Chapter 6: Food Groups and Human Digestive System PDF

Chapter 6: Food Groups and Human Digestive System Name: ______________________( ) Class: ______ Date: ____________ CHAPTER OVERVIEW Ch 6.1 Food Groups Learning Outcomes Students will be able to: 1. state the main group of nutrients in fo...

Chapter 6: Food Groups and Human Digestive System Name: ______________________( ) Class: ______ Date: ____________ CHAPTER OVERVIEW Ch 6.1 Food Groups Learning Outcomes Students will be able to: 1. state the main group of nutrients in food (carbohydrates, fats, proteins, vitamins, minerals and water). 2. state the sources of energy in food 3. describe the uses of carbohydrates, fats, proteins, vitamins (C & D), minerals (iron and calcium) and water in the human body. 4. list the principal sources and describe the dietary importance of carbohydrates, fats, proteins, vitamins (C and D only), mineral salts (calcium and iron only), fibre (roughage) and water. 5. describe what is meant by a balanced diet and how to achieve a balanced diet. 6. explain why diet, especially energy intake, should be related to age, sex, and activity of an individual. Page 1 of 22 Ch 6.2 Human Digestive System Learning Outcomes At the end of the topic, students will be able to: 1. explain what is meant by digestion. 2. explain why most food must be digested. 3. describe the major components of the human digestive system (mouth, buccal cavity, pharynx, oesophagus, stomach, liver, small intestine, large intestine, anus). 4. describe peristalsis in terms of rhythmic wave-like contractions of the muscles to mix and propel the contents of the alimentary canal. 5. describe how a digestive system helps digest food and the part enzymes play in digestion. (Only enzymes such as amylase, maltase, protease and lipase are needed. Specific names of other enzymes are not required) 6. state that large molecules are synthesised from smaller basic units - glycogen from glucose, polypeptides or simpler proteins, proteins from amino acids, and lipids such as fats and oils from glycerol and fatty acids. 7. describe and carry out tests for starch (iodine in potassium iodide solution/iodine solution) reducing sugars (Benedict's solution) protein (biuret test) fats (ethanol emulsion) 8. describe the effects of temperature and pH on the rate of enzyme-catalysed reactions Page 2 of 22 Ch 6.1 Food Groups Food for Thought Have you ever thought about why you eat food? We eat food mainly to gain various nutrients needed for our life processes, including cellular respiration, tissue growth and repair and to keep us strong and healthy. However, we sometimes eat even when we do not feel particularly hungry and wish to enjoy a delicious meal. What and when we eat depends on complex emotional, social and physical factors. Boredom or depression may act as triggers for eating. Foods that smell good or are attractively presented compel us to consume a more significant quantity. Many types of nutrients in our food support different functions in the human body. In this chapter, we will explore the different types of food we eat and how our body absorbs the nutrients from food through digestion. 4.1 Food Groups The Need for Food Food is a source of energy and raw material for organisms. Like other organisms, we require food to: 1. provide energy for the vital activities of the body, 2. synthesise substances for the growth and repair of cells, tissues and organs, 3. stay healthy. Nutrients are the chemical substances present in food and are necessary for the correct functioning of the body—the food we eat and the liquids we drink from our diet. There are three groups of macronutrients, namely carbohydrates, fats and proteins. They are required in large quantities and supply energy and materials to make new cells and tissues. Vitamins and minerals are micronutrients in our diet and are required in small quantities. They are needed for normal functioning of the body but do not have any energy value. Water acts as a solvent for many compounds. It is a medium for chemical reactions and is a major blood component. In the subsequent pages, you will learn about the "what, where, why and how" of the different nutrients. Page 3 of 22 Carbohydrates What are carbohydrates? Carbohydrates are organic compounds made up of the elements carbon, hydrogen and oxygen. Foods containing carbohydrates come from plants and are a good energy source for the body. There are three main groups of carbohydrates: Carbohydrates Polysaccharide Monosaccharide Disaccharide (Many monosaccharides ->Complex (single sugar-Basic unit) (Double Sugar) carbohydrates) E.g: Glucose E.g: Starch, E.g: