TejaNaga Puram

Chapter 4 Rocks And Minerals Different Types Of Rocks

Rocks are so common in nature that we come across them, every time, we visit a hill station in the form of the hard substance that makes up a mountain or while travelling on a train, we find these rocks lying near.

The railway tracks or at a riverside in the form of a rounded pebble or simply in heaps by the side of a road ready to be used in construction.

The earth’s crust is actually made up of various types of rocks that differ from one another in colour, structure, mode of formation, resistance to erosion, etc. The surface rocks are covered by soil or clay in most places.

Rocks are natural substances composed of solid crystals of different minerals that have been fused together to make solid lumps.

These may be classified into three major types- Igneous, sedimentary and metamorphic according to their mode of origin and appearance.

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Chapter 4 Rocks And Minerals Igneous Rock

The word igneous comes from the Latin word ‘ignis’ meaning fire. This is a clue to the fact that the rocks were originally very hot.

It is believed that just after the earth was created, it was very hot and was made up of molten rocks. In the course of time, these molten rock materials cooled down slowly into solid rock.

Thus, the first hard rock formed on or under the earth’s crust is called igneous rock, also known as the primary rock.

Igneous rocks are formed by the cooling and solidification (hardening) of lava on the earth’s crust or magma under the earth’s crust.

Formation & types: Deep inside the earth due to increasing temperature and pressure the rocks remain in a molten state as magma. This magma rises to the surface through cracks in the crust.

While coming out it undergoes changes in temperature and pressure that cause it to cool, solidify and crystalize beneath the surface of the Earth’s crust.

These rocks are known as intrusive igneous rocks. Intrusive igneous rocks are very hard and often coarse-grained in texture.

Examples of these types of rock are granite and gabbro. When the magma comes out of the cracks of the crust or through the crater (vent) of a volcano it is called lava.

This lava cools and solidifies on the earth’s surface quickly to form another kind of igneous rock, known as extrusive igneous rock.

Extrusive igneous rock is fine-grained. Examples of this type include basalt and pumice.

Granite, basalt and pumice are the three commonest types of igneous rocks.

Granite is a light-coloured igneous rock with grains large enough to be visible to the unaided eye. Granite is widely used in most construction activities because of its strength.

Basalt is a fine-grained dark-coloured (usually black) rock of volcanic origin. They are the stones commonly seen near railway tracks.

Pumice stone is actually a volcanic rock which may or may not contain crystals. It is dark-coloured and denser.

It is usually ejected from a volcano. Pumice is formed when there is rapid cooling and depressurization. Holes are usually seen on the pumice stone.

These holes are formed when the dissolved gases of the hot magma escape in the air and the froth at the top of the hot magma quickly cools and solidifies.

Pumice stones are commonly used as abrasive materials in consumer products and aggregate in concrete mixtures.

Chapter 4 Rocks And Minerals Sedimentary Rock

Rocks that are formed through the layerwise deposition and solidification of sediments, especially sediments transported by water (rivers, lakes and oceans), glaciers and wind, over a long time span are called sedimentary rock.

Formation:

Sedimentary rocks are formed by the deposition and subsequent cementation of sediments, within the bodies of water like seas, lakes, etc.

The sediments are actually broken rock fragments derived from the primary igneous rocks.

These rocks were exposed to the action of the agents of erosion like rain, wind, rivers, glaciers etc. and the eroded materials were transported and deposited in layers over a long time, underwater.

When sedimentation continues the older rock layers become buried deeper. Over a long period due to the increase of heat and pressure of the overlying sediments, the underlying

Chapter 4 Rocks And Minerals Metamorphic Rock

Metamorphic rock is a type of rock that is formed when the igneous or sedimentary rocks transform or change physically and/or chemically, due to very high heat and pressure.

The upper layer of the earth is mainly formed of primary (igneous) and secondary (sedimentary) rocks.

The metamorphic rocks are found under the earth’s surface and their sediments get compacted and cemented and turn into sedimentary rocks.

We find petrified remains (fossils) of animals, plants and other microorganisms in the sedimentary rocks as these rocks were formed underwater.

Three common examples of sedimentary rocks are sandstone; limestone and shale.

Sedimentary rocks are deposited in layers as strata and they extensively (73%) cover the earth’s current land surface.

These rocks exist as a thin sheet over the earth’s crust consisting mainly of igneous and metamorphic rocks.

original character and appearance are greatly altered due to metamorphism.

Some common metamorphic rocks are gneiss transformed from granite, marble transformed from limestone, and slate metamorphosed from shale.

Metamorphic rocks are of two types-Foliated (or layered) and non-Foliated metamorphic rocks.

Chapter 4 Rocks And Minerals Minerals And Ore

In the previous chapter, you have learnt about metals, which are solid objects, hard, shiny, good conductors of heat and electricity, can be turned into sheets and their thin pieces can be easily bent.

Iron, copper, aluminium etc. from which nails, wires or utensils can be made are metals. Metals have played a very vital role in the progress of civilisation.

Now the obvious question is how do we get metals? The answer is that our earth is the main source of metals. We extract metals from the earth’s crust.

Earth’s crust is made up of aluminium (8.1%), iron (5%), calcium (3.6%), sodium (2.8%), potassium (2.6%)

What do these indicate? It shows that metals react in the open air to make new compounds.

From the above examples, it can be concluded that metals like iron or copper are found as compounds in nature and not in a pure state.

Likewise aluminium, zinc etc. are similar metals found as compounds.

Gold however does not react when exposed to air or water. It usually remains an element in nature.

Since metals do not occur freely in nature, they are found as compounds mixed with sand and soil, i.e. they occur as minerals.

A mineral is a naturally occurring solid. an inorganic, crystalline substance with a definite chemical composition.

They are formed naturally by geological processes. A mineral can be made of a single chemical element or more usually a compound. Minerals are most commonly associated with rocks.

Rocks may consist of one type of mineral or may be an aggregate of two or more different types of minerals.

When minerals are explored or mined, metals are separated from them. The process of separating metals from the minerals is known as metal extraction.

The type of mineral from which metal can be extracted easily and economically is known as its ore.

Examples: haematite (ferric oxide: Iron + Oxygen) is the mineral ore of iron, bauxite and magnesium (2.1%) among others.

Thus aluminium is the most abundant metal on this planet. It is now important to know, whether, these metals remain as elements or compounds in nature.

If you notice carefully you will observe that an iron object develops a yellowish-red coloured rust, if it remains exposed to air and moisture over a long time.

Again a greenish stain appears on copper utensils when it is left unused for a long time.

(Aluminium + Oxygen) is the mineral ore of aluminium and copper is extracted from its ore copper glance or chalcocite (copper sulphide: Copper + Sulphur).

If a metal has more than one mineral form, then it is not necessary that all of them are ores.

For every mineral deposit, there is a set of conditions, such as the level of concentration of the metal and the size of the deposit that, the deposit may be worked at a profit.

If a mineral deposit is sufficiently rich to be worked at a profit, it will then be called an ore deposit, otherwise not.

So, all ore deposits are mineral deposits, but the reverse is not true.

Chapter 4 Rocks And Minerals Alloys

Metals, after they are extracted from ores, look different from their ores. This is because a chemical change takes place in the process of metal extraction.

The use of steel, brass, bell metal, bronze, etc. in our daily lives is quite common nowadays. These metals are, however, not pure metals like iron, copper etc.

They are combinations of two or more metallic elements.

The homogeneous mixture or combination of different metals or metal and non-metal in a fixed ratio (especially to give strength) are called alloys.

For example, bronze is made up of copper and tin; iron and carbon are mixed to obtain steel; brass is formed when copper and zinc combine.

The two or more component elements that combine to form an alloy are inseparable, i.e. they cannot be readily separated by any physical means.

The major metallic component of the alloy is called the main metal or parent metal or base metal.
Today, more than 90% of metals used are in the form of alloys.

This is because alloys have many advantages, that a single metal does not have.

1.  Alloys are much stronger than a single metal,
2. An alloy has the ability to withstand heavy weight,
3.  It does not readily respond to chemical reactions and
4. Alloys are resistant to corrosion.

Alloys are not always a mixture of two or more metals but may contain one metal combined with other substances, non-metals etc.

An alloy is made by melting two or more elements together, one of which is a metal. When the mixture cools down, a solid substance called alloy is obtained.

Example: Iron mixed with carbon forms steel which is stronger than iron and can support huge weight.

Chromium mixed with iron forms stainless steel which is resistant to corrosion and hardly responds to chemical reactions.

Besides these, gold, duralumin, solder, the metal used to make the electric fuse, etc. are common alloys.

Chapter 4 Rocks And Minerals Fossils

The pictures show the remains of a fish-

1. The shell of a sea snail
2. And the remains of a sea star

We find all these remains engraved in rocks. Once all these were living but with the passage of time their dead remains got petrified or buried in rocks.

These are called fossils. luas After undergoing different changes under the earth over a period of millions of years, the remains of dead animals and plants (living beings of the geologic past) got transformed into rocks.

These rock-like remains of once-living things are called fossils. The preserved impression of an extinct organism’s body parts is also called a fossil.

The trapped body of a dead insect inside the resin of a tree is also called a fossil.

It is really interesting to know how the dead bodies of these animals came inside the rock and got preserved in a hard, petrified form. This process is known as fossilization.

Fossilization:

Millions of years ago the fish, the snail and the sea star were all alive. After the death of these animals, their bodies got buried under water or under the surface of the earth.

The soft fleshy parts of their bodies decayed in the course of time. Soon after the initial decay process, the remains of their bodies got covered with sediments.

The remains, after undergoing a variety of physical and chemical changes over a long span of time, got transformed into rocks.

The impressions or rocky remains of once-living organisms are thus converted into fossils through fossilization or petrification.

Fossils found in sedimentary rocks, act as useful tools for dating the rocks. They also show us the long history of life and the past.

Like animal fossils, plant fossils are commonly seen on coal formed many million years ago. At that time our earth was covered with forests where varieties of plants, ferns, seeds, mosses etc. grew.

The plants grew and eventually died and fell into the shallow waters. New plants grew in their places and later died, got uprooted and fell on the previous layer of decaying plants.

This process of plant growth and their death added layers Raad of decaying plants in the swampy water. Soil, mud and other sediments subsequently covered the decaying plants.

They were gradually pushed underground by the weight. of the overlying layers. The weight of the top layers and heat and pressure caused chemical and physical changes in the plant layers.

As a result, rich coal deposits were formed with impressions of leaves left behind on them.

Chapter 4 Rocks And Minerals Fossil Fuels

The materials such as coal, gas or oil that are burnt to produce heat and power are called fuels.

Coal, gas and oil are obtained from the remnants or dead remains of plants and animals that lived a long time ago.

These dead remains had undergone changes for millions of years and were transformed into fossils.

The trapped solar energy inside the fossils (in the form of chemical energy) produces heat and light energy when these fossilized remains are burnt.

Hence, coal, petroleum (oil) and natural gas are known as fossil fuels.

There are several other types of fuels like wood, paper, hay etc., which do not take millions of years to form. Hence, they are not called fossil fuels.

The pictures show the processes of the formation of petroleum. The pictures show that about 300 million years ago marine animals and plants died and were eventually buried under layers of sediments (silt, sand etc.).

