Soil Conservation, Water – A Precious resource

Soil Conservation

Did you observe that after heavy rain, the top soil get washed off.
What will happen if the top soil is washed off?
How can we prevent it ?

We know that most of the organic matter is found as nutrients on the upper layer of soil and make it fertile. Storms and floods wash away or erode this fertile layer and the soil becomes barren. The loss of the upper fertile layer of soil is known as soil erosion.
Let us do an activity to see how soil is washed off.


Aim: To Know about soil erosion.
What to do: Cut three disposable bottles sidewise and fill with soil as shown in the figure. Put some sprouts of green gram or any other seeds in one bottle and water regularly. Cover the second bottle with dry leaves and leave the third bottle without sowing anything. In a week days the sprouts in the first bottle will grow more. Now make arrangement to collect the drained water from each bottle by arranging small vessels. Now blow air and pour equal amount of water slowly, in each bottle. Observe and record from which bottle less soil is blown out by air and washed off by water.

Soil Conservation, Water - A Precious resource 1

From this activity we can infer that top soil is washed off by air and water. Plants help to prevent soil erosion.

What are the other causes of soil erosion?
Apart from storms, floods and rains, unplanned and excessive usage of agro chemicals over grazing, deforestation, digging the earth for construction and mining also cause soil erosion. Due to soil erosion, the nutrients in the top soil is washed away and as a result the crop production decreases. Hence the soil erosion is to be prevented. Preventing the degradition of soil is called soil conservation. We can conserve the soil by:

  • Controlling the destruction of forests.
  • Growing trees in areas where there was no previous tree cover (Afforestation).
  • Constructing dams, reservoirs and bunds
  • Planned modern agricultural practices
  • Crop rotation to retains soil fertility.
  • Planting trees as shelter belt (wind breaks) reduces the effect of winds
  • Preventing overgrazing, of land by animals.
  • Not leaving the land vacant without any vegetation.

We have learnt that soil is an important natural resource and we need to conserve it.
Let us now learn about another important natural resource – Water.

Water – A Precious resource

On account of World Water Day, i.e. 22nd of March, Purvika participated in the fancy dress compititon ‘Water’ with a tag – “Water is precious. Save every drop.”

Water Resources
We know that water is a precious resource, let us know how much water is available for our usage.

Soil Conservation, Water - A Precious resource 2

Do You Know?

Water action decade 2018-2028
The UN General Assembly announced that the world will face 40 percent shortfall in freshwater resources by 2030 coupled with a rising world population the world is careening towards a global water crisis. Recognizing the growing challenge of water scarcity UNO launched the Water Action Decade ( 2018-2028) on 22 March 2018, to mobilize action that will help and transform our veiws of management of water.

Soil Conservation, Water - A Precious resource 3

Observe the above table and answer the following question given below.

♦ Is water from seas and oceans useful for drinking and agriculture?
♦ Where is fresh water available from?
♦ How much percentage of fresh water is available?

We understand that only one percent of water from surface and ground water sources is available for our domestic needs. The United Nations has recommended a minimum amount of water 50 litres (Two and a half buckets) per person per day for his daily activities and maintaining proper hygiene.

Soil Conservation, Water - A Precious resource 4

Think and Respond
There is huge amount of water on earth, then why is water called a precious resource?

All the places on earth do not have access to surface water sources for their needs. There ground water is used for drinking, agriculture and many other purposes.
The rivers and lakes get water through rain water. But how does the water reach the ground?

Ground water as an important resource

How does water reach the ground?
The rainwater moves down through the soil and fills the spaces and cracks deep below the ground as Ground water. This process of entry of water into the ground is called Infiltration. The upper level at which water stands in the ground is called water table.
Is the water table level same at all places?

Soil Conservation, Water - A Precious resource 5

The water table varies from place to place. It may be at a depth of less than a meter (near the bank of a river) or may be several meters below the ground (as in a desert).
Ground water is stored between layers of hard rock below the water table. This is called Aquifer. The wells, tube wells and hand pumps, get water present in the aquifers.
We have learnt how the water reaches the ground. Let us see the causes for the depletion of water table.

Depletion of Water Table

As many people are using ground water for their needs, will it be available for our future? Why do wells dry up?
Let us do the following activity to analyse the consequences of industrialisation and urbanization on the Ground water table.


Inquire from your grandparents about the difference in water table in your locality due to increase in the constructions and industries nearby and discuss in the class.

The groundwater gets replenished naturally by the see page of rainwater. However the water table may go down if the ground water is being used at a faster rate than it is being renewed by the natural process. Some ofthe factors which deplete the water table are: Population explosion, Increased industries and agriculture activities, Deforestation, decrease in the effective area for seepage and Scanty rainfall.

What will happen if the ground water table go down?
Are the water resources being increased along with our increased needs? Why?

Think and Respond
A thirsty crow finds an earthen pot with little water in it. Collects pebbles and drops in the pot. The water rises up and the happy crow quenches its thirst. The world appreciates its tact. But, the crow which knows only to drop pebbles and get water, dies of thirst after few days.
The reason is crow tried only to draw the leftover water in the pot but never tried to increase the water in it.
Man for his needs found the water under the ground.
Rigged the earth, inserted pipes, set motors and drew water.
His needs were fulfilled. Man who utilised the resources never tried to save or conserve them, falls in a danger. If the situation still continues, won’t it happen to man same as that happened to the clever crow.

Soil Conservation, Water - A Precious resource 6

Most of the times we do not think about the importance of fresh water. You might be living in an area where there is sufficient rainfall, yet there is shortage of drinking water. Can we attribute this to mismanagement of water resources?

Soil and Water: Management of water

Management of water

Why is it essential to manage the water?
The prevailing conditions of water scarcity can be resolved by the proper management of water resources. We all need water for drinking. At the same time all the water available in water resources is not potable. The potable water is the one that should not contain any impurities..
Let us know how water can be purified and made potable.

Purification of Water

How can we make water fit to drink?
What are the methods to purify water ?
Water in rivers, reservoirs and lakes may contain many impurities. Under Safe Drinking Water Supply Scheme, the water is purified through chemical and physical treatment which includes: Coagulation- Adding chemicals to bind with impurities in water, forming heavy particles Sedimentation- Making these heavy particles to settle at the bottom Filtration- Passing the upper water through filters to remove remaining undissolved particles. Disinfection- Adding chlorine or bleaching powder to kill disease causing micro organisms.
During epidemics, doctors advice us to drink boiled water. Proper boiling of water kills the disease causing germs.

Do You Know?
Do you know how modern water purifiers work?
Modern Water purifiers that are used to purify water at home have a filter unit and facilities to let Ultra Violet rays to pass through. Ultra Violet rays are used instead of chlorine treatment to kill the germs.

Soil and Water Management of water 1

Not only drinking water but also household and industrial waste water can be treated and purified. Let us know the details.
What happens if the wastes generated from our daily household activities and industries contaminate the water resources? How can we prevent the contamination of water resources?

Waste water produced from household areas and industries is called sewage. Sewage contains the soluble and insoluble organic, inorganic impurities and disease causing micro organisms. If this contaminated water mixes up with drinking water it causes diseases such as diarrhoea, cholera, dysentery, typhoid and hepatities.

Contamination of water resources can be prevented by trating sweage water properly before releasing it into water resources. How can the sewage water be treated? Let us learn now.

