std. 6, general science, maharashtra board€¦ · the biosphere (from greek bios = life, sphaira =...

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STD. VI General Science

10350_10840_JUP

Printed at: Repro India Ltd., Mumbai

P.O. No. 24980

Written as per the new syllabus prescribed by the Maharashtra State Board of Secondary and Higher Secondary Education, Pune.

PREFACE The new Science Text Book for class VI with a revised syllabus took us by an element of surprise. We had a mixed bag of opinion after we were done with the content review. There was a good part and a tough part to it. The good part is that the syllabus is more knowledge oriented and focused on concept building rather than just encouraging mugging. The tough part is that students would have to rummage through a number of external resources to get a holistic grip of the topic. We thought of this opportunity as a perfect platform to step in. Here, we intended to create a book that would act as a single point of reference for students. We wanted this book to provide students, the much needed answers for their textual questions as well as build up their knowledge quotient in the process. We have infused the book with a liberal sprinkling of real life examples, pictorial explanations and additional questions. Questions titled under 'Use your brain power', 'Can you tell' and a series of 'In-text Questions', pave the way for a robust concept building. Every chapter begins with Point wise Theory and pictorial illustrations. It follows through by covering all the textual content in the format of Question - Answers, Give Reasons and a host of Formative and Summative assessments. The chapter also includes Activity Based Questions that explain scientific concepts to students in a point wise manner through the medium of an activity. The chapter eventually ends with a Chapter wise Assessment that stands a testimony to the fact that the child has understood the chapter thoroughly. With absolute trust in our work, we hope, our holistic efforts towards making this book as a knowledge hub for students to understand scientific concepts pays off. The journey to create a complete book is strewn with triumphs, failures and near misses. If you think we’ve nearly missed something or want to applaud us for our triumphs, we’d love to hear from you. Please write to us at : [email protected] A book affects eternity; one can never tell where its influence stops.

Best of luck to all the aspirants! From, Publisher

No. Topic Name Page No. 1. Natural Resources - Air, Water and Land 1 2. The Living World 17 3. Diversity in Living Things and their Classification 30 4. Disaster Management 45 5. Substances in the Surrounding – Their States and Properties 58 6. Substances in Daily Use 71 7. Nutrition and Diet 83 8. Our Skeleton System and the Skin 96 9. Motion and Types of Motion 110

10. Force and Types of Force 121 11. Work and Energy 131 12. Simple Machines 143 13. Sound 153 14. Light and the Formation of Shadows 165 15. Fun with Magnets 176 16. The Universe 185

Note: Textual Questions are represented by * mark.

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Chapter 01: Natural Resources: Air, Water and Land Std. VI

Natural Resources 1. The elements available in the nature that fulfill the basic needs of living things on earth, thereby

allowing life to sustain on earth are known as Natural Resources. 2. Air, water and land are the most important natural resources, to which all things on earth are related in

some way or the other. 3. Air, water and land are called the earth’s atmosphere, hydrosphere and lithosphere respectively. 4. The biosphere (from Greek bios = life, sphaira = sphere) is the layer of the planet earth where life

exists. Biosphere can be classified as: 1. Air in the atmosphere around the earth comprises of various gases. 2. Composition of atmosphere: Atmosphere majorly comprises of nitrogen,

oxygen, carbon dioxide, six inert gases, nitrogen dioxide, sulphur dioxide, water vapour and dust particles.

The amount of the gases in air is maximum in the layer near to the earth’s surface.

The troposphere contains about 80% of the total mass of gases in the air, stratosphere contains 19%, while it decreases to a much lower extent in mesosphere and ionosphere.

Exosphere lacks gases completely.

Natural Resources : Air, Water and Land 1.

Air

Let’s Study

Proportion of land and water on earth’s surface

Atmosphere i. The envelope of

air surrounding the earth.

Biosphere

Hydrosphere i. The water portion on the earth’s surface. ii. Occupies 71% of the earth’s surface.

Lithosphere i. The land portion of

the earth’s surface. ii. Occupies 29% of

the earth’s surface.

Proportion of various gases in the air

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3. Uses of gases in air: Gas Uses

Nitrogen Helps living things to build necessary proteins. Useful in production of ammonia. Used in food industry for air tight packaging of food items.

Oxygen Essential for respiration (breathing in living things). Essential for burning (combustion).

Carbon dioxide Plants use it for photosynthesis. It is major constituent of fire extinguishers.

Argon Used in electric bulbs. Helium Used for generating low temperature.

Used for generating lift in airships. Neon Used in street lights and decorative lights. Krypton Component of fluorescent tubes. Xenon Used in flash photography.