The plants and animals got decomposed partially. Immense heat and pressure acted on the decomposing materials, which resulted in the formation of sedimentary rocks containing petroleum and natural gas.

Finally, we drill through the rocks and sediments to discover petroleum accumulations.

Chapter 4 Rocks And Minerals Uses of Fossil Fuel

Coal is perhaps the most widely used fossil fuel It has various uses. The major uses are outlined below:

1.  As fuel- In the past coal was mainly used to provide heat and raise steam. You must have heard of steam engines or steamships which used coal as a fuel.

Clay ovens used in many households, even today, in rural areas depend on coal for generating fire. Nowadays, the use of coal in both these fields is gradually being replaced by oil or electricity.

2.  Electric power- Coal is still widely used in thermal generators (thermal power plants) to produce electricity. Coal is burnt to generate heat which in turn produces electricity.

3. As coke in the Iron and steel industry-coal is still irreplaceable in the smelting (heating and melting) of iron and steel. Coal can be used to make metallurgical coke for use in blast furnaces.

Coke is produced when coal is heated at a high temperature (about 1100°C) in the absence of oxygen. Coke is essential in the process of extraction of pig iron or hot metal.

Coal tar is also produced from coal as a by-product of coke production. Organic compounds having active hydrogen are separated from tar. The Coke oven gas is used as fuel after it is refined.

Chapter 4 Rocks And Minerals Uses of Petroleum

Oil or petroleum has a wide range of uses as a fuel, as a lubricant, as a raw material for a variety of products etc. The major use of petroleum is in the field of transportation as a fuel.

1. Transport sector :

Petrol (gasoline) and diesel oil are mostly used to drive vehicles like cars, buses, motorcycles, lorries, small boats, military tanks etc.

2. Domestic and commercial cooking gas:

LPG (Liquefied Petroleum Gas) cylinder is used in our kitchen as a common and clean household fuel.

3. Petroleum products:

Petroleum or rock oil is a naturally occurring yellow-to-black liquid which is actually a sticky mixture of various organic compounds, water and soil.

This unprocessed crude oil is refined in a refinery and is made free of water, soil or other impurities to produce various types of fuels. This process is known as the refining of petroleum.

A large number of consumer products like gasoline (petrol), kerosene, asphalt, bitumen or tar etc.

are produced from refined petroleum. Gases such as butane and propane are also produced. LPG cylinders mainly contain liquid propane, butane, propylene, butylene etc.

Chapter 4 Rocks And Minerals Uses Of Natural Gas

Natural gas usually occurs in the uppermost part of an oil trap. The principal constituents of natural gas are a mixture of gaseous hydrocarbons.

Of these methane alone constitutes about 80 to 90 per cent while the other gases include, ethane, propane and butane.

Compressed Natural Gas or CNG is made when purified natural gas is compressed (put under pressure) and stored in a cylinder and used as fuel.

In our country as well as in many other countries CNG is used to run public transport, especially buses, because it Besides its use as fuel, petroleum has become the raw material of a number of chemical industries.

Fertilisers, insecticides and other chemicals for agricultural use; solvents and detergents; plastics, lubricant oil, paint etc.

Are also made from petroleum causing less pollution than other commonly used fuels like diesel or petrol.

In some parts of India, CNG is supplied through underground pipelines to homes and factories to be used as fuel.

CNG is also used in power generation.

 

Chapter 3 Element Compound And Mixture

If we look around us, we can see a wide range of objects. All these objects are made up of a variety of materials.

The tables and chairs are made of wood, the chalk is made of calcium carbonate, and mugs and buckets are made up of plastic.

The almirah is either made of wood or steel, the glasses and plates are made up of stainless steel or plastics, and some of the cooking utensils such as pressure cookers, etc.

Are made up of aluminium, electrical wires are made up of copper or aluminium and so on. A variety of materials are used to build a house.

Concrete and iron [mild steel is required to make bridges. So we can conclude that whatever we see around us is made up of matter.

A matter has some mass; it occupies some space and we can see, touch, smell and taste it. Some examples of matter are air, water, stones, clouds, sand, plants, wood, food etc.

For example, take a piece of stone and put it on the pan of an electronic weighing balance. The balance will show the weight of the piece of stone.

Read And Learn More: WBBSE Notes For Class 6 School Science

So the piece of stone has a mass. Now take a glass completely filled with water. Now carefully drop the same piece of stone in it.

You will find that some amount of water comes out of the glass. This happens because the stone is not soluble in water.

It occupies some space within the glass and so it displaces some water from the glass.

Hence we can see that the piece of stone has some mass and it occupies some space. The space occupied by the piece of stone is called its volume.

This type of experiment can be repeated with almost all the matters and it can be shown that each matter has mass and each of them occupies some space.

Chapter 3 Element Compound And Mixture Three States Of Matter

Matter can exist in three different states- solid, liquid and gaseous.

From our everyday experience we know that at ordinary temperatures, plastic is solid and so are iron and aluminium. Hair oil, water, after-shave lotion, petrol, diesel, kerosene, etc.

are all liquid at ordinary temperatures. Air is a mixture of a number of gases. When water is boiled, then steam is formed. Steam is gaseous.

But we should keep in mind that the state of some of the matters can be changed by changing the temperature.

You must have observed that during winter, coconut oil freezes (i.e. solidifies). If we warm it, then it again becomes liquid.

Similarly, water can be transformed into a solid or gaseous state.

Take some water in a plastic container and place it inside the freezer compartment of the refrigerator. Wait for some time.

You will observe that water has transformed into ice. You take out the container containing ice and place it on a table inside the room.  After some time you will find that the ice has melted.

Again take some water in a kettle and heat it by placing it on a gas burner. After some time you will see that steam is coming out from it.

This is an example of a transformation of a liquid state (i.e. water) into a gaseous state (i.e. steam).

If we place a stainless steel plate over the emitting steam, the steam will condense on the steel plate in the form of very small water droplets.

From the above experiments, we can very well understand that one state can be converted into the other by changing the temperature.

Chapter 3 Element Compound And Mixture Classification Of Matter Elements Compounds And Mixture

One may wonder how a particular matter can exist in three different states at different temperatures. For that, we should know how matter is formed.

All matter around us is either pure or impure. Pure matter means that it contains only one kind of particle. Thus it is homogeneous in nature.

For example, sugar is a pure substance since it is made of particles of the same kind.

An impure matter contains two or more pure matters mixed in a certain proportion. Thus it contains more than one type of particle in it.

For example, milk is an impure matter since it contains different types of substances like water, fat, protein etc.

Based on the above matter may be classified as shown below:

particles of extremely small size. If we go on dividing such particles further, a time will come when it will be impossible to recognize each of the very, very tiny particles even by a powerful microscope.

Each of the smaller particles is known as atoms and molecules.

The ancient Hindu philosopher and sage, Kanad first proposed the existence of the atom (para Manu), the smallest part of the matter.

Much later, Avogadro proposed the concept of molecules the smallest part of an element or compound that can exist freely.

A molecule is composed of one or more atoms. A molecule of a particular substance possesses all the properties of that substance.

We have just mentioned two words elements and compounds. Let us know a little Every pure matter can be divided into a bit more about them.

Chapter 3 Element Compound And Mixture Elements

An element can be defined as a pure substance made of one kind of atom which can not be further subdivided by any physical or chemical means.

Examples: Copper, gold, silver, oxygen, mercury, chlorine etc. Thus atom is the smallest particle of an element.

It cannot be further broken into two or more simpler substances. For example, copper is made of only copper (Cu) atoms and silver is made of only silver (Ag) atoms.

There are more than 110 elements known to us to date. Among them, 92 are found in nature (i.e. they are naturally occurring).

The rest have been prepared by the scientists in the laboratory.

The naturally occurring elements are available in the earth’s crust, in the atmosphere and in the seas and oceans.

Oxygen (46.4%) and silicon (27.7%) are the two most abundant elements present in Earth’s crust. Besides, aluminium, iron, calcium, sodium, magnesium etc. are also present.

abundant element present in the earth’s atmosphere followed by oxygen.

Very small amounts of other elements such as hydrogen and ‘inert’ gases are also present in the atmosphere.

All these elements can be classified into three groups:

1. Metals, such as iron, silver, gold, copper, lead, magnesium, aluminium, zinc, mercury, sodium, potassium etc. About 70 of all naturally occurring elements are metals.
2. Non-metals, such as carbon, hydrogen, nitrogen, phosphorous, sulphur, chlorine etc. Non-metals have properties almost opposite to those of metals as is indicated by the name. Only 18 of the naturally occurring elements are non-metals.
3. There are some elements which show properties of both metals and non-metals. They are called metalloids. Examples of metalloids are arsenic, antimony, bismuth etc.

It is important to know the differences between metals and non-metals. While comparing, we should always keep in mind that exceptions are always there.

Comparison Of The Properties Of Metals And Non-Metals

Let us illustrate the above-mentioned properties of metals and non-metals in some detail.

Activity 1: Take a one rupee coin (made of metal) and a piece of charcoal (a form of carbon- a non-metal).

Now drop them from a height onto the concrete floor. When the one rupee coin hits the floor, a sonorous (dong) sound is heard.

This sound is typical for metal. So it is usually referred to as “metallic sound”. But when a piece of charcoal hits the concrete floor, no such sound is heard.

Activity 2: Take a clean stainless steel plate and place it in the sunlight for some time.

The plate shines when sunlight falls upon it. Then if you touch the plate it feels hot. So a metal plate shines in the light and becomes hot quickly.

But this is not the case for any object made up of non-metals. Of course, graphite is an exception.

Activity 3: The surface of a clean, polished metal sheet, say a sheet of aluminium appears to shine in the light, but the surface of charcoal does not. In general, we can conclude that metals have shining surfaces.

Activity 4: Hold one end of a stainless steel spoon over a flame.

Within a very short time, it will become impossible to hold the spoon by hand.

This is because heat is conducted through the metal spoon very quickly from one end to the other.

Although the other end of the spoon is not in direct contact with the flame, heat is conducted pretty quickly from one end to the other through the spoon.

Cooling utensils and water boilers etc are usually made up of copper or aluminium metals since these are the best conductors of heat.

In general, we conclude that metals are good conductors of heat. Non-metals are, in general, not a good conductor of heat.

Activity 5: Take a few pieces of copper wire, one battery, a small flashlight bulb (or a small LED bulb), a pair of iron nails and a piece of charcoal.

First make an assembly as shown in with the bulb, battery and copper wires.

Now connect two ends of the iron nails with the copper wire. The bulb will glow, indicating that an electric current is flowing through the iron nail.

When the copper wire is touched with the piece of charcoal, the bulb does not glow. This proves that electricity cannot flow through the charcoal.

Hence, in general, we can say that metals are good conductors of electricity, but non-metals are not.

The metals are also malleable and ductile. If you go to the workshop of a blacksmith, you will see that iron pieces are being heated and hammered to give them different shapes.

This happens because of the malleability and ductility of iron.

Chapter 3 Element Compound And Mixture Compounds

A compound is a pure substance, consisting of two or more elements, which are combined chemically in a definite proportion.

Let us elaborate on the following experiments.