Sewage water treatment

What can we do to remove the contaminants from water?
Where is it done?
Water consisting domestic and industrial wastes is treated at Sewage or waste water treatment plant. At the Sewage water treatment plant, we can examine these processes of treatment namely

I. Primary treatment (Physical Process)
II. Secondary treatment (Biological Process)
III. Tertiary treatment (Chemical Process).

Let us know about these processes in detail with the help of a reading diagram given below. The step wise description will help you to know the various processes that take place in a sewage treatment plant.

Soil and Water Management of water 2

We know that water is precious and we should conserve it. Let us know how water can be conserved.

Conservation of water resources

Conservation of water can be done using the 4R principle. They include recharge, reuse, revive and reduce.
Recharge: The ground water can be recharged by collecting the rain water from the top of the buildings by the process of rainwater harvesting. Percolation tanks, Check Dams and Contour Trenches also help to recharge ground water.

Reuse: The waste water treated in sewage treatment plants can be used for household activities such as washing vehicles, watering plants and for construction purpose.

Revive: The practice of reviving the groundwater in drought prone areas is very familiar in olden days. At present the problem of water scarcity can be solved by renovating and reviving the step wells or Bavis or Digudu Bavulu.

Reduce: The use and wastage of water can be reduced through different measures. For example we can reduce the wastage of water in agriculture using modern methods of irrigation such as Drip irrigation.

We, as responsible citizens can also play an important role in reducing the wastage of water by imbibing certain good habits. Some of them are given below, you have to add on!

Close the taps when not in use
Turn off taps while brushing
Mop the floor instead of washing

Many people litter and dump the waste into the drainages and public places. Is it correct to dump waste in this way?
If all the waste generated at public places is not disposed off regularly, ultimately it may reach the water bodies and could break out into an epidemic. To prevent it, all of us should maintain sanitation at public places by observing some simple practices as given below:

  • We should not scatter litter at public places and use dustbins.
  • We should never urinate or defecate in open places.
  • We should never dump solid waste in drains.
  • We should separate dry and wet waste before disposing it.
  • We should inform the sanitation department, if we find in our neighbourhood is not cleaned.

We have understood that water is a precious natural resource. And our selfish deeds has made it scarce and unfit to use. It is the need of the hour to think and act.

Mahatma Gandhi said, “No one need to wait for anyone else to adopt a humane and enlightened course of action.” Based on this won’t it be a nice idea to carry out a campaign to conserve the natural resources in our school and locality. Design posters, pamphlets and slogans to bring awareness on conservation of natural resources in our life. Are you ready?

Soil profile, Sandy, Clayey, Loamy, Percolation, Moisture content, Soil erosion, Crop rotation, Soil conservation, Sewage, Contaminants, Activated Sludge, Check dams, Aerobic bacteria, Bar screens, Ground water, Water table, Aquifer.

What we have learnt?

  • All most everything in nature depend directly or indirectly on soil.
  • Soil is formed by the process of Weathering.
  • A vertical section through different horizontal layers (horizons) of soil is known as Soil profile.
  • The soil can be classified mainly as sandy, clayey and loamy.
  • Percolation is the downward movement of water through soil.
  • Soil testing guides the farmers to improve their crop production.
  • Loss of the upper fertile layer of soil is known as soil erosion.
  • Water is essential for all living beings. There can be no life without it
  • The groundwater stored between layers ofhard rock below the water table is called Aquifer.
  • Only 1% of all water sources is available as usable freshwater.
  • The domestic and industrial wastes in the form of liquid is called as sewage.
  • Waste water is treated in a Waste water treatment plant.
  • Sewage treatment involves physical, biological and chemical process done at three stages.
  • Water must be conserved for future generations

Types of Soil, Soil and Crops

Types of Soil

Satyam wanted to make an eco-friendly Ganesh idol on the occasion of Vinayaka Chavithi celebrations. He wanted to identify the suitable soil to make idols.
How can you identify which soil is suitable for this purpose?
We find different types of soils based on the size of the soil particles. Let us do an activity to understand this.


Aim: To identify the type of soil
What to do: Take different soil samples collected from various places. Measure nearly 25 gms of soil from each sample. Remove pebbles, grass, dry leaves from these samples. Add water drop by drop, knead the soil and try to make a ball from the wet soil. Do this with all the samples separately.

Note down whether all the wet soil samples can be made into a ball.
If a ball can be formed, put that ball on a flat surface and try to roll it into a cylindrical shape. Try to bend the cylindrical shaped soil and form a ring shape without breaking it.
Note down your observations and compare them with the below table to know the soil types of your samples.

Types of Soil, Soil and Crops 1

From the above table we can conclude that the soil is classified on the basis of the proportion of particles of various sizes as sandy, clayey and loamy. Apart from these three main types, there are light clay, heavy loam, sandy loam and so on.
We have learnt about various types of soil, let us know more about the properties of soil.

Properties of Soil

Do all types of soils have same properties?
The properties of soil depend on the size of the particles. The size of the particles influence the total moisture content and percolation rate of soil.
The ratio of the mass of water held in the soil to the dry soil is called moisture content of the soil. The mass of water is determined by the difference in the mass before and after drying the soil.
In the same way work in groups to find the moisture content of different soil samples and record them in the table.
The water spilled on soil is absorbed. The absorption and downward movement of water through the soil layers is called Percolation.
Does water percolate at the same rate in all types of soils? Let us see through the activity.
Depending on the type, different soils differ in their percent moisture content and percolation rate.

Soil and Crops

In order to participate in the state level – National Children’s Science Congress, Purvika reached the venue with her teacher at in Kadiri Ananthpur district. There she found the soil different from that of her place. To satisfy her curiosity, she collected information from different participants. She introduces herself and, that is as follows

Types of Soil, Soil and Crops 2

Let us now discuss about the soils and the crops grown in them.

What types of soils are generally seen in our state?
Can we grow a crop in all types of soil?
What type of soil is required for growing paddy?
Is there any relationship between the crops and soil?
For instance, paddy crop can be grown in the clayey soil, which retains water for a longer time.
So, we can identify the relationship that the crop grown in a region depends on the types of soil.
Let us now learn what farmers need to do when they get any problem regarding their soil.

Soil testing and its benefits

If a farmer gets a low production of crop. Where shall he go and seek suggestion?
We can suggest him to test his farm soil in a soil testing centre.

Why is soil testing done?
How do the farmers benefit by soil testing?

Soil testing helps a farmer to make soil suitable for growing crops. Testing the soil involves, the collection of soil sample from the farm in a specified process, its examination and analysis to determine the soil health.
The common soil problems which are tested at soil testing centres include: low organic matter such as carbon, available minerals in soil – nitrogen, phosphorus and potassium, available micronutrient level, poor drainage, soil temperature, soil moisture, soil contamination, acidic or basic nature of soil (PH) etc.

Soil testing

helps the farmer to know about the current health of the farm’s soil and how to improve it.
helps farmers to prevent the degradation of soil quality.
helps to minimise usage of fertilizers.
By testing soil, one can make his field healthier and resourceful by conserving nutrients useful for plant growth. Let us know about soil conservation.

Types of Soil, Soil and Crops 3

Soil – the Earthy Resource, Soil profile

Soil - the Earthy Resource, Soil profile 1

What do you observe in the above picture?
Where are the trees rooted?
Where do animals and humans live?
What would happen if there is no soil on the Earth?
Why is woman in the picture using hand pump?
For water. Isn’t it?
How will be the nature if there is no avaliability of soil and water at all!
The soil and water are the most important resources for the living things. There is no life without these resources.
Let us learn more about soil, water and their management in detail.

