Digestive system — Paper 4 · IGCSE Sciences - Co-ordinated (Double) 0654

1 Fig. 1.1 is a diagram of the alimentary canal and associated organs. A J H B C G D E F Fig. 1.1 (a) Use the letters in Fig. 1.1 to identify a site of protease secretion, … site of bile production. … [2] (b) Describe how bile aids digestion. … … … [2] (c) The wall of the small intestine is covered in villi. Explain the importance of the villi that line the small intestine. … … … [2] (d) Crohn’s disease is a long-term disease that causes inflammation and damage to the small intestine. Suggest one long-term effect of Crohn’s disease if it is left untreated. … … [1]

7 marks

Mark scheme: 1(a) B / C / D ; J ; 2 1(b) emulsifies fats ; increases surface area (of fat globules) ; for the action of enzymes ; max 2 1(c) increases surface area ; for absorption ; 2 1(d) malnutrition / weight loss / dehydration / fatigue ; 1

This question in 0654/43 Oct/Nov 2017

7 Fig. 7.1 shows an X-ray of a molar tooth. A B C Fig. 7.1 (a) Identify the parts labelled A, B and C in Fig. 7.1. A … B … C … [3] (b) Consuming sugary food and drinks can increase the risk of tooth decay. Describe, in detail, the process of tooth decay. … … … … … [3] (c) Describe the role of teeth in terms of mechanical digestion. … … [1] (d) Chemical digestion also occurs in the mouth. Describe the role of enzymes in the chemical digestion that occurs in the mouth. … … … … … [3] [Total: 10]

10 marks

Mark scheme: 7(a) A enamel ; B dentine ; C pulp ; 3 7(b) bacteria (and food coat teeth) ; ref to respiration ; acids (produced by bacteria) dissolve enamel and dentine ; 3 7(c) break food into smaller pieces ; 1 7(d) ref to (salivary) amylase ; breaks down starch ; to (simple) sugars ; large insoluble to smaller soluble molecules ; max 3 3

This question in 0654/43 Oct/Nov 2019

4 (a) A person monitored the concentration of glucose in their blood for 12 hours. The results are shown in Fig. 4.1. 10 8 6 concentration of glucose 4 in the blood / mmol per dm3 2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 time / hours Fig. 4.1 (i) The concentration of glucose in the blood increases rapidly after a meal is eaten. Suggest the number of meals the person had during the 12 hours. … [1] (ii) Complete the sentences to explain the results between 2 and 3 hours. The brain detects an increase in the concentration of glucose in the blood. The … releases insulin. The insulin stimulates the … to convert glucose to … and store it. This lowers the concentration of glucose in the blood. [3] (b) Name two hormones that increase blood glucose concentration. 1 … 2 … [2] (c) Name the term used to describe the mechanism that is used to return blood glucose concentrations to a normal level. … [1] (d) Glucose is absorbed in the small intestine. (i) Define the term absorption. … … … [2] (ii) Describe how the small intestine is adapted for efficient absorption. … … … … [2] [Total: 11]

11 marks

Mark scheme: 4(a)(i) 3 ; 1 4(a)(ii) pancreas ; liver ; glycogen ; 3 4(b) adrenaline ; glucagon ; 2 4(c) negative feedback ; 1 4(d)(i) movement of digested food molecules ; across the (wall of the) small intestine / into the blood ; 2 4(d)(ii) presence of villi ; large surface area for absorption ; AVP 2

This question in 0654/42 Feb/March 2021

7 (a) Fig. 7.1 is a diagram of a villus. X Y Z Fig. 7.1 (i) Table 7.1 shows some of the names, functions and letters in Fig. 7.1 of parts of a villus. Complete Table 7.1. Table 7.1 name letter in Fig. 7.1 function absorption of fats epithelial cell contain microvilli transport of nutrients around the body [3] (ii) Describe how villi aid the process of digestion. … … … … [2] (b) Fig. 7.2 is a diagram of the alimentary canal and associated organs. A B C H D G E F Fig. 7.2 (i) Identify the letter on Fig. 7.2 that represents: where egestion occurs … where bile is produced … where dental decay can occur. … [3] (ii) State the name of the type of organism that causes dental decay. … [1] (c) Bile is mixed with gastric juice when they enter the small intestine. Describe the effect of bile on the pH of the gastric juice. … … [1] [Total: 10]