Activity 6: Take a small rubber cork and fix two iron nails in it. Now place it inside a glass beaker. Pour some water on it.

Add one teaspoonful of lime juice to the water. Stir it thoroughly.

With the help of pieces of copper wire, connect the two iron nails with the two opposite ends of a 9-volt battery.

 

As soon as the iron nails are connected with the two opposite ends of the battery, gas bubbles start evolving from each of the iron nails.

Gas coming out from each of the iron nails can be separately collected and analyzed.

It will be found that hydrogen gas evolves from the iron nail connected with the negative end of the battery and oxygen gas evolves from the iron nail connected with the positive end of the battery.

A word of caution: Never perform this experiment using a connection from the electrical mains of the house or inverter.

You must use a 9-volt battery or 1.5-volt torchlight battery for this purpose.

So you find that when electricity is passed through the acidulated water, it breaks up (or dissociates) to form hydrogen and oxygen.

The phenomena of dissociation of water into hydrogen and oxygen due to the passage of electricity through it is known as the Electrolysis of water.

Properties of Hydrogen 1 It is a colourless, odourless and tasteless gas.

2 It is lighter than air, In fact, it is the lightest element in the universe. Air is approximately 14.4 times heavier than hydrogen.

Oxygen and hydrogen are elements. They are gaseous at ordinary temperature and pressure. But when they “chemically” combine, water is formed in a liquid state.

The properties of water are also different from the properties of oxygen and hydrogen.
Some of the properties of hydrogen, oxygen and water have been summarized below in.

Activity 7: Let us take a gas jar filled with hydrogen. Now a burning taper is introduced in the gas jar.

It will be seen that the flame extinguishes but the gas burns with a “pop” sound with a pale blue inflame.

It proves that hydrogen is not all or supporter of combustion but itself burns (i.e. combustible)

Activity 8: Let us take a gas jar filled with oxygen gas. A glowing splint is slowly introduced into the gas jar.

It is found that the glowing splint rekindles inside the gas jar.

This observation confirms that oxygen gas itself does not burn but it allows other substances to burn, which means it supports the combustion.

From this and it is evident that hydrogen itself burns (i.e. combustible) and is not a supporter of combustion, whereas oxygen does not burn but it supports combustion.

Both these properties are absent in water. In fact, when a fire breaks out accidentally, the first thing we all do is pour water on the fire to extinguish it.

Hence we find that the properties of water are quite different from those of its constituent elements.

Also, if we can analyze water, we will find that each molecule of water is composed of two atoms of hydrogen and one atom of oxygen.

So hydrogen and oxygen combine in a definite proportion to form water. So, we can conclude that water is a compound.

More Examples of Compound

1. When a burning magnesium ribbon is introduced in a gas jar filled with oxygen, it burns very brightly producing blinding white light.

A white powdery substance, called magnesium oxide, is formed due to the burning of magnesium ribbon in oxygen.

Magnesium oxide is a compound formed by a chemical combination of two elements-magnesium and oxygen.

2. When a piece of glowing charcoal (a form of carbon) is introduced in a gas jar filled with oxygen, the charcoal burns more brightly throwing sparks.

Due to this burning, a gaseous compound called carbon dioxide is formed. Its properties are different from that of its constituting elements-carbon and oxygen.

Hence comparing the various properties of carbon dioxide, carbon and oxygen, we can very well understand that in a compound individual properties of its constituent elements are lost.

The characteristic properties of compounds may thus be summarised as:

1. A compound is always homogenous in nature.
2. In a compound, the constituent elements are present in a definite proportion.
3. The properties of a compound are different from those of its constituent elements.
4. The constituent elements of a compound om cannot be separated by simple physical processes.
5.  The formation of a compound is usually accompanied by an evolution of energy in the form of heat and light.

Chapter 3 Element Compound And Mixture Mixture

We have already mentioned that matter can be classified as elements, compounds and mixtures. Let us now understand a little bit about mixtures.

We have mentioned the names of elements such as oxygen, hydrogen, carbon etc. We have mentioned the names of compounds such as carbon dioxide and water.

All these are components of air. In other words, the air is a mixture of nitrogen, oxygen, hydrogen, carbon dioxide, water vapour, etc.

So, scientifically speaking, the air is an impure substance.

1. A mixture is an “impure” substance in the sense that it may contain several elements or compounds or both.
2.  A mixture is prepared by simply mixing some elements or compounds or both in any proportion by weight or volume but without any chemical combination occurring between them.
3. In a mixture, the constituting components remain side by side and each of them retains its individual characteristic properties.
4. The constituents of a mixture can be separated by simple processes.

Compounds also contain more than one element but in a particular compound, the constituting elements chemically combine in a definite proportion.

Also, the individual properties of the constituting elements are lost when they combine to form a compound.

Activity 9: Let us take some iron filings and sulphur powder and mix them together in any proportion. Both iron and sulphur are elements.

Now a magnet is brought closer to the mixture. It will be found that iron filings are attracted towards the poles of the magnet.

So, the characteristic To property of iron (i.e. being attracted towards a magnet) is retained when it is simply mixed with sulphur powder.

So, it is a mixture of iron filings and sulphur powder. Using a magnet, one of the constituents of this mixture can be separated from the other.

Activity 10: Let us now take 7 grams of iron filings and 4 grams of sulphur in a porcelain dish. Heat this mixture until it begins to glow.

A new substance, called iron sulphide (it is actually called ferrous sulphide) is formed. Its appearance is distinctly different from both sulphur and iron.

It is a compound of iron and sulphur. It is not attracted by a magnet. So individual properties of constituting elements of a compound are lost.

Also, unlike a mixture, the constituting elements of a compound cannot be easily separated from one another.

A mixture may be prepared by simply mixing more than one element or compound or both in any proportion.

For example, air is a mixture of mainly nitrogen and oxygen. Other compounds such as carbon dioxide, water, hydrogen, etc.

are present in a very small amount. The relative proportion of nitrogen to oxygen varies with altitude.

At higher altitudes, the oxygen level falls and hence climbers and mountaineers experience respiratory trouble.

The amount of water vapour present in the air also fluctuates from place to place and from season to season.

In places, nearer to seas and oceans, the water content in the air is high. Again during the rainy season the water content in the air increases.

Due to the presence of a higher amount of water in the air, wet clothes require much more time to dry during the rainy season.

So, a mixture may be defined as a material which consists of two or more pure substances (elements or compounds) present in any. proportion.

The pure substances forming a mixture are called the components or constituents of the mixture.

No chemical reaction takes place during the formation of a mixture and all the constituents retain their properties in a mixture.

The mixture is abundant around us. Milk is a mixture of water, fat and proteins. Gunpowder is a mixture of sulphur, charcoal and potassium nitrate.

Crude oil is a mixture of several hydrocarbons. Air, blood, seawater, lemon water, soft drinks, smoke, etc. are other examples of mixtures.

Depending on the state of the mixture and the state of the components of the mixture, several types of mixtures are possible. Such types are listed in Table.

Differences Between Compound And Mixture

Chapter 3 Element Compound And Mixture Types Of Mixtures

Homogeneous and Heterogeneous Mixtures

We have already mentioned that the proportion of different components may or may not vary within a mixture.

Considering the distribution of components, a mixture can be classified as a homogeneous or heterogeneous mixture.

1. Homogeneous mixture:

A homogeneous mixture is one where all the components are uniformly mixed throughout the mixture.

This means that the relative proportion of different components is the same everywhere within the mixture.

For example, let some amount of salt be dissolved in a glass of water. It is stirred very well so that the salt dissolves completely in water.

The salt is now uniformly distributed throughout the water. The water is equally salty throughout. Hence, it is an example of a homogeneous mixture.

“Sharbat” (or a uniform mixture of sugar and water) is also an example of a homogeneous mixture.

2. Heterogeneous mixture:

A heterogeneous mixture is one where the constituting components are not uniformly mixed throughout.

This means the relative proportion of different components varies from place to place within such a mixture.

A mixture of sand and water, a mixture of sand and sugar, muddy water, etc. are examples of heterogeneous mixtures.

Chapter 3 Element Compound And Mixture Solution

Usually, a homogeneous liquid mixture of two or more chemically non-reacting substances is called a solution.

When some amount of sugar is dissolved completely in water, we get a sugar solution.

When some amount of common salt is dissolved completely in water, a salt solution is obtained.

The substance which is dissolved is called the solute, and the substance in which the solute is dissolved is called the solvent.

In the case of sugar solution or salt solution, water is the solvent and sugar or salt is the solute.

In general, we can write, Solution= Solvent+ Solute

Usually, in a solution, the component which is present in a larger proportion is called the solvent and the other component, which is present in a smaller proportion, is called the solute.

The characteristic properties of the solution may be briefly mentioned:

1. A solution is homogeneous and transparent in nature.
2. The solution may be coloured or colourless.
3. The solute particles in a solution easily pass through a filter paper.
4. Solute particles in a solution are so small in size that they cannot be seen with the naked eye or even under a simple microscope.
5. The properties of solute are retained in a solution.
6. The solute particles in a solution do not settle down on keeping.

When solid sugar particles are dissolved in water, they become invisible. Though we cannot see them, we can realize that they are within the solution. Its taste is sweet.

So, the characteristic property of sugar is retained in the

sugar solution. Then why can’t we see them even with a simple microscope? This is because a sugar particle is composed of a huge number of smaller particles.

When dissolved in water, water separates the very, very tiny particles from one another.

Due to this “break up”, the solid sugar particle becomes so small, they spread all over the solution and becomes invisible through our naked eyes or even by simple microscopes.

Chapter 3 Element Compound And Mixture Separation Of Mixture Into Its Components

We have already mentioned that components of a mixture can be separated from one another by simple physical processes.

In our daily lives, we use several techniques to separate the components from a mixture.

For example, milk or curd is churned to separate the butter.

While preparing tea, tea leaves are separated from the liquid by using a strainer.

In villages, farmers use a method called winnowing to separate lighter husk particles from heavier seeds of grains.

If some small pieces of stone are mixed with rice grains, then we remove the pieces of stone by handpicking them.

In our homes, we use a water filter to separate some impurities from water to make it suitable for drinking.

In a flour mill, impurities like husk and stones are removed from wheat by sieving it.

Many of you must have seen that pebbles and stones are being removed from sand by sieving them. Sieves of different sizes holes are used.

the holes should be such that smaller sand grains will pass through the holes of the sieve while the pebbles and stones can’t.

Hence different techniques of separation of constituents of a mixture are used depending upon the characteristic properties of the substances to be separated.

Some methods for separating mixtures are:

1. Winnowing
2. Sieving
3. Hand-picking
4. Decantation
5. Sublimation
6. Filtration
7. Crystallization
8. Magnetic separation
9. Sedimentation, etc.

Below we shall discuss some of the techniques in little more detail.

1. Filtration:

This technique is utilized to separate an insoluble solid from a liquid component.
Principle: Filtration is done by sieving.

The sieve has holes of a particular size. The size of the holes of the sieve should be smaller than the insoluble solid particles which are to be separated from the liquid solution.

The molecules of the liquid are so small that they can pass through the holes of the sieve.

The insoluble solid particles remain on the sieve. Thus the liquid obtained after filtration is pure and devoid of any impurity. Let us illustrate this with an example.