Maltose Cellulose Note: The human body cannot break down cellulose into simple sugars, so we cannot obtain energy from cellulose. Cellulose plays an important part in the diet as cellulose is the main part of the fibre, which assists the bulk movement of materials through the digestive system. Where to find carbohydrates (sources) and Why carbohydrates (functions)? Food Sources Uses Sugars: fruit, sweets Main source of energy to carry on life processes. Starches: rice, cereal, bread Essential for cell respiration. Energy is released when glucose combines chemically with oxygen in respiration. During cellular respiration, glucose can be broken down to release energy (ATP) to provide cells with energy for growth and development. Excess carbohydrates are stored as glycogen or converted to fat. How do we identify starch? Name of Test Procedure Positive Result Negative Result Iodine Test Add a drop of iodine The solution changes from The solution remains solution to 1 drop of brown to blue‐black. brown. starch suspension on a white tile. **state the initial observation of the test reagent and the final observation of the test reagent. Page 4 of 22 How do we identify reducing sugars? All monosaccharides and disaccharides are reducing sugars except sucrose. Name of Test Procedure Positive Result Negative Result Benedict's Test For liquid sample: The blue solution turns green. The blue solution Trace amount of reducing sugar remains blue. 1. Place about 2 No reducing sugar is cm3 of sample in The blue solution forms a yellow present. test‐tube. precipitate. Small amount of reducing sugar 2. Add an equal volume of The blue solution forms an Benedict's orange precipitate. solution. Moderate amount of reducing sugar 3. Place test‐tube in a boiling water The blue solution forms a brick‐ bath for 3 min. red precipitate. High amount of reducing sugar **state the initial observation of the test reagent and the final observation of the test reagent. Page 5 of 22 Fats What are fats? Fats, like carbohydrates, are organic compounds made up of carbon, hydrogen and oxygen. However, fats contain much less oxygen in proportion to hydrogen compared to carbohydrates. Fats are energy storage compounds. One gram of fats yields twice as much energy as 1 gram of carbohydrates. However, fats are more difficult for the body to break down than carbohydrates and proteins. Where to find fats (sources) and Why fats (functions)? Food Sources Uses Animal fats: 1. Source of energy Meat*, Lard, dairy 2. Long-term storage of energy in adipose tissue products. 3. An insulating material under the skin Plant fats: Nuts, palm oil. * From the nutritional point of view, meat is considered a rich essential amino acid source and contains mainly saturated fatty acids. Meat and meat products are considerable sources of cholesterol in the diet. How do you identify fats? Name of Test Procedures Positive Result Negative Result Ethanol- 1. Add a drop of the A colourless solution forms a A clear colourless emulsion Test sample into a dry white emulsion solution is observed test tube. 2. Add ethanol to about 1/3 of the test tube and shake hard for about 2 minutes. 3. Add a few drops of deionised water, one drop at a time, and shake well to mix. Page 6 of 22 Proteins Proteins are complex organic compounds made up of carbon, hydrogen, oxygen and nitrogen. Sometimes, sulfur and phosphorous might be present. The basic building block of protein is amino acids. Proteins consist of amino acids linked together. Amino Acids --> Polypeptides --> Proteins Where to find proteins (sources) and Why proteins (functions)? Food Sources Uses Animal Protein: 1. Required for growth and repair of cells Lean meats, eggs, 2. Source of energy dairy products, fish 3. Excess amino acids from proteins can be converted into glucose and used as a source of energy Plant proteins: 4. Form enzymes, hormones and antibodies in the body Soya beans, nuts, grains 5. Build body mass How do you identify proteins? Summary of Food Test Name of Test Procedures Positive Result Negative Result Biuret Test 1. Add 2 cm3 of the The solution/mixture changes The solution remains unknown sample to a from blue to violet. blue test tube. 2. Add an equal volume of 8% sodium hydroxide solution to the test tube. 3. Mix well. 4. Add 1% copper (II) sulfate solution dropwise, shaking after every drop. **state the initial observation of the test reagent and the final observation of the test reagent. Page 7 of 22 Vitamins & Minerals What are vitamins? Vitamins are complex organic chemicals which the body requires in small amounts. Vitamins have no energy value but are vital for many