.

5 Section B: Short questions (20 marks) 1. An experiment was carried out to investigate the effect of ph on the rate of reaction of a digestive enzyme. The results are shown in the table below. ph Reaction rate (arbitrary units) (a) Suggest in which part of the human digestive system this enzyme would be found. (1 mark) (b) The experiment was repeated with ph 2 but the enzyme was boiled before use. Suggest how the results will be different and explain why. (2 marks) (c) The experiment was repeated with ph 2 and in a medium of high mercury ion level. Suggest how the results will be different and explain why. (2 marks) 2. (a) State three properties of enzymes. (3 marks) (b) Enzymes are widely used in food industry. Give one examples and briefly explain them. (2 marks)

6 3. Lactase is an enzyme that can digest lactose into simple sugars. An experiment was carried out to investigate the effect of temperature on the activity of lactase. Dialysis tubings were filled with equal volumes of lactose and lactase solution. The tubings were then immersed in water baths of different temperatures. lactose + lactase distilled water Temperature (ºC) Reaction rate (arbitrary units) (a) Name the simple sugars formed from the digestion of lactase. (1 mark) (b) According to the results, describe and explain the effect of temperature on lactase activity. (4 marks) 4. Fill in the blanks to complete the following paragraph. (5 marks) At low temperatures, most enzymes are usually (a). As the temperature rises, more (b) is supplied to the substrate and enzyme molecules, causing them to move faster. They collide with one another more often, an (c) will be more likely to be formed. The reaction rate is the highest at the (d)_ temperature. If the temperature further increases, the shape of enzyme molecules start to change, the enzymes are said to be (e)_.

7 Section C: Structured questions (10 marks) 1. The table below shows the contents in five test tubes in an experiment which demonstrates the digestive action of lipase. Test tubes Test tube contents A B C D E Whole fat milk (cm 3 ) Sodium hydrogencarbonate solution (cm 3 ) Bile salt solution (cm 3 ) Lipase solution (cm 3 ) (boiled) Distilled water (cm 3 ) After one hour, ph paper was used to test the ph of the solutions of the five test tubes. It was found that only solutions in test tubes C and D were acidic. (a) Which substance present in the milk is the substrate of the reaction catalyzed by lipase? (1 mark) (b) What is the purpose of adding sodium hydrogencarbonate solution to each test tube? (1 mark) (c) State the final product of the reaction which made the solution in test tubes C and D acidic. (1 mark) (d) Is bile salt an enzyme? Explain your answer. (2 marks) (e.) Compare the acidity of the solutions in test tubes C and D. Explain briefly. (3 marks) (f.) Explain the results of test tube E. (2 marks)

8 G.T. College G10 Term One Biology Form Test 2 Marking scheme Section A: Multiple choice questions (10 marks@ 1 mark each) No Ans D B C C A B C A B A Section B: Short questions (11 marks) 1 (a) Stomach (b) There will be no reaction. This is because high temperature will cause the denaturation of the enzyme. (c) The reaction rate decreases. This is because mercury is an enzyme inhibitor. (5 marks) 2 (a) Any three of the following: (1 mark each) (3m) Enzymes can speed up chemical reactions. Enzymes are proteins. Enzymes are reusable. Enzymes are specific in action. Some enzyme reactions are reversible. (b) Any one set of the following examples or other reasonable answers: (Each example 1 mark, each explanation 1 mark) (2m) Examples Explanation Meat tenderisers Meat tenderisers contain proteases which soften meat by breaking down the proteins. Fruit juice extraction Pectinases are used to break down the fruit cell wall and release the juice. Baby food Enzymes are added to break down complex food molecules into simpler form for direct absorption by babies. (5 marks)

9 3 (a) glucose and galactose (b)between 4ºC and 38ºC, the rate of enzymatic reaction increases with temperature because the substrate and enzyme molecules have more kinetic energy at higher temperature and the chance of enzyme substrate complex formation is increased. From 38ºC to 100ºC, the rate of enzymatic reaction decreases to 0 because enzyme denatures at high temperature. (5 marks) 4. (a) inactive (b)kinetic energy (c) enzyme substrate complex (d) optimum (e) denatured (5 marks) Section C: Structured questions (10 marks) (a) fat / lipid (b) To provide a slightly alkaline condition for the lipase to work. (c) fatty acids (d) No, bile salt is not an enzyme. It will not be denatured after boiling. (e) Solution in test tube D is more acidic than that in test tube C, because the bile salts in D emulsified the fat (broke down the fat into smaller droplets) and increased the surface area for the action of lipase. With a larger surface area, the rate of breakdown reaction was faster in D and more fatty acids were formed. (f)the shape of the active site of the lipase was altered after boiling. The substrate could not fit into the active site to form the products and the lipid breakdown reaction is inhibited. (10 marks)