Unit 3: Human Biology and Health PDF

Human biology and health Unit 3 Contents Section Learning competencies 3.1 Food and List the major nutrients needed by the human body and their sources. nutrition List the main sou...

Human biology and health Unit 3 Contents Section Learning competencies 3.1 Food and List the major nutrients needed by the human body and their sources. nutrition List the main sources of some of the vitamins and minerals needed by the (page 51) human body. Carry out laboratory tests to identify different nutrient groups in a food sample. Explain the concept of a balanced diet and what it involves. Define nutrition and malnutrition and describe the effects of malnutrition on the human body. Understand the concept of height/weight tables and how they can be used to help maintain a healthy body mass. Analyse a local diet and if necessary suggest ways in which it might be improved to become more balanced. 3.2 The digestive Label a diagram of the human digestive system. system Describe the functions of the structures of the human digestive system. (page 69) Define enzymes and describe their role in the process of digestion. Describe the structure of the teeth and explain their importance. Describe the processes of digestion in the mouth, stomach and small intestine. Demonstrate that starch digestion begins in the mouth using saliva and bread. Explain how the products of digestion are absorbed and assimilated by the body. Discuss constipation, care with canned, bottled and packed foods and food hygiene as issues of digestive health. 3.3 The respiratory Explain the importance of breathing in humans. system Describe the structure and functions of the human respiratory system. (page 82) Examine the structure of a lung from an animal such as a cow or sheep. Explain the mechanism of breathing using a lung model. Explain the process of gas exchange. Demonstrate the presence of CO2, water vapour and heat in exhaled air. Compare the composition of inhaled and exhaled air. List the factors which affect breathing and explain how they affect it. Explain the effects of cigarette smoking and inhaling gaya, suret and shisha on health and on the economy of the family. List the methods of maintaining the hygiene of breathing. Describe the steps followed during artificial respiration and be able to demonstrate these steps. 3.4 Cellular Explain cellular respiration and describe the formation of ATP and its respiration importance to the body. (page 99) Define and compare aerobic and anaerobic respiration, and explain their importance in cells. 50 Incomplete advance copy Grade 9  UNIT 3: Human biology and health 3.5 The Explain how oxygen and nutrients are transported in the blood. circulatory Indicate the structures of the heart on a diagram/model. system Explain the functions of the structures of the heart. (page 104) Examine a mammalian heart using fresh or preserved specimens. Take your own pulse, counting the heartbeats using your fingers. List the three types of blood vessels. Explain the functions of the blood vessels. Name the components of the blood. Tell the functions of the components of the blood. List the four blood groups. Indicate the compatibility of the four blood groups. Explain the causes and prevention of anaemia and hypertension. 3.1 Food and nutrition By the end of this section you should be able to: List the major nutrients needed by the human body and their sources. List the main sources of some of the vitamins and minerals needed by the human body. Carry out laboratory tests to identify different nutrient groups in a food sample. Explain the concept of a balanced diet and what it involves. Define nutrition and malnutrition and describe the effects of malnutrition on the human body. KEY WORD Understand the concept of height/weight tables and how heterotrophs organisms they can be used to help maintain a healthy body mass. that feed on other Analyse a local diet and if necessary suggest ways in which organisms it might be improved to become more balanced. People, like all living organisms, need a source of energy to survive. In our case this is our food. We are heterotrophs – we cannot make our own energy supply by photosynthesis so we have to eat other living things. Throughout human history almost anything that can be eaten has been eaten, and around the world the variety of food taken in by people is still quite amazing. However, it doesn’t matter what the food is – from tibs to injera be wot, from kifto to kocho – as long as it contains the right balance of chemicals to provide your body with everything it needs to live, grow and reproduce. Figure 3.1 Food comes in all shapes and sizes – but whatever it looks like, the chemicals it contains are surprisingly similar. Grade 9 Incomplete advance copy 51 Unit 3: Human biology and health KEY WORDS The human diet macronutrients food you What is food? Food is the source of nutrients and energy for the need in large amounts body. It usually comes from animals or plants and is taken into the carbohydrates major food body where it is broken down to provide the nutrients needed by group made up of carbon, the body. hydrogen and oxygen Each one of us has to take in all of the chemicals we need from the proteins molecules made food that we eat. We use our food in three main ways: up of amino acids that To provide energy for our cells to carry out all the functions are needed for the body to of life. function properly To provide the raw materials for the new biological material minerals inorganic needed in our bodies to grow and also to repair and replace compounds required by the damaged and worn out cells. body for good health To provide the resources needed to fight disease and maintain a vitamins organic healthy body. substances required by Some types of food are needed in large amounts – these are known the body in order for it to as the macronutrients. There are six main classes of food needed function properly by the body. The main macronutrients are carbohydrates, proteins sucrose a complex and fats. Other substances are equally important in your diet, carbohydrate found in but only in tiny amounts. They are known as the micronutrients many plants and used as a and they include minerals and vitamins. You also need water. sweetening agent In this section you are going to look at all of the most important components of a healthy human diet. glucose sugar made by plants during photosynthesis Carbohydrates photosynthesis the process Carbohydrates provide us with energy. Much of the carbohydrate a plant uses to combine you take into your body is broken down to form glucose, which is used in cellular respiration to produce energy in a form that can sunlight, water, and carbon be used in all your cells (see section 3.4). Your body stores very dioxide to produce oxygen little carbohydrate apart from glycogen, which is found in your and sugar (energy) liver, muscles and brain. Any excess carbohydrate that you eat is starch a nutrient converted to fat, which is stored all too easily in your body. carbohydrate required The most commonly known carbohydrates are the sugars and by the body for healthy starches. You will already be familiar with a few types of sugar: the functioning sugar that is such an important product of many African countries, including Ethiopia, is known as sucrose; glucose is the sugar made by plants in photosynthesis and it is vital in cells for energy. It is also the energy supplier in sports and health drinks. Another more complex carbohydrate known as starch is a storage carbohydrate in plants and it is commonly found in teff and potatoes. Carbohydrate-rich foods include anything containing sugar or flour, such as injera, fatira and honey. Potatoes, rice and dabo are also carbohydrate-rich foods. The basic structure of all carbohydrates is the same. They are made up of carbon, hydrogen and oxygen. They fall into three main types, depending on the complexity of the molecules: simple sugars, double sugars and complex sugars. 