Activity 11: Let us take some amount of muddy water. We want to separate the “mud”, which is an insoluble impurity present in water by filtration.

For this, we need a sieve. A filter paper is used for this purpose. Mud particles are small. But a filter paper has even smaller holes.

The shows the steps involved to fold a filter paper in the form of a cone. The cone-shaped folded filter paper is then placed on a funnel.

The muddy water is then poured into the filter paper. The molecules of water pass through the holes of the filter paper but the mud particles can’t. They remain on the filter paper.

The liquid which is coming out through the filter paper is in general called filtrate while the solid particles that remain on the filter paper are called residue.

 

If the solid is soluble in water, as in the case of a sugar solution or salt solution, the size of the dissolved solid becomes so small that even a filter paper with very small holes cannot separate the sugar or salt from the solution.

In modern days, several water filters are available which can separate very small particles from the water using advanced techniques.

But in ancient times, people used to filter water by passing it through gravels of different sizes and layers of sand.

Application: Filtration tank in public water works.

2. Sedimentation and Decantation:

If the size of the insoluble solid impurity in the liquid solution is big enough, as in the case of sand and water, then sand can be separated from water by sedimentation followed by decantation.

Principle:

The mixture containing solid insoluble impurities is allowed to settle for some time. As a result, the bigger and heavier sand particles gradually settle at the bottom of the container.

This process is called sedimentation. The top layer of the liquid is now free from sand particles and is clear.

This clear top layer of water can then be poured gently into another container without disturbing the bottom layer of sand particles (decantation).

Application: Before cooking, rice and pulses are washed with water and then the water is separated by decantation.

3. Crystallization:

We have just mentioned that salt cannot be separated from salt solution (or sugar cannot be separated from sugar solution) by filtration or sedimentation decantation but since it is a mixture, there must be some simple means to separate salt (or sugar) and water.

Let us go through the undermentioned Activity 12 to learn the technique.

Activity 12: Let us take some amount of salt water in a beaker or any other container. Now boil it for some time.

As a result, some water will vapourize and the solution will become more concentrated. Now allow this concentrated solution to cool down undisturbed.

You will find that some solid salt particles are separated from the mixture. These solid salt particles are called crystals.

The liquid (called mother liquor) can now be slowly decanted and the crystals can be collected.

If we keep the solution for a longer period more water will evaporate and the crystals so formed will be bigger in size.

This process by which crystals of solids are obtained from a solution is called crystallization.

This technique is frequently used by Chemists in the laboratory to separate a particular solid into a pure form.

 

Crystallization is a process of separation of dissolved solid salt from the solution.

During crystallization impurities are retained in the mother liquor and the crystals obtained are of the pure substance.

Application: Purification of salt from seawater, purification of sugar and alums.

4.  Separating a Mixture by using Magnet:

The magnetic separation technique is employed in the case of solid-solid mixtures. We know that iron is attracted towards a magnet. Cobalt and nickel are also attracted by magnets.

They are called magnetic substances.

So, when iron (or any other solid magnetic material) is mixed with some other non-magnetic solid materials like sand, then iron can be easily separated by using a magnet.

When a magnet is brought near to such a mixture, only iron particles are attracted and attached to the poles of the magnet. This way iron is easily separated from the sand.

Application: A strong magnet (such as an electromagnet) is used in the industry to separate scrap iron from the heap of waste materials.

Chapter 3 Element Compound And Mixture Symbol Formula And Valency

By now you have got some preliminary ideas about elements, compounds and mixtures. We already know that elements consist of only one kind of atom.

It cannot be further divided. So the smallest particle of an element is an atom.

A compound is a substance, consisting of two or more elements, which are combined chemically in a definite proportion. The smallest particle of a compound is a molecule.

The molecules of a particular compound can be broken down into its constituting atoms representing the elements.

A molecule of a particular compound has all the characteristic properties of that compound. A molecule is formed when two or more atoms combine chemically in a definite proportion.

The number of each atom in a molecule can be determined by analysis in the laboratory. Below we have listed some compounds and the elements present in each of its molecules.

But the names of the elements and compounds are often quite big. Scientists don’t use such big names when they represent elements and compounds.

They have devised some ways for shorthand representation of elements and compounds.

Chapter 3 Element Compound And Mixture Symbols

Elements are represented by a symbol which is the abbreviated English name (and in some cases the Latin or German name) of an element.

The symbol is given in different ways. For example, some of the elements are represented by the first letter of the name of the element.

But there are only 26 letters in the English alphabet and there are more than 110 elements discovered so far.

So you can clearly understand that using only the first letter of an element will not do. Two or more elements can have the same first letter.

For example, carbon, cobalt, and calcium all begin with the letter “C”. So, only the first letter of the element is not enough to conclusively represent an element.

In the case of barium and beryllium, both have the same first letter (i.e. “B”); the first two letters are used to represent the two elements.

So some elements are represented by the first two letters of the name of the element. Some examples are given.

Chapter 3 Element Compound And Mixture Formula

When two or more atoms combine chemically in a definite proportion, they form molecules. Atoms usually cannot exist in a free state, but molecules can exist in a free state.

But atoms of inert gases [such as helium (He), neon (Ne), argon (Ar) etc. and metals such as gold (Au), platinum (Pt) etc. can exist in a free state.

Molecules of elements or compounds are formed by the combination of the same or different atoms.

It is the smallest unit (or particle) of a substance that can independently exist.

Using the first two letters of an element particular element. For example, thinking of sometimes is not sufficient to represent the first two letters (i.e. “M” and “A”).

In the case of manganese and magnesium-both have the same chromium and chlorine same problem persists.

So in this case, instead of the first two letters, the first and third letters have been used.

Sometimes, to represent some elements, their Latin names have been used. Examples are mentioned below:

Significance of the Symbol:

1. It denotes the name of an element.
2.  A symbol also represents one atom of that element. So “H” means one hydrogen atom, and “2Cl” means two chlorine atoms.
3. It represents the atomic weight of an element. For example, O stands for 16 parts by weight of oxygen element.

A chemical formula represents symbolically the composition of one molecule of a compound or an element.

The formula of an element is written by its symbol with a number placed to its right and a little below it.

The number indicates how many atoms of the element are contained in one molecule of it.

Let us illustrate this with the formula of elemental molecules of hydrogen.

The hydrogen molecule is made up of two hydrogen atoms. So a molecule of hydrogen is represented as “H₂“.

You can see that the symbol of hydrogen (i.e. “H”) is written first and the number of hydrogen atoms in a hydrogen molecule (i.e. “2”) is written as a subscript after the symbol of hydrogen.

In a similar way, the formula of some common compounds may be represented as follows. All these compounds have only one type of element.

The number of atoms present in a molecule is called the atomicity of that molecule.

So atomicity of H₂, N₂, and O₂, is 2; the atomicity of ozone is 3 and that of white phosphorous is 4.

one atom of an element is present in a molecule, then only its symbol is written and is not followed by the subscript ” 1″. So the formula of carbon dioxide is CO₂ (and not C₁O₂).

But not all the molecules contain only one type of atom. Most of the compounds contain two or more different types of atoms.

For, example, a molecule of carbon dioxide contains two different elements-carbon and oxygen. Each molecule of carbon dioxide has one carbon atom and two oxygen atoms.

According to the internationally accepted rule, carbon should be written first followed by oxygen. So it should be represented by the formula C₂O_2.

When only Below we have provided some more examples.

While writing the names of the compound prefixes indicating the number of a particular atom are used before the name of that element.

Mono is used for 1, bi or di is used for 2, tri is used for 3, tetra is used for 4, Penta is used for 5, Hexa is used for 6, and so on. Some examples are given below.

The formula of a compound, therefore, expresses its composition as well as the number of atoms of each of its components.

The formula Na₂CO₃ shows that the elements composing the molecule are sodium, carbon and oxygen and the corresponding number of atoms of the said elements are 2, 1 and 3. Therefore, the atomicity of Na₂CO₃ is 6.

Significance of formula:

1. It states the name of a compound or an element. It also represents one molecule of a compound or an element.
2. A formula expresses the names as well.
3. The formula of an elemental molecule tells the number of atoms present in one molecule of it.
4. A formula expresses the molecular weight of an element or compound.
5. From a formula, it can be known which elements form the compound and in what proportion of their weights they exist.
6. The formula of a gaseous element or compound can give information about its volume and pressure.

Chapter 3 Element Compound And Mixture Valency

Atoms of various elements combine with each other to form the molecules of compounds.
We now know the formula of hydrogen sulphide. It is H₂S.

So in this case one sulphur atom is combined with two hydrogen atoms in a molecule. Similarly, in methane (CH₄), one carbon atom is combined with 4 hydrogen atoms.

In ammonia (NH₃) one nitrogen atom is combined with 3 hydrogen atoms.

The valency of an element means its combining capacity with another element with which it chemically combines to form one or more compounds.

This combining capacity of an element is measured by the number of hydrogen atoms with which one atom of the element combines the number of atoms of the elements present in one molecule of a compound.

The number of hydrogen atoms that combine with one atom of a particular element to form a compound is called the valency of that element in that particular compound.

The valency of the element is determined by assuming the valency of hydrogen to be unity, ie. 1. This is called the valency with respect to hydrogen.

It may so happen that the same element combines with different numbers of hydrogen atoms forming another compound.

So in that case the valency of that element will be different.

We will not elaborate on this at this stage. Below we have listed the valencies of some elements with proper explanation.

You should remember the valency of different elements. This will help you to write the formula of a compound. You will learn more about this in higher classes.

 

Chapter 2 Phenomena Around Us

Changes are acts or processes through which something becomes different. In nature, various changes are taking place continuously.

Even if we do not notice, changes are occurring on a regular basis.

Changes in the weather, drying of clothes, cooking of rice and vegetables, formation of curd or paneer from milk, electric light and fan being switched on or off, burning of wood or kerosene oil, etc. are only a few instances. Some of the changes are taking place around us on their own, while some of the changes are occurring due to our activities.

For example, in our body, hairs and nails grow on their own. As we eat food, they are digested in our stomach. As you grow up, you slowly become taller and gain weight.

All these processes occur “naturally”. You cut a piece of paper with a pair of scissors or you draw a picture in your drawing book. Your mother cooks food in the kitchen.

All these changes occur because we “do” it.

So, you can very well understand that not all the changes are of the same type.

Read And Learn More: WBBSE Notes For Class 6 School Science

Let us systematically study these changes. As a first step, we need to group them. If we find similarities, then we can classify such changes in a particular group.

This will help us to understand the process changes better. Classification of changes into groups can be done in more than one way.

All changes can be categorized into one of the following ways

1. Reversible and Irreversible changes
2. Periodic and Non-periodic changes
3.  Desirable and undesirable changes
4. Natural and Man-made changes
5. Slow and Fast changes
6. Physical and Chemical changes Let us illustrate changes in some detail.

Reversible And Irreversible Changes

Let us take some water in a plastic container. Keep it inside the freezer compartment of a refrigerator. Close the door of the refrigerator and wait for some time.

Now open the door and you will find that all the water has been transformed into ice. Now take out the plastic container containing ice, and keep it on the table in your room.

Again wait for some time. You will find that the ice has melted and has been transformed into water.

