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Key Stage 4 Digestion © Boardworks Ltd 2003 Teacher’s Notes A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000). Notes Page View Normal View Flash Files A flash file has been embedded into the PowerPoint slide wherever this icon is displayed – These files are not editable. © Boardworks Ltd 2003 The 7 food groups represent large chemicals. These chemicals are often chains of smaller, more useful chemicals, joined together. One example is Carbohydrates. Carbohydrates are made of long chains of identical small sugar molecules. Carbohydrate Sugar molecule © Boardworks Ltd 2003 The small sugar molecules are very useful. The body can use them to make… ENERGY So the body has to break these large food molecules up into smaller pieces. However! © Boardworks Ltd 2003 Problem One It is not enough to cut these foods up into pieces using a knife. This would not release the sugars. i.e. cutting a loaf of bread (carbohydrate) into slices does not produce sugar. This is because we can’t release sugars from carbohydrates by physically breaking them up. © Boardworks Ltd 2003 The chain of sugars is held together by… Chemical bonds. Chemical bonds require a chemical technique if they are to be broken. © Boardworks Ltd 2003 Problem 2 The food we start with is often large in size. Being large, the food tends to be unable to dissolve. We say it is large and insoluble. This is a real problem. The food needs to be soluble so that it can dissolve in the blood and thus, be transported around the body. The smaller the food, the more likely they will dissolve. So the digestive system has to cope with both these problems. © Boardworks Ltd 2003 Remember…. The digestive system, being an organ system, is made of a group of organs all working together. i.e. Each organ has a particular function but together they get the job done. The only visible parts of the digestive system are the entry and exit points Mouth Anus © Boardworks Ltd 2003 Food looks very different when it leaves, compared to when it enters! Therefore the body must be doing something to the food during its journey. It is digested. This means it is broken down. However, breaking something up happens in 2 ways. As we know all food has a physical shape and is made of chemicals. These chemicals are held together by chemical bonds. © Boardworks Ltd 2003 It must be broken down using physical and chemical methods. physical This allows it to pass through the small diameter of the digestive system. To be broken down physically, the shape of the food must be changed. chemical This allows useful chemicals to be released and dissolve in the blood. To be broken down chemically, the bonds must be broken. © Boardworks Ltd 2003 Our digestive system uses both these methods of digestion. Chemical Digestion Physical Digestion As we move through the digestive system, we will see one or both of these methods in action at any one time. So, in summary so far… © Boardworks Ltd 2003 Digestion is the chemical and physical breakdown of large insoluble molecules into small soluble molecules. Let’s take a close look at how this happens… Open wide! © Boardworks Ltd 2003 All food enters our digestive system through the mouth and waste material leaves through the anus. Mouth If we stretch the digestive system out, we can see that it is really one long tube with an opening at each end. However, it is a 9m tube! Anus © Boardworks Ltd 2003 But how does a 9m tube fit into a space, which is less than a metre long? It is extremely folded ! In addition, the tube passes through organs on its route from the mouth to the anus. © Boardworks Ltd 2003 The Digestive system © Boardworks Ltd 2003 As food moves through the system, it passes through these organs. Each organ has a slightly different effect on the food. Let’s start in the mouth. © Boardworks Ltd 2003 The mouth is where digestion begins. It is therefore where we first meet chemical and physical methods of digestion. We will consider physical digestion first. If you look in the mirror and smile, you immediately notice your teeth. You will also realise that your teeth are different shapes. You have 4 basic types of teeth. © Boardworks Ltd 2003 Each is designed to do a different job. Premolar Molar Canine Central Incisor Incisor Latent Incisor Canine 1st Premolar 2nd Premolar 1st Molar 2nd Molar 3rd Molar © Boardworks Ltd 2003 © Boardworks Ltd 2003 The shape and size of each tooth is related to the function they have in digesting (breaking down) food. If we look at the teeth of other living organisms they too have these 4 types of teeth. However, the size and shape maybe different. This is because other organisms may have a different