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CHAPTER 2

CHAPTER 2. NUTRITION. CLASSES OF FOOD. 7 classes of food: Carbohydrates Proteins Fats Vitamins Minerals Fibre Water Carbohydrates, proteins, fats, vitamins and mineral also called nutrients (contain useful substance require for our body)

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CHAPTER 2

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  1. CHAPTER 2 NUTRITION

  2. CLASSES OF FOOD • 7 classes of food: • Carbohydrates • Proteins • Fats • Vitamins • Minerals • Fibre • Water • Carbohydrates, proteins, fats, vitamins and mineral also called nutrients (contain useful substance require for our body) • Nutrition = the process of obtaining and using the nutrients from food

  3. CARBOHYDRATES • Organic compounds made up carbon, hydrogen and oxygen • Supply most of the energy • Can be found in: • Sugars (honey, sugar cane, fruits) • Starches (rice, bread, potatoes). Glycogen is stored in the liver and muscles • Cellulose (plants cell walls) • Examples of food : flour, bread, rice, sugar, potatoes

  4. PROTEINS • Organic compounds containing carbon, hydrogen, oxygen and nitrogen • Sometimes sulphur and phosphorus are present • A molecule of protein made up of a large number of subunits called amino acids • Amino acids can be made by our body cells or supplied through the food that we eat • Needed for growth and repair the body tissues • Required for the formation of enzymes, hormones, haemoglobin, antibodies • Example of foods : chicken, fish, eggs, milk

  5. FATS • Compounds of carbon, hydrogen and oxygen • Stored under the skin or around organs in our body • Helps to keep warm and protects organs from damage • Helps to transport vitamin A, D, E and K • Can store a lot of energy • Fats are solid, while oils are liquid at room temperature • Example of foods : margarine, butter, oil, peanuts

  6. VITAMINS • Organic compounds needed in small amounts for health and growth • 2 groups: • Water-soluble vitamins (B and C) • Fat-soluble vitamins (A, D, E and K) **Copy table 2.1 (page 41)**

  7. MINERALS • Inorganic substances needed in small amount for healthy growth and development ** Copy table 2.2 (Page 42)**

  8. FIBRE • Also known as roughage • Cannot be digested • Can hold a lot of water for faeces remain soft and can pass easily • Helps to stimulate peristalsis • Fibre can prevent constipation • Examples of foods : fruits, vegetables, cereals

  9. WATER • Main component of blood and body fluid • Function: • Control the body temperature • Control the concentration of blood • Removing excretory products

  10. THE IMPORTANCE OF BALANCED DIET • Diet = all food that we eat each day • Balanced diet = contains the right amounts of the 7 classes of food to meet the daily requirements of the body • The factors influenced the amount of food for daily intake: • Sex (the males need more than females) • Age (the adults need more than children) • Body size (the bigger need more than smaller) • Occupation (the sedentary worker need more than office worker) • Climate (people live in cold area need more than people live in hot area) • People who do not eat a balanced diet can suffer from malnutrition and deficiency disease

  11. ENERGY VALUE OF FOOD • Unit of energy in food = calories (cal) or joules (J) • Calorific value / energy values : the amount of energy released from 1g of a particular type of food • Energy value of carbohydrates, proteins and fats 1 cal = 4.2 J

  12. HUMAN DIGESTIVE SYSTEM • Digestion = the process of breaking down large food molecules into smaller molecules that can be readily absorbed by the body • Occurs in 8m long tube called gut / alimentary canal • Begins at the mouth and ends at the anus • Physical digestion : chewing by the teeth and the churning in the stomach • Chemical digestion : action of enzymes on food • Enzymes = substances which act as catalysts and generally speed up the chemical reactions in our body

  13. 3 main kinds of enzymes : • Amylase – breaks down carbohydrates molecules • Proteases – breaks down proteins molecules • Lipases – breaks down fats molecules • End products of digestion : • Glucose from carbohydrates • Amino acids from proteins • Fatty acids and glycerol from fats • Cellulose is not digested in humans because not have enzyme cellulase

  14. Mouth • food is chewed into smaller pieces and mixed with saliva • Amylase break down starch into maltose (kind of sugar) • Oesophagus • Digested food is shaped into a bolus • The bolus moves down the oesophagus in a wave-like action called peristalsis • Peristalsis occurs when the oesophageal wall contracts and relaxes alternately

  15. Stomach • Stomach wall produces gastric juices contain proteases and hydrochloric acid • Hydrochloric acid : - stops the action of salivary amylase - provides an acidic medium suitable for action of proteases - changes the inactive forms of proteases to its active forms - kills bacteria in food • Proteases break down proteins into polypeptides or peptones • Mucus protects stomach wall from digested by proteases • Food in stomach wall mixed with gastric juice to form the semi-solid food called chyme

  16. Duodenum • First part of small intestine • Receive bile from the gall bladder and pancreatic juice from the pancreas • Bile = greenish fluid produced by the liver and stored in gall bladder • Bile : - emulsifies fats into oil droplets for lipase to act - neutralises the acidic chyme • Pancreatic juice contains amylase, protease & and lipase • Amylase break down starch into maltose • Protease break down proteins into polypeptides • Lipase break down fats into fatty acids and glycerol

  17. Small intestine • Secretes intestinal juice contains maltase, protease and lipase • Maltase break down maltose into glucose • Protease break down polypeptides into amino acids • Lipase break down fats into fatty acids and glycerol

  18. ABSORPTION OF DIGESTED FOOD • Small intestine is well adapted for the absorption of digested food • The surface of small intestine is highly folded and has millions of tiny finger-like projections called villi • The surface of small intestine increase the absorption of digested food • Digested food is absorbed into bloodstream mainly by diffusion • From the bloodstream, the digested food passed into the liver and then to the heart and to all parts of the body

  19. REABSORPTION OF WATER AND DEFECATION • Digestion of food is completed in our small intestine • The residue from small intestine is mainly water, undigested food, mucus and digestive juices • From here, the watery residue moves to the large intestine • Water together with dissolved minerals and vitamin, is absorbed into the blood

  20. HEALTHY EATING HABITS • Healthy eating habits help to maintain the healthy body • Unhealthy eating habits cause various health problems

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