Let Us Consider Another Two Examples.

1. Take some amount of wax on a steel spoon with a plastic handle. Now carefully heat it by keeping it over a flame.
2. The solid wax will melt and form hot molten wax. Now keep the spoon away from the flame. The hot wax slowly cools down and the melted wax again solidifies.
3. Take a balloon and blow it carefully so that it does not burst. The shape and size of the balloon change.
4. Now allow the air to escape from the balloon. The deflated balloon regains its original size and shape.

 

The above three examples are such types of changes that are called Reversible Changes. But not all the changes can be reversed.

Let us take a balloon. Blow it hard. It grows bigger and bigger and ultimately it bursts. You know very well that there is no way you can get the balloon back to its original shape and size.

Consider Two More Examples :

1.  Take a candle. It is made of wax. If you light the candle, some wax will melt. As the candle continues to burn, its length goes on decreasing.
2. After some time, almost all the wax will “disappear”. The portion of a candle which has been burnt can never be regained.
3. Take a raw egg. Keep it in water and then boil it very well for some time. The egg is now boiled.
4. Again you know that it is not at all possible to transform the boiled egg into a raw egg by any means.

Hence from the above examples, you can understand that there are some changes which
Changes cannot be reversed by any means. Such changes are called Irreversible Changes.

So you can say that these changes are permanent.

Once it occurs, the substances undergoing it can never go back to their original/initial conditions.

The changes that can be reversed whereby the substances undergoing them can return to their previous states after the changes are complete are termed Reversible Changes.

The changes which cannot be reversed whereby the substances undergoing them can not go back to the previous states after the changes are complete are termed Irreversible Changes.

We have listed some common changes and categorized them as reversible or irreversible changes.

Hence, you can see that all the changes, happening around us can be categorized either as a reversible process or as an irreversible process.

Think about some more examples and try to classify them as reversible/irreversible.

Periodic And Non-Periodic Changes

You must have seen a pendulum clock. It is basically a clock with a pendulum. A pendulum resembles a metal ball (called the bob) tied at the end of a thread.

If you hold the other end of the thread and push the ball slightly in any direction, the ball will swing up to a certain distance.

Then it will stop momentarily and then start swinging in the opposite. direction. Again, after traversing some distance it will momentarily stop and will reverse its direction of motion.

Unless stopped, this pendulum continues to move to and fro for some time.

Thus, after a certain period of time, the pendulum repeats its motion (between leftmost and rightmost extreme positions through mean position), again and again.

 

Every one of us has seen a clock. The hands of the clock rotate continuously. The bigger hand counting minutes comes back to the same position after every hour.

The smaller hand counting hours comes back to the same position after every 12 hours. Another hand, counting seconds, comes back to the same position after every 60 seconds.

We have all seen that day changes into night and night changes into day. The monsoon season or rainy season (or any other season) comes back after every year.

So all the above changes are repeated after a fixed time interval. These changes are called Periodic Changes.

But not all the changes are periodic. For example, during the rainy season sometimes there occurs flood in some places. But floods do not occur periodically.

This means floods do not occur regularly in the same place every year. In the year 2004, a tsunami struck some coastal cities of India like Chennai. But this type of natural disaster never occurs after a fixed interval of time.

The same is true for storms, cyclones or landslides mud-slides. All of these are examples of a type of change called non-periodic changes.

The changes which occur again and again after a fixed interval of time are called periodic changes.

The changes which do not take place after a regular or fixed interval of time are called non-periodic changes.

Below in we have listed some changes and categorized them as either periodic or non-periodic changes with short justification.

 Desirable And Undesirable Changes

Changes occurring around us can also be classified as desirable changes and undesirable changes.

For example, if we cut trees unnecessarily, then it is an undesirable change. This is because this leads to deforestation, which can harm Mother Nature.

On the other hand, when a tree grows, then it is a desirable process. When flowers blossom then that also is a desirable change.

Let Us Study Some More Examples.

1. If we throw away the garbage and waste materials on the streets then it is definitely an undesirable change because this can create health hazards.

But if we throw the garbage and waste materials into the garbage bin or litter bin, then it is a desirable process, because this keeps the locality clean and beautiful.

2. If an automobile emits black smoke while moving, then it is an undesirable change. Black smoke creates air pollution.

3. During some functions or social gatherings if someone plays music very loudly using loudspeakers, then certainly that is an undesirable phenomenon.

This creates noise pollution. Playing music very loudly in a densely populated locality can harm old people and those people suffering from heart ailments.

It also disturbs the students from concentrating on their studies.

4. If cow dung is converted into bio-gas, then it is a desirable change. Biogas can be used as fuel and this fuel is environmentally friendly.

5. A thunderstorm or an earthquake is not at all desirable. These natural calamities bring devastation in the form of loss of lives and properties.

Hence, undesirable changes are those which harm nature or affect mankind adversely. Desirable changes are those which do not harm nature or mankind.

Natural And Man-Made Changes

Changes can also be classified as natural changes and man-made changes. For example, any natural calamity such as thunderstorms, earthquakes, floods, etc. are all natural changes.

We cannot control them. Those phenomena which occur on their own or “naturally” and are not controlled by human beings are called natural changes.

But we should also keep in mind that some of the above-mentioned natural processes can also occur due to severe and prolonged detrimental activities of man.

It is easily understood that activities or processes like agriculture, the industrial revolution, and progress in trade & commerce, all major forms of pollution are man-made phenomena.

Below, in we have listed some phenomena which can occur both naturally and also by the activities of men.

Phenomena which occur due to the activities of men are called man-made phenomena. These phenomena are initiated by men.

Man-made activities and natural activities can be either desirable or undesirable.

Below, we have listed some phenomena and categorized them both as natural man-made and desirable undesirable changes.

In the above table, we have described processes which are natural but can be either desirable or undesirable. The same is true for man-made processes also.

We will now briefly discuss a man-made process which can also harm nature if not properly controlled.

Fertilizers, Pesticides And Insecticides

For the growth of plants, they need food and nutrients. These are absorbed by the plants from the soil.

But in various parts of the world, the amount of different nutrients present naturally in the soil varies.

Some are present in higher amounts while some may be present in smaller amounts.

So depending upon the nature of the soil, we have to apply such “food and nutrients” externally, into the soil for balanced growth of the plants. These are called fertilizers.

With the progress of time as the human population started increasing rapidly, they needed more food.

Cultivation of vast amounts of food grains within a short span of time was not possible naturally.

So scientists developed artificial fertilizers in the laboratory and applied them to the plants for enhancing their growth. That way the production of food grains was increased.

Some commonly used fertilizers are urea, ammonium nitrate, diammonium phosphate, ammonium sulphate, superphosphate (or calcium hydrogen phosphate) etc.

But another thing which has to be kept in mind is that fertilizers alone are not enough to guarantee the enhanced production of food grains.

There are several pests and insects which destroy the food grains.

Earlier farmers used to depend on other animals such as frogs and birds to get rid of such harmful pests and insects.

But a significant part of the food grains was lost due to this dependence.

With the advancement of science and technology, scientists developed some chemicals in the laboratory which are “poison” to those pests and insects.

These “poisons” are called “pesticides” (or pest-killers) and “insecticides” (or insect-killers) which need to be sprayed over the agricultural crops to kill harmful pests.

So it seems that preparing pesticides and insecticides are man-made phenomena and they are desirable. But these pesticides and insecticides have harmful impacts on nature also.

After all, these are poison. These are used to kill living beings. So these must be used carefully and judiciously.

Some common pesticides are BHC (benzene hexachloride), malathion, methyl parathion, heptachlor, etc.

The pesticides are sprayed on the crops. As a result pests and insects staying on those plants die.

Correct and scientific use of these chemicals demands that the pesticides and insecticides must be used in small amounts.

After spraying those chemicals, we are to wait for some days.

These poisons are made in such a way that during this time period, they are destroyed naturally in the presence of sunlight and are converted into harmless or much less harmful chemicals.

Only then do the crops become suitable for consumption.

It is a matter of concern that sometimes sections of farmers spray these poisons in large amounts without knowing the consequences.

Some of them also do not wait till the recommended period of time.

As a result, a substantial part of these poisons is not destroyed naturally and remains with the food grains.

If we eat such contaminated food grains, these pesticides and insecticides directly enter our bodies and remain stored in different human organs such as the liver, kidney, brain, etc. for a long time.

They, therefore, cause damage to such organs and result in diseases like cancer, asthma, mental depression etc.

Besides this, indiscriminate use of pesticides and insecticides can kill other small animals also apart from the pests.

If birds eat those “poisoned” food grains they may die prematurely due to toxicity.

The insecticides may dissolve in water and can ultimately reach the nearby ponds and water bodies.

As a result, the small fish living there may die. If we eat those fishes we indirectly experience the toxic effects of pesticides and insecticides.

Even some man-made fertilizers are also harmful to our bodies when present in large excess food grains.

In the past few decades, nature has been severely harmed by uncontrolled and indiscriminate use of fertilizers and insecticides.

Older people sometimes true that they don’t find small fishes used to be found in the agricultural land during the rainy season in their childhood.

A number of varieties of fish have just disappeared within the last few decades.

Scientists blame the uncontrolled use of pesticides, insecticides and fertilizers for this catastrophic phenomenon.

So we must consciously use man-made chemicals only after assessing the threats they pose to nature and wildlife.

Slow And Fast Processes

We have so far classified different processes as reversible or irreversible, natural or man-made; periodic or non-periodic and desirable or undesirable.

But we have not considered the time it takes for a particular process to occur. If we consider this aspect then we can classify all the changes as either slow or fast processes.

Let Us Illustrate With A Few Examples.

1. If you plant a sapling of the mango plant in your garden, then it will take years for the plant to grow up and get mangoes from it. So it is a slow process.
2.  If you pour some common salt in water and stir it with a spoon, it dissolves fairly quickly in water.
3.  When you light a candle, it takes a long time to burn completely. So we get light from the candle for a long time.
4.  If a bomb is exploded, within seconds everything around it is destroyed. So explosion is a very fast process.
5. It takes time to dry wet clothes.
6. It takes time to boil raw rice or egg.
7. It takes time to digest the food materials we consume.
8. It takes years to construct a multi-storied building or a bridge across a river.
   School Science
9. If someone pours some acid slowly into the water with stirring, the solution immediately becomes hot.
10. The process of making curd from milk is a slow process. During this process, a small amount of curd is added to warm milk. It is stirred well and is then set aside for a few hours at a warm place.
    After that milk is converted into curd. So you can see that it is a slow, irreversible process.

Hence, depending on the time required for a process to occur, we can classify the processes as slow or fast processes.

A process occurring within a short time is termed a fast process, while a process taking a long time to occur is called a slow process.

A chemical reaction can also be classified as a slow reaction or a fast reaction. But in some cases, a slow reaction can be made faster by some means.

This can be illustrated by an example.

Activity 1: Take some clear lime water in a glass. Keep it in the open air for a few days. You will see that clear lime water has become milky.

This occurs because lime water reacts with the carbon dioxide gas present in the air and forms an insoluble, solid substance (known as calcium carbonate).

This solid, insoluble substance remains suspended within the solution. So, lime water turns milky.