10 marks

Mark scheme: 7(a)(i) name letter in Fig. 3.1 function lacteal X absorption of fats ; epithelial cell Y contain microvilli ; capillary Z transport of nutrients around the body ; 3 7(a)(ii) increases surface area ; for more absorption ; 2 7(b)(i) F ; H ; A ; 3 7(b)(ii) bacteria ; 1 7(c) increases ; 1

This question in 0654/41 Oct/Nov 2021

1 Enzymes have an important role in the process of digestion. (a) Define the term enzyme. … … [2] (b) Fig. 1.1 shows the effect of pH on two different enzymes. AA BB enzyme activity 0 1 2 3 4 5 6 7 8 9 10 11 12 pH Fig. 1.1 (i) State the pH at which enzyme B is most active in Fig. 1.1. … [1] (ii) Explain the results for enzyme B at pH 10 in Fig. 1.1. … … … … … [3] (iii) State where in the alimentary canal enzyme A is most likely to be found. … [1] (iv) Suggest the name of enzyme A. … [1] (c) Once food is digested, nutrients are absorbed across the villi walls. (i) State where villi are found in the alimentary canal. … [1] (ii) State the function of the lacteal in the villi. … [1] [Total: 10]

10 marks

Mark scheme: 1(a) a protein ; (that acts as) a biological catalyst ; 2 1(b)(i) 7.5 ; 1 1(b)(ii) any three from: ref to denaturation ; active site changes shape ; substrate can no longer fit into the, enzyme / active site ; no products released / no breakdown of substances ; 3 1(b)(iii) stomach ; 1 1(b)(iv) protease ; 1 1(c)(i) small intestine ; 1 1(c)(ii) fat absorption ; 1

This question in 0654/42 Oct/Nov 2021

4 (a) A student investigates the effect of bile and lipase on the digestion of fat in milk. Fat is digested into fatty acids and glycerol. The student: • sets up three test-tubes, as shown in Table 4.1 • uses an indicator which turns pink when fatty acid is present • records how long it takes the indicator to turn pink in each test-tube. Table 4.1 test-tube volume of volume of volume of volume of time taken milk bile solution boiled lipase lipase for indicator / cm3 / cm3 solution solution to turn pink / cm3 / cm3 / seconds 1 5 0 0 1 378 2 5 1 1 0 never turns pink 3 5 1 0 1 196 (i) Explain the results for test-tube 2. … … … … … [3] (ii) Calculate the difference in time taken for the indicator to turn pink between test-tubes 1 and 3. … seconds [1] (iii) Explain the difference between the results for test-tube 1 and 3. … … … … … [2] (b) State the name of the organ that produces bile. … [1] (c) After food has been digested, it is absorbed. (i) Explain how villi increase the rate of absorption of digested food. … … [1] (ii) State the part of the alimentary canal where villi are found. … [1] [Total: 9]

9 marks

Mark scheme: 4(a)(i) any three from: enzymes were denatured (due to boiling) ; change in shape of active site ; enzyme is no longer complementary to substrate ; bile alone does not digest fats / fats weren’t broken down into fatty acids and glycerol ; 3 4(a)(ii) 182 (seconds) ; 1 4(a)(iii) any two from: bile, emulsifies the fat ; increases surface area of fat ; so there is faster, breakdown / digestion (by lipase) ; 2 4(b) liver ; 1 4(c)(i) large surface area ; 1 4(c)(ii) small intestine ; 1

This question in 0654/42 Feb/March 2022

1 (a) Fig. 1.1 is a diagram of parts of a tooth. A B C D E F Fig. 1.1 (i) State the letters from Fig. 1.1 that identify two parts that are dissolved by acid during dental decay. … and … [2] (ii) State the letter from Fig. 1.1 that identifies part of the nervous system. … [1] (iii) State the type of organism that causes dental decay. … [1] (iv) State the names of two different types of human teeth. 1 … 2 … [2] (b) Table 1.1 shows some information about deficiency of some of the components in the diet. Complete Table 1.1. Table 1.1 component effect of deficiency in the diet protein causes the disease … … causes the disease scurvy fibre causes … … develop weak bones or rickets [4] (c) One risk factor for coronary heart disease is an unhealthy diet. State two other risk factors for coronary heart disease. 1 … 2 … [2] [Total: 12]