4. Importance of atmosphere: i. Acts as an important filter a. Allows light and heat to reach the earth’s surface in quantities required for life to sustain on

earth. b. Protects the earth’s surface from harmful substances like ultraviolet radiations. ii. Maintains the temperature of the earth’s surface. 5. Any undesirable change in the normal composition of the air by addition of harmful gases is known as

“air pollution”. 6. Causes of air pollution: 1. Harmful gases given out through combustion of fuels in vehicles and big industries. 2. Incomplete combustion of fuels like coal and wood. 7. Pollutants released in air by combustion of fuels are: i. Nitrogen dioxide ii. Carbon dioxide iii. Carbon monoxide iv. Sulphur dioxide v. Soot 1. A layer of ozone (O3) gas is present in the lower part of the stratosphere. 2. It mainly functions as a shield to protect the earth's surface from the harmful ultraviolet rays of the sun. 3. The increase in air pollution causes depletion of ozone layer. 4. Chemical gases like carbon tetrachloride, chlorofluorocarbons used in air conditioners and refrigerators

mix with the air and destroy the ozone layer. 1. Along with air, another important factor absolutely essential for survival is “water”. 2. Characteristics of water: i. Colourless, odourless ii. Dissolves many substances readily (universal solvent) iii. Tasteless iv. Occurs in three states: Solid (ice), Liquid (water), Gaseous (water vapour) 3. The blood of animals and the sap in plants contain a very high proportion of water. 4. Water available on earth: i. Water in seas and oceans: 97% ii. Ground water, frozen state (ice): 2.7% iii. Fresh, drinking water: 0.3% Thus, only 0.3% of total water covering the earth’s surface can be utilized for the purpose of drinking.

Water

Ozone Layer

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5. Sources of water: ‘Water cycle’ that leads to rainfall is the major source of water on earth. 6. Water Cycle: Water evaporates from the oceans, gets stored in the clouds and condenses as rain. Thus, fresh water

enters the ocean, thereby completing the cycle. 7. Rain water also seeps into the ground, thereby increasing the ground water level. This gives rise to

other sources of water like rivers, ponds, springs, lakes, streams. 8. Uncontrolled use of water for the ever increasing population, industry and farming has resulted in

shortage of water. 9. Tips to save water: i. Do not waste water, use it wisely. ii. Allow water to seep into the ground by storing or blocking it. iii. Reuse water (stored water doesn’t become stale at once). 1. Land is seen in the form of stones, soil, big rocks. 2. Both plants and animals need land. 3. Humans live on land as well as utilize it for other purposes like shelter, farming etc. 4. Buried within the land are minerals, crude oil and natural gas, which are useful for humans in many

ways. 5. Land can be divided into the following layers: Humus: Topmost mature layer. Most fertile layer. Formed by decomposition of animals and plants. Usually found in dense forests. Top soil: Made up of soil, small stones, insects and worms. Sub soil: Made up of sand and small stones. Immature layer. Bed rock: This layer has less of soil and more of rocks. Minerals are obtained from this layer. Responsible for colour and texture of the soil. 6. Soil is composed of: Biotic components: Living things constituting the soil. Example: plants, microbes, worms etc. Abiotic components: Non-living things constituting the soil. Exmaple: Rocks, small stones, sand,

pebbles etc. 7. Process of soil formation: i. It is a slow, continuous natural process. ii. Heat, cold and water are responsible for breakdown of the bedrocks. This process is known as

“Weathering” of rocks. iii. Weathering brings about formation of stones, sand and soil particles. iv. Roots of trees also contribute in weathering of rocks.

Land

Humus

Sub soil

Bedrock

Top soil

Layers of land

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8. Soil degradation/soil erosion: Soil can get degraded/destroyed by natural as well as artificial means. i. Natural process: Natural calamities like earthquakes, floods, storms etc. ii. Artificial process: Human activities like mining, farming, deforestation etc. 9. Effects of soil degradation/soil erosion: The top fertile soil is lost in this process of soil erosion. This results in loss of fertility of the soil which

thereby makes the land “barren”. 10. Ways to prevent soil erosion: Plant more trees, as the roots of trees/plants/grasses and bushes hold the soil particles tightly together,

thereby preventing erosion. 11. Formation of fossil fuels: Geographical upheavals led to burial of the trees and animals deep inside the land. Burial of the remains of plants and animals for many ages led to formation of fossil fuels. Fossil fuels give us many useful substances. Example: Crude oil, a type of fossil fuel, which gives us petrol, diesel, kerosene, paraffin, tar and wax. 12. Utilization of resources: All living things utilize the natural resources for their survival but the availability of natural resources