52 Incomplete advance copy Grade 9  UNIT 3: Human biology and health The simple sugars KEY WORD In these simple sugars there is one oxygen atom and two hydrogen fructose a sugar found in atoms for each carbon atom present in the molecule. This can be sweet fruits and honey written as a general formula: condensation reaction (CH2O)n when two simple sugars The best-known simple sugar is glucose, which has the chemical combine to form a double formula C6H12O6. There are lots of other simple sugars, including sugar, removing a molecule fructose, the sugar found in fruit. of water The double sugars Fructose Glucose Double sugars are made up of two simple sugars joined together, OH and sucrose (the substance you know as sugar) 6 is one of the 1most HOH2C O CH OH H C H common. It is formed by a molecule of glucose joining with a 2 5 molecule of fructose. When two simple sugarsC join together 2 C to form C O a double sugar, a molecule of water (HH2O) is removed. This typeOH H H H OH H C C of reaction where water is produced is known as a condensation OH O HO OH reaction (see figure 3.3). 4 C 3 C C C When different simple sugars join together, notOHsurprisingly H H OH different double sugars result. Here are some of the more common Fructose Glucose ones: 6 1 Table 3.1 Sources of disaccharides HOH2C O CH2OH H 5 Disaccharide Source C 2C H H H OH OH Sucrose Stored in plants such as sugar beet and C sugar cane C C HO 4 3 Lactose Milk sugar – this is the main carbohydrate found in milk OH H Maltose Malt sugar – found in germinating seed Figure 3.2 Glucose and the such as barley other simple sugars are fairly complicated molecules – they are often arranged in rings rather than simple chains. monosaccharide monosaccharide disaccharide condensation OH + HO O ++ H2H O2O hydrolysis Figure 3.3 The formation of Most simple and double sugars have two important properties in sucrose. The condensation common. They dissolve in water and they taste sweet. reaction between the two simple sugars results in a double sugar The complex sugars and a molecule of water. The most complex carbohydrates are formed when many single sugar units are joined to form a long chain. The sweet taste that is common to simple and double sugars is lost – and so is the ability to dissolve in water. But linking lots of sugar monomers (single units, in this case simple sugars) produces some complex polymers (long- chain molecules made up of lots of smaller repeating units). These Grade 9 Incomplete advance copy 53 Unit 3: Human biology and health polymers or complex sugars have some very important biological KEY WORDS properties. They often form very compact molecules that are ideal complex sugars when for storing energy. The sugar units can then be released when they many single sugar units join are needed to supply energy. And as complex sugars are physically to form a long chain and chemically very inactive, storing them does not interfere with glycogen carbohydrate the other functions of the cell. energy store found in Starch is one of the best-known complex sugars. It is particularly animals important as an energy store in plants. The sugars produced by cellulose the main photosynthesis are rapidly converted to starch. Particularly rich constituent in plant cell sources are plant storage organs such as potatoes. walls Glycogen is sometimes referred to as ‘animal starch’. It is the only carbohydrate energy store found in animals. It is found mainly in muscle and liver tissue, which is very active and needs a readily available energy supply at all times. Figure 3.4 Starch grains found in potato cells are larger than those found in most plants. Cellulose is an important structural material in plants. It is the main constituent in plant cell walls. Just like starch and glycogen it consists of long chains of glucose – but in this case the glucose molecules are held together in a slightly different way. This is very important, because human beings, and indeed most other animals, cannot break down these linkages and so they cannot digest cellulose. So carbohydrates, from the simple sounding combination of carbon, hydrogen and oxygen, form a very varied group of molecules whose functions are vital to most living processes. There are a number of chemical tests that you can carry out to test for the presence of carbohydrates of different types. Here you are given several tests which you can try first on known samples of carbohydrates. Later you can use these same tests to discover the chemical make-up of different foods that you eat. 54 Incomplete advance copy Grade 9  UNIT 3: Human biology and health Activity 3.1: Starch test You will need: Method a 1% starch solution 1. Pour about 1 cm3 of starch solution into a clean test tube made by boiling a mixture and the same volume of water into the other test tube. of starch powder and cold 2. Add two drops of iodine solution to each tube. water 3. Record your observations and conclusion in tabular form. two clean test tubes The colour of iodine solution is iodine solution brown. Starch reacts with iodine to form a characteristic blue- black. In this test it is important to note that there is no heating involved. Only a few drops of iodine solution are necessary. Figure 3.5 The reaction of iodine with starch solution Activity 3.2: Benedict’s test for simple (reducing) sugars Some sugars react readily Method with Benedict’s solution. 1. Bring the water in the beaker to the boil, using the Bunsen They reduce copper(II) ions burner. to copper(I) ions and for this reason they are known 2. In one boiling tube add water to a depth of about 2 cm – as reducing sugars. So there this will act as your control. is a straightforward chemical 3. In another tube add a sample of glucose powder and water test for the reducing sugars. to a depth of about 2 cm. The reducing sugars include 4. Place any food samples to be tested in other boiling tubes all of the single sugars and in the same way. some double sugars. 5. Add a few drops of Benedict’s solution to each boiling tube. You will need: Add enough to colour the mixture blue. a Bunsen burner 6. Place the tubes in the boiling water and leave for several tripod, gauze and heat- minutes. TAKE CARE with the boiling water. proof mat 7. If a reducing sugar is present the clear blue solution will a large beaker half filled change as an orangey-red precipitate appears. with water 8. Write up your method and results, including the different some glucose powder or foods you have analysed. food to be tested boiling tubes Benedict’s solution different food samples to Figure 3.6 Results of analyse (e.g. bread, fruit) the Benedict’s test for simple sugars before and after heating Grade 9 Incomplete advance copy 55 Unit 3: Human biology and health Proteins Proteins are used for body-building. They are broken down in digestion into amino acids that are then rebuilt to form the proteins you need. Protein-rich food includes all meat and fish, dairy products such as cheese and milk as well as pulses, such as white pea beans, chick peas and red kidney beans. About 17–18% of your body is made up of protein – a high percentage second only to water. Your hair, skin, nails, the enzymes that control all the reactions in your cells and digest your food, many of the hormones that control your organs and their functions, your muscles and much, much more depends on these complex molecules. By understanding the way in which protein molecules are made up and the things that affect their shape and functions, you can begin to develop an insight into the biology not only of your cells but also all living things. Just like carbohydrates and fats, proteins are made up of the elements carbon, hydrogen and oxygen, but in addition they all contain nitrogen. Some proteins also contain sulphur and various KEY WORDS other elements. Proteins are polymers, made up of many small units joined together. These small units are called amino acids. nitrogen a colourless, In the same way that monosaccharide units join together to form tasteless, odourless, polysaccharides, so amino acids combine in long chains to produce gaseous chemical element proteins. There are about 20 different naturally occurring amino amino acid building block acids and they can be joined together in any combination. Amino of protein acids are joined together in a condensation reaction and a molecule peptide link when amino of water is lost. The bond formed is known as a peptide link. The acids are joined together long chains of amino acids then coil, twist, spiral and fold in on in a condensation reaction themselves to make the complex structures we know as proteins. The structure of the proteins is held together by cross-links between and a molecule of water is the different parts of the molecule, and they can end up with very lost complex 3-D structures, which are often very important to the way they work in your body (see page 70 on enzymes). condensation + + water amino acid 1 amino acid 2 hydrolysis dipeptide + water long chain of amino acids Figure 3.7 Amino acids are the building blocks of proteins and they can be joined in a seemingly endless variety of ways to produce an almost infinite variety of proteins. Amino acids dissolve in water, but the properties of the proteins that are produced vary greatly. Some proteins are insoluble in water and are very tough, which makes them ideally suited to structural functions within living things. These proteins are found 56 Incomplete advance copy Grade 9  UNIT 3: Human biology and health in connective tissue, in tendons and the matrix of bones (collagen), Did you know? in the structure of muscles, in the silk of spiders’ webs and silkworm cocoons and as the keratin that makes up hair, nails, horns and There are some amino feathers. acids that you must eat as Others are soluble in water. These form antibodies, enzymes part of your diet because and some hormones, and are also important for maintaining the your body cannot make structure of the cytoplasm in your cells. them. They are known as essential amino acids and The complicated way in which the structures of proteins are built if they are lacking in your up means that they can be relatively easily damaged and denatured. diet for too long you will The relatively weak forces that hold the different parts of the amino die. acid chains together can be disrupted very easily. As the functions of most proteins rely very heavily on their structure, this means that the entire biochemistry of cells and whole organisms is very KEY WORD sensitive to changes that might disrupt their proteins. A rise in pH measure of the acidity temperature of a few degrees or a change in pH is enough to destroy or alkalinity of a solution the 3-D structure of cellular proteins – and so destroy life itself. This is why your body has so many complex systems that keep the internal conditions as stable as possible and why very high fevers are so dangerous and can lead to death. Activity 3.3: Biuret test for proteins When we test for proteins sometimes we add two separate chemicals (5% potassium or sodium hydroxide solution and 1% copper sulphate solution) to our test food. You will need: test tubes 5% potassium or sodium hydroxide solution and 1% copper sulphate solution OR Biuret reagent different food samples Figure 3.8 Results of the Method Biuret test for proteins 1. In one test tube add water to a depth of about 2 cm – this will act as your control. 2. In another tube add a sample of protein powder, e.g. albumin, and water to a depth of about 2 cm. Shake to mix. 3. Place any other food samples to be tested in other test tubes in the same way. 4. Add an equal volume of dilute potassium or sodium hydroxide solution in all the test tubes and mix. 5. Add a few drops of dilute copper sulphate solution. (If you are using Biuret reagent steps 4 and 5 are combined in one.) 6. A purple (mauve) colour will develop if protein is present. 7. Write up your method and the results for the different foods you have tested. Grade 9 Incomplete advance copy 57 Unit 3: Human biology and health Lack of protein in the diet may well be linked to an overall lack of energy intake, and results in a number of diseases known as protein-energy malnutrition. The best known of these are marasmus and kwashiorkor. In marasmus, both protein and overall energy intake is far below what is needed by the body. An increase of both protein and calories can save a child or adult. But if the body has not got enough protein to make the enzymes it needs it can cause death. In contrast, kwashiorkor is thought to be caused by a lack of protein in the diet even if the overall energy intake is reasonable. It is particularly common around the time a child is weaned, when a diet high in starchy foods and very low in protein is often substituted for mother’s milk. It is important to introduce protein Figure 3.9 Children suffering in limited amounts as the liver is damaged and can’t deal with any from kwashiorkor can have excess. big distended bellies, but the plumpness is swelling due to lack Fats and oils of protein, not health. Another group of organic chemicals that make up your body KEY WORDS cells are the fats and oils, also known as the lipids. Lipids include some of the highest profile chemicals in public health issues at the lipids general name for fats moment – cholesterol and fat. Lipid-rich foods include anything and oils containing large amounts of fats and oils. So, butter, beef fat, sesame cholesterol compound oil, niger seed oil (nug) and olive oil are all lipids. Plant seeds like produced by the body; groundnuts and coconuts are also lipid-rich, providing an energy- raised blood levels indicate rich store for the embryo plant. Meat, oily fish and eggs are high in lipids too. Any food that is cooked in fat or oil is also rich in lipids a high risk of heart disease and the energy that they supply. oils viscous liquid at room temperature Fats and oils are an extremely important group of chemicals with major roles to play in your body. They are an important source of glycerol a syrupy, sweet energy in your diet and they are the most effective energy store in liquid obtained from fats your body – they contain more energy per gram than carbohydrates and oils or proteins. This is why your body converts spare food into fat for saturated fat with no use at a later date. Combined with other molecules, lipids also play double bonds in the vital roles as hormones, in your cell membranes and in the nervous structure system. unsaturated fat with one All lipids are insoluble in water, but dissolve in organic solvents. or more double bonds in its This is important because when they are present in your cells structure they do not interfere with the many reactions that go on in the cytoplasm, because the reacting chemicals are all dissolved in water. single covalent bond created when two atoms The best-known lipids are the fats and oils. They are chemically share a single electron extremely similar, but fats, e.g. butter, are solids at room temperature and oils, e.g. niger seed oil (nug), are liquids at room double bonds created temperature. The lipids found in animals are much more likely to be when atoms share two solid at room temperature than plant lipids. electrons Just like the carbohydrates, the chemical elements that go into all lipids are carbon, hydrogen and oxygen. There is, however, a considerably lower proportion of oxygen in lipid molecules. Fats and oils are made up of combinations of two types of organic chemicals, fatty acids and glycerol. 58 Incomplete advance copy Grade 9  UNIT 3: Human biology and health Glycerol is always the same, with the chemical formula C3H8O3. On the other hand, there is a wide range of fatty acids. Over seventy different ones have been extracted from living tissues and the nature of the lipid depends a lot on which fatty acids are in it. All fatty acids have a long hydrocarbon chain – a pleated backbone of carbon atoms with hydrogen atoms attached. There are two main ways in which fatty acids vary; the length of the carbon chain can differ, and the fatty acid may be saturated or unsaturated. In a saturated fatty acid each carbon atom is joined to the one next to it by a single covalent bond. In an unsaturated fatty acid the carbon chains have one or more double bonds in them. Unsaturated fatty acids are more common in plant lipids. An example of each type of fatty acid is shown in figure 3.10. H H H H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H Stearic acid H H H H H H H H H H H H H H H H H O H C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H C Linoleic acid Figure 3.10 One of these fatty acids is saturated and one is unsaturated – which one is which? When a molecule of glycerol combines with three fatty acids, a lipid is formed. The molecules combine in a condensation reaction and a molecule of water is produced for each fatty acid that reacts with the glycerol. Recent medical research seems to indicate that high levels of fat, and particularly saturated fat, in our diet are not good for our long- term health. Fatty foods are very high in energy, and so a diet high 3 in fats when food is in plentiful supply is likely to result in obesity. fatty acids Worse than this, however, is the implication that saturated fats – found particularly in animal products such as dairy produce and meat – can cause problems in your metabolism. They seem to cause raised levels of a lipid called cholesterol in your blood. glycerol