12 marks

Mark scheme: 1(a)(i) A ; B ; 2 1(a)(ii) F ; 1 1(a)(iii) bacteria ; 1 1(a)(iv) any two from: incisor ; canine ; pre-molar ; molar ; 2 1(b) protein kwashiorkor / marasmus ; vitamin C ; scurvy fibre causes constipation ; vitamin D / calcium ; rickets / weak bones 4 1(c) any two from: stress ; smoking ; genetic predisposition ; age ; gender ; AVP ; 2

This question in 0654/43 May/June 2023

7 (a) A scientist measures the activity of the enzyme amylase at different temperatures. Fig. 7.1 shows a graph of the results. 120 100 80 enzyme activity 60 / arbitrary units 40 20 00 10 20 30 40 50 60 70 80 temperature / °C Fig. 7.1 Complete the sentences to describe and explain the results in Fig. 7.1. Amylase breaks down the substrate … into smaller molecules of … . As temperature increases, the activity of amylase increases until it reaches its optimum temperature of … °C. As the temperature increases, the amylase particles gain … energy. This results in more frequent successful collisions between amylase and its substrate. At temperatures above 75 °C, all of the amylase has become … . This means the … of amylase has changed shape and is no longer complementary to the substrate. [6] (b) State two parts of the alimentary canal which secrete amylase. 1 … 2 … [2] (c) Enzymes are proteins. (i) List the chemical elements present in all proteins. … … [2] (ii) State the name of the chemical test for the presence of proteins. … [1] [Total: 11]

11 marks

Mark scheme: 7(a) starch ; 6 simpler sugars ; 25 ; kinetic ; denatured ; active site ; 7(b) any two from: 2 salivary glands ; pancreas ; small intestine ; 7(c)(i) carbon 2 hydrogen oxygen nitrogen ;; four correct = 2 marks two or three correct = 1 mark 7(c)(ii) biuret ; 1

This question in 0654/41 Oct/Nov 2023

7 (a) Fig. 7.1 is a diagram of a villus. X Y Fig. 7.1 (i) State the name of the part labelled Y in Fig. 7.1. … [1] (ii) Describe the function of the part labelled X in Fig. 7.1. … … [1] (iii) State where villi are found in the alimentary canal. … [1] (b) Coeliac disease is a condition which causes the villi to become inflamed and flattened. Explain why coeliac disease may cause weight loss. … … … … [2] (c) Table 7.1 shows some digestive enzymes, their substrates and product(s). Complete Table 7.1. Table 7.1 enzyme substrate product(s) simpler sugars … … protease … … [2] (d) State two parts of the alimentary canal where protease is secreted. 1 … 2 … [2] [Total: 9]

9 marks

Mark scheme: 7(a)(i) capillary ; 1 7(a)(ii) absorption of fats ; 1 7(a)(iii) small intestine ; 1 7(b) smaller surface area (of villi / small intestine) ; 2 (idea of) less nutrients absorbed ; 7(c) 2 enzyme substrate product(s) amylase starch simpler sugars protease protein amino acids ;; four correct = 2 marks two or three correct = 1 mark one correct = 0 marks 7(d) any two from: 2 stomach ; pancreas ; small intestine ;

This question in 0654/42 Oct/Nov 2023

1 Fig. 1.1 is a diagram of the alimentary canal and associated organs in humans. B A H C D G E F Fig. 1.1 (a) State the letter that identifies a part in Fig. 1.1: that contains villi … that produces bile … that produces insulin … where mechanical digestion occurs. … [4] (b) Identify the name of the enzyme secreted by part B in Fig. 1.1 and describe its function. name … function … … … [3] (c) Teeth are involved in the process of digestion. State the names of two different types of teeth. 1 … 2 … [2] (d) Outline the different roles of bile in digestion. … … … … … … … … [4] [Total: 13]

13 marks

Mark scheme: Question Answer Marks 1(a) F ; 4 H ; D ; A and / or C ; 1(b) (salivary) amylase ; 3 breaks down, starch / carbohydrates ; to, (simpler) sugar(s) ; 1(c) any two from: 2 incisor ; canine ; pre-molar ; molar ; 1(d) any four from: 4 neutralises, (stomach) acid / gastric juice ; to provide suitable pH (for enzymes) ; emulsifies fats ; to provide a larger surface area (for chemical digestion) ; to increase the rate of digestion ;

This question in 0654/41 Oct/Nov 2024