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Functions of Food

Functions of Food. to maintain life to supply energy & give warmth carbohydrates fats proteins for growth and repair Proteins keep healthy & help to fight against disease. Carbohydrates. elements : C, H, O ratio of H : O = 2 : 1 monosaccharides C 6 H 12 O 6

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Functions of Food

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  1. Functions of Food • to maintain life • to supply energy & give warmth • carbohydrates • fats • proteins • for growth and repair • Proteins • keep healthy & help to fight against disease

  2. Carbohydrates • elements : C, H, O • ratio of H : O = 2 : 1 • monosaccharides • C6H12O6 • all are sweet & soluble in water • all are ReducingSugars • include Glucose, Fructose & Galactose

  3. surcose Carbohydrates • disaccharides(from 2 monosaccharides) • C12H22O11 • all are sweet & soluble in water • Maltose ( 2 glucose molecules ) • Sucrose ( glucose + fructose) • (non-reducingsugar) • Lactose ( glucose + galactose)

  4. Carbohydrates • polysaccharides (NOT sugar) • for energy storage • starch (store in plants)glycogen (store in animals) • Hydrolysis:Polysaccharide +H2O Disaccharides +H2O  Monosaccharides

  5. Functions of Carbohydrates • main source of energy • cellulose: - fibrous material of Plant Cell Wall - dietary fibre: stimulates Peristalsis • excess carbohydrates - stored as glycogen in liver & muscle - stored as fats under skin

  6. Investigation 5.1 Test for Reducing Sugars (Benedict’s Test)

  7. A B glucose solution + Benedict’s solution distilled water + Benedict’s solution water bath Is there any colour change in tubes A and B ? Ans: Only the mixture in tube A has a colour change.

  8. A B glucose solution + Benedict’s solution distilled water + Benedict’s solution water bath What is the sequence of change when there is a colour change ? Ans: The blue solution changes first to green, then to a yellow coloration and eventually a brick-red precipitate is produced.

  9. Investigation 5.2 Test for Starch (Iodine Test)

  10. iodine solution distilled water starch solution B A What is the final colour in tube A ? Ans: The solution in tube A changes from brown to blue black.

  11. iodine solution distilled water starch solution B A What is the purpose of setting up tube B ? Ans: To act as a control.

  12. Proteins • elements: C, H, O, N, sometimes S, P • components : amino acidsforms dipeptides & polypeptides • Condensation: Amino acids–H2O Dipeptides –H2O  Polypeptide

  13. Proteins • are compounds of carbon, hydrogen, oxygen, nitrogen and sometimes sulphur, phosphorus • amino acids: • unit of proteins • about 20 different types • essential and non-essential types

  14. An amino acid molecules R C COOH carboxyl group H2N amino group H

  15. The condensation and hydrolysis of a polypeptide 4 1 2 5 3 condensation hydrolysis 1 2 3 4 5

  16. Condensation of two amino acid to form a dipeptide O R1 H H C H2N C N C COOH OH H H R2 H2O R1 H O C H2N C---N C COOH H H R2

  17. Proteins • cannot be stored -excess proteins are deaminated by liver ~to Urea which will be excreted away by Kidney ~ to Carbohydrates (Glycogen) which will be stored in Liver

  18. Functions of Proteins • for growth and repair of body cells (as structural components (cell membrane and cytoplasm) of cells) • to produce hormones and enzymes and antibodies • to give energy • for making Haemoglobin in blood • for making Antibodies

  19. Deficiency disease of proteins Kwashiorkor

  20. Investigation 5.3 Test for Proteins (Biuret Test)

  21. Test for proteins / Biuret test egg white solution 1 cm3 NaOH solution Put CuSO2 solution drop by drop, and shake the mixture after addition of each drop Positive result: purple colour

  22. copper sulphate solution egg white + sodium hydroxide solution water + sodium hydroxide solution B A What colour changes in tubes A and B ? Ans: Mixture in tube A changes from blue to purple while mixture in tube B remains blue without any change.