chemical reactions in the body. They act as catalysts that speed up the chemical reactions involving other essential minerals and enzymes. Where to find vitamins (Sources) and Why vitamins (functions)? Vitamins Sources Uses Deficiency Overconsumption Vitamin C Citrus fruits Prevents gums Scurvy which Vitamin C is a water- like orange from bleeding causes swollen, soluble vitamin. Excess bleeding gums and Vitamin C is excreted in Helps the body joints. the urine. to resist infection Vitamin D Fish, Egg For the Deficiency in Nausea and appetite yolks formation of Vitamin D in loss bones as it children can lead promotes to rickets, where Long-term ingestion of absorption of bones remain soft large doses of vitamin D calcium. and deformed. can cause calcium levels to rise. Deficiency in Vitamin D in adults High levels of calcium leads to can cause calcium osteomalacia, deposits to form in where bone organs and blood fractures are vessels, and this can common. lead to heart disease or the formation of kidney stones Page 8 of 22 What are Minerals? Minerals are inorganic nutrients required by the body in very small amounts. There are about 20 chemical elements, such as calcium and iron, which are minerals. Each mineral has a specific function but has no energy value. Where to find minerals (Sources) and Why minerals (functions)? Minerals Sources Uses Deficiency Overconsumption Calcium Dairy products, Needed for the Depleted calcium Severe fatigue, spinach and formation of bones stores in the bones, nausea, vomiting broccoli and teeth thinning and irregular heartbeat weakening of the and low blood Proper functioning bones, and risk of pressure. of muscles and osteoporosis. assistance in the Pain in the area of the clotting of blood kidney would suggest the formation and passing of stones. Iron Liver, beef, Formation of Dietary anaemia, Nausea, vomiting beans and haemoglobin in the characterised by liver failure spinach red blood cells tiredness and breathlessness. Water The human body consists of about 60 per cent water. Water is essential for all body cells and fluids, such as blood, digestion and absorption of food, excretion of waste products in the kidneys, and regulation of body temperature through sweating. Page 9 of 22 Energy in food During cellular respiration, energy is released when glucose is combined with oxygen. The energy is measured in kilojoules or kilocalories. The body uses this energy for maintaining its temperature at around 370C chemical reactions involving the growth and repair of tissue muscular activity, which is involuntary (heartbeat) and voluntary (walking) The table below shows the energy content of the different nutrients. Energy density Food component kJ/g kcal/g Carbohydrate 17 4 Protein 17 4 Fat 37 9 *1 cal ≈ 4.2J Balanced diet Our diet refers to all the food that we eat. The nutrients in the food are broken down in the digestive system through the process of digestion. Once digested and absorbed, the nutrients can be used to provide energy or be reassembled to build and repair tissue. A balanced diet supplies all the necessary nutrients in the correct amounts and proportions. The amount of nutrients needed varies from person to person, depending on age, gender, size and activity level. For example, younger people tend to be more active and need more energy from their food. Food intake should be matched to energy needs as much as possible. Eating too little may cause a person to be underweight while overeating may make a person overweight. No one food can provide all the nutrients that our body needs. Therefore, we must eat a wide variety of food, all in moderation and balance. As a rough guide to the type of food we should be eating, our diet should typically contain foods from each of the following food groups: rice and alternatives fruits and vegetables meat and alternatives (including milk and dairy products) Page 10 of 22 For Your Information The infographic below shows the Health Promotion Board's recommendations for a balanced diet. Source: https://www.healthhub.sg/programmes/55/my-healthy-plate My Healthy Plate is an easy-to-understand visual tool designed by the Health Promotion Board (HPB) specifically for Singapore residents. You can use My Healthy Plate to help you remember and practise healthy habits that can aid with weight control and protect against chronic diseases such as diabetes. The key healthy habits communicated by My Healthy Plate are: Fill half of your plate with fruit and vegetables Fill a Quarter of your plate with whole grains Fill a Quarter of your plate with meat and others Use healthier oils Choose water Be active Compare