CHAPTER 2NUTRITION

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2.1 Classes of foodCarbohydrates • Supply energyProtein • Needed for growth • Produce new cellsFats• Act as insulator of heat for the body • Supply energyVitamins • Maintain good health

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Water • Helps in the digestion of food• Transports digested food to cells• Transports excretory products from cells to

excretory oragnsFibre• Helps in peristalsis• Prevents constipationMinerals• Maintain good health

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1. All the classes of food are also called nutrients are as they contain substances that are needed by our body.

2. Nutrition is a process of obtaining and using from food.

3. Vitamins are needed in small amounts to keep us healthy.

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VitaminVitamin A • Prevents night blindness, xerophthalmia, keratomalacia Vitamin B • Prevents beriberi, pellagra, dermatitis, anaemia,

dementia Vitamin C• Prevents scurvyVitamin D• Prevents rickets, osteomalacia, dental cariesVitamin E• Prevents sterilityVitamin K• Helps in the clotting of blood 5

4. Minerals play a vital role in regulating many body function Minerals Sources of food Deficiency diseases

Calcium Milk, cheese, eggs, vegetables RicketsTooth decay

Sodium Common salt Muscle cramps

Iron Meat, eggs, liver, vegetables Anaemia

Iodine Seafood, seaweed, vegetables Goire

Phosphorous Milk, cheese, eggs, vegetables RicketsTooth decay

potassium Meat, fish, grains Muscle cramps

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5. Fibre is made up of cellulose and cannot be digested.

6. Fibre helps food to move aesily through the alimentary canal.

7. An adult needs at least 6 to 8 glasses ofwater a day.

8. We can detect the presence of a nutrient or a class of food by using certain reagents in a laboratory.

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Food test Positive result Conclusion

A few drops of iodine solution is added to the food sample

It turns dark blue Starch is present

Benedict’s solution is added to the food sample and heated

Brick-red precipitate is formed

Glucose is present

Millon’s reagent is added to the food sample and heated

Brick-red precipitate is formed

Protein is present

A little food sample to placed on a piece or filter paper

A translucent spot is detected

The food sample contain fats

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2.2 The importance of a balanced diet

1. Diet is the food and drinks that we consume everyday.

2. A balanced diet is a diet that contains all the classes of food in the correct quantities and proportions.

3. The importance of a balanced diet :- to provide enough energy for daily activities- to maintain good health

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4. Factors that must be considered when planning a balanced diet are- age - job- size - climate- sex - state of health

5. The food pyramid can help you plan a balanced diet.

Fat(little)

Protein (2-3 servings daily)

Fruits & vegetables(5 servings)

Cereals and rice (8-11 servings daily) 10

6. The calorific value or energy value of food is the amount of heat energy released when one gram of food is burnt completely.

7. The unit of energy in food can be measured in joules of calories.

1 calories = 4.2 joules

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2.3 The human digestive system• Digestion is the process of breaking down

large insoluble food molecules into smaller soluble food molecules that can be readily absorbed by the body.

• Digestion occurs in the digestive system. This system consists of the alimentary canal, glands and organs.

• Food is broken down into smaller and simple forms by physical and chemical digestion.

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• Physical digestion includes chewing by the teeth and churning of the food in the stomach.

• Chemical digestion involves the action of enzymes on food.

• Enzymes are substances that act as catalysts and usually speed up the chemical reactions in our body.

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Digestion system Alimentary canal

This consists of al the parts which take part in the digestion of food

This consists of the parts of the digestive system through which food passes from the mouth to the anus

Pathway of food through the Alimentary canal

Mouth oesophagus stomach duodenum small intestine

Large intestine anus

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Organ Enzyme Reaction

Mouth Amylase STARCH MALTOSE

Stomach Proteases PROTEINS POLYPEPTIDES

Duodenum AmylaseProtease

Lipase

STARCH MALTOSEPROTEINS POLYPEPTIDESFATS FATTY ACIDS + GLYCEROL

Samll intestene MaltaseProtease

Lipase

MALTOSE GLUCOSEPOLYPEPTIDES AMINO ACIDS LIPASE FATTY ACIDS + GLYCEROL

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2.4 Absorption of digestion food• Absorption of digestion food takes place in the small

intestine. • Villi are tiny hair-like projections inside the small

intestine.• Products of digestion in the small intestine:

- glucose- amino acids - fatty acids and glycerol

• The digested products diffuse through the villi to the blood system and are carried to all parts of the body.

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2.5 Reabsorption of water and defecation

• Digested food is absorbed in the small intestine. The undigested food moves to the large intestine where water is reabsorbed.

• Faeces is undigested food in the large intestine kept in the rectum.

• Defecation is the process of removing faeces from the body through the anus.

• Constipation is the condition where defecation is difficult.• Ways to overcome constipation:

- increase the intake fibre- drink 6 to 8 glasses of water a day

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