diet. © Boardworks Ltd 2003 Canine Sharp pointed teeth, which are used to bite and tear food. Incisors Small rectangular shaped teeth, which are found between the canines. They are used for cutting food. Premolars Found behind the canines and are used to grind soft food. Molars Found behind the premolars and are used to grind hard food. © Boardworks Ltd 2003 Together, these teeth deal with most foods that we put into our mouths. Although they break the food up, they do not effect the chemical bonds. Therefore, they are physically digesting the food. Once the teeth have digested the food, it may be small enough to be swallowed. However, some food can be sharp and it would be uncomfortable to swallow. The food also needs chemically breaking down. Therefore, the mouth produces a substance that solves both of these problems at the same time. © Boardworks Ltd 2003 These glands (a special type of tissue) produce saliva, a sticky liquid. As mentioned, the saliva has two jobs. Being a liquid, it softens the food and allows the digested food to be rolled into a ball just before it is swallowed. It also contains a chemical known as an enzyme. © Boardworks Ltd 2003 What is an enzyme? Enzymes are chemicals, which act to speed up chemical reactions. They are produced from glandular tissue, which is found all over the body. In order to understand how an enzyme works, you have to think of it as having a particular shape. We will use the shape below to represent on particular enzyme. © Boardworks Ltd 2003 Somewhere on the surface of the enzyme is an important region known as the active site. Enzyme In order for an enzyme to be able to speed up a reaction, it must attach to the chemicals that are reacting. It does so using its active site. © Boardworks Ltd 2003 + The red area on these two reacting chemicals represents the area where the active site of the enzyme will attach. The enzyme will attach to both at the same time. Enzymes are very specific Enzymes can only speed up certain reactions. If the shape of the reacting chemicals does not match the shape of the active site, the enzyme will not be able to work. © Boardworks Ltd 2003 Therefore, enzymes are specific to certain reactions. As well as being specific to certain reactions, enzymes are very particular about the environment that they work in. To understand this, think of how you do homework. You probably have a certain place to work, or you work at a certain time, you may like listening to music whilst you work or else you can only work if it is completely silent. Well, different enzymes work best in different conditions. If the condition is wrong, their active site can change shape. One particular enzyme works best in acidic conditions (pH less than 7). If the pH rises and the conditions become alkaline, the enzyme changes shape and stops working. It can no longer fit with the reacting particles of the chemical reaction. © Boardworks Ltd 2003 pH 10 Which enzymes are made by the digestive system? The bulk of the food that enters the digestive system is from the three main food groups: Proteins Carbohydrates Fats © Boardworks Ltd 2003 Therefore, it is not surprising that the digestive system has glands that produce enzymes that digest these three types of food. Remember that the shape of the chemicals within the different food groups will be different. Therefore the shape of the enzymes that digest these chemicals will also be different. This means that an enzyme that digests fats will not be able to digest proteins. Let us look at the chemical structure of Fats, proteins and carbohydrates to see why they require different enzymes for their digestion. © Boardworks Ltd 2003 Carbohydrates As we mentioned previously, carbohydrates are chains of identical sugar molecules. The enzyme that digests carbohydrates must be able to break the chemical bonds between the individual sugar molecules. Sites of enzyme attack Sugar The product of the chemical breakdown of carbohydrates is sugar. The sugar is known as Glucose. An enzyme that digests carbohydrates is known as a Carbohydrase. © Boardworks Ltd 2003 The digestion of carbohydrates can be represented by the following equation. Carbohydrase Carbohydrates Sugars © Boardworks Ltd 2003 Proteins As with carbohydrates, proteins are made of chains of chemicals. However, instead of the chain containing identical molecules, in protein these molecules are different. Protein is made up of chains of amino acids. There are over 20 different kinds of amino acid. © Boardworks Ltd 2003 Imagine a bead necklace made up of over 20 different kinds of bead. Amino Acids Site of enzyme attack The enzymes that digest proteins must be able to break the chemical bonds between the