Cholesterol is a substance which you make in your liver. It gets carried around your body in your blood. You need it to make Figure 3.11 It is the combination the membranes of your body cells, your sex hormones and of fatty acids in a triglyceride the hormones which help your body deal with stress. Without that decides what it will be cholesterol, you wouldn’t survive. However, high levels of like. Saturated fatty acids give cholesterol in your blood seem to increase your risk of getting heart solid fats like butter, whereas disease or diseased blood vessels. The cholesterol builds up in your unsaturated fatty acids produce a blood vessels, forming fatty deposits which can even block the liquid like corn oil. vessels completely. Heart disease is one of the main causes of death in countries such as the UK and USA where people often eat far too much fatty food. Grade 9 Incomplete advance copy 59 Unit 3: Human biology and health Activity 3.4: Test for lipids a) Filter paper test A permanent translucent mark is formed by lipids on paper. The filter paper test is also A translucent mark is one that does not allow all the light known as the grease spot or to pass through. If you squeeze a food sample between two translucent mark test. bits of filter paper any water that has been squeezed out will evaporate from the paper. Any lipids will leave a translucent You will need: mark that does not dry out and disappear. However, this test, cooking oil or cooking fat although effective, is not very scientific because it does not depend on a chemical reaction. a clean filter paper or sheet of paper b) Emulsion test a dropper You will need: Method clean, dry test tubes – they MUST be dry 1. Put a drop of cooking fat ethanol (or smear a little cooking cooking oil or cooking fat fat) on a clean white sheet of paper. Method 2. Leave the paper for a few 1. Place a sample of ethanol in a dry test tube to a depth of minutes. about 2 cm. 3. Examine the spot where 2. Place a small sample of oil/cooking fat or a food sample in the cooking oil was a dry test tube and add a similar amount of ethanol. dropped while holding the 3. Shake the tube to dissolve any lipid in the ethanol. paper against light (not a flame!). Use light coming 4. Take two more test tubes and about half fill each with in through the window or water. from the electric bulb or 5. Carefully pour the contents of the tube containing the oil, tube. fat or food sample into one of the tubes containing water. 6. Pour about 2 cm3 pure ethanol into the other tube containing water and compare the two. 7. If lipid is present, a white, cloudy layer forms on top of the layer of water. 8. Use this test to investigate a number of common foods and find out if they contain lipids. 9. Write up your method and the results of any foods you have tested. Figure 3.12 Results of the ethanol test for fats 60 Incomplete advance copy Grade 9  UNIT 3: Human biology and health Minerals KEY WORDS It isn’t just carbohydrates, proteins and fats that are important in calcium(Ca) important your food. Mineral salts are needed in minute amounts, but lack of constituent of bones and them in your diet can lead to a variety of unpleasant conditions. teeth, needed for many For example, you need calcium (Ca) in your diet to make your metabolic processes bones and teeth hard and strong. Without it, children develop iron(Fe) vital for making rickets where the bones stay soft and cannot support the weight of the body so the legs become bowed. Milk and other dairy products haemoglobin in red blood such as ergoo and ayeeb are a very good source of this calcium. cells However, calcium alone is not enough to protect you from rickets. haemoglobin red pigment You also need vitamin D (see Vitamins). in the blood cells that Iron (Fe) is vital to make the haemoglobin found in your red blood carries oxygen around the cells that carry oxygen around your body (see section 3.5). If your body diet lacks iron you will suffer from anaemia. Iron is found in food sodium vital element such as red meat, liver, red teff and eggs. Without iron you don’t needed by the body for have enough haemoglobin in your red blood cells – in fact you can survival, by maintaining lack red blood cells – and so you don’t get enough oxygen in the fluid levels tissues of your body. This makes you look pale (lack of red blood deficiency disease any cells) and feel tired and lethargic (lack of oxygen). disease caused by a lack of Your mineral needs change throughout your life – growing children an essential nutrient need plenty of calcium for their bones to grow, whereas girls and women who have menstrual periods need more iron than others to replace the blood lost each month in their periods. The sodium ions found in your food and in the salt we often add to food are needed to survive. Without it, your nervous system would Table 3.2 Several of the main minerals needed in the diet and the deficiency diseases associated with them Mineral Approximate Location or role in Examples of foods Effects of deficiency mass in an adult body rich in mineral body (g) Calcium 1000 Making bones and Dairy products, fish, Rickets teeth bread, vegetables Phosphorus 650 Making teeth and Most foods Improper formation bones; part of many of teeth and bones; chemicals, e.g. DNA failure of metabolism Sodium 100 In body fluids, e.g. Common salt, most Muscular cramps blood foods Chlorine 100 In body fluids, e.g. Common salt, most Muscular cramps blood foods Magnesium 30 Making bones; found Green vegetables Skeletal problems; inside cells cell chemistry affected, defects in metabolism Iron 3 Part of haemoglobin Red meat, liver, Anaemia in red blood cells; eggs, green leafy helps carry oxygen vegetables, e.g. spinach Grade 9 Incomplete advance copy 61 Unit 3: Human biology and health KEY WORDS not work and the chemistry of all your cells would be in chaos. But for about a third of the population, too much salt in your diet night blindness inability can lead to high blood pressure. This can damage your heart and to see clearly in dim light kidneys and increase your risk of a stroke. In some countries people due to vitamin A deficiency can eat too much salt each day without knowing it. That’s because beri-beri deficiency disease many processed, ready-made foods contain large amounts of salt. from lack of vitamin B But you can control your salt intake by doing your own cooking – or by reading the labels very carefully when you buy ready-made food. In fact there is enough salt in the cells of the animals and Did you know? plants we eat to supply our needs without adding any extra for flavour. Table 3.2 shows you several of the main minerals needed in If you ate a polar bear’s the diet and the deficiency diseases associated with them. liver you would die of vitamin A poisoning. Mammals store vitamin A Vitamins in their livers. The liver of a Just like minerals, vitamins are needed in very small amounts. polar bear is so rich in the They are usually complex organic substances that are nevertheless vitamin that eating only capable of being absorbed directly into your bloodstream from the 500 g (half a pound) would gut. If any particular vitamin is lacking from your diet in the long give you a lethal dose of term it will result in a deficiency disease. Different foods are rich vitamin A. in different vitamins and it is important to take in a range of all the important vitamin-rich foods in your diet. For example, vitamin A is needed to make the light-sensitive chemicals in the retina of your eye (you will learn more about the eye in Grade 10). If your diet lacks vitamin A – found in fish liver oils, butter and carrots – your eyesight is affected and you find it almost impossible to see in low light levels. This is known as night blindness. Vitamin B1, found in yeast extract and cereals, is needed for the reactions of cellular respiration to take place. If you don’t eat enough of it you get a condition called beri-beri, when your muscles waste away and you become paralysed. It can be fatal. Lack of vitamin C causes scurvy, which used to kill many thousands of sailors as they travelled the world in sailing ships. Vitamin C is Figure 3.13 The liver of a polar needed for the formation of the connective tissue which holds your bear could kill you! body together! You find vitamin C in fruits, particularly citrus fruits and green vegetables, and once people started to take limes and lemons on sea voyages, scurvy became a thing of the past. Table 3.3 Several of the