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Enzymes and the digestive system 2.1 Enzymes and digestion 22/05/2017 1 Settler Activity: Can you find today's 16 key words? O L E S A R D Y H O B R A C E E E N I T S E T N I L L A M S S T N O I T S E G E Q U A R A O A S S I X B T A E M Y Z N E P F N A K T B F Z D U N T S T H N U E H C A M O T S S F L O A G E R S D I L A Y F S E I R G A E C E B D P I O K N B P P U I V N R E C T U M N U R A E S D N A L G Y R A V I L A S T N H O P H Y D R O L A S E E N E W E C B H Y D R O L Y S I S T E N I T S E T N I E G R A L A A B S O R P T I O N I O N T 22/05/2017 2 Learning Objectives All students should be able to: • Define digestion. • Give the structure and function of the major parts of the digestive system. • Understand how the digestive system breaks down food both physically and chemically. • Understand the role of villi and microvilli. • Outline the role of enzymes in digestion. Specification reference: 3.1.2 22/05/2017 3 Success Criteria • I can rearrange fragments of a sentence to give the correct definition of digestion. • I can label the digestive system. • I can name the structures of the digestive system when given their function and vice versa. • I can draw a labelled diagram of the lining of the small intestine and answer questions related to its key features. • I can answer exam questions on digestion and digestive enzymes. 22/05/2017 4 Starter Activity: Can you rearrange these fragments of a sentence to give the correct definition of digestion? hydrolysed by Digestion Digestion is the process in which large and assimilated. molecules are hydrolysed by enzymes molecules which molecules are into small molecules which can be enzymes which large absorbed and assimilated. can be into small 22/05/2017 absorbed is the process in 5 Activity 1: The human digestive system • The human digestive system is made up of a long muscular tube and its associated glands. • The glands produce enzymes that break down large molecules into small ones ready for absorption. • The digestive system therefore provides an interface with the environment because food substances enter the body through it. Missing words: small interface glands enter enzymes muscular large absorption 22/05/2017 6 Activity 2: Can you label the human digestive system? X W A V B C U D T E F G S R Q 22/05/2017 P O N M H I J K L 7 Activity 4: Question 1 • Which parts of the digestive system does the food pass through? • Mouth, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (caecum, colon, rectum), anus. 22/05/2017 8 !!! • The contents of the intestines are NOT inside the body! Molecules and ions only truly enter the body when they cross the cells and cell-surface membranes of the epithelial lining of the intestines. 22/05/2017 9 ??? Activity 5: How well do you know the major parts of the digestive system? ??? 22/05/2017 10 This part is the final section of the intestines. The faeces are stored here before periodically being removed via the anus in a process called egestion. RECTUM 22/05/2017 11 These are situated near the mouth. They pass their secretions via a duct into the mouth. These secretions contain the enzyme amylase, which breaks down starch into maltose. SALIVARY GLANDS 22/05/2017 12 This part is a muscular sac with an inner layer that produces enzymes. Its role is to store and digest food, especially proteins. It has glands that produce enzymes which digest protein. Other glands in its wall produce mucus. The mucus prevents this organ being digested by its own enzymes. STOMACH 22/05/2017 13 This is a large gland situated below the stomach. It produces a secretion. This secretion contains proteases to digest proteins, lipase to digest lipids and amylase to digest starch. PANCREAS 22/05/2017 14 LARGE INTESTINE This part absorbs water. Most of the water that is reabsorbed comes from the secretions of the many digestive glands. The food within this part therefore becomes drier and thicker in consistency and forms faeces. 