As you can see that it takes a few days for the above chemical reaction to occur. Definitely, this reaction is a slow process.

It is slow because the concentration of carbon dioxide in the air is very small.

So it requires time to produce a sufficient amount of that insoluble substance to turn the clear lime water milky.

But if we can increase the concentration of carbon dioxide we can speed up this reaction.

 

Activity 2: Take some clear lime water in a glass. Now with a piece of straw, blow some air into it. Within a few minutes, the lime water turns milky.

This is because the concentration of carbon dioxide is higher in the air we breathe out. So the chemical reaction occurs more quickly.

A chemical reaction can be made faster by other means also.

Activity 3: Let us take the dilute solution of muriatic acid (which is used to clean bathrooms) in two separate glasses.

Now, in one glass drop a piece of marble and in another glass add the same amount (weight) of crushed marble. What will you observe?

In the case of the crushed marble added to the acid solution, a gas will immediately start evolving and the solid particles will dissolve very quickly.

But in the case of a piece of marble, it will take a much longer time to dissolve in the dilute acid solution.

Why did that happen? When a piece of marble is crushed to powder, the total surface area of the marble increases manyfold.

This increased surface area helps the marble to interact quickly with the acid solution.

When we chew the food properly, they are converted into very small pieces.

Since digestion involves a series of complex chemical reactions, hence, within our stomach, they are digested quickly.

So we should chew the food properly. When vegetables are cut into smaller pieces, they can be boiled faster.

When we spray pesticides or fungicides on plants or when we apply body spray or increase in surface area of a solid substance when broken into pieces can be easily understood when you break a piece of chalk.

Each time you break it into pieces, a new surface is generated deodorant spray on our body, the liquid is converted into very fine droplets, possessing a much higher surface area. So they can act faster.

 

When chemicals are dissolved in a solvent, they become very fine particles and then they can react with one another at a much faster rate.

We have categorized some more processes as slow fast processes in Table.

 

Physical And Chemical Changes

Matters can undergo different changes. Let us now consider whether during such changes the matters remain the same or any other new substances are formed.

For example, when clear lime water is exposed to air for a few days, it turns milky. This is because a new substance is formed.

Again think of some water which is frozen to ice. In this case, no new substance has been formed. Only its state has been changed. Liquid happens.

Only the physical properties of a state have been transformed into a solid state. If we warm the ice, we will again get back water (i.e. the liquid state).

When the surface of iron is exposed to moist air for a prolonged period, rust is formed on the surface.

Laboratory analysis will tell you that “rust” is a different substance, different from pure iron. It is formed due to a reaction between iron, aerial oxygen and moisture.

Take a magnet near iron nails. The magnet will attract the nails. But here, no new substances are formed.

When you burn a paper, it is reduced to ashes. Ash is different from paper. It is formed due to a reaction between paper (cellulose) and oxygen at high temperature

When you dissolve some sugar in water, it “disappears” in the solution. But no new substances are formed.

If you can vapourize all the water (or most of it) you can recover the sugar.

So sugar has not been transformed into any new substances.

From this discussion, you can very well understand that in some cases new substances are formed while in other cases no such thing substance (such as physical state, shape, etc.) changes.

So on this basis, we can classify all changes as either physical changes or chemical changes.

The change which involves only a change in the physical properties of a substance and in which no new substances are formed is called Physical Change.

For example, dissolution of sugar in water, freezing of water, boiling of water etc.

The changes which involve the formation of one or more new substances having a completely different set of features or properties compared to the original substances are called Chemical Changes.

For example, rusting of iron, lime water turning milky when exposed to air, burning of paper or kerosene oil etc.

Let us give you a bit more detail about some of the physical and chemical processes.

Examples Of Physical Changes

1.  A piece of iron is magnetized. This is an example of a physical change. No new substances are formed during magnetization. When it is heated or dropped from a height, its magnetic property is lost. We get back the same material. So this physical change can be reversed.
2. Change of state of matter is an example of physical change. For example, when water is frozen to ice or when water is boiled, only the physical

state of the matter is changed. No new substances are formed. When the ice is warmed, we get back to the water.

When hot steam is condensed on a cool metallic surface, we get back to the water.

So we can see that the change of state, which is a physical change, can be reversed by changing the temperature.

When a glass vessel is accidentally dropped, it breaks into pieces. It is a physical change. The glass vessel is broken into several small pieces, but no new substances are formed.

Though it is a physical change, of course, we cannot get back the glass vessel from so many broken pieces. So it is an irreversible physical change.

4. Tearing a sheet of paper into pieces is a physical change.

5. When you take an empty glass and breathe out on it, the moisture present in the air we breathe out is condensed on the glass in the form of very small water droplets.

When we keep some pieces of ice in a glass, the glass becomes cool and the moisture present in the air is condensed on the cool surface of the glass.

 Examples Of Chemical Changes

1. When rice is boiled in water, raw rice is converted into boiled rice. Some chemical changes occur during this boiling whereby new substances are formed. We cannot get back the original material (raw rice) by simple means.
2.  When iron is exposed to moist air for a prolonged period, rust is formed on its surface. Rust is a new substance. If we remove the rust slowly from the iron surface using a sand-paper and collect it, we will see that particles of “rust” are not attracted by a magnet. So properties of rust are different from that of pure iron. [Be careful while rubbing the rusted iron surface so that no pure iron should come out].
3. When a piece of paper is set on fire, it quickly burns and reduces to ashes. A new substance is formed. It is not at all possible to get back the original piece of paper.
4.  Digestion of food inside our stomach involves chemical processes. New, simpler substances are formed from complex food materials.
5. Ripening of mango involves chemical change, and this change cannot be reversed.
6.  Respiration also involves chemical changes.

Activity 4: Prepare a slurry of turmeric powder with water in one container and some amount of beetroot juice in another container.

Now take several strips of filter paper. Dip some of them in turmeric slurry and a few other strips in beetroot juice. Dry the strips.

Now dip those strips in two different solutions-limewater and lemon juice. Following changes in the colour of the strips are observed.

You can see that colour of the strips changed differently in different solutions. Chemical changes are responsible for this colour change.

This is an example of a chemical process accompanied by colour change.

Changes Involve Energy

We know that unless heated, rice is not boiled. If water is not heated it will not boil. To melt ice, it has to be warmed.

Solid naphthalene when heated directly, transforms into a gaseous state through a process called sublimation.

At room temperature also, it sublimes, but at a much slower rate. So, we see that heat energy is associated with all the above-mentioned processes.

It affects the rate of change. We have mentioned already that any change of state (which is a physical process) can occur only if heat is absorbed from a substance or is supplied to it.

Physical processes may or may not involve the absorption or liberation of heat. When dilute sulphuric acid is slowly added to water, the solution becomes hot.

So, heat energy is liberated during the mixing. When urea is dissolved in water, the solution becomes cold. So heat is absorbed during this physical mixing process.

When two gases are mixed together, no noticeable change in temperature is observed. So heat is neither liberated nor absorbed here.

Any change of state can be realized using heat energy. When heat is supplied, water boils. When heat is extracted, the vapour condenses.

This is the reason that on winter mornings, dew drops are formed on the leaves of grass.

At night, the moisture in the air cools down and condenses as droplets of water on the leaves of grass.

The chemical change also involves the absorption or evolution of heat. For example, when quicklime is dissolved in water, bubbles of gases are evolved and the solution becomes hot.

A chemical change is always associated with a change in energy- either in the form of heat energy or any other form of energy.

In some cases, a chemical process is initiated by heat energy. For example, when a piece of paper is held in flames, only then it catches fire and is reduced to ashes.

So this process occurs at a higher temperature. At elevated temperatures, the paper (cellulose) reacts with oxygen in the air to produce carbon dioxide and other substances.

When a firecracker is lit with a flame, it starts emitting light and sound. In fact, changes can be initiated with other forms of energy also.

In the laboratory, when the electric spark is passed through a gaseous mixture of hydrogen and oxygen, water is produced.

Again, when electricity is passed through water, it is dissociated to produce hydrogen. In this process, carbon dioxide and oxygen.

Lightning is also a kind of high-energy electric spark. When it strikes a tree, the tree catches fire. Every year, many people around the world die because of lightning.

If lightning strikes in nearby places, the electrical and electronic goods that are attached to the plug points are damaged. So during a thunderstorm, electrical equipment must be detached from the plug point.

You can explode caps either by pressing the trigger of a toy gun or by hitting it hard with a stone.

In this case, a chemical process is initiated by another form of energy known as mechanical energy.

Plants can prepare their “food” on their green leaves by a process called photosynthesis water combine in the presence of solar energy to form a new substance-glucose.

This chemical process can occur only in the presence of sunlight. That is why a plant dies when kept in the dark for a prolonged time.

So photosynthesis is an example of a chemical process being initiated by light energy.

When food matters are digested inside our stomach, heat is evolved.

This heat maintains the body temperature and provides energy for different processes occurring continuously within our body.

When you bring one finger close to your nose and breathe out deeply, you can feel that the air you are breathing out is warm.

This is because the inside of our body is warm. The warmth of the human body is the result of the metabolism of food.

Metabolism of food causes the release of energy in our cells which keeps our body warm and fit for work.

Some More Examples Of Physical And Chemical Processes

Let us provide you with some more examples of physical and chemical changes.

Physical changes:

1. All of you must have seen tools which are used to dig the soil. In these tools, iron blades are fixed on a wooden handle.

But how is this done? The iron blade of these tools has a ring which is slightly smaller in size than the wooden handle.

As the iron blade is heated, the ring becomes slightly larger and then the handle easily fits into the ring. When the blade cools down, it again contracts and fits tightly on the handle.

This mechanism is also used to fix a metal ring on the wooden wheel of a cart.

1. A gap is left at regular intervals between the joints of railway lines. This is because, in summer, the rail lines become hot and expand in length.This is a physical change. If this gap is not present, the railway lines would bend.
2.  In winter our lips are cracked. This is because, in winter, water is lost more from our soft and exposed body parts such as lips, heels etc.As a result, the lips are cracked. To prevent this we apply cream or lip balm on them.This creates a protective layer on the lips and prevents the loss of water from the lips. Such loss of water is an example of a physical process.
3.  When vinegar is mixed in pickles, it absorbs water from the fruit and vegetable pieces.So those “dry” pieces of fruits and vegetables can be preserved 600 for a long time at room temperature.
4. The melting of glaciers is an example of physical change which occurs naturally

Chemical changes:

When a banana is kept for a few days, black spots appear on its skin. This is due to some chemical changes.

When a piece of apple is cut and kept open in the air for some time, brown patches appear on the exposed surface. This happens due to some chemical reaction.

When leaves of eucalyptus trees fall on the ground, they are decomposed slowly and the chemicals present within these get mixed up with the soil.

Due to the presence of these chemicals in the soil, grasses cannot grow properly around these trees.

When a living animal dies and is kept in the open for some time, it is decomposed. Some microbes convert various body parts of the dead body into other substances.

So it is a chemical process.

In cities, chlorine water or halogen tablets are mixed with water to kill the germs present in them.

