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Term 2 Chapter 1 | 5th Science - Food | 5th Science : Term 2 Unit 1 : Food

Chapter: 5th Science : Term 2 Unit 1 : Food


Learning Objectives - After completing this lesson, students will be able to: * know about spoilage of food and the food preservation methods. * list out the deficiency diseases and the prevention methods. * know about obesity and the method of calculation of BMI. * understand the importance of balanced diet. * identify the safety measures to be followed in the kitchen.




Learning Objectives

After completing this lesson, students will be able to:

* know about spoilage of food and the food preservation methods.

* list out the deficiency diseases and the prevention methods.

* know about obesity and the method of calculation of BMI.

* understand the importance of balanced diet.

* identify the safety measures to be followed in the kitchen.



Our body needs nutrients like proteins, carbohydrates and fats for its proper functioning. We get these nutrients from the food we eat. If we do not take all these nutrients in right proportion, it results in some diseases. Sometimes, we do not preserve the food properly and it gets spoiled. Sometimes through the spoiled food also we get diseases. So, we need to preserve the food we eat. In this lesson we will study about spoilage of foods and the ways to preserve them, deficiency diseases, balanced diet and also about kitchen safety.


I. Spoilage of Food

Food items like fruits, vegetables, milk and meat will be fresh for very short time. These are called perishable foods and they get spoiled easily. Some food items like rice have long life time but they also decompose. The change in the normal state of the food is called spoilage of food. Spoiled food becomes unsuitable to eat. We can notice such changes from the taste and smell of the spoiled food. Eating spoiled food results in diseases.

Activity 1

Classify the following into perishable and non-perishable food items.

Salt, Sugar, Apple, Corn, Orange, Wheat, Pulses, Tomato, Papaya, Rice, Cucumber.

Perishable: Apple, Orange, Salt, Tomato, Papaya, Cucumber  Non-perishableSugar, Corn, Wheat, Pulses, Rice

1. Causes

Once the food items are harvested they begin to decompose. Food can be spoiled by factors like air and oxygen, moisture, enzymes, microorganisms, light and temperature.

Air and Oxygen: When oxygen reacts with food contents, it produces changes in the colour and flavour of the food.

Moisture: Moisture keeps the food fresh. When the moisture is gone vegetables and fruits shrink. Due to evaporation, moisture loss occurs in foods like meat, fish and cheese.

Enzymes: Enzymes break down the tissues and components of the food in different ways like oxidation, browning and ripening. So the food items decay.

Microorganisms: Microorganisms such as fungi, yeast and bacteria can grow well in low temperatures. They multiply in food and spoil them.

Light: Light produces colour changes and also vitamin loss.

Temperature: Sometimes rise in temperature causes food spoilage.

Activity 2

Look at the fruits and vegetables in your house. Is there any spoiled one? Find out the reason for that.

2. Effects

Spoiled foods are not suitable to eat. They may not be fresh and tasty. Sometimes it will be harmful to consume them. Microorganisms present in spoiled foods may cause foodborne diseases like stomach pain, fever, dysentery, vomiting and indigestion.


II. Preservation of Food

The process of keeping the food materials for a long time without getting spoiled is called preservation of food. Food will be spoiled if it is not prepared, preserved and handled in the right way. There are many methods used to prevent, delay and reduce the spoilage of food.

1. Food Preservation Methods

Cultivation of food requires lot of efforts. Nowadays food cultivation and the crop yield are decreasing. There are many people suffering in the world without food. So, we need to protect and preserve the food. The following are the ways to preserve food.

Drying: It is the removal of water content from the food by drying it in the sunlight. E.g. Grains

Addition of salt: When salt is added to food, it removes the water from the food. E.g. Fish, Pickles

Addition of sugar: When sugar is added to food, it dissolves in the water content of the food and preserves the food items from spoilage. E.g. Jam, Fruit juices.

Do you know?

While purchasing packed food items, we should check the following details.

1. Manufactured date

2. Expiry date

3. Ingredients

4. Energy content of the food material.

Freezing: The microbial growth and the enzyme activity on the frozen food items can be prevented by this method. E.g. Fruits, Vegetables.

Boiling: It kills the microorganisms present in the food materials. E.g. Milk, Water.