in the environment is limited. For example – Oxygen – 21% Fresh water – 0.3% Land – 29% These resources although available in fewer quantities are sufficient to fulfill the needs of living

organisms, provided these are used wisely and not wasted. *1. The layer of ozone gas absorbs ______ rays that come from the sun to the earth. *2. Of the total water available on the earth, fresh water forms ______ percent. *3. Both ______ and _____ constituents are present in the soil. 4. Atmosphere, hydrosphere and lithosphere constitute the _______. 5. Lower part of _______ contains the ozone gas. 6. Gases are absent in _______ layer of atmosphere. 7. Air becomes _______ at higher altitudes. 8. Fog, snow and rain are formed in _______. Answers: 1. ultraviolet 2. 0.3% 3. abiotic and biotic 4. biosphere 5. stratosphere 6. exosphere 7. rarer 8. atmosphere *1. Land and soil are the same thing. Ans: Wrong Soil is a component of land, along with rocks, small stones, decomposing plants and animals. *2. The water in a lake is called ground water. Ans: Wrong Water seeped deep inside the ground is known as ground water, while that in lake is surface water.

Summative Evaluation

Fill in the blanks

Right or Wrong? If Wrong, write the correct sentence.

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*3. It takes about 1000 years to form a 25 cm thick layer of soil. Ans: Wrong It takes about 1000 years to form a 2.5 cm thick layer. *4. Radon is used in decorative lights. Ans: Wrong Neon is used in decorative lights. 5. Soil has only abiotic components. Ans: Wrong Soil has both abiotic and biotic components. 6. Hydrosphere occupies 71% of the earth’s surface. Ans: Right 7. The land on the earth’s surface is the “lithosphere”. Ans: Right 8. Soil is formed by man-made process. Ans: Wrong Soil formation is a natural process. 1. Soot, nitrogen dioxide, carbon monoxide, oxygen, sulphur dioxide. Ans: Oxygen: Reason: Rest all are harmful substances released in air through combustion of fuels. 2. Petrol, paraffin, diesel, kerosene, chlorofluorocarbon. Ans: Chlorofluorocarbon: Reason: Chlorofluorocarbon is a chemical gas that depletes the ozone layer, while others are products

obtained from crude oil (fossil fuel). *1. Match the natural resources from Group ‘A’ with the related descriptions given in Group ‘B’.

Group ‘A’ Group ‘B’ i. Carbon dioxide a. Generation of soil ii. Oxygen b. Rain iii. Water vapour c. Plants and food production iv. Microbes d. Combustion

Ans: (i − c), (ii − d), (iii − b), (iv − a) 2. Match the name of the gases from Group ‘A’ with their uses given in Group ‘B’.

Group ‘A’ Group ‘B’ i. Xenon a. Used to obtain low temperature ii. Argon b. Used in fire extinguishers iii. Helium c. Used in electric bulbs iv. Carbon dioxide d. Used in flash photography

Ans: (i − d), (ii − c), (iii − a), (iv − b)

Odd One out

Match the Following

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1. Name the following *i. Constituents of the biosphere *ii. Biotic constituents of soil *iii. Fossil fuel *iv. Inert gases in air *v. Gases that are harmful to the ozone layer vi. The topmost fertile natural layer of the soil. vii. The layer of land from which the main minerals are obtained. viii. The initial process of formation of soil. ix. The process that disturbs the balance between the constituents of air. x. The process of destruction of fertile layer of soil by floods, storm and human activities. xi. The institute established for studying the weather changes and making the forecasts about rainfall

in the Indian subcontinent. Answers: i. Atmosphere, hydrosphere, lithosphere and the living things that occupy these spheres. ii. Plants, microbes, worms, insects and rodents like rat, mice [All living things found in the soil] iii. Coal, petroleum, crude oil iv. Argon, Helium, Neon, Krypton, Xenon and Radon v. Carbon tetrachloride and chlorofluorocarbons vi. Humus vii. Bedrock viii. Weathering of rock ix. Air pollution x. Soil erosion xi. India Meteorological Department (IMD) *1. Explain with the help of a diagram how soil is formed. Ans: i. Soil formation is a slow but continuous process. ii. Natural events like earthquakes, floods and

climatic changes such as erosion, wind, rain, snow, heat contribute towards breakdown of rocks. This process is known as ‘weathering’.

iii. Roots of trees also contribute in weathering of rocks.

iv. The rocks get broken down into pieces to further form smaller particles. It takes about thousands of years to form 2.5 cm layer of the soil.

