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  1. 1. Classes of Food•Food is a collection of chemicals taken into anorganism for the following purposes:a. It provides energy for cellular activities.b. It provides raw materials for growth and repair ofworn- out tissues.c. It keeps the organism healthy.Food is not only tasty but also useful
  2. 2. •The process of making or obtaining food is callednutrient.•There are seven classes of food:•Carbohydrates•Proteins•Fats•Vitamins•Minerals•Fibre•water
  3. 3. •Carbohydrates are food substances consisting ofcarbon, hydrogen and oxygen in their molecules. TheH:O ratio in carbohydrates molecules is 2:1.•Carbohydrates include sugars, starch, glycogen andcellulose.•Sugars and crystalline compounds that taste sweet andare water – soluble.•Examples of sugars are glucose( grape sugar), sucrose (cane sugar), lactose (milk sugar) and maltose (maltsugar)Carbohydrates
  4. 4. •Starch is stored in plant cells, rice, potatoes and tapiocacontain plenty of starch.•Glycogen is also known an “animal starch” because itis stored in animal cells. Glycogen is stored mainly inthe liver and muscles.•Cellulose forms the greater part of the cell walls ofplants.•Starch, glycogen and cellulose are all made up ofglucose molecules.
  5. 5. •Starch , glycogen and cellulose are all made up ofglucose molecules.•Starch and glycogen can be readily converted toglucose when needed.Importance of carbohydrates:•Main source of energy for cell activities.•Form supporting structures, such as cell walls inplants.•Can be converted to protein and fats.
  6. 6. •Proteins are food substances that containcarbon, hydrogen, oxygen and nitrogen. Sulphur andphosphorus are present too.•Every protein molecule is made up of basic unitscalled amino acids.•Meat, fish and eggs contain animal proteins whilebeans, nuts and seeds contain plant proteins.Proteins
  7. 7. •Needed for growth and repair of worn – out ordamaged cells.•Used for the synthesis and enzymes and somehormones.•Important component of antibodies which help thebody to fight diseases.•A source of energy.Importance of proteins:
  8. 8. •Fats consists of carbon, hydrogen and oxygen. Unlikecarbohydrates, however, fats contain less oxygen inproportion to hydrogen.•Fats which are liquid at room temperature are calledoils. Examples are palm oil and coconut oil.•Each fat molecule consist of a glycerol molecule andthree fatty acid molecules.•Food rich in fats include butter, margarine, cooking oiland fatty meats.Fats
  9. 9. •An efficient source and storage of energy . Each gram offat provides about twice the amount of energy suppliedby carbohydrates or proteins. Excess fats are stored asfatty tissue under the skin and around internal organssuch as the kidneys and the heart to protect the organsfrom physical injury.•Act as solvent for fat – soluble vitamins A, D, E and K.•An important component of cell membrane.Importance of fats:
  10. 10. •Fats under the skin also act as an insulator to reduceheat loss from the body.•A diet rich in fats, however, increase the risk of heartdisease.
  11. 11. •Vitamins are organic compounds that are required invery small amounts for maintaining good health.•Vitamins are not energy providing foods.•Vitamins are divided into water – soluble vitamins andfat – soluble vitamins.•The water – soluble vitamins are vitamin B and C.•The fat – soluble vitamins include vitamins A, D, E andK.•Diseases caused by a lack of vitamins in our body arecalled vitamin deficiency diseases.•We should eat a varied diet to obtain all the differenttypes of vitamins that our body needs.Vitamins
  12. 12. Vitamins Source Function DeficiencydiseaseA Tomatoes, carrots,fish liver, oil, greenvegetables, egg yolk,liver•For nightvision or visionin dim light.•Healthy skin•Bightblindness•Skin infectionsB Whole grain bread,cereals, eggs, milk,green vegetables•Healthy skin•Healthynervous system•Developmentof red bloodcells•Release ofenergy fromcarbohydrates•Beri – beri(paralysis•Dermatitis(skin disorder)•Pellagra(mentaldisorder andskin disease)•Anaemia(deficiency inred blood cells)
  13. 13. Vitamins Source Function DeficiencydiseaseC Fresh fruits, greenvegetables•Healthy tissues•Healing ofwounds•Resistance ofdisease•Scurvy(bleedinggums, internalbleeding inmuscles andskin)D Liver, fish liver oil,egg yolk, formed inskin by sunlight.•Promotesabsorption ofcalcium andphosphorus•Formation ofhealthy teethand bones.•Rickets(bowed legsand knockknees)•Osteomalacia(softening ofbones)
  14. 14. Vitamins Source Function DeficiencydiseaseE Whole grain, wheatgerm, vegetable oil•Maybe neededforreproduction•Sterility(failure toreproduction)K Green vegetables,tomatoes, egg yolk,made by bacteria inthe large intestine•Essential forblood clotting•Prolongedbleeding
  15. 15. •Minerals are inorganic chemical elements that areneeded in small amounts.•Minerals are required to regulate body processes.•A lack minerals causes deficiency diseases.Minerals
  16. 16. Minerals Source Function DeficiencydiseaseCalcium Milk, cheese, eggs,anchovies, yogurt,green vegetables.•Buildinghealthy bonesand teeth•Clotting ofblood•Normalfunctioning ofmuscles andnerves•Rickets•Delayedclotting•MuscularspasmsSodium Table salt, salty fish,salty eggs, cheese•Normalfunctioning ofnerves•Maintenanceof tissue fluids•Muscularcramps
  17. 17. Minerals Source Function DeficiencydiseaseIron Liver, kidneys, egg,green vegetables•Needed for theformation ofred blood cells•Activatecertain enzymes•anaemiaIodine Iodine salt, sea fish,shellfish•Needed tomake hormoneof the thyroidgland•Control bodygrowth•Goitre(swelling of thethyroid gland inthe neck)
  18. 18. Minerals Source Function DeficiencydiseasePhosphorus Milk, wholegrain bread,cereals meat.•Formation of healthybones and teeth•Proper functioning ofmuscles•Formation of chemicalsubstances that storeenergy•Rickets•weaknessPotassium Meat, milk,fish,mushrooms,bananas•Normal functioning ofnerves.•Maintenance of tissuefluids•Regulation ofheartbeat.•Weakmuscles•paralysis