Soil – the Earthy Resource

Why is soil an important resource?
Human beings depend on soil for their basic needs. It has become an inseparable part of our life. Hence it is an important natural resource necessary for life on the earth. The word, soil is derived from latin word, Solum meaning ‘the substratum in which the plants grow’. The upper most layer of earth’s crust is known as soil. It is thus called the earthy resource. The scientific study of soil is called “Pedology”.
Let us now learn how soil is important in our life.

Soil – its importance
Where do plants get the nutrients from?
Did you ever see earthwarms and snails coming out of soil during rainy season?
Soil is not only a substratum in which plants get the nutrients but it is a habitat for many living organisms. Let us do an activity to know their presence in soil.

Do You Know?
The pleasant smell ‘after the rain’ is known as petrichor scent. It is because of the raising of a substance called geosmin from the soil into the air when it rains. It is produced by the spores of by actinomycetes named bacterium.


Visit the places mentioned in the table given below. Mark an area of 30cm x 30cm. Dig the soil to a depth of 4 to 6cm in the marked area. Carefully sort the soil and observe the presence of plants and small living things with the help of a hand lens. Take care that you don’t harm the living beings. Note down the things you find in the table below

Soil - the Earthy Resource, Soil profile 2

We can infer that soil consists various plants and dried plant parts etc. It is a good habitat for many small organisms.

Is soil useful to us in any other way?
Apart from being a habitat for plant and animals, soil is also needed, for agriculture, for constructing buildings , for mining of mineral ores, for making utensils and pottery (terracotta, china clay), for making toys and idols (Shadu soil), in cosmetics (multani soil)
So we can say that almost everything in our surroundings is connected directly or indirectly with soil.
We have learnt that soil is a very useful resource. Let us know how it is formed.

Formation of Soil

Did you observe stones of different sizes at the bank of a stream?
What happens when rocks get rubbed and scroll due to the flow of water?
You might have observed white coloured crinkles on the rocks at the bank of river. How do they appear?

They are formed by the disintegration of rock due to the abrasion of water stream. In nature due to the action of various natural agents such as wind, water, sun and climate the bigger rocks (parent rock) gradually break down and give small particles which forms the soil. This process is known as Weathering. It takes approximately 500-1000 years for the formation of 1 inch of soil. The process of formation of soil from the parent rock by the process of weathering is called Pedogenesis.

We have known that weathering helps in the formation of soil. Let us know about the components of soil that is formed by weathering.

Think & Respond
You may come across some people breaking large rocks into smaller ones to make road. Is it also the weathering of rocks? Why?

Components of soil

Have you observed the top soil in your surroundings? What is it made of?
Studying the components of top soil is very important as all living things depend on it. Let us conduct an experiment to find out the components present in the soil.


Collect a handful of soil sample in a transparent polythene bag and close it tightly. Leave it under the sun for one or two hours. You will find some droplets of water on the inner side of the bag.
Now fill a beaker with this handful of soil, pour water into it slowly and carefully. Did you observe any bubbles coming out from the soil? Now fill the beaker with water and stir well the soil and water. Leave it undisturbed for some time.

Soil - the Earthy Resource, Soil profile 3

What do you observe floating on the top? Organic substances, dry, rotten leaves and roots float on water. Dead and decayed organic matter that mixes with soil is called humus.
What do you find at the bottom of the beaker?
Do you find any insects and plant parts in the beaker?
What do you infer from your observation?

Compare your observations and inference with the table given below.

Observation Inference
Droplets of water in the bag Presence of water in soil
Bubbles from soil when water is poured Presence of air in soil
Floating of dry plant parts Presence of organic matter in soil
Particles at the bottom Presence of inorganic matter in soil
Insects and plant parts Presence of organisms in soil

We can infer that soil consists of water, air, organic matter, inorganic matter and organisms.

To construct large buildings, soil is dug deep. Have you ever seen such places where soil has been dug? Did you find any layers in the soil? Let us now learn about the layers sequenced in the soil.

Do You Know?
The Science dealing with the influence of soil on organisms, especially on plants is called Edaphology. The factors that contribute to soil composition are called edaphic factors.

Soil profile

How many layers did you observe in the pit?
Do all the layers have same colour, texture and depth?
The sequence of horizontal and various components, layers of soil (horizons) at a place is known as Soil profile. Each layer has a distinct colour, texture, depth and chemical composition. These layers are called Horizons.

Soil - the Earthy Resource, Soil profile 4

O Horizon (surface litter) – is the uppermost, thin horizon, made up of leaf litter and decomposing organic matter.

A Horizon (Top Soil) – is generally dark consisting dead, decomposed organic matter (humus) mixed with mineral particles. It is soft, porous and retains water hence seeds germinate easily. Plants and many other living organisms get shelter in this fertile layer.

B Horizon (Subsoil) has a lesser amount of humus but consists of clay and more amounts of minerals hence it is harder and more compact.

C Horizon (Regolith) consists of broken rocks with very little organic matter.

R Horizon (Bedrock) is made up of unweathered rock (bedrock) which is hard and difficult to dig with a spade.

Do You Know?
Engineers test the soil profile before constructing multi-storeyed buildings, bridges and dams. They conduct environmental site assessment and make predictions on long term effect of soil on the constructions and give necessary suggestions.

Artificial fibres, Maintanence of Clothes – Health Aspects

Artificial fibres

Neelu likes her new chunni very much. The chunni is smooth, sofit, thin and is light-weight.

With which type of fibres the chunni fabric is made?
You know that Fabrics are also made of chemicals. Let us know about them.
Artificial fibres or synthetic fibres are made of chemicals obtained from wood pulp or Petroleum.Various Types of Synthetic Fibres we are going to know about are – Acrylic, Rayon, Nylon, Polyester.

Acrylic: We wear sweaters and use shawls or blankets in winter season. Many of them are not actually made ofNatural wool. These are prepared from a synthetic fibre called Acrylic. Acryclic resembles wool in all aspects though available in cheaper price.

Rayon: It is also known as artificial silk as the texture of fabric prepared by Rayon is just like silk. Rayon is made from wood pulp.

Nylon: Nylon is the first fully synthetic fibre manufactured in 1931 and it was prepared from coal and water. Nylon fibre is strong, elastic and light. Socks, ropes, tooth brush bristles, tents are made from Nylon. It is also used for making strong ropes for parachutes and those used for rock climbing.

Polyester: You might have seen shirts and other dresses commonly worn by people. Fabric made from this fibre doesn’t get wrinkled easily. Terylene is a type of Polyster used for sarees and dress materials.

Artificial Fibres are light, soft and smooth. They are more durable when compared to Natural Fibres. Maintenance of dresses made of Artificial Fibres is relatively easier and they are available at a cheaper price as their production is quite abundant and economical. Except Rayon, other fibres are made of chemicals. Their production leads to Environmental Pollution.

Even after their disposal, they won’t mix in soil for years and they release harmful chemicals into the soil. Recycling is the only solution to reduce adverse effects caused by Synthetic fibres. You will learn about this process in higher classes.

Think and Respond
Parachute ropes are made of silk in olden days. It’s strength and elasticity suit for retaining the weight ofa person when he is flying in air. Water resistance capacity included with the merits of silk, turn parachute manufacturers towards Nylon now a days. What will happen if we use cotton or wool fibres for this purpose?