main vitamins needed in the diet and the deficiency diseases associated with them Vitamin Recommended Use in the body Some good sources of Effect of daily amount the vitamin deficiency in diet A 0.8 mg Making a chemical in the Fish liver oils, liver, Night blindness; retina; also protects the butter, margarine, carrots damaged cornea surface of the eye of eye B1 1.4 mg Helps with cell respiration Yeast extract, cereals Beri-beri C 60 mg Sticks together cells lining Fresh fruits and Scurvy surfaces such as the mouth vegetables D 5g Helps bones absorb Fish liver oils; also made Rickets; poor calcium and phosphorus in skin in sunlight teeth 62 Incomplete advance copy Grade 9  UNIT 3: Human biology and health Vitamin D is needed for your bones to take up the calcium they KEY WORDS need to grow strong. Vitamin D is found in fish liver oils and it is also made in your skin in the sunlight. If children don’t have scurvy a disease caused by enough vitamin D in their diet, or don’t get enough sunlight, they lack of vitamin C in the diet will get rickets even if they have plenty of calcium. retinol vitamin A Table 3.3 summarises four of the most common vitamins, the best calciferol vitamin D food sources for them and the problems that can arise if they are thiamine vitamin B1 deficient in your diet. These deficiency diseases can be avoided or remedied using vitamin supplements if it isn’t possible to get them all from the food you eat. The vitamins were given letters to distinguish them in the days before scientists had discovered exactly what each vitamin was. Although we now know all their chemical names, they are still usually referred to as vitamin A (retinol), vitamin D (calciferol), etc. Some vitamins are soluble in water and these include vitamin B1 (thiamine) and vitamin C. Others are fat soluble, including vitamins A and D. Activity 3.5: Testing for vitamin C You will need: Method freshly squeezed orange 1. Pour about 3 cm3 of DCPIP into a clean test tube. or lemon juice 2. Using a dropper, add orange or lemon juice drop by drop to DCPIP (dichlorophenol DCPIP in the test tube. indophenol) reagent 3. What happens to the colour of DCPIP? three clean test tubes 4. Record your observations in a table. test tube rack pipette or dropper Discussion water Vitamin C is present in citrus fruits like oranges and lemons. Other fruits like tomatoes and apples also contain vitamin C. A gradual fading of the blue colour of DCPIP in the above experiment shows that vitamin C is present in orange juice. This is because vitamin C has a reducing action on the DCPIP reagent which makes it lose its colour. Investigation Design and carry out a suitable experiment to find out which fruits contain the greatest concentration of vitamin C. Activity 3.5a: Copy and complete Table 3.3 provides details of four important vitamins. There are, however, a number of other vitamins that our bodies need. Copy the following table into your exercise book and complete it with as many more vitamins as you can find: conduct your research using reference books, the Internet, your teacher, and any other sources you can think of. Vitamin Recommended Use in the body Some good sources of Effect of daily amount the vitamin deficiency in diet Grade 9 Incomplete advance copy 63 Unit 3: Human biology and health KEY WORDS The role of water urea the main component Another vital constituent of a balanced diet is water. An average of urine person can survive with little or no food for days if not weeks, but a complete lack of water will bring about death in 2–4 days, hydrolysis reaction depending on other conditions such as temperature. Your body is chemical reaction of a actually between 60 and 70% water, depending on your age, how compound with water much you have drunk recently, etc. So it is not surprising that water nutrition the obtaining of is crucial in your body for a number of reasons, including: food in order to survive All of the chemical reactions which take place in your body take place in solution in water – it is a vital solvent. Water is involved in the transport of substances around the body – food, hormones, waste products such as urea and many other substances are all carried around your body in solution in water as part of your blood. Water is involved in temperature regulation as you lose heat from your body through sweating (you will learn more about this in Grade 10). Water is involved in the removal of waste materials from your body in the urine and in your sweat (see section 3.2). Water is a reactant in many important reactions in the body – for example, as you will discover later in this section, many food molecules are broken down in hydrolysis reactions where water is added. Water is needed for the osmotic stability of the body (see page 39, on osmosis in animals). The concentration of the chemicals in your cells and in the body fluids surrounding them must be kept constant. If there is not enough water in the blood and tissue fluid, the body cells lose water by osmosis and can no longer function, causing death. Fibre in the diet A final important part of a healthy diet is something that you can’t even digest or absorb. Roughage or fibre cannot be broken down in the human gut, yet it is an essential part of your diet because it provides bulk for the intestinal muscles to work on. It also absorbs lots of water. In a diet low in roughage the movements of the gut which transport the food through it (peristalsis) are sluggish and the food moves through the gut relatively slowly. This can result in constipation. Why is a balanced diet important? Nutrition is obtaining food in order to carry out life processes. Nutrition in plants involves manufacturing their own food in the process of photosynthesis (you will learn more about this in Grade 10). In animals, including ourselves, nutrition involves taking in food based on other living organisms. 64 Incomplete advance copy Grade 9  UNIT 3: Human biology and health Wherever you live and whatever the basis of your diet, it is not KEY WORDS enough simply to get food. The right balance of food is of enormous importance to your overall health and well-being. A balanced balanced diet taking food diet includes enough of all the major food groups (carbohydrates, from all major food groups proteins, lipids, minerals, vitamins and water) to supply the energy in order to maintain a and nutrients needed to maintain the cells, tissues and organs of healthy body your body in a healthy state. A balanced diet supports healthy undernutrition too little growth and development of your body when it is needed. If too food is eaten little food is eaten (undernutrition) or too much food is taken in (overnutrition), or any one element of the diet is lacking then you overnutrition too much will suffer from malnutrition. Malnutrition affects the health of food is eaten millions of people all over the world. malnutrition diet is lacking One of the most important factors in a balanced diet is that enough in important elements food is eaten to supply your energy needs. But how much energy needed for a healthy body is that? The amount of energy you need to live depends on lots of different things. Some of these things you can change and some you can’t. If you are male, you will need to take in more energy than a female of the same age – unless she is pregnant. During pregnancy the energy needs of a woman increase steadily as she has to provide the raw materials for a developing baby and supply the energy it needs to live. If you are a teenager, you will need more energy than if you are in your 70s. Figure 3.14 A balanced diet The amount of exercise you do affects the amount of energy you use contains a wide variety of foods up. If you do very little exercise, then you don’t that give you everything you need. need so much food. The more you exercise the more food you need to take in to supply energy to your muscles as they work. Table 3.4 Daily energy needs Age/sex/occupation of Energy needed person per day (kj) Newborn baby 2000 Child aged 2 5000 Child aged 6 7500 Girl aged 12–14 9000 Boy aged 12–14 11 000 Girl aged 15–17 9000 Boy aged 15–17 12 000 Female office worker 9500 Male office worker 10 500 Heavy manual worker 15 000 Pregnant woman 10 000 Figure 3.15 Athletes who spend a lot of time training Breastfeeding woman 11 300 and taking part in sport will have a great deal of Woman aged 75+ 7610 muscle tissue on their bodies – up to 40% of their body mass. So they have to eat a lot of food to supply the Man aged 75+ 8770 energy they need. Grade 9 Incomplete advance copy 65 Unit 3: Human biology and health Did you know? People who exercise regularly are usually much fitter than people who take little exercise. They make bigger muscles – and muscle Between 60 and 75% of tissue burns up much more energy than fat. But exercise doesn’t your daily energy needs always mean time spent training or ‘working out’ in the gym. are used up in the basic Walking to school, running around the house and garden, looking reactions needed to keep after small children or having a physically active job all count as you alive. 