different amino acids. An enzyme that digests protein is known as a Protease. © Boardworks Ltd 2003 The digestion of proteins can be represented by the following equation. Protease Protein Amino Acids © Boardworks Ltd 2003 Fats Fats are made up of a molecule of glycerol phosphate attached to three fatty acid molecules. The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids. Fats are also known as Lipids. Its structure can be represented using the following diagram. Fatty Acids Site of enzyme attack Glycerol Phosphate © Boardworks Ltd 2003 The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids. Fats are also known as Lipids. An Enzyme that digests fat (lipid) is known as a Lipase The digestion of fats can be represented by the following equation. Lipase Fat Fatty Acids +Glycerol Phosphate © Boardworks Ltd 2003 Of these three enzymes, the only one that is released within the mouth is Carbohydrase. This is partly because the conditions within the mouth are suitable for Carbohydrase action. It works best within an alkaline (pH > 7) environment. Let’s represent the three food groups using colours. Carbohydrates Fats Proteins © Boardworks Ltd 2003 The digestive action of the mouth can be summarised in the following diagram. Physical Digestion Chemical Digestion The food could now pass down either the Trachea (windpipe) or the Gullet/Oesophagus. Sugars Chemically and physically digested Physically digested © Boardworks Ltd 2003 Swallowing and Peristalsis © Boardworks Ltd 2003 Swallowing Notes The semi-digested food has been formed into a ball by the tongue and is now swallowed. The ball firstly moves to the pharynx, the region at the back of the mouth where there is a junction between two pipes. It needs to pass down through the Gullet. To ensure that it does not fall into the trachea and thus block our breathing, a small flap moves to cover the tube. © Boardworks Ltd 2003 Swallowing Notes The flap is known as the Epiglottis. If ever food accidentally got into the trachea, we would choke and try to cough it back out. How do we swallow? Once the ball of food has passed through the top of the gullet, it is forced downwards by muscle contraction. © Boardworks Ltd 2003 The swallowing process finishes with a muscle known as a sphincter relaxing and the food passes into the stomach. The sphincter muscle found at the entry and exits points of the stomach acts rather like a drawstring on a bag. It allows the stomach to shut off both entry and exit points and hold food inside it. © Boardworks Ltd 2003 The Stomach The stomach is basically a muscular bag, filled with Hydrochloric Acid (HCl). cross section of stomach food enters from the gullet muscle tissue glandular tissue makes: Hydrochloric Acid, Mucus and Protease enzyme digested food leaves liquids mix with the food © Boardworks Ltd 2003 When the food enters the stomach. The sphincter contracts behind it. The food is then subjected to a coordinated attack. Firstly the the hydrochloric acid …attacks any microbes (bacteria) that may have been swallowed accidentally when the food was eaten. © Boardworks Ltd 2003 Secondly, the hydrochloric acid provides the perfect conditions for Protease Enzyme …to work in. These enzymes begin digesting the proteins in the swallowed food. These proteins are broken down to release the amino acids. Protein Protease © Boardworks Ltd 2003 Protease enzymes work best under acidic conditions (pH < 7) Amino Acids Thirdly, the muscular tissue of the stomach has the ability to contract and relax and in doing so, physically grinds the food inside it. The mucus is produced to protect the lining of the stomach from the acid. If the mucus were not present, the hydrochloric acid could actually digest the tissue that had made it. © Boardworks Ltd 2003 Presence of HCl Wall of stomach is protected Muscle and Glandular tissue Layer of Mucus The hydrochloric acid, mucus, food and enzyme solution is given the name, Gastric Juice. © Boardworks Ltd 2003 A summary of the digestive action of the stomach can be represented in the diagram below. Protein Sugar Fat Carbohydrate Physical Digestion Chemical Digestion Muscular tissue of stomach Protease enzyme and Hydrochloric Acid Sugars Carbohydrates Fats Amino Acids Proteins © Boardworks Ltd 2003 It is clear that the large insoluble foods are slowly being digested to produce the small soluble foods. Carbohydrates Amino Acids Proteins It is also clear that the Fat has yet to be chemically digested. This happens in the next section of the digestive system. © Boardworks Ltd 2003 The Small Intestine The name of this organ is deceiving. Although it is called small, it can stretch up to 6 metres in length. In order to fit into the body, it