My Healthy Plate with the Healthy Food Pyramid used previously. Source: http://www.areyoueatingright.com/wpcontent/uploads/HPB%20food%20pyramid.jpg What are the differences? Page 11 of 22 Ch 6.2 Human Digestive System Complex molecules such as starch, proteins and fats are too large to diffuse through the selectively permeable membranes of the cells of the small intestine. Hence, they cannot be absorbed into the bloodstream. Digestion breaks down large food molecules into smaller and soluble ones so that they can be absorbed and used by our body cells There are two types of digestion – physical and chemical. Physical digestion Chemical Digestion Physical digestion is the breaking up food into Chemical digestion is the breaking down smaller pieces without chemical change. of large food molecules into smaller molecules due to the chemical action of Physical actions such as the chewing of food in enzymes. the mouth, the churning action of the stomach and the action of bile salts in the small intestine It allows smaller molecules (end products) to help increase the surface area of the food be absorbed (by diffusion and active transport) particles so that chemical digestion by into the walls of the villi, into the bloodstream enzymes can take place faster. and be transported into other cells in the body. Page 12 of 22 Enzymes An enzyme is a special type of protein that speeds up chemical reactions in the body but remains unchanged at the end of the reaction. Enzymes are specialised, and they can only work on specific substrates. (A substrate is a molecule upon which an enzyme acts on) Lock and Key Model of Enzyme Action Enzymes are made in the cytoplasm under instructions from genes on the chromosomes in the nucleus. Enzymes work best at an optimum temperature and pH, and they will be denatured by excess heat and extreme pH. Effect of temperature on enzyme action Enzymes work within a temperature range. Each enzyme has an optimum temperature where it is most effective, about 40-45°C. Below the optimum temperature, the enzyme is inactivated. Above the optimum temperature, the enzyme is denatured. The rate of reaction doubles with an increase in temperature of 10°C until the optimum temperature is reached. Page 13 of 22  Optimum temperature (Enzyme activity) Rate of Reaction Temperature / oC Effect of temperature on the rate of an enzyme-catalysed reaction An increase in temperature increases molecular motion. Thus, the molecules of the substrate and enzyme gain more kinetic energy and move more quickly, increasing the frequency of effective collisions between the substrate molecules and the enzyme's active site. The rate of enzyme-substrate complex formation increases. As a result, there is a greater probability of a reaction occurring. The rate of reaction increases until the optimum temperature is reached. An enzyme's optimum temperature produces the highest rate of contact between the substrate molecules and the enzyme's active site. The rate of enzyme-substrate complex formation is at its highest. Above the optimum temperature, the rate of reaction drops rapidly despite the increasing frequency of effective collisions. This is because, at high temperatures, the specific three- dimensional conformation of the enzyme active site is altered and is no longer complementary to the shape of the substrate. No enzyme-substrate complex is formed, and the enzyme is denatured. If the temperature is much lower than the optimum temperature for the enzyme, enzyme- substrate complexes are formed slowly, and the rate of reaction is slow. The enzymes are inactivated if the temperature is reduced to near or below freezing point. The enzymes will regain their catalytic influence when higher temperatures are restored. Page 14 of 22  Effect of pH on enzyme action Enzymes work best at their optimum pH, at which the maximum rate of reaction occurs. When the pH is altered above or below its optimum pH, the rate of enzyme activity diminishes. Extremes of pH will denature the enzyme. The effectiveness of an enzyme depends on the pH of its surrounding medium. The optimum pH for each enzyme depends on where it is found in the body. For example, pepsin in the stomach is most effective in an acidic medium (pH 2), while trypsin in the small intestine functions best in a slightly alkaline medium (pH 8-9). The pH of saliva, produced by salivary glands in the mouth, is neutral. Salivary amylase thus functions best at pH 7. Effect of pH on the rate of an enzyme-catalysed reaction Effect of pH on two different enzymes Below are five enzymes that are involved in the digestion process. The enzyme amylase catalyses