10% is needed exercise too. to digest your food – and only the final 15–30% is Malnutrition due to too little food is a major problem in many affected by your physical parts of the world. Yet it is also important that too much food is activity! not consumed. As you have seen the energy requirements of each individual vary depending on their age, sex and levels of activity. If you take in more energy than you need, the excess is stored as fat and obesity may result. In the developed world, overeating and the Did you know? health issues linked to it are becoming more and more of a problem. Most of us look about Up to a third of the population of America is thought to be seriously the right size but there overweight, mainly due to eating a diet rich in high-energy fat. will always be extremes. You need some body fat to cushion your internal organs and to act Some people are very as an energy store for when you don’t feel like eating. But when this overweight and others is taken to extremes, and you consistently eat more food than you appear unnaturally thin. need, you may end up obese, with a BMI of over 30. Scientists and doctors don’t just measure what you Our Ethiopian diet contains a wide range of foods, and by eating weigh. They look at your a good combination we can easily achieve a balanced diet. For body/mass index or BMI. example, a daily menu such as: This compares your weight Breakfast: bread and groundnuts or chick peas with tea or milk to your height in a simple Lunch: kei wot with injera and orange or banana formula: Dinner: shiro wot with injera and fresh green pepper weight BMI = These meals would give you a good balanced diet. If food is short (height)2 in times of drought or other difficulty, then the diet becomes Most people have a BMI unbalanced and lacking in calories and various nutrients. On the in the range 20–30. But, if other hand, if we are tempted by too much processed or fried food you have a BMI of below then we can become obese and put ourselves at risk. Use activity 3.6 18.5, or above 35, then you to help you think about balanced diet and good nutrition. may have some real health problems. Activity 3.6: A diet diary In this activity you should record everything you eat and drink every day for a week. Decide how you want to display your record – a table is a useful tool – and note down everything you eat at meal times. Also note down anything you eat between meals. Analyse your food each day and decide if you have eaten something from all of the main food groups. At the end of the week, think carefully about your diet. Is it balanced? If not, how could you improve it? If it is balanced, could you make it better still? 66 Incomplete advance copy Grade 9  UNIT 3: Human biology and health Summary Did you know? In this section you have learnt that: The heaviest man ever A balanced diet contains carbohydrates, proteins, lipids, recorded was Jon Brower minerals, vitamins and water in the right proportions to keep Minnoch (USA, 1941–83) your body functioning effectively. Fibre is also important. He was 185 cm (6’1”) tall and was overweight all Carbohydrates are the main energy supply for the body. his life. At his heaviest Carbohydrates are found as simple sugars, double sugars and he weighed 635 kg. The complex sugars. heaviest recorded woman Iodine is used to test for the presence of starch and was another American, Benedict’s solution for the presence of simple reducing Rosie Bradford, who sugars. weighed 544 kg in 1987. Proteins are used as the building blocks of the body. They are made up of small units called amino acids. The Biuret test using 5% sodium hydroxide solution and 1% copper sulphate solution is used to show the presence of protein in the food. Lipids are fats and oils. They provide energy for the body. They are made up of fatty acids and glycerol. The translucent smear test and the ethanol test identifies lipids in foods. Iron is needed in the body for the production of haemoglobin to carry oxygen in the red blood cells. Lack of iron in your diet causes anaemia. Calcium is needed for healthy bones and teeth. Lack of calcium in your diet can cause rickets. Vitamins are needed in small amounts for your cells to work properly. Vitamins A, B1, C and D are all vital for health. Figure 3.16 Manuel Uribe who holds the record for being the Malnutrition is when your diet is unbalanced. This can fattest man in the world at the result from too little food, when you are at risk of deficiency moment. At his peak he weighed diseases, and also too much food, which can give rise to 559 kg. obesity. Review questions Select the correct answer from A to D. 1. Which of the following is NOT part of a balanced diet? A carbohydrates B proteins C cellulose D lipids 2. Which of the following molecules are the building blocks of proteins? A monosaccharides B glycerol C fatty acids D amino acids Grade 9 Incomplete advance copy 67 Unit 3: Human biology and health 3. Which of the following groups are classed as macronutrients? A proteins, minerals, vitamins B carbohydrates, proteins, fats C fats, fibre, folic acid D carbohydrates, proteins, milk 4. Vitamin A is also known as: A tocopherol B retinol C ascorbic acid D calciferol 5. In what type of reaction do fatty acids and glycerol join together to form lipids? A hydrolysis B condensation C reduction D oxidation 6. A student carried out a Benedict’s test on an unknown food sample and the blue liquid turned orange when it was heated. What food substance was present? A protein B starch C simple sugar D lipid 7. Which of the following will NOT cause obesity, even if you eat very large amounts of it in your diet? A fat B fibre C carbohydrate D protein 68 Incomplete advance copy Grade 9  UNIT 3: Human biology and health 3.2 The digestive system By the end of this section you should be able to: Label a diagram of the human digestive system. Describe the functions of the structures of the human digestive system. Define enzymes and describe their role in the process of digestion. Describe the structure of the teeth and explain their importance. Describe the processes of digestion in the mouth, stomach and small intestine. Demonstrate that starch digestion begins in the mouth using saliva and bread. Explain how the products of digestion are absorbed and assimilated by the body. Discuss constipation, care with canned, bottled and packed foods and food hygiene as issues of digestive health. Carbohydrates provide the body with an energy source for respiration. Proteins are needed for building new cells and repairing old ones. Lipids are also an energy source and they provide a way of storing spare energy. However, in the form that they are usually eaten neither carbohydrates, proteins nor fats are useful to the body. The link between what comes in and what the body needs is the digestive system. The human body needs small, soluble molecules to use in all the reactions of metabolism such as releasing energy and making new larger molecules. The food we eat usually arrives in the system as large chunks bitten off by the teeth, chunks that contain large insoluble molecules such as starch, proteins and fats. These large molecules cannot be absorbed into the bloodstream and used by your body so they need to be broken down into smaller, simpler, soluble molecules. This is the main job of the digestive system – food substances are broken down into small soluble molecules as they pass through the gut. As you have seen earlier in this chapter, the large molecules that make up the carbohydrates, proteins and fats are built up from small molecules that are joined together by condensation reactions, with a molecule of water being lost each time. When these large molecules are broken down during digestion it involves the opposite process – hydrolysis (splitting with water) reactions. As water molecules are added to the large food molecules, the