is heavily folded. When the gastric juices leave the stomach, they pass into the small intestine. small intestine © Boardworks Ltd 2003 Problem! The gastric juices are acidic! There could be a danger of the lining of the small intestine being digested. Luckily two substances are produced to stop this happening. The first is mucus and we have seen how this works. The second is Bile. Bile is made in the Liver. It is a yellow/green liquid that is naturally alkaline (pH > 7). © Boardworks Ltd 2003 This means that when Bile and the Gastric Juices meet, …the result is neutralisation of the acid. pH >7 + pH <7 Neutralisation This is essential for the lipase (the enzyme that digests fat) to function properly. © Boardworks Ltd 2003 Part of the Small Intestine © Boardworks Ltd 2003 Let’s consider the process of fat digestion. This section of the digestive system exemplifies the true idea of an organ system as a group of organs working together for a common function. The influential organs in the digestion of fat are the: Liver Gall bladder, Pancreas Small intestine. Each organ plays its part in turning Fat into fatty acids and glycerol phosphates © Boardworks Ltd 2003 Liver produces Bile Fat within the gastric juice It is released from the Gall bladder and passes down through the bile duct The Bile and the fat meet within the small intestine. The Bile emulsifies the fat. This basically means the fat is physically broken into smaller pieces. Emulsification Notice that the fat has not been chemically digested, only physically. The result is a greater surface area over which the enzyme, lipase, can attack the fat. © Boardworks Ltd 2003 small intestine The pancreas and the small intestine now release enzymes. Both organs produce all three enzymes, Carbohydrase, protease and lipase. pancreas If we just consider fat, the lipase begins to break its chemical bonds. © Boardworks Ltd 2003 Lipase Glycerol Phosphate Fat Fatty Acids © Boardworks Ltd 2003 In summary the digestive action of the small intestine and associated organs can be represented in the following diagram. Fat Sugar Carbohydrates Amino Acids Physical Digestion Bile emulsifies the fat. Muscular action of the small intestine Protein Chemical Digestion Lipase enzyme Protease enzyme Carbohydrase enzyme Sugar Amino Acids Fatty Acids Glycerol Phosphate © Boardworks Ltd 2003 We have now digested all the large insoluble foods into small soluble foods. The three processes of chemical digestion can be summarised as follows. Large insoluble food Enzyme Small soluble food. Carbohydrates carbohydrase Sugars Proteins protease Amino acids Fats lipase Glycerol phosphates and fatty acids. © Boardworks Ltd 2003 There is a further advantage for the small intestine in being a narrow tube. With the enzymes being produced in the lining of the tube, it is essential that the food be forced to mix with them to ensure that there is efficient digestion before the food passes through the organ. If the tube is tight, the food is forced against the sides of the tube and thus, mixes directly with the enzymes. Enzymes come into contact with food. © Boardworks Ltd 2003 Now that the large insoluble molecules have been digested down into the small soluble molecules, the body must separate them from the waste food that has not been digested. No food is 100% useful and so there will always be some waste that needs excreting. In order to understand how the body carry’s out this selection procedure, we need to take a closer look at the lining of the small intestine. At first glance, it appears to have a flat surface. However, if we consider what it has to do, we will understand why this idea cannot be correct. © Boardworks Ltd 2003 The small intestine is the site of absorption of useful molecules of digested food. These molecules must pass across the lining of the small intestine and enter the blood stream. Their destinations are the cells of the body. The cells constantly need these chemicals and therefore the absorption process must be very efficient to keep up with demand. Energy Therefore….. © Boardworks Ltd 2003 If the absorption process had to occur across a normal lining, it would not be able to satisfy the demand of the body for these soluble food molecules. i.e. not enough molecules would pass across the lining in the desired time. The only way to improve this situation would be to create a larger surface area over which absorption could occur. That is exactly what is present in the small intestine What looks like a normal lining, is in fact a highly folded lining, which creates an enormous surface area in a small space. © Boardworks Ltd 2003 © Boardworks Ltd 2003 The result of this folding means that the surface area of