Canning and bottling: In this method, food is packed in air tight cans so that germs do not grow on them.E.g. Milk powder.

Addition of chemical preservatives: Chemical preservatives are added to stop the growth of micro-organisms in certain food materials. E.g. Sodium benzoate is added with fruits, Sulphur dioxide is added with dry fruits, Vinegar is added with pickles.

Do you know?

Irradiation is a modern method by which, food is exposed to gamma rays or ultra violet rays to kill the bacteria and the mould. It does not affect the taste of the food or nutritive value of the foods. E.g. Onion, Potatoes.

2. Purpose of Food Preservation

Modern technologies have increased the food production. But, practicing agriculture is abandoned in many places as there is failure of monsoon. At that same time many people suffer in the world without food. So, food should not be wasted by any means. Preservation of food is important for the following reasons.

1. To retain the colour, taste and nutritive value of the food.

2. To make food available throughout the year.

3. To prevent the growth of microorganisms like bacteria and fungi in the food items.

4. To reduce the wastage of food materials.

5. Preserving food not only protects our health but also makes food available to the people who need it.


III. Obesity

Obesity and overweight are defined as abnormal or excessive fat accumulation in the body that may affect the health. Obesity is most commonly caused by excessive food intake, lack of physical activity and also genetic reasons. Obese people take more food but work very less. When they eat more and work less, excess energy is accumulated as fat and creates problems. Obesity increases the likelihood of heart disease, diabetes and high blood pressure.

1. Prevention

Obesity is mostly related to our life style and habits. Eating healthy foods and having regular physical activity can reduce obesity and overweight. It is important that you maintain proper weight in the young age. 

In order to avoid obesity and overweight you need to do the following.

1. Avoid fast foods, fried items and meat with more fat.

2. Eat fruits and vegetables, legumes, whole grains and nuts.

3. Do regular physical exercises.

4. Don’t play games in computer and mobile phones.

5. Have proper sleep time.

2. Body Mass Index

People are generally classified as obese and overweight based on Body Mass Index (BMI). Body mass index is obtained by dividing as a person’s weight in kilograms by the square of his height in metres (kg/m2).

Do you know?

People with BMIs between 18.5 and 25 have less chance of developing diseases like cancer, heart disease and diabetes.

If the BMI is over 30 kg/m2 people are said to be obese and the range of 25– 30 kg/m2 denotes overweight.

BMI of a person with 60 kg weight and a height of 190 cm can be calculated as below.

BMI = Weight in kg / Height in m2

       = 60 / [ 1.90 × 1.90 ]

       = 60 / 3.61 = 16.62

Activity 3

Find your B.M.I

My B.M.I = [ My weight ---- kg ] / [ My height ---- in m2 ]



A disease is an abnormal condition that affects a living organism. This abnormal condition affects the structure and function of the organism. Diseases may be caused by external factors as well as internal dysfunction. Each disease has symptoms. We come to know about the diseases from their symptoms.

1. Causes of Diseases

Diseases are caused by microorganisms like bacteria, virus, protozoa and fungi. They are transmitted by insects, and also through contaminated air and water. Some diseases are caused when the function of the organ is affected. In general, causes of diseases can be classified as below.

* Metabolic factor. E.g. Diabetes

* Genetic factor. E.g. Colour blindness

* Microorganisms. E.g. Bacterial diseases

* Nutritional factor. E.g. Marasmus

* Environmental factor. E.g. Cholera

Activity 3

Find out the common disease prevalent in your area. Find out the reason for them and discuss with your teacher how to get remedy for them.

2. Types of Diseases

There are four main types of diseases. They are:

* Infectious diseases

* Hereditary diseases

* Physiological diseases

* Deficiency diseases

Do you know?

More number of people die every year due to heart disease than any other diseases.

a. Infectious diseases

Infectious diseases are caused by microorganisms which invade our body and multiply inside them. These diseases are spread from one person to another. E.g.Common cold.

b. Hereditary diseases

Hereditary diseases occur due to abnormalities in the gene. These diseases are passed from parents to children. E.g.Heart disease.

c. Physiological diseases

Diseases which are caused due to malfunction of the body organs are called physiological diseases. E.g.Asthma.

d. Deficiency diseases

A diet which contains all essential nutrients in correct proportion is indispensable for maintaining good health. Deficiency in one or more of the nutrients causes various diseases. These are called deficiency diseases.