22/05/2017 15 This is a long muscular tube. Food is further digested here by enzymes that are produced in its walls and by glands that pour their secretions into it. The inner walls of this organ are folded into villi, which gives them a large surface area. The surface area of these villi is further increased by millions of tiny projections, called microvilli, on the epithelial cells of each villus. This adapts this organ for its purpose of absorbing the products of digestion into the bloodstream. SMALL INTESTINE 22/05/2017 16 The lining of the small intestine 22/05/2017 17 This part carries food from the mouth to the stomach. It is therefore adapted for transport rather than for digestion or absorption. It is made up of a thick muscular wall. OESOPHAGUS 22/05/2017 18 Activity 6: Question 1 • Can you distinguish between the terms ‘absorption’ and ‘assimilation’? • Taking soluble molecules into the body. (Absorption) • Incorporating absorbed molecules into body tissues. (Assimilation) 22/05/2017 19 !!! • All organisms are made up of the same biological molecules and therefore our food consists almost entirely of other organisms or parts of them. We must first break them down into molecules that are small enough to pass across cell surface membranes. 22/05/2017 20 Activity 6: Question 2 • Unscramble the anagrams to reveal the two stages of human digestion. breakdown) •(Physical Hysipalc robewkand •(Chemical Halcmice digestion) tindogies 22/05/2017 21 Activity 7: Physical Digestion • If the food is large, it is broken down into smaller pieces by means of structures such as the teeth. This not only makes it possible to ingest the food but also provides a large surface area for chemical digestion. Food is churned up by the muscles in the stomach wall and this also physically breaks it up. Missing words: surface area physically stomach teeth chemical ingest large muscles 22/05/2017 22 Activity 8: Chemical Digestion • This breaks down large, insoluble molecules into smaller, soluble ones. It is carried out by enzymes. • All digestive enzymes function by hydrolysis (the splitting up of molecules by adding water to the chemical bonds that hold them together). The general term for such enzymes is hydrolases. • Enzymes are specific and so it follows that more than one enzyme is needed to break down a large molecule. Usually one enzyme splits a large molecule into sections and these sections are then hydrolysed into smaller molecules by one or more additional enzymes. Missing words: specific enzymes hydrolysed hydrolysis smaller large additional insoluble soluble hydrolases splits 22/05/2017 23 Activity 9: Question 1 • Can you name the three different types of digestive enzyme? 1. These breakdown carbohydrates, Carbohydrases ultimately to monosaccharides. 2. These breakdown lipids (fats and oils) Lipases into glycerol and fatty acids. 3. These breakdown proteins, ultimately Proteases to amino acids. 22/05/2017 24 Chemical digestion continued... • Once the large food molecules have been hydrolysed into monosaccharides, glycerol, fatty acids and amino acids, they are absorbed by various means from the small intestine into the blood. • They are carried to different parts of the body and are often built up again into very large molecules, although these are not necessarily of the same type as the molecules from which they were derived. • These molecules are incorporated into body tissues and/or used in processes within the body. This is called assimilation. Missing words: fatty acids, tissues, large, monosaccharides, glycerol, amino acids, assimilation, derived, blood, 22/05/2017 25 Plenary Activity: Answer these 4 questions under test conditions! 1. State one way in which the stomach is adapted: a) To churn food b) To prevent the enzymes it produces from digesting the surface of the stomach. 2. What is hydrolysis? 3. Which two structures produce amylase? 4. Suggest a reason why the stomach does not have villi or microvilli. 22/05/2017 26 Answers 1. a. By having a muscular wall. b. By secreting mucus. 2. Hydrolysis is the breakdown of molecules by the addition of water to the bonds that hold these molecules together. 3. Salivary glands, pancreas 4. Villi and microvilli increase surface area to speed up the absorption of soluble molecules. As the food in the stomach has not yet been broken down into soluble molecules they cannot be absorbed and so villi and microvilli are unnecessary. 22/05/2017 27 Learning Objectives All students should be able to: • Define digestion. • Give the structure and function of the major parts of the digestive system. • Understand how the digestive system breaks down food both physically and chemically. • Understand the role of villi and microvilli. • Outline the role of enzymes in digestion. Specification reference: 3.1.2 22/05/2017 28