the lining of the small intestine is enormous! This increases the number of places where small soluble food molecules can pass across and move into the blood. © Boardworks Ltd 2003 Where is the blood? The blood is found in minute small vessels known as capillaries. The capillaries are found protruding into the villi. The blood approaches the villus, picks up the absorbed food molecules and then leaves. © Boardworks Ltd 2003 Remember that the small intestine lining is made up of thousands of villi. Here is a summary of the process of absorption. A B Sugars S O R Amino Acids P T Fatty Acids and Glycerol Phosphates B L O O D I O N Any indigestible food will leave the small intestine without having been absorbed © Boardworks Ltd 2003 Let us now move on to the next organ in the system, the large intestine (colon). As the food enters this organ, all that is left is waste material and water. The body will want to leave the waste material within the digestive system but the water is valuable. © Boardworks Ltd 2003 This water will need to be retained by the body in order to prevent dehydration. Remember that all the liquids you drink provide the largest source of water for the body. All this fluid passes through the digestive system. Again, this is the job of the blood. The blood reabsorbs the excess water that is mixed with the waste food. Again, if something is going to be absorbed, it must have somewhere to go. © Boardworks Ltd 2003 Again, this is the job of the blood. The blood reabsorbs the excess water that is mixed with the waste food. LARGE B L O O D INTESTINE © Boardworks Ltd 2003 Once the excess water has been reabsorbed, the waste material then passes into a storage organ called the rectum. This waste material mainly consists of indigestible food. It makes up the bulk of the faeces (solid excrement) that will be excreted. rectum It is stored here until the body is ready to excrete. In order for this to happen, another sphincter muscle must relax. This opens the anus and the faeces can pass out of the system. © Boardworks Ltd 2003 We have now finished our journey through the digestive system. We have seen the chemical and physical digestion of large insoluble into small soluble food. It is important to remember that the digestive system relies heavily on the presence of two important types of body tissue. 1. Glandular Tissue This is responsible for the production of the digestive enzymes. 2. Muscular Tissue Through constant contraction and relaxation, the food is kept moving through the system, from the mouth to the anus. © Boardworks Ltd 2003 Digestion Activity one Chew it all over Copy and complete the following statements which summarise the topic of digestion. In each case, choose which of the two words is correct. Digestion is the process of breaking LARGE / SMALL molecules of food into LARGE / SMALL molecules of food. The LARGE / SMALL molecules we start with are INSOLUBLE / SOLUBLE which means they CAN / CAN’T dissolve in water. The LARGE / SMALL molecules produced by digestion are INSOLUBLE / SOLUBLE which means they CAN / CAN’T dissolve in water. These molecules need to be SMALL / LARGE and INSOLUBLE / SOLUBLE so that they can pass through the lining of the LARGE / SMALL intestine and into the WATER / BLOOD. © Boardworks Ltd 2003 Activity two Fill in the gaps in the text below. two “Digestion involves ___________ types of process. These mechanical digestion and secondly _________ chemical are firstly ____________ carried digestion. Chemical digestion is __________ out by enzymes which are chemical produced from ___________ glandular tissue. Specific enzymes break down ___________ specific types of food. For example ____________ carbohydrase __________ enzyme breaks down carbohydrates ___________ . Mechanical digestion muscle involves teeth and the tongue but mostly ____________ contraction e.g. the squeezing of the muscular lining of the stomach __________.” enzymes muscle carbohydrates chemical mechanical glandular specific two carried stomach carbohydrase © Boardworks Ltd 2003 Activity three Help! Use the words below to create 3 equations to show what happens when we digest: 1. Carbohydrates 2. Fats 3. Protein. Carbohydrates Fats Amino acids Double Sugar Lipase Single Sugar Glycerol Phosphate Glucose 3 Fatty Acids Maltose Protein Protease Carbohydrase © Boardworks Ltd 2003 Activity four True or False? Work your way along the route, answering each statement with simply ‘true’ or ‘false’. There are 15 questions. Saliva contain enzymes? Blood transports the nutrients to the needy parts of the body Digestion turns large insoluble molecules into small soluble molecules All food is digested by the body Nutrients are absorbed by