Maintenance of Clothes – Health Aspects

Why do we wash clothes?
It is necessary to wash clothes every time after wearing them to avoid skin diseases.

Artificial fibres absorb less water on washing and dries off easily. They won’t shrink or wrinkle after washing. Clothes made from Natural fibres are heavier and absorb more water. Hence washing and preservation should be done carefully. Always enquire manufacturer or cloth seller about maintenance of the cloth and its durability.

Readymade dresses are available in market nowadays. Always check the manufacturers care label to confirm whether the fabric is suitable for hand wash or machine wash. Some of the clothes should be cleaned by dry wash only.


Observe Manufacturer’s care label given in fig.

Artificaial fibres, Maintanence of Clothes - Health Aspects 1

Discuss the following questions in your class room.
Which garment the dress is made of?
Which type of wash the dress/garment is suitable?
What are the measures to be taken for long durability ofthe garment?
It is recommended that woolen clothes are washed after 4 to 5 wearings only because frequent washes may loosen the jfg 21 Manufacturer’s label firmness of knitting resulting in loss of shape of fabric. Even after washing woolen clothes, they should not be squeezed. It is advised to wrap them in a towel to remove extra moisture before drying off. Mild detergent should be used to wash wool and silk clothes, Cotton and silk clothes readily shrink on washing. Starching and Ironing of cotton and rolling of silk can unshrink the garments.

Think why fabrics made of natural fibres get faded on washing?
At which stage are the Natural fibres dyed? Synthetic fibres are mixed with dyes when they are in the form of pulp of chemicals. Later they are made as fibres.
It is also necessary to store wool and silk clothes away from the attacks of insects. Insects can readily feed on the protein substance present in fibres, strong fragrance of phenophthalene balls, boric acid, fragrant oils like sandal oil and lavender oils can successfully repel the insects. By keeping these substances between the clothes, we can protect silk and woolen clothes from insects. To remove shrinkage silk sarees are being wrapped around a uniform wooden log and kept dried for six to eight hours.
Then they are allowed to steam iron. This process of removal of shrinkage from silk clothes is called Rolling.
Let us do an activity to know the effect of rolling on silk cloth.


Collect two long pieces of silk fabric of ribbon width from a tailor. Dip them in water and observe the wrinkles that appeared on the clothes. Dry off one cloth simply and wrap the second one around a wooden or metal rod tightly without foldings. Allow it to be dried off in the same state. Observe both the cloths after two to three hours.

Which cloth looks fine without shrinkage and wrinkles?
The cloth that is wrapped around the rod. Maintenance of clothes made of Artificial fibres is comparatively easier. Hence people prefer to wear them. Natural fibres are made of biological substances hence they are friendly to skin.

Clothes made of artificial fibres are widely used to make swim wear, sports wear, under garments because of their elastic, thermoplastic (becomes soft on absorbing heat) nature. The chemicals used in manufacturing these clothes are generally toxins, which mostly cause skin allergies.

Wearing offace masks in public places became today’s protocol as well as a part ofour dailylife. Masks provide protection from entry ofviral and bacterial bodies and dust particles into our respiratory tract by filtering the air. It is good for our health to continue wearing face masks even after the pandemic COVID 19. It reduces the risk in public places where air is polluted due to crowds.

Though various types of masks made of different material are available in the market, WHO recommends a three layered cotton fabric mask to protect ourselves from COVID 19. Masks made of Natural Fabric avoid skin allergies and itching caused by longtime usage.

Artificaial fibres, Maintanence of Clothes - Health Aspects 2

Though we wear synthetic fabrics on a daily basis, fIg Fabric Face mask wearing ofsilk fabrics on special Occasions is our habitual practice. Their beauty, lustre and fine texture make them a symbol of aesthetic sense and pious felling.
We feel cool when we wear cotton clothes during summer. We buy Woolen clothes specially for winter.

Do You Know?
Diapers and Sanitary napkins are completely made of synthetic materials. They harm the skin on long term usage they are harmful to the environment also. To overcome this we have to think about environmental friendly and skin friendly, liquid absorbant materials like Cotton, banana or bamboo fibres and water proof cotton like Canvas cotton to be used in diapers and sanitary napkins.

Our cloths and clothing style reflects our dignity and culture. No matter whether the cloths are cheep of costly, we should choose them basing on quality and comfort. We should maintain them clean and neat.

Wearing cloths made of natural fibers not only reflects our traditions and culture, but also eco-friendly and helping hand to the weavers too.

Mohair, Shearing, Scouring, Sorting, Dyeing, Combing, Carding, Spinning, Knitting, Cocoon, Seri culture, Reeling , Bleach, Keratin, Fibroin, Acrylic, Nylon, Polyester, Synthetic fabrics, Recycle, Wrinkles.

What we have learnt?

  • Sheep is the main source for production of quality wool.
  • Removing fleece of the animal along with outer thin skin by using sharp blades or scissors like tool is called shearing.
  • The process of deriving wool from fibre includes scouring, sorting, dyeing, combing, carding and spinning.
  • Woolen fabrics are made by knitting and weaving.
  • Life cycle ofsilkworm includes 4 stages. They are egg, larva, pupa/cocoon and Adult stage.
  • Besides mulberry, Tasar, Eri, Muga are different types of silk produced in various states ofIndia.
  • Stiffling is done by treating cocoons in steam to kill larvae inside cocoon.
  • Animal fibres can be identified by their unique properties.
  • Acrylic, Rayon, Nylon, Polyester are the examples for synthetic fibres.
  • Clothes made of artificial fibres are not expensive and easy to maintain.
  • Clothes made of Animal fibres should be stored carefully preventing the attacks of
  • Animal fibres are made of proteins like keratin and Fibroin.

How to identify Quality in clothes made of Animal Fibres

How to identify Quality in clothes made of Animal Fibres?

Neelu went to a saree shop with her parents. They wanted to buy a silk saree for her mother. The salesman showed them a number of varieties of silk sarees. He told them that all the varieties of silk sarees are of high qualitaty. Neelu wanted to know whether the saree is made of pure silk or not? How can she know?

Let us know about the properties of Animal fibres. These properties of animal fibres are also useful for us to know the quality of silk and woolen clothes.

Animal Fibres – How Do They Burn?
Burning properties vary in plant and animal fibres as well as articial fibres.


Get some threads of wool, silk and cotton or any other fibres collected from a textile shop or a tailor shop. Burn them on a candle flame. Observe the flame and fumes coming from the flames.
Note down the Observation in the following table.

How to identify Quality in clothes made of Animal Fibres 1

Animal fibres burn slowly but not continuously when compared to plant fibres. They release fumes emitting the smell of burning hair or meat. The ashes formed are black in colour and appear as beads and can be made as powder.

Animal fibres dissolve in bleach.
Animal fibres dissolve in Chlorine based bleach. Sodium Hypochlorite is one such chlorine based bleach. It is present in toilet cleaners, disinfectants and cloth whiteners.


Take some toilet cleaner or disinfectant or cloth whitener containing Sodium Hypochlorite in a beaker or ceramic bowl. Keep woolen and silk fibres in the toilet cleaner and observe for 20 minutes. What happened to the fibres? They dissolve in bleach. If not, they are not pure woolen or silk fibres.
Repeat the same experiment with plant and synthetic fibres. Observe them after 20 minutes. These fibres do not dissolve in bleach.
Conduct the same experiment with your hair and any animal hair. Note down the changes in your notebook.