monomer units, whether they are simple sugars, amino acids or fatty acids, are released. hydrolysis O + H2O OH + HO condensation Figure 3.17 The large food molecules are broken down by hydrolysis reactions – the opposite of the condensation reactions by which they are built up in the first place. Grade 9 Incomplete advance copy 69 Unit 3: Human biology and health The working of your digestive system is based on two things: The physical (or mechanical) breakdown of the food: The food you eat is physically broken down into smaller pieces in two main ways. Your teeth bite and chew the food up in your mouth. Then your gut, which is a muscular tube, squeezes the food and physically breaks it up, while mixing it with various digestive juices to make it easier to move. By breaking the food up in this way, there is a much larger surface area for the digestive enzymes to work on. The chemical breakdown of the food: The large insoluble food molecules must be broken down by hydrolysis reactions into small, soluble molecules so they can be absorbed into your body. This chemical breakdown is controlled by enzymes. Enzymes are proteins that speed up (catalyse) other reactions. They do not actually take part in the reaction or change it in any way except to make it happen faster. Enzymes are biological catalysts that usually work best under very specific conditions of temperature Figure 3.18 A piece of meat is and pH. broken down by hydrochloric acid in a few days – but we can’t wait More about enzymes that long to get energy and useful Enzymes play a vital role in digestion – but that is not all they do. chemicals from our food. In the For life to carry on successfully it is important that the hundreds human stomach a similar piece of reactions that occur in your body, making new materials and of meat is broken down in a few breaking things down, take place in a rapid and controlled way. This hours, thanks to the action of the control is brought about by biological catalysts known as enzymes. enzyme pepsin. Enzymes are made of protein, and like any catalyst are not affected by the reaction they speed up, so they can be used many times. Did you know? Enzymes are very specific – each type of reaction that takes place in your body is controlled by a specific enzyme that does not catalyse Your gut is actually a any other type of reaction. Some enzymes work inside your cells hollow tube that runs (intracellular enzymes) and some of them are secreted into organs from your mouth to your of your body such as the gut where they catalyse specific reactions anus. Some things (such (extracellular enzymes). The digestive enzymes are extracellular – as a bead or a penny) can they work outside your cells in the lumen of your gut. be taken in at the mouth and reappear completely Enzyme names usually (but not always) end in –ase, e.g. amylase unchanged at the other breaks down starch, lipase breaks down fats, catalase breaks down end. Do NOT try this – hydrogen peroxide – but pepsin breaks down proteins! objects can get stuck and block the tube, making you very ill. 70 Incomplete advance copy Grade 9  UNIT 3: Human biology and health Activity 3.7: Investigating the activity of amylase Amylase is an enzyme that is Method made in the salivary glands 1. Place drops of iodine solution in the depressions on both of in your mouth and in your the spotting tiles. pancreas; it catalyses the breakdown of starch to the 2. Place 5 cm3 of starch suspension in each of two boiling tubes, sugar maltose. You can use one labelled starch and the other labelled starch/amylase. the reaction of starch with 3. Place 5 cm3 of amylase solution in another boiling tube, iodine solution to indicate labelled amylase. how quickly the enzyme does its job – and use this 4. Place the three tubes in the water bath at 30 °C. Leave for to investigate the effect of five minutes for the temperatures to equilibrate. temperature on the way the 5. Measure out 5 cm3 of amylase solution and add it to the enzyme works. labelled boiling tube of starch. You will need: 6. Start the stopwatch and immediately take a small sample of amylase solution the starch/amylase mixture and add it to the first drop of iodine on the spotting tile. starch suspension 7. Take regular samples of the mixture – every 30 seconds – iodine solution for about ten minutes and record the colour of the iodine each a stopwatch or clock with time. clear second hand 8. At the end of the ten minutes, test a sample of the simple two spotting tiles or starch suspension in one well of the spotting tile and compare white tiles it with the sample which has been mixed with amylase. This beaker of water heated to will confirm that any change is due to the enzyme rather than 30 °C the temperature of the solutions. boiling tubes 9. This investigation can be repeated with the starch suspension two 5 cm3 syringes or and the starch/amylase mixture kept at a range of different pipettes temperatures and the results recorded in a table like the one shown below: thermometer marker pen Colour of iodine/starch/amylase mixture at different temperatures Time (min) 20 °C 30 °C 40 °C 50 °C 60 °C 0.5 1.0 1.5 2.0 etc. 10.0 10. You can make a graph of your results, looking at the time taken to break down all the starch at different temperatures or looking at the rate at which the enzyme broke down 1 cm3 of starch at each temperature. 11. Write up your investigation, explain your results and suggest ways in which your investigation could be made more reliable. Grade 9 Incomplete advance copy 71 Unit 3: Human biology and health KEY WORDS The working of the gut ingestion taking in food The process by which the food you eat is taken into your body, mastication chewing broken down and used by your cells, with the indigestible material removed, is very complex and it involves the various areas of your enamel the top surface of digestive system or gut. teeth As we eat our food, it sets off on a journey of digestion. The first stage is ingestion, or taking foodstuff into your body through the mouth. We bite off a chunk of food using our teeth, and then physically chop the food up into smaller pieces by chewing it. Your teeth play a very important role at the beginning of the process of digestion, physically breaking down your food and providing a greater surface area for your digestive enzymes to work on. This process is known as mastication. salivary gland mouth tongue oesophagus (gullet) trachea (windpipe) liver stomach gall bladder pancreas duodenum small intestine ileum colon large appendix intestine rectum anus Figure 3.19 The human digestive system Teeth have evolved to be very strong – in fact the enamel that covers them is the strongest substance made by the human body. Teeth are needed for a variety of different jobs – gripping food, tearing food and chewing food, for example. The shape of different teeth means they are ideally suited to their different functions. Because humans have a very varied diet (we are omnivores so we eat animals and plants) we also have a variety of different types of teeth. The incisors and canines are used for biting while the premolars and molars are used for chewing and crushing food. 72 Incomplete advance copy Grade 9  UNIT 3: Human biology and health All of your teeth have a similar make-up. The top surface is covered enamel dentine by a layer of non-living enamel, and under this is the living dentine. This is not as hard as enamel, but it is still very hard, being similar pulp cavity to bone. In the centre of the tooth is the pulp cavity, which contains containing nerves and blood vessels. The dentine contains many fine channels nerves crown and blood filled with cytoplasm. These are supplied with oxygen and nutrients vessels by the blood vessels in the pulp cavity. Your teeth are set into your gum jaw bone, and they are held in place by a layer of fibrous cement. This cement keeps your teeth firmly in place but at the same time allows a certain amount of flexibility as you are chewing. Your adult teeth should last you all through your life. This doesn’t root always happen, because your teeth can be affected by the bacteria bone of that cause dental caries. There are many different bacteria that are jaw found naturally in your mouth. These bacteria, combined with food and saliva, form a thin film known as plaque on your teeth. If these cement bacteria are given a sugar-rich diet (in other words, if you eat a lot of fibres attaching sweet, sugary food) they produce a lot of acid