1. Marble floors and tiles are often cleaned with “solid acid” (actually it is called oxalic acid). This cleaning process involves a chemical reaction.
2. The weakening of our bones, the colour of our urine and faeces, the yellowing of teeth and cataracts in the eyes are all the results of some chemical processes.
3. From the examples discussed so far about the physical and chemical changes, we can compare them as follows:

We conclude this chapter by classifying some common changes into different types.

You can add some more examples to this list.

Chapter 1 Interdependence Of Organisms And Environment Man And Other Animals Depend on Plants

Our Family and Our Society

Human beings are social organisms, they live in a society and they have specific roles to play as a teacher teaching, a student studying.

the doctor and nurse look after the ailing patients, a shopkeeper sells items, a policeman ensures the maintenance of law and order and protects the common man, municipal workers keep the city clean etc.

The judges and lawyers ensure that everybody gets justice, a civil servant and minister run the government and in this way, the society remains functional.

and it includes the grandparents, father, mother and the children.

The grandparents usually lead a retired life. They should be looked after properly. They guide the family with their wisdom.

The father usually earns money and does the marketing and the mother or any elderly member does the cooking and looks after the children.

The children study, play and make the place enjoyable. Interdependence means two or more people working together on a common activity or towards a common goal.

Examples of interdependent behaviour among family members may include helping one another to prepare the family meals.

Family represents the unit of society,

Read And Learn More: WBBSE Notes For Class 6 School Science

Again, there are circumstances when family members may have to take the help of someone outside of the family for some reason.

Such instances include taking help from a plumber to repair the tap, from a tailor to stitch the clothes, an electrician to repair faults in electric lines or gadgets and so on.

Thus there exists an enduring interdependence between society and family for mutual benefit, functional and emotional support, economic well-being and above all, overall societal prosperity.

Interdependence Between Plants And Animals

A group of mutually adjusted plants and animals inhabit a natural area as a community.

There is a great deal of interdependence or mutual dependence between plants and animals in a community.

No organism can live alone, they need other organisms to survive. The mutual interactions among the organisms are vital for the survival and functioning of the community as a whole.

Plants depend on animals for CO₂ (raw material of photosynthesis), insects & other animals help in the pollination and dispersal of seeds, earthworms and other organisms making the soil fertile for the proper growth of plants.

On the other hand, animals depend on plants for food, medicines, fibres, clothing, other useful products, supply of O₂, and removal of CO₂, plants are homes and shelters for a variety of animals and provide materials for building and furniture etc.

Thus all organisms depend on one another for survival. This is known as interdependence

Dependence Of Animals On Plant

Green plants and similar organisms (autotrophs or primary producers)produce food for all other living organisms on the Earth.

Food provides energy and nutrients for organisms, such as animals (heterotrophs), that cannot trap energy from the sun through photosynthesis.

Some animals, called primary consumers, eat only plants. Others, known as omnivores, eat plants and animals both. Most humans are omnivores.

However, some people choose to eat only food that comes from plants. Plant-based food supplies vital nutrients that our bodies cannot make for themselves.

These nutrients include vitamins, which are chemicals necessary for the proper functioning of the body; sugar and other carbohydrates, which provide energy; amino acids, which are the building blocks of proteins; oils.

Another concentrated energy source; and minerals, such as potassium, magnesium and calcium.

Humans consume a remarkable variety of plants and plant parts. However, agriculture-the cultivation of plants is a relatively recent innovation in human history.

Many historians believe that the farming of plants began about 10,000 years ago in several parts of the world.

The plants we use as food today are very different from their wild ancestors.

Most food plants evolved through selection by many generations of farmers to produce larger fruits, grains and other edible parts and to be easier to plant, harvest and process.

The wide variety of food we eat today originated in many different and geographically separated parts of the world.

Uses Of Plants

Use Of Plants As Food

Root: Many foods come from plant roots. Important root crops include carrots, parsnips, beets, sweet potatoes, radishes and turnips These food help in the procurement of starch.

Stem: Potatoes, the underground modified stems, are specialized for the storage of Animal Kingdom of Starches. The bulb of onion is also an underground modified stem having an apical bud surrounded by multiple layers of fleshy leaves.

Rhizome includes the irregular fleshy stem of ginger, whose nodes are protected by scaly leaves. It has medicinal importance and is also used in cooked food as a flavouring agent.

The Corm of Amorphophallus is also a large club-shaped structure, consumed as a vegetable.

Other stems used as food include sugarcane, which is enriched in sucrose and Asparagus, and also used as a flavouring agent.

Leaf: Leafy food includes spinach, lettuce, brussels sprouts, and cabbage. All of these look like leaves.

However, food that comes from bulbs, such as leeks and garlic, is also made of leaf parts (the enlarged bases of long, slender leaves).

Celery and rhubarb stalks actually are the supporting stems (petioles) of leaves.

These leaves are a rich source of cellulose, which does not have much food value but is used as roughage.

Flower: Flowers are not eaten frequently, but cauliflower, broccoli and artichokes all are made up of flowers or flower buds. Flowers of gourd and other legumes are also consumed as vegetables.

Fruits and seeds, which develop after flowers are pollinated, are important food sources.

Fruits: Familiar fruits include. oranges, lemons, grapefruit, limes, apples, peaches, pears, grapes, melons, cherries, plums, tomatoes, all squashes, blueberries, green beans etc.

Mangoes, bananas, avocados, figs, breadfruit, eggplant, cucumbers, guava, pomegranates, dates, papaya, olives and zucchini are also fruits.

Fruits are useful sources of citric acid and vitamin C that commonly act as antioxidants.

Sometimes the entire inflorescence is consumed as a compound fruit like pineapple and jackfruit.

Seeds: Seeds often contain stored food resources (carbohydrates, oils, proteins) to fuel the growth of the tiny plants that they contain.

Important seeds that we eat are beans, peas, lentils and chickpeas. All of these are members of the bean or legume family.

Food in these seeds is stored in the fleshy leaves (cotyledons) of the plant embryo. Many nuts consist of seeds or parts of seeds. Examples are walnuts, pecans, almonds and peanuts.

Grains: These are considered to be among the first cultivated crops, and are the small, dry fruits of members of the grass family. Grains look and behave very much like individual seeds.

The commonly cultivated food grasses are called cereals, after the Greek goddess Ceres. Major grain crops include barley, millet, oats, rice, rye, sorghum, wheat and corn (maize).

Rice, probably the most important grain, is the primary food source for more than 1.6 billion people.

Use Of Plants As Fibres

Fibres: Fibre crops are plants that have elongated woody cells in stems, leaves, bark and seeds for support and transport.

These form fibres which can be used to make ropes, textiles, paper, upholstery and mattresses.

the 17th century. This fibre (Gossypium species) which is made from hairs that grow on the surface of the seeds, is the most important source of fibre used in textiles.

Cotton fibres: Cotton comes from plants that produce seed pods filled with ball-shaped clumps of cotton fibre. The seeds are separated from the cotton fibre mechanically.

The process continues by spinning threads from the remaining, seedless white fibre.

The threads are then woven to make cloth, which can be dyed. Cotton was grown in Pakistan’s Indus Valley more than 5,000 years ago.

Cotton was grown and used to make clothing in ancient Egypt. Cotton plants were exported to the Southern United States.

Fibre cells in the leaves of sisal (Agave sisalana) are used to make string, rope and rugs (small carpets); a wide variety of fibre sources, but mainly wood pulp, is used to make paper.

Hessian is a thick rough cloth used for making things such as bags and ropes, made from a plant, either hemp or jute.

Cotton fibres are used for making different types of cloth, they are as follows:

Bark cloth: A type of cloth made from the inner bark of various trees, used in Indonesia, Malaysia and the Pacific Islands.

Buckram: A stiff cotton cloth used for covering books.

Calico: A cloth made of cotton with a coloured pattern printed on it, very often these coloured dyes are made from plant-based pigment.

Cambric: A thin white cloth made from cotton or linen.

Canvas: A strong heavy cotton cloth used for making tents, shoes and sails.

Cheesecloth: A thin light cotton cloth suitable for tropical climates.

Crepe: A soft thin cloth with small folds on its surface, made from cotton or silk.

Denim: A thick cotton cloth that is usually blue and is used especially to make jeans, it was originally introduced for industrial workers but later became a trend in fashion.

Flannel: A soft cotton cloth made of soft fibre used for making clothes and sheets.

Gauze: A white cotton cloth that is very thin and has a loose interwoven texture, used in layers for protecting and treating an injury.

Khaki: Tough cotton cloth used in the making of soldiers’ uniforms, it has a typical brown colour.

Muslin: A light thin cotton cloth used for making dresses, curtains and sheets, it is one of the finest cloth made by human beings.

Organdie: A thin stiff cotton cloth that is used as dress material with a lot of starch.

Rayon: A light smooth cloth made from cellulose (from plant cells).

Flax fibre: Linen is made from fibres made from the stem of flax. Flax grows to a height of 4 feet and has leaves that consist of long, tough fibres.

Flax has been used since ancient times to make clothing. The ancient Egyptians used flax to create linen cloth more than 4,000 years ago and it was used in Medieval Europe to make cloth.

Flax is still used to make fabrics for clothing and it is commonly blended with synthetic materials and wool to add strength to fine yarns.

Hemp Fibre: Hemp comes from the Cannabis sativa plant and has been used to make cloth since ancient times.

In the 1980s, producers were able to make fine cloth suitable for clothing from hemp. This development occurred following the discovery of a process using enzymes that removed the fibres’ roughness while still allowing the fibre to retain its durability.

Designers currently use hemp, blended with other textiles, to make fine cloth, in contemporary designs.

Hemp fibre is resistant to stretching, which allows clothes made or woven with hemp fibre to retain their shape and size.

Hemp typically grows in warm climates, such as those found in tropical regions.

Ramie fibre: Ramie is grown in East Asia and is known as China grass. Ramie fibres have been found in fabrics used to wrap mummies in ancient Egypt.

Ramie fibres are fine and produce delicate silk-like threads when spun, although the fibres can become brittle when a dry process is used to spin them.

Cloth made from Ramie is resistant to stain and has a slight sheen that reflects light. Ramie fabrics are also used in the manufacture of garments because the cloth does not readily shrink.

Plant materials used as building materials

Resins: Resins obtained from plants like pine, sal etc. are used in paints.

There are many other building materials obtained from plants, such as timbers of sal are used in making window frames and furniture. Softwoods are used for insulation purposes.

Plant excretory products may include pitches for waterproofing or making organic solvents for dissolving paints. Fibres are used as thatching material.

Rattans: Rattans (climbing palms) are used for all kinds of purposes, from building shelters to making cane furniture, baskets, mats and fish traps.

Coirs: Coirs are used for making door mats and also for making the lining of the floor.

Use Of Plant Excretory Material

The plant excretory materials are used for different purposes as described below:

1. organic acids like citric acid is obtained from fruits of lemon tartaric acid is obtained from fruits of tamarind.

2. The latex of rubber plants obtained from the bark is used in the making of rubber

3. The resin from Pinus wood is used for producing turpentine, which is used in the making of organic solvent, or as a polishing agent.

4. Essential oil from the flowers of the lavender plant is used in the making of perfume, and lemongrass oil from the leaf is used as a pesticide.

5. Tannin obtained from the leaves and twigs of different plants like tea, and Emblica are used in the making of printing ink or processing of leather.