How to identify Quality in clothes made of Animal Fibres 2

Animal fibres are made of proteins. Keratin is the major protein present in wool while silk fibres are made of protein called fibroin.

Do You Know?
Surgical sutures are used to hold tissues together after a surgery and even for deep cuts. Silk is widely used for sutures as it is easy to stitch and remove it due to its texture.

Other Properties Of Animal Fibres

  • Animal fibres as well as Plant fibres are more water absorbant.
  • Silk is stronger and has more tensile strength. Wool posses low tensile strength.
  • Silk can withstand more heat while wool is a poor conductor of heat.

Think and Respond
Think about the dresses we prefer to wear in winter or when we are going to visit cooler places. Which natural fibre are they made of? Why do we choose woolen dresses like sweaters, shawls, scarfs etc.? Wool is a bad conductor of heat. It won’t allow our body to lose heat.

Wool – Wool yielding Animals, Silk

Wool - Wool yielding Animals, Silk 1

Observe what do people wear in these two different Situations.

Which clothes do people wear in cold regions?
Which fabrics are used to make these clothes?
Which fabric do you choose to wear in important celebrations like marriages?

These fabrics are derived from animal sources. You know that fibres are derived from plants, animals as well as chemicals. Wool and silk fabrics are derived from fibres of animal source.
Silk is derived from silk moth and wool is derived from animals like sheep, goat, yak, camel, alpaca and rabbit. Let us know about the fibres and fabrics derived from animals.

Wool – Wool Yielding Animals

You might have read stories of saints who wore animal skins. The earliest form of clothing used by primitive man was Animal fibre in the form of skin or fur. It was known that by the 7th Century B.C., people started buying woolen clothes and raw wool was the tool for exchange of other goods and Metals.

Why do people in our area rear sheep and goats in large farms?
People in our area rear them for meat. Wool is another product that we get from them. Let us know about some of the animals that yield wool in the world.

Marino sheep is the world famous breed for wool rearing. A part from Marino there are hundreds of varieties of sheep in the world which give us wool. Deccani is the common variety reared for meat and wool in Andhra pradesh, Telangana and Karnataka. Sheep is the main source of wool production in Andhra Pradesh. | |HT ‘ sheep

Wool - Wool yielding Animals, Silk 2

Angora goat is the world wide famous breed for wool. The wool derived from Angora goat is known as Mohair. Cashmere is the goat variety which gives luxurious wool in India. The name is derived from their place of origin the Himalayan area of Kashmir.

Wool - Wool yielding Animals, Silk 3

Camel produces coarse hair when compared to other animals which yield wool. Though it is coarse, it has similar properties to wool. Hence the fibre is used to make coats and Blazers. This animals shed their hair every year. The hair is collected and used for making coats.
Camels are reared in Rajastan, Haryana and Gujarat for milk, meat and wool.

Wool - Wool yielding Animals, Silk 4

Yak: An animal with long hair that is found very common in Ladakh in India and Tibet. These animals are reared for milk, Wool and Meat.

Wool - Wool yielding Animals, Silk 5

Rabbit: Angora is a breed of cute rabbits with soft and white hair or fur which is used to make colourful coats.

From Fleece To Fabric: Woolen dresses like sweaters, Shawls, Monkey caps, gloves, socks etc. are made from woolen fibres. These fibres have to undergo many changes before we wear them as beautiful woolen dresses.

Do You Know?
Alpaca and Lama are long haired animals reared for wool in South America for yielding wool and they resemble camel. The wool derived from them is as fine as mohair, that is considered to be the best Quality wool.

Wool - Wool yielding Animals, Silk 6

Now, Let us see the processes involved in getting woolen fabric.
Rearing of Sheep: In Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Arunachal Pradesh,Sikkim, Haryana, Punjab, Rajasthan and Gujarat, sheep as well as goats are reared in large farms.

Rearing or farming of sheep is a branch of Animal husbandry in India. Apart from grazing sheep, sheep rearers also fed them on pulses, oil cakes and maize. Once the reared sheep develops thick hair, it is shaved off. Generally sheep and other wool yielding animals possess two types of hair, outer long coarse hair and inner short, fine hair which are known as fleece. Fleece is used to make wool.

Processing Fibres into wool: The process involved in manufacturing of woolen threads includes 6 Stages. They are Shearing, Scouring, Sorting, Dyeing, Carding followed by Combing and Spinning. Machines are used in all these steps of processing of woolen yarn in industries. Spun yarn is used to knit Fabric.

Do You Know?
Wool fibres grow from small sacs or follicles in the skin of the sheep just like our hair. The fibre is a dead material, just like horn, nail and feathers.

Think and Respond
Sharp razor/scissors like tools are used to shear fleece of an animal.Does it hurt the animal? Remember how we tonsures our heads. Does it hurt? If the shearer shaves carefully by preventing cuts and bruises, shearing won’t hurt the animal.

Step 1 – Shearing
Removing fleece of animal along with the outer thin layer of skin is called shearing. Shearing is done by using sharp scissors like tool. Now a days gun like machines are used. Generally shearing is done during spring season. During winter season, possessing fleece causes good insulation to the animal from severe cold. But it is not needed in summer.
As spring preceeds summer, it is good for the animal to leave fleece before the arrival of summer season.

Wool - Wool yielding Animals, Silk 7

Step 2 – Scouring
Have you see, Sheep’s hair sticked of dirt, twigs and stings ever?
As the skin of sheep secrete grease like oily substance, fleece is generally attracted with much dust and dirt. Fleece is thoroughly washed to remove grease, dust and dirt by keeping it in tanks containing hot water mixed with detergents and stirred well. Now a days, scouring is done by machines also.

Wool - Wool yielding Animals, Silk 8

Step 3 – Sorting
The process of separating the fleece of animal into sections based on its quality is known as sorting. Wool is classified according to its length, softness and strength. Fleece with medium length, soft and strengthy are determind qualitative.

Step 4 – Dyeing
We generally see sheep or goat fleece is black, brown or white in colour.
How do we get colourful woolen clothes? It is by the process of Dyeing. Fleece can be bleached to remove colours and then dyed in various colours.

Step 5 – Carding & combing
The process of wrapping the fleece between the two surfaces to make the fibre into a fluffy roll is called carding. Carding machines separate and mix the fibres thoroughly to make the fibres into a fluffy mass. Carding also removes twigs and stings from fleece. Then the Fleece is pulled out through the metal teeth of the combing machine in order to remove short fibres. Remember combing one’s hairs to align them parallel to one another. Combing is done in the same way.

Wool - Wool yielding Animals, Silk 9

Step 6 – Spinning
Process of winding together the fibres to form a yarn is called Spinning.
What do you observe in fig. ?
Do you see the needle like instruments?
Those needle like instruments are used to knit the garment. Knots, loops and rings of long threads are formed by using two long needles to knit woolen garment. This process of making woolen garment is known as Knitting. Machines are also used to make woolen garments. Those machines are called handlooms and power looms. Powerlooms use electric energy to weave.

Wool - Wool yielding Animals, Silk 10
Wool - Wool yielding Animals, Silk 11

Now you have learnt the process of obtaining woolen fabric. Try to prepare a flow chart showing stages in the preparation of woolen fabric with the name “From Fibres to woolen Fabric” with the same stages involved in woolen fabric making.

