CHANGES AROUND US Class VI Chapter VI

Introduction-

In our day today life almost everything is changing. Some are changing fast and easily visible, some others are very slow and not easily recognizable. e. g- Day, Night, Rotation of the Earth, Seasons, Weather, Daily Routine, Drying of Clothes, Cooking of Food, Rusting of Iron, Glowing of Bulb, Movement of Vehicles, Cutting of fruits, Inflating of balloons,  Revolution of the Planets around the Sun, Melting of Ice, Iron rod becomes hot due to heating etc. So, changes are only permanent things in this world.

Types of Changes- There are many ways to classify the changes.

A. Reversible and Irreversible changes- Those changes in which the newly formed substance can be reversed back to get the original substance is called as reversible change.

A------> B-------> A

Or,  A-------->B

     A<-------- B

e. g.- Melting of Ice to form water on heating and then formation of ice on cooling.

e. g.- Inflating and deflating  of balloon

Those changes in which the newly formed substance cannot be reversed back to get the original substance is called as irreversible change.

A -------> B

e.g.- The cooked rice cannot reverse back to raw rice.

e. g.- The Jaggery  cannot used to get the juice of sugarcane.

B. Physical and Chemical Changes- Those changes in which no new substance are formed are called as physical changes. Only the shape, size, state and colour of any substance change in the physical change. e.g.- Crumpling of Paper causes change in its shape, Tearing of paper in small pieces, Melting of Ice cubes to liquid water and Freezing of water forms ice cubes, Iron rod becomes hot due to heating etc.

C. Slow and Fast Changes-  Some changes occurs very fast. They are called fast changes. E.g.-  Burning of paper, melting of ice, etc. Some changes take lots of time to occur, they are called slow changes. E. g.- Growth of plants and animals etc.

D. Periodic and Non-periodic changes- Changes that repeat at regular interval of time are called periodic changes. E. g- Swing of pendulum, phases of moon etc.  Changes that do not repeat at regular interval of time are called non-periodic changes. They are irregular in terms of time.  E. g- Volcanic eruption, earthquake, Forest fire etc.

E. Desirable and Non-desirable changes- Changes that occur as per our desire and will are desirable changes. They are natural as well as man –made. E.g.- Seed-germination, Ripening of fruits etc. Changes that are unwanted or unnatural are called non-desirable or undesirable changes. E.g.- Rusting of iron, spoiling of food, etc.

 

Causes of Changes-

1. Changes by Heating- Due to heating the metal objects expands and their size increases. On cooling their size decreases. E. g.- Iron rim of wooden wheels . The length, area and volume increases on heating.

2. Changes by Mixing- The changes also occur on mixing one thing with other. e.g.- Curd is formed by adding some curd in lukewarm milk, Water and sugar solution etc.

3. Changes by Applying Pressure- When pressure is applied, change in shape occurs in shape and size.

e.g.- Changing the shape of flattened balloon

EXERCISE QUESTIONS

REPRODUCTION IN PANTS Class 7 Chapter 12

 INTRODUCTION-

Living organisms have a limited lifespan. Unless they are not going to form new organism, they will finish. Their continuity of life will be lost. So, fertile organisms form new organism of same kind either by self or by the help of other individual of same species. The process of formation of similar types of organisms by existing organism is called reproduction.

    There are two types of reproductions-

     (a) Asexual Reproduction – New organism is formed by single parent. It is common in plants     

          and animals.

     (b) Sexual Reproduction- New organism is formed by two parents. It is common in plants     

          and animals.

A. ASEXUAL REPRODUCTION IN PLANTS - New organism is formed by a single parent. It occurs by following methods-

1. Vegetative Propagation- The vegetative parts of plant is used to grow the new organism. e. g.- Roots in case of Sweet Potato and Mint, Stem in case of Strawberry and Chrysanthemum, Modified stem in case of Potato tubers, Leaves in case of Bryophyllum and African violet is used to develop new organism.

Vegetative Propagation also occurs by artificial methods like- Cutting, Grafting, Layering and Tissue culture. It is very useful for fruit yielding plants.

2. Budding- Bud is an asexual reproductive structure. This is an outgrowth of mother body in which a nucleus is found. The bud grows to form the new organism. e.g. – Yeast (A Fungus)

3. Fragmentation- Fragments are small asexual reproductive structures formed by fragmentation of mother body. Each fragment grows into a new organism. e. g.- Spirogyra

 

4. Spore Formation- Spores are small asexual reproductive structures that germinate to form new organism. Spores are formed in large number. They float in air and on finding suitable surface for germination, they form new organisms. The germinating surface must contain organic matter and water. e. g.- Ferns (Pteridophytes) and Fungi like Rhizopus, Mucor, Penicillium, Agaricus (Mushroom) etc.

B. SEXUAL REPRODUCTION IN PLANTS-   The reproduction in which two parents, one male and one female are required to form the new organism is called as sexual reproduction.