6. Alkaloids obtained from different plant resources have medicinal importance; some of them are as follows:

1. Caffeine from coffee seeds is a stimulating agent.

2. Quinine from Cinchona bark is a malarial drug.

3. Amarogentin from chirata leaves is used against Salazar.

4. Atropine from the flowers of Atropa is used to dilate pupils.

5. Reserpine from the stem and twigs of Rauwolfia is used to treat high blood pressure

Plants Are The Dwelling Place For Animals

Birds like sparrows, crows, and common mynah directly use the plants as their dwelling places.

They use plant parts like fragments of stems, twigs, and leaves to prepare beautiful nests.

Other animals like squirrels and monkeys live in the trees. Bats hang from the branches of trees. Insects also live in the trees and get their food from them.

Ants and other stinging insects often take shelter on big trees, particularly fruit trees like mango and litchi.

These insects act as an army and protect the plants from enemies whenever necessary.

In some American acacias, a certain part of the leaf becomes hollow to be used as an abode for the insects and even some food materials are kept ready for them.

The insects, in return, render defence service in times of necessity.

Plants As A Source Of Oxygen

Plants have chlorophyll, with which they carry photosynthesis. The process of photosynthesis has two phases, the light-dependent phase and the light-independent phase.

The light phase produces energy-rich compounds and also photolysis of water which generates oxygen.

The dark phase or light-independent phase is involved in the production of sugar by fixing carbon dioxide.

Thus plants provide food and oxygen to other members of the biotic community and absorb harmful carbon dioxide from the atmosphere.

Hence the environment is purified due to the maintenance of O2 & CO2 and global warming is reduced by the prevention of the abundance of CO2 in the earth’s atmosphere.

 Dependence Of Plants On Animals

Pollination

The process of transfer of pollen grains from the anther to the stigma is called pollination.

When it occurs within the same flower, it is called self-pollination but when it occurs between two S different flowers, it is called cross-pollination.

Pollination leads to fertilization, the formation of plant embryos and the subsequent creation of new plants.

Thus the process of pollination is absolutely essential for the existence of the plant kingdom.

The process of cross-pollination is helped by different agents like air, water, animal, etc.

Animals Helping In Pollination

The animals that help in cross-pollination include insects, snails, birds, bats and other mammals like cattle.

1. Insect-pollinated flower:

These flowers have bright colours, they have nectaries and the petals are suited enough to allow the insects to settle down.

In the case of ant-pollinated flowers, the inflorescence is completely closed with an apical pore, through which only the ants can enter, e.g. Calotropis, Salvia, and Sunflower.

2. Snail pollinated flower:

These flowers are semi-aquatic and are protected by a fleshy bract, e.g. arum

3. Bird-pollinated flower:

The flowers are large, and bright in colour, e.g. Bignonia

4. Bat-pollinated flower:

These flowers are large in size, and nocturnal, e.g. Kadam.

5. Cattle pollinated flower:

These flowers are large and are not destroyed even after being trampled by cattle, e.g. Rafflesia.

Fruit And Seed Dispersal

Seed and fruit (which contains the seed inside) dispersal is the movement, spread or transport of seeds or fruits away from the parent plant.

This method has several benefits for different plant species. First, seed survival is higher away from the parent plant.

This higher survival is due to the prevention of actions of seedling predators or pathogens which often target the high concentration of seeds beneath adult trees.

Secondly, competition with adult plants may also be lower when seeds are transported away from their parent plants.

This allows plants to reach specific habitats that are favourable for survival.

Thus dispersal of seeds or fruits is very important for the survival of plant species by spreading out in a wide area and avoiding competition with one another for the same resources.

Since plants are mostly immobile, thus they rely upon several abiotic agents (like wind, water etc.) and biotic agents (birds and animals including human beings) for the dispersal of seeds and fruits. The animals help in the dispersal of fruit and seed in the following way:

1. Berry and other fleshy fruits are consumed by birds. After that, the fruit rot within the alimentary canal and the seed come out with the egested matter and germinate in a different place.

2. Sometimes seeds or fruits have spiny projections, which get adhered to the hoofs of cattle and get dispersed, for example., Xanthium.

3. Seeds of chorkanta get adhered to the fur of animals or in the clothes of human beings and are dispersed through a wide area.

Nature Of The Relationship Of One Living Organism With Another

Symbiosis

It is a unique long-term association between two organisms of the same or different species where they two remain in close association and are mutually benefitted by each other.

Each of the participatory organisms is called a symbiont. There are different examples:

1. Cattle egrets and cattle:

These egrets are small birds (Heron) that remain along with cattle. When the cattle (eg. cows) walk, insects fly out of the grass.

The egrets feed on the insects sitting on the cattle’s bodies and thereby protect them.

2. Clownfish and sea anemones:

The clown fish keeps away the enemy of the sea anemone ie, the butterfly fish and in return, they feed on the remnants of food left over by the sea anemone.

Sometimes the enemies are devoured by the sea anemone.

3. Ants and aphids: The aphid is a sap-sucking insect. The aphids feed on plant

sap producing a sugary compound called the honeydew as excreta which is consumed by the ants.

The aphids remain well protected in the ants’ nest and the ants also carry them from one host plant to another as and when necessary.

4. Mynah and Rhinoceros:

Rhinoceros have very thick skin commonly inhabited by mites. The Mynah or other egrets feed on these mites and thereby provide relief to the Rhinoceros.

5. Hermit crab and sea anemone:

Since they have a soft abdomens, hermit crabs live inside the empty shell of marine animals to protect their vulnerable abdomen. The hermit crab carries the sea anemone on its shell.

The stinging tentacles of the sea anemone protect the crab while the sea anemone can move freely on top of the hermit crab and in return, has a share of food left behind by the hermit crab.

6. Azolla and bacteria:

Azolla is a kind of floating plant. A kind of bacteria called cyanobacteria (Anabaena azollae) takes shelter on its leaves.

This bacteria in turn fixes atmospheric nitrogen to help Azolla. Nitrogen is an essential ingredient of fertilizer. For this reason, Azolla is cultivated in the cropland.

2. Predation

The phenomenon by which one animal feeds on another animal is called predation.

This habit has created a food chain and the animal that is fed upon is called prey, while the animal which is feeding on the prey is called predator.

Some of the predators and prey are given below Predation helps to maintain biodiversity and provides energy to prolong life and promote the reproduction of the predator to the detriment of the prey.

It thus has a controlling effect on the prey population in a community.

3. Parasitism

The relationship in which one organism lives on another living organism derives its nourishment from that organism and thereby gets benefits while the other organism is harmed is called parasitism.

Parasites influence the food web because they function as both predators and prey. Parasites that feed on hosts engage in a special type of predation.

Alternatively, parasites can also serve as important sources of prey.

For example, predators on islands in the Gulf of California (like lizards, scorpions and spiders) are more abundant on islands with seabird colonies because they feed on the bird ectoparasites.

Predators also inadvertently consume parasites during the consumption of infected hosts.

Parasites can be classified in different ways:

1. On the basis of the host:

Plant parasites: Dodder, fungi.

2. Human parasite: TB bacteria, Pig tapeworm.

3. Animal parasite: Dog tapeworm.

On the basis of the part affected:

Stem parasite: Dodder or Swarnalata.

Root parasite: Viscum.

Leaf parasite: Rust fungus or Puccinia growing on wheat plants.

On The Basis Of The Location:

Ectoparasite:

The parasite that remains outside the host’s body is usually on the external surface, e.g. Lice growing on the scalp.

Endoparasite:

The parasite that grows inside the host’s body, very often they are anaerobic in nature, e.g. Pork tapeworm.

On the basis of nature, parasites may be classified as:

Obligatory parasite:

The parasites which are always parasitic and never survive as saprophyte is called obligatory parasites, e.g. Puccinia graminis causing black stem rust of wheat.

Facultative parasite:

These parasites may survive both as saprophytes and parasites in nature, e.g. Aspergillus.

Some of the major parasites:

 Dependence Of Man On Animals

The earth, its ecosystem and its creatures are all deeply connected. Thus, the existence of many species depends on the survival of others.

Human beings are no exception. There are many animals we rely on for our benefit and well-being.

In fact, many animals actually help people just by performing their natural roles in their environment.

Human beings depend on animals with respect to food, clothing, medicines, reduction of pollution and also as a mode of transport.

1. Animals as food:

The animals are the source of different types of food like meat, fish, eggs, milk, honey etc.

Meat is obtained from different animals like goat, cattle, pork and also chicken from poultry birds.

Eggs from poultry birds are useful sources of fat, protein, sulphur, and calcium.

Honey obtained from the honey bee is a useful source of sugar, minerals and vitamins.

2. Animals used for preparing clothes:

Silk thread produced by silkworms is a protein thread used in the making of quality dress material.

The quality of silk varies with the type of silkworm and the plants on which they feed.

Wool obtained from sheep and goats (Angora goats, Kashmiri goats etc.) is another important variety of thread used for making warm clothes.

3. Medicines from animals:

Animal lovers are a very good source of vitamins. The liver of cod and halibut fish are a potential source of vitamins A and D.

Vitamin D is good for bone formation while vitamin A is a potential source of retinol, which helps in the synthesis of rod cells in the retina that are responsible for low-light vision.

4. Animals helping in the reduction of pollution:

Some animals help in the reduction of pollutants. Crows are ideal scavengers feeding on leftover food and organic matter, animal waste and carcasses.

Vultures also feed on animal carcasses and reduce pollution. Pigs feed on animal waste and other organic waste and thus clean the environment.

Some animals like guinea pigs feed on their own excreta, the phenomenon is called coprophagy and thereby they absorb the essential nutrients which they cannot digest at first time.

5. Animals used as transport:

Animals have been used as a mechanism of transport, like bullock carts, horse carriages etc.

In the present day, with the increasing speed of life, these carriages are mostly used in rural areas as means of transport and less used in urban areas.

6. Animals used in agriculture:

Cattle (cow, buffalo or lamb) were previously used in ploughing agricultural land but presently with the increasing use of mechanized agricultural equipment, the use of animals in agriculture has been mostly discontinued.

Microbes Useful To Human

Microbes include microscopic organisms like bacteria, fungi, algae, protozoa etc. which are not visible to the naked eye.

Many of these organisms are useful to humans and are used in the preparation of curd, bread and medicines.

1. Preparation of curd:

Curds are formed from milk by the lactic acid bacteria, Lactobacillus lactis which helps in the fermentation of lactose sugar to lactic acid.

The formation of lactic acid prevents the growth of pathogenic bacteria in the curd.

2. Production of bread:

The dough made of wheat or flour is fermented by a unicellular fungus called yeast to produce bread. Yeast breaks down the sugar present in the wheat or flour.

Carbon dioxide and alcohol are also produced in the process.

Mild heating causes the carbon dioxide to be liberated thereby causing the porous texture of the bread. This way bread becomes soft and spongy.

3. Production of Medicines:

Microbes are a useful source of medicines like antibiotics.

The green mould Penicillium notatum produced the first antibiotic, penicillin as was discovered by Sir Alexander Flamming.

Streptomyces is a bacteria-like organism belonging to the actinomycetes group, which produces antibiotics like streptomycin and erythromycin which are used against pathogenic organisms.