waste. This acid attacks tooth to jawbone and dissolves the tough enamel coating of your teeth. Once through the enamel, the acid also dissolves away some of the dentine and then Figure 3.20 The structure of teeth the bacteria can get into the inside of your tooth. The bacteria will makes them very well adapted to then reproduce and feed, eating away at your tooth until they reach their various functions. the nerves of the pulp cavity causing toothache. The bacteria and the acid they produce can eat away at your teeth to the extent that they KEY WORDS break up completely if you don’t get effective dental treatment. dentine living layer What’s more, the bacteria don’t only attack your teeth. The same underneath tooth enamel bacteria can affect your gums, causing periodontal disease. The symptoms include tender gums, bleeding when you clean your teeth pulp cavity centre of the and eventually the possible loss of all your teeth, not from tooth tooth which contains nerves decay but from gum disease. and blood vessels Taking in lots of acidic food and drink, such as fruits and cola, can cement fibrous layer that also weaken the enamel on your teeth. This is particularly the case if holds the teeth into the jaw you clean your teeth straight after an acidic drink such as fruit juice bone or cola, when the softening effect on the enamel is strongest and periodontal disease brushing your teeth can actually wear the enamel away. bacterial infection of the Tooth and gum disease are extremely common all over the world. gums They cause pain, bad breath, loss of teeth and difficulty eating. The good news is that they can both be avoided, especially if you have good dental care available. Ways to avoid tooth decay include: Regular brushing of your teeth and gums twice a day. This removes the plaque from the teeth, preventing the build-up of a sticky, acidic film over the enamel. Avoiding sweet, sugary foods – if the bacteria in your teeth are deprived of sugar, they cannot make acidic waste and your teeth are safe. If they are available: Have regular dental check-ups. A dentist can clean your teeth Figure 3.21 Tooth decay not only more thoroughly than you can, and any early signs of decay can causes pain and bad breath – it be treated. Your teeth won’t heal themselves, but any tooth decay doesn’t look very nice either! can be removed and replaced by a filling. Grade 9 Incomplete advance copy 73 Unit 3: Human biology and health Did you know? Moving the food on Around 40 million people The breaking down of your food into smaller pieces by the chewing in America have lost all of your teeth isn’t the only part of digestion that takes place in their own teeth and have to your mouth. Your food is also coated in saliva from the salivary wear dentures (false teeth)! glands. Saliva contains a carbohydrase enzyme called amylase. They use tiny amounts of Carbohydrases break down carbohydrates. The amylase in your fluoride in their toothpaste saliva begins the digestion of the starch in complex carbohydrates and water to help them such as bread or potatoes, turning it into simpler sugars. The saliva- prevent tooth decay. Here coated chunk of food (known as a bolus) moves to the back of your in Ethiopia, some of our throat to be swallowed. Swallowing is a reflex action that takes place water- courses contain when food reaches the back of your throat. As you swallow, your so much fluoride that it epiglottis closes over the trachea, preventing food going down into damages our teeth. We use your lungs; you can’t swallow and breathe in at the same time. If you defluorination plants to take try to, you will choke and your body will produce violent coughing fluoride out of our water to and heaving movements to make sure the food doesn’t get down protect our teeth and keep into your lungs, where it can cause serious problems. them healthy! When your food is swallowed it travels down the oesophagus or gullet, squeezed along by muscular contractions known as peristalsis. As a result you can eat at any angle you like – even standing on KEY WORDS your head – because food does not rely on gravity to arrive in your stomach. Peristalsis is not confined to your oesophagus – it is carbohydrase an enzyme in important all the way through your gut to move the food through as saliva it is digested, to mix the food with the digestive enzymes produced bolus a saliva-coated chunk in the various parts of the gut and to continue the physical break-up of chewed food of the food. The walls of your gut have a layer of circular muscles forming rings around it and a layer of longitudinal muscles that run reflex an automatic the length of the gut. Waves of alternate contraction and relaxation of reaction in the body that the different muscles (see figure 3.23) move food through from one cannot be controlled end of the gut to the other. oesophagus passage that food travels down from mouth to stomach peristalsis wavelike muscle tongue pushes food to back of contractions to move food mouth along food trachea oesophagus epiglottis (covers entrance to trachea) Figure 3.22 The swallowing reflex means you don’t get food down into your lungs – and you can’t breathe in while you are swallowing food. 74 Incomplete advance copy Grade 9  UNIT 3: Human biology and health longitudinal muscle layer Stomach churning activity circular muscles contract At the lower end of the oesophagus your food passes through a ring of muscle called a sphincter into your stomach. This sphincter is position of food usually closed except when you are swallowing food, or being sick. The stomach is a muscular bag that produces protease enzymes to digest protein. The main protease made in the stomach is pepsin. The stomach also produces a relatively concentrated solution of hydrochloric acid. This acid kills most of the bacteria that are taken in with our food. The acid also helps indirectly in the breakdown direction of peristalsis of the protein in your food, because pepsin works best in acid circular muscles relax conditions. Your stomach also makes a thick layer of mucus, which circular muscle layer protects the muscle walls from being digested by the protease enzymes and attacked by the acid. The muscles of your stomach Figure 3.23 Muscular action in squeeze the contents into a thick creamy paste containing partly your gut pushes the food along. digested protein along with all the rest of your food. After a time – usually between one and four hours – a paste of partly digested food is squeezed out of the stomach through another KEY WORDS sphincter into the first part of the small intestine known as the sphincter ring of muscle duodenum. As soon as it arrives the food is mixed with two more liquids: bile and enzymes. stomach muscular bag that produces protease enzymes Bile to digest protein pepsin enzyme that breaks Bile is a greenish-yellow alkaline liquid that is produced in the liver down proteins (a large reddish-brown organ that carries out lots of important jobs in the body). It is made by the liver cells and then stored in the gall hydrochloric acid produced bladder until it is needed. As food comes into the duodenum from in the stomach to kill the stomach, bile is squirted onto the stomach contents. The bile bacteria does two important jobs: gall bladder muscular sac It neutralises the acid from the stomach and makes the semi- connected to the liver that digested food alkaline. This is ideal for the enzymes in the stores bile small intestine, which work most effectively in an alkaline bile produced by the liver environment. to aid in breakdown of food Bile also emulsifies the fats in your food – it breaks down large in the duodenum drops of fat into smaller droplets. This provides a much bigger surface area of fats for the lipase enzymes to work on to break down the fats completely into fatty acids and glycerol. Enzymes Rate of reaction of pepsin The first part of the small intestine (the duodenum) cannot make its own enzymes, but this doesn’t matter because they are supplied by the pancreas. Part of the pancreas makes the hormone insulin, which helps to control your blood sugar levels (you will learn more 0 2 4 6 about this in Grade 10). The rest of the pancreas makes and stores pH enzymes that digest carbohydrates, proteins and fats. As food enters Figure 3.24 The protein-digesting the small intestine from the stomach these enzymes are released to enzymes of the stomach only work be mixed with the food paste by muscle action. at their best in low pH, so the acid