Wool - Wool yielding Animals, Silk 12
Wool - Wool yielding Animals, Silk 13

Do You Know?
Parla, a village located just 20 kms away from the Kurnool is famous for fine quality woolen carpets (Kamballu). Rearing sheep and making carpets is the major occupation of the villagers. It is being practiced by the villagers for centuries as cottage industry.

Apart from wool, Silk fibre is also an example for Animal fibre. Let us know about silk now.


Life Cycle of Silk worm
Observe fig., Discuss the following.
How many stages does the silk moth undergo to complete its life cycle?
What are the stages involved in the life cycle of a silk moth?
Among the four stages of Silk Moth, fig Life cycle of silk moth larval stage is important for obtaining silk. Let us know how the larval form is useful to yield silk. For this, first we have to know the stages in the life cycle of Silk moth.

Wool - Wool yielding Animals, Silk 14

Eggs: The female silk moth lays hundreds of eggs and then dies. These eggs will be hatched within 10 days, to give out larvae.

Wool - Wool yielding Animals, Silk 15

Larvae: These larvae or caterpillars are also called silk worms. These silk worms eat mulberry leaves day and night, to grow in size.

Wool - Wool yielding Animals, Silk 16

When they are ready to pass to the next stage Pupa, which is generally after 30-35 days, it stops eating and settles down on leaves.
Now it starts to weave a net around it. For this, the silkworm moves its head from side to side in the form of the number 8. During its movements, the silk worm secrets a glue like substance containing protein. This protein dries up on exposure to air to form silk fibre.

Cocoon: Soon after, silk worm completely covers its body with silk fibre.The capsule like structure formed now is known as cocoon (pattukaaya). Silk worm undergoes further development inside the cocoon.

Wool - Wool yielding Animals, Silk 17

Adult Moth: After 10 – 12 days, larvae undergo changes and turns into an adult moth. Then it emrges out by breaking the cocoon.

Do You Know?
There are trails executing to find sources of silk derived from other than silgk worms. Tongbran Bijay Santhi, Manipuri silk inventor introduced to draw silk like threads from Lotus stem.

From cocoon to Silk
Rearing ofsilkworms for obtaining silk is known as Sericulture. At present India is producing 15% of the silk in the world. Andhra Pradesh stood in second place in the production ofsilk in the country. Silkworm prefers to eat mulberry leaves, so mulberry crop is cultivated by farmers who run Sericulture units. Hence Sericulture can be inferred as Agro – Based industry.
When the eggs are hatched the larvae come out, these larvae are kept in chandrikalu, specialized cane structures where mulberry leaves are also kept for larval feeding. This larva forms the cocoons. These cocoons are used for obtaining silk fibres.

Wool - Wool yielding Animals, Silk 18

After 2 -3 days cocoon formation, farmers remove them from chandrikalu and treat them under steam for 10 to 15 minutes. The process of killing larvae inside the cocoon by putting them in steam is called stifling. The cocoons have to be stiffled to kill larvae otherwise larvae inside cocoons will come out by breaking open the cocoons. We cannot derive continuous thread of silk. This will reduce the quality of silk fabric.Stiffled cocoons can be stored for a long time and can be sold in market. Think of the ways to get silk without killing the larvae.

Wool - Wool yielding Animals, Silk 19

After stifling, cocoons are placed in boiling water to loosen the fibres/ threads.

Do You Know?
Ahimsa silk is the silk obtained in nonviolent way ofsilkworm breeding. In this method of preparation of silk fibre, the pupa of silk moth is allowed to hatch and the leftover cocoon is then used to derive silk. This method was been introduced and followed by Kusuma Rajaiaha, Handloom Technologist and a former employee in Andhra Pradesh Handloom Department.

The process ofextracting threads from cocoon is called Reeling. As we can obtain continuous threads from cocoon, spinning is not required for getting silk yarn. Reeling is done by specialized machines. These machines can unwind the threads of silk yarn from the cocoon. One cocoon can yield 500 – 1500 meters of yarn. Yarn is then bleached, dyed and woven into fabric by the weavers.

The Scientific name of the Silk moth that yields silk is known as Bombyx mori, the silk obtained from this moth is called Mulberry Silk. Besides this, Eri, Muga, Tasar are also different varieties of silks obtained by different types of moths. All these are wild varieties of moths. Comparatively these silk threads are coarse and less lustrous. Spinning is required, as the threads obtained from the opened cocoons of wild silk moths is not continuous.


Collect pieces of silk cloth of various types and paste them in your scrap book.

Silk Cities In India
Dharmavaram ofAnantapuram District in Andhra Pradesh, Ramanagara in Karnataka, Surat of Gujarat, Chanderi ofMadhya Pradesh, Kanchipuram of Tamil Nadu, Pochampalli of Telangana, Varanasi ofUttar Pradesh are known as Silk cities of India because of the high quality silk weaving industries established. There Sericulture industry is established through out Andhra Pradesh.
Here are the details of district wise Sericulture units established in A.P.

Sl.No. Name of the District Region where Sericulture units are established
1. Srikakulam Laveru, Etcherla
2. Vijayanagaram Nellimerla
3. Visakhapatnam Paderu
4. East Godavari Kakinada,Chebrolu, Gollaprolu
5. West Godavari Vijayarai
6. Krishna Ghantasala
7. Guntur Pedakakani, Bollapali, Tadikonda
8. Prakasam Giddaluru, Cumbham
9. Nellore Marripadu, Kaligiri,Rapuru
10. Chittoor Palamaneru, Madanapalle, Kuppam
11. Kadapa Chennuru
12. Kurnool Atmakur, Kothapalle, Pathikonda, Nandyala
13. Ananthapuram Hindupur, Kadiri, Penugonda

Do You Know?
Tasar silk is a variety of popular wild silk obtained from silk moth scientifically named Antheraea mylitta. The silk moth generally grows on Arjuna and Sal trees of deep forests in agency area of East Godavari District. Tribals collect cocoons and sell them in the market. ITDA strives to create market for cocoons and to train tribals in reeling the cocoons to earn more money.

Though there are many types of silks available, it is very difficult to pick out the pure silk.

Environmental issues due to physical and chemical changes

Environmental issues due to physical and chemical changes

Chemical and physical changes occur all around us. These changes are essential parts of our daily lives. However a few of the physical and chemical changes that occur daily are harmful to the environment. For example plastic decomposition, global warming, effects of acid rain and oil spills, earthquakes, floods etc.,

Plastic waste is a widely recognised source of pollution. Most plastics are non biodegradable. They take hundreds of years to decompose. Hence their disposal causes pollution.

Environmental issues due to physical and chemical changes 1

Global warming is due to drastic increase in the emission of carbon dioxide by the burning of fossil fuels.The climate change affects not only the atmosphere and living things on land but also creatures of ocean. Acidic gases are produced when fossil fuels such as coal and oil are burned in power station, factories and homes. Oil spills occur when liquid petroleum is released into the environment by human interference causing damage to creatures of ocean.

Changes are quite common in nature. Human beings are misusing the natural resources for their needs. But we should take care that our deeds should not bring drastic changes that causes harm to the nature and mankind.

Reversible change, irreversible change, periodic change, nonperiodic change, physical change, crystallization, chemical change, galvonization, rusting, global warming.

What we have learnt?