blood in the pharynx Blood flows along the digestive system picking up nutrients The food we eat can pass through the digestive system in 1hr © Boardworks Ltd 2003 The small and large intestine basically perform the same function, just at different speeds Solid food must be turned to liquid before it can be absorbed Food is broken down by chemical process only? Water is mainly reabsorbed in the small intestine. The small intestine is shorter than the large intestine Starch and sugar are examples of carbohydrates The presence of villi increases the surface area of the small intestine Lipase enzyme works best in acidic conditions © Boardworks Ltd 2003 Activity five Down the Hatch! Questions * * • What type of acid is found in the stomach? (12) • The ___________ (10) links the stomach to the pharynx. • The __________ (7) juices are found within the stomach. • What happens to the water in the large intestine? (10) • Where does the process of digestion actually begin? (5) • This organ stores waste material before it is discharged from the body? (6) • The _________ (6) moves the food around in the mouth, preparing it for its journey. © Boardworks Ltd 2003 * * * * • ___________ (5) transports the dissolved nutrients around the body. • The first section of the digestive system is known as the l________. (5) • The chemicals that help to break down food are collectively called __________. (7) • We eat or ________ food. (6) • This is the name for the soft fleshy part of the throat that stops food going down the trachea. E___________. (10) • At the rear of the mouth, this region receives the bolus of food from the tongue. (7) • The main part of the small intestine is known as the D____________. (8) © Boardworks Ltd 2003 * * * • These provide the mechanical breakdown of food in the mouth? (5) • This organ can be SMALL or LARGE? (9) • The collective name for the useful chemicals that are absorbed across the lining of the small intestine? (9) • The product of the previous question? (5) • The name for the muscular bag that contains acid? (7) • Food is __________ (7) down in the digestive system using both chemical and mechanical methods. Now for the bonus 5 points © Boardworks Ltd 2003 Activity six You will notice that 9 of the questions have a small green asterisk beside them. Take the first letter of each of the answers to these questions. Put these letters in the box below. Now rearrange them to find the mystery word! © Boardworks Ltd 2003 Word Search H Y D R O C H L O R I C S O P V L M T M H G F Z B A U R S B C U N G S U M H O G G O E T T N R U D K Y T I V A C L A R O D W T I S I L C H S F I B P N G B R O K E N P E T B N S G G B J I S U L O B Y R Q T O C U L X E M C S A H R I L E R N E O B N B E L T Z R C H S B J N O A T O K E Y O S D P T E U H D U O D E N U M M I D I D L V Z C N T U Z I Q T A M N J O M V P H A R Y N X E G C E T N I U Y V O F M G J S Q X H Y Z A M T N H K E E W F W I X P J Q R D S G O S S F B G N J X P K E P I G L O T T I S Q O L P R © Boardworks Ltd 2003 Multiple choice questions © Boardworks Ltd 2003 1. Which type of tissue helps to move food along the digestive system? A liver tissue B muscle tissue C glandular tissue D brain tissue © Boardworks Ltd 2003 2. Which type of tissue makes digestive enzymes? A liver tissue B muscle tissue C glandular tissue D brain tissue © Boardworks Ltd 2003 3. Which of the following are examples of carbohydrates? A amino acids, glycerol B starch, fatty acids C sugar, amino acids D starch, sugar © Boardworks Ltd 2003 4. What is/are the breakdown product/s of starch? A fatty acids B amino acids C glycerol D sugars © Boardworks Ltd 2003 5. What is/are the breakdown product/s of proteins? A fatty acids B amino acids C glycerol D sugars © Boardworks Ltd 2003 6. What is/are the breakdown product/s of fat? A fatty acids and glycerol B amino acids C glycerol D sugars © Boardworks Ltd 2003 7. Which of the following are examples of large, insoluble molecules? A protein, amino acids, starch, glycerol B starch, fats, proteins C fatty acids, glycerol, glucose, amino acids D fats, amino acids, starch, glycerol © Boardworks Ltd 2003 8. Which of the following are examples of small soluble molecules? A protein, amino acids, starch, glycerol B starch, fats, proteins C fatty acids, glycerol, glucose, amino acids D fats, amino acids, starch, glycerol © Boardworks Ltd 2003 9. Which of the following are examples of molecules that can be absorbed across the lining of the small intestine and into the blood? A fatty acids, glycerol, glucose, amino acids B starch, fats, carbohydrates, proteins C protein, amino acids, starch, glycerol D fats, amino acids, starch, glycerol © Boardworks Ltd 2003 10. Water is absorbed across