* Protein deficiency diseases

Marasmus and Kwashiorkor are the protein deficiency diseases. In marasmus, the child loses weight and it will appear as though bones are covered by skin. In Kwashiorkor, the child develops an enlarged belly with swollen face and feet. By eating protein rich foods like egg, milk, fish and green leafy vegetables we can avoid protein deficiency diseases.

Do you know?

Kwashiorkor disease is found more among people in developing countries. It is because their diet is high in carbohydrates which is cheaper and low in proteins. As they live below poverty line, they couldn’t afford protein rich food which is costly.

* Vitamin and mineral deficiency diseases

Certain diseases are caused by deficiency of vitamins and minerals. By eating vitamin and mineral rich food items, we can avoid these diseases. The following table gives some of the diseases caused by deficiency of vitamins and minerals and the food items which rectify them.


V. Food Pyramid

Food pyramid is designed to make healthy eating. Depending upon our work, age and sex, the requirement of various nutrients vary from person to person. For example, growing children need more proteins in their food. People doing hard physical work (labour) needs more carbohydrate and fats in their diet. Eating healthy breakfast helps to improve concentration and it boosts metabolism.

Balanced diet: The food we normally eat in a day is our diet. For growth and maintenance of good health, our diet should have all the nutrients that our body needs, in right quantities. Such a diet is called balanced diet. Pulses, groundnut, soya beans, sprouted seeds, fermented foods, banana, jaggery, seasonal vegetables and fruits provide more nutrients. Therefore, one can have a balanced diet without much expenditure. Some major food items are given in the table below.

Major Food Items / Sources

Carbohydrates: Honey, Sugarcane, Fruits, Whole grains, Vegetables, Rice

Proteins : Legumes, Pulses, Nuts, Soya bean, Green leafy vegetables, Fish, Egg, Milk

Fats: Egg yolk, Saturated oil, Meat

Do you know?

Spinach and Ponnanganni keerai are some of the low cost, highly nutritive food materials. They contain more minerals, vitamins, fibrous nutrients available in all seasons.


VI. Kitchen Safety

Kitchen is an important place in our homes. We prepare our food in the kitchen. We use gas cylinders for cooking. Some of us may use electric stoves. The equipments and the environment in the kitchen may be little dangerous. So we need to be cautious and careful. What we should do and shouldn’t do in the kitchen are given below.

* Gas

Gas catches fire easily. Once gas is leaked there may be dangerous consequences. So, we need to be careful while handling cylinders. The following table gives what should we do and what we shouldn’t do while handling gas cylinders.


Keep the cylinder in vertical position at plain level and in a well aired place.

Keep the lighter ready and then turn on the gas stove knob.

Keep the windows and doors open to ensure ventilation in case of gas leakage.

Always use I.S.I standard gas stoves, regulators and gas tubes.


 Do not keep the cylinder in horizontal or inverted position.

Do not turn the knob before lighting the lighter. It may lead to gas leakage.

Do not turn on electrical appliances in the kitchen, if there is a gas leakage. It may Lead to fire.

Don’t use low quality gas stoves, tubes and regulators. It may lead to gas leakage.

* Electrical appliances

Do not operate electrical appliances with wet hands, because it leads to electric shocks.

* Fire

Do not keep the inflammable materials like kerosene etc, near the stoves.

In case of person’s clothes catching fire, cover the person with a thick blanket or carpet.

If kerosene or oil catches fire, use sand to put out the fire.

If solid materials like wood catch fire, use water to put out the fire.

If an electrical appliance catches fire, unplug the appliances and disconnect the electricity.

Use proper fire exitinguishers to put out the fire.

Type of Fire

Class-A: Wood, Paper

Class-B: Liquid, Gaseous fuels

Class-C: Electrical sources

Do you know?

In order to avoid fire any one of the following sources is removed.

1. Cut off the fuel

2. Cut off the air supply.

3. Lower the temperature.

* Burns

In case of minor burns, the burnt area should be held under cool running water for some time and proper medical treatment should be given.

Any blister if formed, should not be pricked.

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