*2. Why is there a shortage of water even though it occupies about 71% of the earth’s surface? Ans: i. Water occupies 71% of the earth’s surface. Out of the water available, a. 97% constitutes the sea and oceans, which is salty to taste. b. 2.7% makes up the ground water, ice and other forms (water vapour). c. Only 0.3% forms the fresh drinking water. ii. Since the sea water (97% of the total water) is salty, it cannot be used by living forms to fulfill

their needs of drinking, domestic use or other uses like farming and cultivation. iii. Out of the remaining 3% of the water available on earth, around 2% of the water is trapped in the

form of ice glaciers, snow, etc which again cannot be used by living forms.

Answer in one word

Answer in your own words

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iv. Thus, the living forms have to suffice their needs from the remaining 0.3% of water available through the rivers, streams and some amount of ground water.

v. The increasing population has largely exploited these available water resources (for example drilled bore wells to tap the ground water) at a rate faster than they are recharged or refilled.

vi. Furthermore, water bodies with potable water are being polluted by discharge of industrial effluents, domestic waste, etc. thereby degrading its quality.

vii. Increasing deforestation (cutting down of trees) has led to an imbalance in the water cycle, i.e. lowered the average yearly rainfall thereby contributing indirectly to the water scarcity.

Thus, there is shortage of water even though it occupies 71% of the earth’s surface. *3. What are the various constituents of air? Write their uses. Ans: The various constituents of air are nitrogen, oxygen, carbon-dioxide, six inert gases, nitrogen dioxide,

sulphur dioxide, water vapour and dust particles. The uses of constituents of air is as follows:

Gases Proportion Uses i. Nitrogen 78% Helps living things to build necessary proteins.

In production of ammonia. In food industry for air tight packaging of food items.

ii. Oxygen 21% Essential for respiration (breathing in living things). For burning (combustion).

iii. Argon 0.9% Used in electric bulbs. iv. Carbon dioxide 0.03% Plants use it for photosynthesis.

Major constituent of fire extinguishers. v. Helium

0.07%

Used for generating low temperature. Generating lift in airships.

vi. Neon Used in street lights and decorative lightings. vii. Krypton Component of fluorescent tubes. viii. Xenon Used in flash photography. ix. Radon Used for treatment of cancer x. Sulphur dioxide Used for leaching and as a fumigant xi. Nitrogen dioxide Used in chemical reactions. xii. Water vapour Helps in maintaining temperature.

Condenses to give rain thereby maintaining the water cycle.

*4. Why are air, water and land considered to be valuable natural resources? Ans: i. The elements available in the nature that fulfill the basic needs of living things on earth, thereby

allowing life to sustain on earth are known as “Natural Resources”. ii. Air, Land and Water are considered important natural resources, because a. Air: It forms the atmosphere that acts as filter by allowing light and heat to reach the earth’s

surface in quantities required for life to sustain on earth and also protects the earth’s surface from harmful substances. For example: the ultraviolet radiations.

Air is a mixture of gases of which major constituents are 1. Nitrogen (78%): necessary to build proteins. 2. Oxygen (21%): necessary for respiration (breathing) and combustion (burning). 3. Carbon dioxide: necessary for plants in order to carry out photosynthesis. Without these gases, life would have not existed on earth.

Do you know? It is costlier to desalinate sea water as compared to fresh water. The largest desalination project is ‘Ras-Al-Khair’ in Saudi Arabia which produces 1,025,000 cubic metres per day. Israel produces 40% of its water by this technique.

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b. Water: Majority of earth’s surface is filled with water (71%) but only 0.3% is potable. The remaining 99.7% is in the form of water in sea, oceans, ground water, water vapour,

ice etc. Water forms the basis of life processes in all living organisms. Blood of animals and cell

sap of plants have large proportion of water. Thus, organisms cannot survive without water. Therefore, water is an important resource, without which life cannot exist. c. Land: Land is considered as a valuable natural resource because: It provides the necessary environment (i.e. support) for the plants to grow. Plants in turn

form the basic level (producers) on which the other organisms depend. It provides habitat for the terrestrial animals. Humans exploit the land by using it for farming and building houses and roads. They also utilise the various fossil fuels like coal, crude oil, natural gas buried deep inside

the land. Thus, air, water and land are of prime importance for the life to sustain on earth. Hence, all these

natural resources should be used wisely. 5. Can you tell ? (Textbook page no. 5) i. What is land made of? Ans: Land is made up of various components. a. Living components of land: Plants, animals, especially rodents that dig furrows and live