  • Ice converting to water, water converting to steam are reversible changes.
  • Ripening of fruits is irreversible change.
  • Formation of day and night, occurance of seasons are periodic changes.
  • Flowers changing to fruits and curding of milk are useful changes.
  • The change occurs only in size, colour and shape of the substance and no change in chemical composition are called physical changes.
  • Chemical change occurs with the formation of new substance in different chemical composition.
  • The process of depositing zinc on either metals is called Galvanisation.
  • The process ofseparating a soluble solid from the solution on heating is called Crystallisation.

Physical – Chemical changes, Environmental issues due to physical and chemical changes

Physical changes

In our daily life we observe many changes. In the changes like melting of ice, solidification of ghee or coconut oil in winter etc., there is a change in state of the substance. In certain processes like filling balloons with air and pumping of cycle tubes etc., we notice change in shape. In some other changes like burning of wood and rusting of iron we find that new substances are formed. Are all these changes the same?


  • Have you seen large crystals of sugar (Missri) or crystal salt?
  • Do you know how we get these crystals?
  • Have you ever observed the formation of small sugar crystals on sweets like Jilebi and badushah, which are kept aside for a long period?
  • What is the reason for this?
    Let us find out.


Take a big size test tube. Fill half of it with water add some sugar to it and stir it. Keep adding sugar and stirring until total sugar dissolve in it. Then heat this sugar solution and add some more sugar to it while stirring continuously. Continue adding sugar till no more sugar can be dissolved in it. Now filter the solution and allow it to cool for half an hour.

What changes do you notice at the end?
Do you find any crystals in the solution?
We notice the formation of large size crystals of sugar at the bottom of the beaker. When the small granules ofsugar combine to form large sized sugar crystals.

What type of change it is?
In this acitivty the soluble sugar granules are separated from the solution by heating. The process of separating a soluble solid from the solution by heating or evaporating is called crystallization.

Can you say what type of change it is?
In crystallization no new substances are formed.
Hence it is a Physical Change.

Characteristics of a Physical change

During a physical change, no new substances are formed. The chemical properties of a substance do not change.
For example, when ice cube melts, water is formed. In melting of ice, change in physical state takes place.

A physical change is usually temporary and reversible in nature.
For example, when water is heated, water vapours are formed, once water vapours are cooled, water can be obtained again.

In a physical change, the chemical properties of a substance do not change.
For example, when a piece of gold is melted, its chemical composition remains the same in the solid form and also in the liquid form.

In a physical change, change in physical properties such as colour, shape and size of a substance may undergo a change.
For example, in cutting of vegetables changing physical properties such as size, shape and colour of a substance.
Melting of wax in a lighted candle, ice converts to water on heating, water converts to water vapour on heating, bulging out of balloon when we blow air into it, stretching of rubber bands, change in colour of zinc oxide and lead oxide on heating are some more examples to physical changes.

Let us check our understanding.
Here some changes are given in the table put () in the appropriate column.


Physical - Chemical changes, Environmental issues due to physical and chemical changes 1

In which cases new substances are formed?
The substances which undergo change in colour or state or size or shape are Physical changes. But in some changes new substance are formed. What do we call them?

Chemical Change

Have you observed rusting of iron, curdling of milk?
Do we get the same substance after change? Is the change is temporary or permanent?
To know more about such type of changes let us do an activity in the lab.


Take a small piece of Magnesium ribbon. Burn it on a flame. You will find brilliant white dazzling light leaving a powdery substance behind.

Physical - Chemical changes, Environmental issues due to physical and chemical changes 2

Does the ash formed look like Magnesium ribbon?
Do you think the magnesium ribbon and the ash have the same composition?
When magnesium burns in the presence of oxygen , it forms magnesium oxide in the form of powdered ash. This is a new substance. Thus there is a change in the composition.
Magnesium + oxygen → Magnesium Oxide Collect ash and mix it with a small quantity of water and dissolve it. Another new substance is formed
Magnesium Oxide + Water → Magnesium Hydroxide

What do you observe?
Do you observe any change in the state of the substance?
Is it an acid or base?
Test the dissolved mixture with blue and red litmus papers to decide whether it is an acid or a base.
Changes that occur with the formation of new substance with different chemical composition or transformation of a substance into another substance with the evolution or absorption of heat or light energy are termed as chemical changes.

Characteristics of a chemical change

  • During chemical change new substances are formed.
  • It is a permanent change and irreversible in nature.
  • Chemical composition of the substance changes.
  • Heat, light may be released or absorbed.
  • A colour change may take place and sound may be produced.

Think & Respond
When food gets spoiled, it produces a foul smell. Shall we call this change as a chemical change?

You know that plants produce their food by a process called photosynthesis. Can we call photosynthesis a chemical change?
Discuss in the class. Give reflections.

Physical - Chemical changes, Environmental issues due to physical and chemical changes 3

Rusting of Iron

Did you observe iron nails, iron gates, iron benches or pieces of iron left in the open ground for a long time?
Did you observe any change in colour?
We observed that a brown layer on the surface ofiron articles. When iron reacts with atmospheric oxygen and moisture and forms a new substance called Iron oxide as rust on iron artciles. This process is known as rusting. iron + oxygen (from air) + water → rust (Iron oxide)
How can we protect the iron articles from rusting?

Physical - Chemical changes, Environmental issues due to physical and chemical changes 4

Do You Know?
The Iron pillar at Delhi
Amazingly there is an iron that did not rust! There is an iron pillar at the Qutub complex in Delhi which is more than 1600 years of age. Even after such a long period, the iron pillar kept in open space has not rusted at all. Do you know how? It is made by 98% wrough iron, a special type of iron that has 1% of phosporous. It don’t have Sulphur and Magnesium. More over the pillar is covered by a thin layer of compound called misawitea. So rusting of this iron piller is too slow and it will take thousands of years to get rusted.

Physical - Chemical changes, Environmental issues due to physical and chemical changes 5

Ways to prevent iron from rusting
Do not allow the iron articles to come in direct contact with oxygen in the air and water. Apply a coat of paint or grease on iron articles.
Are there any other ways by which rusting of iron can be prevented?

Think and Respond
Do all the materials react with oxygen in the air?
Observe Gold and Silver. You wear them in the form of ornaments. Even if they get exposed to air for long time, they do not change their colour. Why?


Have you observed the handles of bicycles, metal rims of bicycle and motor cycles?
Do these articles rust? If not why?
You will notice that all the above mentioned articles are made up of iron .They didn’t rusted even though they are exposed to air.
If we observe carefully we notice that there is some metallic coating on these objects.
To prevent iron articles from coming contact with oxygen in air and water, a layer of another metal like chromium or zinc is coated on them.
This process of deposition of a layer of zinc on iron is called Galvanization.
Browning is not only observed on iron articles but also on cut fruits and vegetables.
Let us discuss about it

Browning of cut fruits and vegetables

Take an apple, a brinjal, a potato, a tomato, a cucumber, a banana and cut each into small pieces. Place them in separate plates and expose them to open air for sometime.
What changes do you notice?
We can see brown layer on their outer surface.

Can you prevent the browning of cut vegetables and fruits?
Have you observed your mother keeping the cut potatoes or brinjals in cold water?
Why does she put in cold water? Cold water prevents the outer surface of the potato and brinjal from colouring. Small quantities of acids like vinegar or lemon juice in water will also prevent browining of vegetables.
You can also rub the surface of cut fruits with juices of citrus fruits like lemon to avoid from browning. The layer of lemon juice reduces the reaction on the surface of the fruit.Ascorbic acid (vitamin C) can also be used to prevent browning.
Let us check our understanding.