Flower is the reproductive part of the plant. The complete flowers have all the four whorls but incomplete flowers have less than four parts. It has male part called stamen and female part called pistil (or carpel). Stamen forms pollen grains that contain male gametes. Carpel has ovary that contains eggs.

Uni-sexual and Bisexual Flowers- Those incomplete flowers which have either pistil or stamen are called uni-sexual flowers. e. g.-Papaya, Maize, Cucumber etc.

Those flowers which have both pistil as well as stamen are called as bisexual flowers. e. g.- Rose, china-rose, mustard, marigold, lotus etc.

Pollination- The transfer of pollen grains from anther to the stigma is called pollination. There are two types of pollinations-

A. Self fertilization

B. Cross fertilization

When transfers of pollen grains occur from anther to the stigma of same flower, it is called as self fertilization. When transfers of pollen grains occur from anther to the stigma of different flower, it is called as cross fertilization.

On stigma, pollen grains germinate to form pollen tube in which male gametes are found. The pollen tube moves below inside the ovary for fertilization.    

Fertilization- The fusion of male gamete with female gamete to form zygote is called fertilization. As a result of fertilization, single celled zygote is formed.

Formation of Fruits and Seeds- As a result of fertilization some post-fertilization changes starts. The ovary changes into fruit and ovules change into seeds. So, fruit is ripened ovary.

Seed- The seed develops from the fertilized ovules. They have an outer protective covering called seed coat. The Seed has either one cotyledon or two cotyledons. Cotyledons are nutritive cells that give food to developing radical and plumule.

Seed Germination- The seeds can remain in dormant stage for many months to many years. On finding suitable conditions, the seed germinate to form radicle and plumule. The small embryo develops into radicle and plumule. The root system develops from radicle and shoot system develops from plumule.

Seed Dispersal- The method of going of seed from one place to other by an agent is called seed dispersal. The agents to seed dispersal can be- air, wind, water, animals including humans, bats, explosion etc.

Some seeds have hairy structures and wings so they are carried away by wind to other place.

 

 

 

 

 

SEPARATION OF SUBSTANCES CLASS VI CHAPTER V

Introduction-

We see and use a number of substances in our daily life. These are pure as well as impure mixture. Most of them are mixture. E.g.- Air, Water, Milk, etc.The separation of harmful or useless component is done from useful ones by different methods.

Pure Substance-

Those substances which are made up of only one kind of particles are called as pure substances. e.g.- All elements like Hydrogen, Gold, Carbon etc.  and Compounds like Water, Sodium Chloride etc.

Mixture-

Those impure substances in which two or more other substances are found are called mixture.

The ratio of components in the mixture is not fixed. Their individual chemical characteristic is retained. Components of a mixture can be separated. A mixture can be solid, liquid or gas. The mixtures can be –homogeneous or heterogeneous. The components of homogeneous mixture cannot be seen separately. e. g.- Steel, Petroleum, milk, Air etc. The components of heterogeneous mixture can be seen separately. e. g.- Rice and stone, sand and iron etc. etc.

 

Separation of substances-

The separation of substances is done to remove harmful component or unwanted component or to obtain pure or useful component from a mixture. The common methods are-

1. Hand Picking- The process of separating of large unwanted components of the mixture by hand is called handpicking. e. g.- Small pieces of stones from rice, pulses etc.

2. Threshing- The process of separating of grains from their straw and chaff is called threshing. It is done manually by hand or by thresher machines.

3. Winnowing- The process of separating of lighter components from heavier component by using wind is called winnowing. e. g. Husk (lighter) from the grains (heavier).

4. Sieving- The process of separating different size components of a mixture by using sieve is called sieving.  e. g. Tea from tea leaves by sieve, Fine sand from gravels and pebbles of stone by using wire-mesh.

5. Magnetic separation- The process of separating of a non-magnetic component from a magnetic component of the given mixture is called magnetic separation.

e.g.- Separation of iron objects from scrap yard, Iron nails, from sand etc.

6. Sedimentation, Decantation and Filtration- The process of separating of insoluble solids from liquid in its solution is done by sedimentation, decantation and filtration. These are interrelated processes.

The heavier insoluble particles are allowed to settle down at the bottom of container. It is called sediment.

The pouring of liquid part without disturbing the sediment is called decantation.

The process by which very fine insoluble components are removed using filter/ filter paper is called filtration.

7. Evaporation and Condensation- The changing of water into water vapour is called evaporation or vaporization. Evaporation is used to separate water soluble solids from liquids.

Evaporation is used to make salt from salty water. The liquid evaporates and heavy solid component is left behind.

Condensation is changing of water vapour into liquid form by cooling. The solid impurities are left behind on evaporation. Then pure liquid is obtained from this vapour by condensation.

8. Centrifugation or Churning- The fine insoluble solid is separated from liquid-solid mixture by rotating at very high speed is called centrifugation. e. g.- Butter from milk, drying of wet clothes by squeezing water in washing machine, blood cells from plasma etc.

 

Saturated Solution-

The solute and solvent together is called as solution. e. g.- Sugar is a solute and water is a solvent that together forms a solution.