the wall of this structure. A liver B large intestine C oesophagus D pancreas © Boardworks Ltd 2003 11. What is digestion? A The breakdown of large molecules into small molecules. B The building up of large molecules from small molecules. C The absorption of large molecules across the lining of the small intestine. D The removal of waste products from food. © Boardworks Ltd 2003 12. What is absorption? A The movement of large molecules from the small intestine into the circulatory system. B The movement of small molecules from the large intestine into the circulation. C The movement of small molecules from the circulation into the small intestine. D The movement of small molecules from the small intestine into the circulation. © Boardworks Ltd 2003 13. A carbohydrase is an enzyme that speeds up the breakdown of A vitamins. B fats. C carbohydrates. D proteins. © Boardworks Ltd 2003 14. A lipase is an enzyme that speeds up the breakdown of A vitamins. B fats. C carbohydrates. D proteins. © Boardworks Ltd 2003 15. A protease is an enzyme that speeds up the breakdown of A vitamins. B fats. C carbohydrates. D proteins. © Boardworks Ltd 2003 16. Where are carbohydrases produced? A stomach, pancreas and small intestine B salivary glands, pancreas and small intestine C pancreas and small intestine D salivary glands and small intestine © Boardworks Ltd 2003 17. Where are lipases made? A stomach, pancreas and small intestine B salivary glands, pancreas and small intestine C pancreas and small intestine D salivary glands and small intestine © Boardworks Ltd 2003 18. Where are proteases made? A stomach, pancreas and small intestine B salivary glands, pancreas and small intestine C pancreas and small intestine D salivary glands and small intestine © Boardworks Ltd 2003 19. Which of the following conditions best suits the action of the protease enzymes in the stomach? A alkaline B neutral C acidic D doesn’t matter © Boardworks Ltd 2003 20. What is the name of the acid that is found in the stomach? A citric acid B sulphuric acid C nitric acid D hydrochloric acid © Boardworks Ltd 2003 21. Which of these is a function of the acid found in the stomach? A speed up the reproduction of bacteria B neutralise the food entering the stomach C kill bacteria D make the food entering the stomach more alkaline © Boardworks Ltd 2003 22. What is the name of the alkaline fluid that is produced by the liver and stored within the gall bladder? This liquid will then be released into the small intestine. A urea B bile C lipase D hydrochloric acid © Boardworks Ltd 2003 23. What does the bile do to the acidity of the food arriving from the stomach? A breaks it down B nothing C neutralises it D makes it alkaline © Boardworks Ltd 2003 24. Bile also causes the emulsification of fats. What does this mean? A This is the break-up of a large fat droplet into many smaller fat droplets. B This is the change in colour of food when it comes into contact with bile. C This is the joining together of fat droplets to make a chain. D This is the breakdown of fats into fatty acids and glycerol. © Boardworks Ltd 2003 25. Why is the emulsification of fats useful? A It reduces the surface are of the fats so lipases work more effectively. B It increases the surface area of fats so that lipases work less effectively. C It increases the surface are of fats so that lipases work more effectively. D It reduces the surface area of fats so that lipases work less effectively. © Boardworks Ltd 2003 26. Enzymes in the digestive system “speed up” the digestion of food. The scientific word for “speeding up” such chemical reactions is A acceleration B catalysis C absorption D neutralisation © Boardworks Ltd 2003 27. The scientific name for the material that leaves the digestive system via the anus is… A urine. B fibre. C faeces. D solids. © Boardworks Ltd 2003 28. Which of the following foods are examples of carbohydrates? A meat, pulses, cereals and eggs B milk, butter, margarine, eggs C cereals, fruits and vegetables D meat, fruits and milk © Boardworks Ltd 2003 29. Which of the following foods would be useful if you wanted to make cell membranes? A fish, eggs and pulses B cheese, butter and margarine C vegetables, cereals and cheese D eggs, cereals and fruits © Boardworks Ltd 2003 30. If a piece of food was passing through your digestive system, which of these is the correct order of organs that it would pass through? A mouth, gullet, pancreas, small intestine, large intestine, anus B mouth, gullet, stomach, large intestine, small intestine, anus C mouth, gullet, stomach, pancreas, large intestine, anus, rectum D mouth, gullet, stomach, small intestine, large intestine, rectum, anus © Boardworks Ltd 2003