Name of the Fruit Whether turned brown or not
Yes No
1. Apple
2. Brinjal
3. Potato
4. Tomato
5. Cucumber
6. Mango

Record your observation in the above table.

In which fruit or vegetable do you notice change in colour?
Why does this change occurs?
Some fruits and vegetables when cut, react with oxygen in the air. The process of reaction with oxygen is called oxidation. Due to this oxidation process brown layer is formed on the surface of fruits and vegetables.

Reversible changes – Irreversible changes, Periodic changes – Non periodic changes

Reversible and Irreversible changes

In our sorroundings some changes we can get the original substance by reversing the conditions. In some changes we can not get the original substance by reversing the conditions. Let us discuss in detail to know about such type of changes.

Reversible Changes
Have you ever noticed the following changes in our daily life?

Weight suspended from a spring.
Water changed to water vapour.

In the above situations we can regain the original substance by reversing the conditions. Let us understand this through an activity.


Take few pieces of ice in a beaker and heat them on burner. What do you observe?
We notice that ice slowly melts and converts to water. Now remove the beeker from the burner and keep it in deep fridge for one hour. What change you notice?
On heating ice converts to water. On cooling water converts to ice. Such type of changes are called reversable changes.

Reversible changes - Irreversible changes, Periodic changes - Non periodic changes 1

The changes in which the formed substance can be converted into their original substance are called reversible changes. Some more examples are Melting of wax, magnetising a needle using bar magnet etc. But in some changes we cannot regain the original substance. Let us discuss in detail.

Irreversible changes

Have you observed white wash on the wall, burning a paper, death of man or animal? In all these cases can we gain the original substance again? In some changes we cannot get the original substance.
Let us discuss through a lab activity.


Reaction of Vinegar with Baking soda:
First set up the apparatus as shown in Fig. Take a teaspoon ofvinegar (acetic acid) in first test tube and add a pinch of baking soda (Sodium bi Carbonate) to it. If you do not have vinegar, you can use lemon juice. You observe bubbles coming out with a hissing sound. Gas also coming out of the test tube. With gas is this? Pass this gas through freshly prepared Limewater (Calcium Hydroxide) What change you observe? Limewater changes to milky white showing that the gas sent into another test tube is Carbon dioxide.

Reversible changes - Irreversible changes, Periodic changes - Non periodic changes 2

Vinegar + Baking Soda → Sodium acetate + Carbondioxide + water
Carbon dioxide + Lime water → Calcium carbonate + water

Do the formed substance differes from original substance?
Can we get original substance by reversing the conditions?

Changes in which we cannot get the original substance by reversing the experimental conditions are called irreversable changes. Buring of wood, burning of diwali crackers, ripening of fruits, rusting of iron are some more examples of Irreversable changes.
Till now we studied about so many changes. Do all these changes repeating? Let us discuss about them.

Periodic and Non periodic changes

You have observed the formation of day and night. Are they repeating? For every twelve hours, sun rise and sunset are repeating. What do we call these changes? These changes are repeating at regular intervals of time and are called periodic changes.

Seasons like summer, rainy, winter and spring occur every year at regular intervals. The full moon and new moon repeats every month. Heart beats of human being takes place periodically. Low and high tides in sea are periodic.
Changes which do not occur at regular intervals of time and which cannot be predicted are called non periodic changes.


Here are some natural changes which repeats. Note the approximate time after which they repeat.

Natural Period of time of repetetion (Approximate)
1. Change of day and night 12 Hours
2. Withering of leaves
3. Rising of the pole Star
4. Change of Seasons
5. Appearance of full moon

Do You Know?
The Lonar lake in Buldhana district of Maharashtra was created by plummeting meteor about 5200 years ago. The water of Lonar lake turned into pink color recently due to Haloarchaea microbes present in the salty water. But the color is not permanent. When the biomass of the microbes settled at the bottom, then the water again becomes transparent.

Reversible changes - Irreversible changes, Periodic changes - Non periodic changes 3

Out of all the changes around us some are temporary and some are permanent.Let us discuss about them.

Natural changes – Man made changes, Fast changes – Slow changes

Natural changes - Man made changes, Fast changes - Slow changes 1

What change do you observe after removing mehandi applied on your palms?
Can we clear the printed letters on paper. Why?
Does the sun rise and set everyday?
Water dispenser gives hot, normal and cold water. Is this natural or manmade?

The hands get a red colour after removing mehandi. We cannot clear the letter printed on the paper. The Sun rises and sets everyday. The water that we collect from dispenser is a manmade change.

In our daily life we might have noticed many changes, colour of tender leaf changing from red to green, hard raw fruit becoming soft ripen fruit, colour changes observed in slices of brinjal and apple after being cut, change of milk into curd, raw rice becoming soft after cooking, ash produced on burning paper etc., are some of the changes that occurs around us.

Of all the changes we observe in our daily life, we know the reasons for some of them and may not for others.

What is change?
How do we know that something has changed?
What are the possible reasons for that change?
Changes are of different types. Let us discuss in detail.

Natural changes – Man made changes

Have you observed the process of formation of day and night, changes of weather, developmental changes of a child into an adult, growth of a seed into plant? How do these changes happen?

Is there any involvement of human beings?
We notice that all these changes are brought about by nature itself. So we can call them as natural changes.

Natural changes - Man made changes, Fast changes - Slow changes 2

Do You Know?
Belum caves are naturally formed caves located near Kolimigundla mandal ofKurnool district. These are the second largest caves in Indian subcontinent after Meghalaya state caves. The name is derived from “Bilum” Sanskrit word for caves. The caves reach its deepest point (120 feet from entrance level) at the point known as “Paathalaganga” only 1.5 km is open to tourists.
In 1988 Andhra Pradesh Tourism Development Corporation (APTDC) declared them protected and developed the caves as a tourist attraction in February 2002.

Natural changes - Man made changes, Fast changes - Slow changes 3

Manmade Changes
Have you observed cooking of rice, construction of buildings and preparation of laddu? Who involved in all these processes? All these changes happened by the involvement of humans. Such changes which were taken place by the involvement of human beings are called man made changes.
Let us do an activity to understand it.


Take a balloon and blow it.
Is there any change in its shape?
How does it happen?
Is it by itself or by anybody else?
So what type of change it is?
Change in the shape ofballoon is done by blowing air into it. This is a manmade change. Some more man made changes are preparation of bricks, making of paper, weaving of clothes etc.

Fast and slow changes

Have you observed burning of paper, cutting a piece of cake, firing of crackers, spinning of a top etc. They require less time. Changes which occur in short duration of time are called fast changes. Observe growing of a plant from seed to a tree, developmental changes in the child, rusting of iron, change of season, formation of mountains etc.

How much time they require?
These changes require more time. Changes which takes longer duration of time to happen are called slow changes.
Observe changes mention in the following table. Mention time taken for it as fraction of second, few minutes, few hours, few days, some years. Basing on that clasify them into fast and slow changes.



Time taken shorter / longer duration

Type of change Fast / Slow
Digestion of food
Burning a small candle
Occurance of lightening
Construction of Dam
Rusting of iron

Based on the above observations we can say that changes take place at different speeds. Some changes are very fast we call them as fast changes. Some changes occur very slow we call them as slow changes.
We get curd from milk. Can we get milk again from curd after reversing the conditions. Can we reverse the changes what we observed? Let us discuss.