Solute (Sugar) + Solvent (Water) = Solution

If more solute is added in the solution it will become denser. A solution in which no more solute can be dissolved is called saturated solution. The solute will be seen more at the base of container.

On increasing temperature of saturated solution, more solutes can be added. On the other hand on decreasing the temperature of saturated solution more solutes cannot be added.  

Exercise Questions

SORTING MATERIALS INTO GROUPS CLASS VI CHAPTER IV

Introduction-

We see a number of things around us. These can be classified into natural, man-made, solid, liquid, gases, lustrous, non-lustrous, opaque, transparent, translucent etc.

In our home, school, library, kitchen etc. we classify the objects into different categories. The process of grouping of objects based on their known properties is called classification.

Materials around Us-

Different kinds of materials are made up of may form any object. Also, different objects can be can be made from same material.

Same material forming different objects (Products)

Material	Objects (Products)
Wood	Chair, Table, Wheel, Plough
Paper	Book, Notebook, Newspaper, Toys
Leather	Shoes, belt, Jacket
Plastic	Toys, Bucket, Tumbler

 

Different materials forming one object (Product)

Materials	Object
Plastic, Paper, Steel, Wood, Soil	Plate (Thali)
Plastic, Metal, Wood	Pen
Wood, Plastic, Metal	Door
Glass, Plastic, Gold, Silver	Bangle

 

Natural and Man-made materials-

Those materials which are made in nature are called as natural materials.

e. g- Cotton, Wood, Gold, Coal, Rocks etc.

Those materials and objects which are made by humans are called as artificial or man-made or synthetic materials. E.g.-Furniture, Books, Cars, Clothes, Trains, Ornaments etc.

   

Properties of Materials-

We choose any object/product on the basis of their properties and uses.

The important properties of the objects can be –

1. Appearance-The metallic objects and objects made up of alloy shine (lusture). They reflect the light falling on them. But due to rusting sometimes they may appear dull. e. g.- Objects of Gold, Silver , Iron, Brass, Bronze etc.

Non-metals do not shine as like metals. They usually have rough surface. e. g.- Clothes, Notebooks, Leather, wood products etc. Except- Diamond. Diamonds actually do not shine. Diamonds are made shining and glittering by cutting and polishing.

 

2.  Hardness- Many objects can be hard or soft. Hard objects are difficult to be compressed or scratch. e. g- Metal Spoon, Locks and Key, Candle, etc.

Many other objects can be compressed or scratched easily. These are soft objects. e.g.- Cotton and Sponge

3. Solubility- Many substances get dissolved in water. They are called as soluble substances. e. g.- Sugar, Salt, Copper sulphate etc.

   Sugar (Solute) + Water (Solvent) = Solution

Some others do not get dissolved in water or other liquids. They are called as insoluble substances. e.g.- Sand, Soil, Chalk, etc.

Those liquids which get mixed with each other are called miscible liquids.

e.g.- Water and Vinegar, Water and Lemon Juice

Those liquids which do not get mixed with each other are called immiscible liquids.

e.g.- Water and Kerosene, Water and Ghee

4. Floating or Sinking Materials- The density of any material decides that the given object will float or sink in the water.

Objects lighter than water will float. e. g.- A dry leaf, Wooden piece, cork etc.

 

 

Objects lighter than water will float. e. g.-A coin, an iron nail, rock piece etc.

5. Transparency- The property of objects which allow the light to pass, partially pass or not pass through it is called as transparency.

There are three types of objects on the basis of transparency.

A. Transparent objects- Light can pass through them. e. g. Clear glass, Water, Air

All Light Passes through transparent objects.

B. Translucent Objects- Light can partially pass through the. e.g.- Muddy water, Smoke, Smoky Glass, Sun glass, Butter paper, Oiled paper etc.

Some Light Passes through translucent objects.

 C. Opaque Objects- Light cannot pass through them. e. g- Stone, Rock, Wood, Metal, Bricks etc.

No Light Passes through opaque objects.

6. Malleability- The property of metals by which they can be beaten into thin sheet/foil is called malleability. Such metals are called malleable. e.g.- Gold, Iron, Aluminium etc.

 

7. Ductility- The property of metals by which they can be drawn into thin wires is called ductility. Such metals are called ductile. e.g.- Aluminium, Copper, Iron etc.

8. Conductivity- The property of materials by which they allow the heat and current to pass through them is called conductivity. Such materials are called as conductors. e.g.- Objects of metals like Iron, Copper, Silver, Zinc etc.

Non-conductors (insulators) do not allow the heat and current to pass through them. e.g.- Wood, Clothes, Rubber, Plastic etc.

9. Combustibility- The property of materials by which they can catch fire is called combustibility and such substances are called as combustible substance. e. g.- LPG, Petrol, diesel, Kerosene, Wood etc.

 

Non-combustible substances do not catch fire. e.g.- Brick, Stone, Marble etc.

Exercise Questions (Solved)