the breakdown of starch into maltose Maltose is further catalysed to break down into glucose by the enzyme maltase. The enzyme pepsin catalyses the breakdown of proteins into polypeptides. Polypeptides are catalysed to break down into amino acids by other types of proteases (e.g., peptidases) The enzyme lipase catalyses the breakdown of fats into fatty acids and glycerol. Page 15 of 22 Digestive System The alimentary canal is a continuous tube in the body starting from the mouth and ending at the anus, while the digestive system is a broader term that includes other structures, including the accessory organs of digestion. Alimentary Digestive canal system Mouth Mouth Mouth Oesophagus Oesophagus Stomach Stomach Salivary gland Small Small Intestine Intestine Oesophagus Large Large Intestine Intestine Rectum Rectum Stomach Anus Anus Liver Salivary Pancreas glands Gall Liver bladder Gall bladder Large Small Intestine Pancreas Intestine Rectum Anus 1. Mouth Digestion begins in the mouth. The teeth help to break up large food pieces into smaller pieces (physical digestion), increasing the surface area exposed to digestive enzymes. Concurrently, food is mixed with saliva produced by the salivary glands. Saliva contains the enzyme salivary amylase, which catalyses the breakdown of starch into maltose (chemical digestion). Salivary Amylase Starch Maltose The tongue helps to mix the food with the saliva and rolls the partially digested food into a small ball (bolus), which is then swallowed down the oesophagus. Page 16 of 22 2. Oesophagus The oesophagus is a long and narrow tube joining the mouth to the stomach. No enzymes are secreted by the oesophageal cells; hence, only the digestion of starch into maltose occurs as the boli (singular: bolus) are swallowed. The oesophagus has strong muscles in its walls. These circular and longitudinal muscles contract and relax, producing a wave-like movement that pushes the food into the stomach. This involuntary wave-like pattern of muscular contractions is called peristalsis. Source: http://www.passmyexams.co.uk/GCSE/biology/i mages/swallowing.jpg Peristalsis helps to push food along the alimentary canal. Peristalsis begins in the oesophagus once a food bolus is formed and ends in the anus. For your information When the circular muscle and longitudinal muscle contract, the circular muscle decreases the diameter of the muscle, and the longitudinal decreases the length. The circular and longitudinal muscles are antagonistic muscles. Their contraction and relaxation lead to the peristaltic movement. When there is a bolus of food, circular muscles behind the bolus contract and relax in the front, whereas longitudinal muscles behind the bolus relax and contract in the front. Page 17 of 22 3. Stomach The stomach stores food. It has elastic walls and can expand to fit in a large meal. It also produces gastric juice. This is a mixture of hydrochloric acid and the enzyme pepsin. Hydrochloric acid provides acidic conditions in the stomach for pepsin to work and also kills bacteria which may have been swallowed with the food. The acidic condition also stops the action of salivary amylase in the stomach. Peristalsis in the stomach wall churns and breaks up the food (physical digestion). Peristalsis also mixes the food well with gastric juice. The pepsin in the stomach catalyses the breakdown of proteins into shorter chains of polypeptides (chemical digestion). Pepsin Protein Polypeptides Food normally remains in the stomach for about 3-4 hours. The partially digested food becomes liquefied, forming chyme (pronounced as 'kyme'). Let's Think… Why does the stomach not "digest" itself? Cells lining the stomach produce a thick layer of mucus which coats the inner wall of the stomach. The mucus protects the stomach from digesting itself and from the corrosive action of hydrochloric acid. Source: http://ehealthmd.com/yms_images/1345.jpg Page 18 of 22 4. Small Intestine The stomach slowly releases chyme into the small intestine. The small intestine is a long and narrow tube joining the stomach and the large intestine, where most of the chemical digestion and absorption of food takes place. As the chyme enters the small intestine from the stomach, it is mixed with secretions from the liver, pancreas and the small intestine. (Recall: liver, gall bladder and pancreas are not part of the alimentary canal, but they are the accessory organs of the digestive system) The pancreas produces pancreatic juice, which contains amylase, proteases and lipase, while the small intestine produces intestinal juice, which contains maltase, peptidases and lipase. Starch is catalysed