  23. Lipids ( fats & oils ) • elements : C, H, O • components of 1 lipid molecule: 1 glycerol + 3 fatty acids • insoluble in water • soluble in organic solvent

  24. Functions of Lipids • give energy • component of cell membrane • form fatty tissues under skin > to store energy > acts as insulator to keep warm • to transport fat-soluble vitamins (A, D, E, K)

  25. Investigation 5.4 Spot Test for Fat

  26. Which substance, oil or water, leaves a permanent translucent spot on the filter paper ? Ans: Oil.

  27. Investigation 5.5 Emulsion Test for Fat

  28. 2 drops of cooking oil 2 cm3 of alcohol 2 cm3 of distilled water A after shaking to form a clear solution shake and then allow to stand emulsion 2 drops of cooking oil 2 cm3 of distilled water 2 cm3 of distilled water B oil shaking shake and then allow to stand water Which test tube has an emulsion formed ? Ans: Test tube A.

  29. 2 drops of cooking oil 2 cm3 of alcohol 2 cm3 of distilled water A after shaking to form a clear solution shake and then allow to stand emulsion 2 drops of cooking oil 2 cm3 of distilled water 2 cm3 of distilled water B oil shaking shake and then allow to stand water What happens to the other tube ? Ans: The mixture separates into two layers because fats do not dissolve in water.

  30. Vitamins • no energy value • essential for small amount to maintain good health • water soluble vitamins ( B, C ) • fat soluble vitamins( A, D, E, K ) • excessive of some vitamins may be harmful

  31. Vitamin A • formed in the body from Carrotene (a yellow pigment in carrots) • destroyed at high temperature • essential for forming visual purple (maintain dim light vision)

  32. Vitamin C • Destroyed after prolonged cooking • Necessary for wounds-healing Vitamin D • Formed in Skin from Ultraviolet Light • Help to regulate Ca & P metabolism

  33. Investigation 5.6 Detection of Vitamin C in Lemon Juice by using DCPIP

  34. syringe lemon juice DCPIP solution What colour change has occurred ? Ans: The blue DCPIP decolourizes.

  35. syringe lemon juice DCPIP solution What conclusion can you draw ? Ans: Lemon juice contains vitamin C which decolourizes blue DCPIP.

  36. Vitamin Sources Deficiency Disease A Egg yolk, milk, cheese, carrot, green vegetables Night blindness C Fresh fruits & green vegetables Scurvy D Cod liver oil & egg yolk Rickets

  37. Substances Test Original Colour Positive Result Reducing Sugar Benedict’s Blue Orange ppt Starch Iodine Brown Blue-black Protein Biuret Blue Violet Fats/Oils Spot --- Translucent spot Fats/Oils Emulsion Clear Milky emulsion Vitamin C DCPIP Blue Colourless (decolourize) Food Tests

  38. Mineral Salts • regulate body metabolism • essential for healthy growth • necessary for construction of certain tissues • needed in small amount • include Ca, S, K, Na, Mg, Fe, I

  39. Mineral(s) Sources Functions Deficiency Disease Calcium & Phosphorus Cheese, milk, vegetables Making bones & teeth Important for blood clotting & muscle contraction Rickets Iron Liver, eggs, beef, green leafy vegetables Structural component of Haemoglobin Anaemia

  40. Dietary Fibre • mainly cellulose • indigestible material for human • give bulk to food & stimulate peristalsis  preventConstipation • lack of dietary fibre: Large Intestine Cancer • sources: wholemeal cereals, unpolished rice, fresh vegetables & fruits

  41. Balanced Diet • have enough food to supply enough • energy • carbohydrates, fats, proteins • body building materials • proteins • substances to maintain health • vitamins, minerals, water & dietary fibres • malnutrition :not having balanced diets for long time

  42. Energy Contents in Food • Calorimeter is used to measure the amount of energy contained in a particular type of food • Carbohydrate (17kJ/g) • Protein (18kJ/g) • Fat (39kJ/g)

  43. Factors affecting energy requirement • Sex • Age • Occupation • Physical Activities • Stage of individual(pregnancy, breast-feeding)

  44. Investigation 5.8 Measure the Energy Value of Food

  45. boiling tube thermometer water burning peanut Explain why the energy value of the peanut is lower than those from standard tables. Ans: Because there are a number of inaccuracies associated with this method due to incomplete combustion and heat loss.

  46. Basal Metabolic Rate (BMR) • minimum amount of energy needed by an individual lying awake in bed to maintain breathing, body temperature & heartbeat • varies from one individual to another • daily energy requirement > basal metabolic rate

  47. ~ END ~

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