to break down into maltose by amylase (in the pancreatic juice). Maltose is catalysed to break down into glucose by maltase (in the small intestinal juice). Protein is catalysed to break down into polypeptides by proteases (in the pancreatic juice). Polypeptides are catalysed to break down amino acids by peptidases (in the small intestinal juice). Fat is emulsified into tiny fat droplets by bile (secreted by the liver and stored in the gall bladder) and then catalysed to break down into fatty acids and glycerol by lipase (small intestine) 5. Liver The liver is the largest organ in the body. It has many functions, including the regulation of blood glucose concentration by storing glucose reserves (in the form of glycogen) or breaking them down. The liver also produces bile, which is stored in the gall bladder and released into the small intestine through the bile duct. Bile emulsifies fats by breaking them up into small droplets (physical digestion), increasing the total surface area of fat droplets to speed up digestion by lipase (chemical digestion). Big Droplet of fat + Bile Salts Emulsification of Fats (physical digestion) Tiny droplets of fat Page 19 of 22 Summary: Digestion of different foods Starch/Carbohydrate Digestion: Salivary amylase Maltase Starch Maltose Glucose Protein Digestion: Protease (from pancreatic juice) Protein Polypeptides Protease (e.g: Peptidases) Polypeptides Amino Acids Fat Digestion: Lipase Fats Fatty Acids + Glycerol The main end products of digestion are glucose, amino acids, fatty acids and glycerol. These products are now small enough to be absorbed through the walls of the small intestine and into the bloodstream. Page 20 of 22 Absorption of different nutrients Products of digestion such as glucose, amino acids, fatty acids and glycerol are absorbed in the small intestine. The absorbed nutrients pass through the small intestine into the bloodstream. Source: http://www.daviddarling.info/images/small_intestine_cross-section.jpg Important Terms: Villi Finger-like projections along the inner walls of the small intestine Singular: Villus Microvilli Under the microscope, the epithelial cells of villi have numerous microvilli. Singular: Microvillus Adaptation of Small Intestine for Absorption Adaption Explanation The small intestine is long This allows sufficient time and presents a large total surface area for absorption of digested food. Presence of numerous folds This increases the total surface area for diffusion and/or active with finger-like projections transport / absorption of digested food to occur more efficiently. called villi. The epithelial cells of the This further increases the surface area to volume ratio of each villus have microvilli. epithelial cell for absorption of digested food to occur more efficiently. The villus has a one-cell thick There will only be a short distance to allow faster and more efficient epithelium. absorption of digested food. There is a dense network of This ensures that absorbed nutrients can be transported away blood capillaries, and a quickly to maintain a steep concentration gradient of nutrients for lacteal/lymphatic capillary is efficient absorption by diffusion. found in each villus. The blood capillaries transport sugars and amino acids from the intestine while the lacteals transport fats. Page 21 of 22 More information Gallstones may develop when bile contains too much cholesterol and not enough bile salts. This may be caused by diet, weight or medication. Gallstones can be removed surgically or through the use of medication to dissolve them slowly. 6. Large Intestine The undigested food moves from the small intestine into the large intestine by peristalsis. Water, fibres, and mineral salts pass into the large intestine. The main function of the large intestine is to absorb water and dissolved mineral salts. 7. Rectum Any undigested and unabsorbed matter is stored temporarily in the rectum before it is discharged as faeces through the anus. The removal of undigested matter from the body is known as egestion or defaecation. Summary Starch is catalysed to break down into maltose by amylase (mouth, pancreas) Maltose is catalysed to break down into glucose by maltase (secreted by the small intestine) Protein is catalysed to break down into polypeptides by pepsin in gastric juice and proteases in pancreatic and intestinal juice. Polypeptides are catalysed to break down by peptidases into amino acids. Fat is emulsified into tiny fat droplets by bile (secreted by the liver and stored in the gall bladder) and then catalysed to break down into fatty acids and glycerol by lipase (small intestine) Page 22 of 22