inside like rats and mice, microbes, worms, insects. b. Non-living components of land: Stones, rocks, soil particles, dead decomposing plants

and animals, sand. Land can be divided into the following layers: Humus : Topmost mature layer. Most fertile layer. Formed by decomposition of animals and plants. Usually found in dense forests. Top soil : Made up of soil, small stones, insects and worms. Sub soil : Made up of sand and small stones. Immature layer. Bed rock : This layer has less of soil and more of rocks. Minerals are obtained from this layer. Responsible for colour and texture of the soil. ii. Is land flat every where? Ans: a. No, land is not flat everywhere. Natural events like earthquakes, floods and natural

processes such as erosion, wind, rain, weather changes like snow, heat contribute towards making the land an uneven structure.

b. Any piece of land that is subjected to more weather changes and natural events will show more erosion and will form furrows or pits, making the land uneven and will give rise to various geographical structures like hills, valleys.

iii. Does man produce soil / land? Ans: a. Soil or land is not produced by man. It is formed by a natural process. b. The abiotic components of soil are supplied through the weathering of the bedrock. c. Due to the heat, cold and water of the sun, wind and rain respectively, the bedrock breaks

down into pieces. d. Stones, sand and soil are formed from these pieces. e. Microbes, worms and insects are found among them. Rodents like mice and rats are also

found here. The roots of trees growing on the land also help in weathering of rocks. Thus, the process of soil formation is a slow and continuous process.

Humus

Sub soil

Bedrock

Top soil

Layers of land

9


iv. If a deep pit is dug in the ground, what do you find there? Ans: If a deep pit is dug in the ground, the following layers would be observed: a. While digging, the layer of humus and soil would be observed first. b. Below that, deep layers of the land will be present which consists of immature soil made up

of sand, soil, small rocks, stones, worms and insects. c. Below this, is the layer of huge rocks known as ‘bed rock’. 1. Why is it said that ____? *i. The ozone layer is a protective shell of the earth. Ans: The ozone layer shields the earth’s surface from the harmful ultraviolet rays of the sun. These

ultraviolet rays can lead to cancer and have other long term harmful effects. Thus, ozone is known as a protective shell of the earth.

*ii. Water is life. Ans: Living things cannot sustain on earth without water, as large proportion of blood in animals and

sap of plant is water. Thus, it is said that water is life. *iii. Seawater is useful even though it is not potable. Ans: Sea water is useful even though it is not potable because: a. It forms channel for transportation. b. It provides the habitat for marine ecosystem, thereby maintaining the biodiversity. c. Evaporation of sea water gives us salt. iv. Atmosphere is an important filter. Ans: Atmosphere is an important filter because: a. It allows light and heat to reach the earth’s surface in quantities required for life to sustain

on earth. b. It prevents the earth’s surface from harmful substances such as the ultraviolet radiations. v. Individuals suffering from high blood pressure and asthma are advised not to visit hill

stations. Ans: a. Patients suffering from asthma and high blood pressure require greater amount of oxygen

as compared to normal individuals. b. Hill stations are at a much higher altitude with respect to the sea level. Thus, as we go to a

greater height, the density of the air decreases, i.e. the amount of gases in the air decreases and the air becomes rarer.

c. Thus, air at a higher altitude in hill stations will have less amount of oxygen, which will not fulfill the needs of patients suffering from high blood pressure and asthma, thus in turn causing trouble to them.

Hence, individuals suffering from high blood pressure and asthma are advised not to visit hill stations.

vi. Humus is an important layer. Ans: Humus, is the topmost mature soil layer formed by decomposition of dead plants and animals by

the microbes. The layer of humus functions to: a. provide nutrients to the soil b. aerate the soil c. hold water in the soil 1. What will happen if: *i. Microbes in the soil get destroyed. Ans: Humus, the most fertile layer of the land is formed from decomposition of dead plants and

animals by the microbes. Thus if microbes in the soil get destroyed, the top fertile soil will not be formed making the land unsuitable for growth of plants, trees etc. Wastes will accumulate on land surface releasing bad smell.

Give reasons

Answer the following

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*ii. The number of vehicles and factories in your surroundings increases. Ans: Harmful gases given out through combustion of fuels in vehicles and big industries are the major

causative agents of air pollution. An increase in the number of vehicles and factories will lead to an increase in air pollution. This

will have an adverse effect on the environment and also on the health of the people living in the surrounding areas.

*iii. The total supply of potable water is finished. Ans: Water forms the basis of life on earth, as blood of animals and cell sap of plants is majorly

composed of water. Thus if the total supply of potable water is finished, existence of life would be difficult. Living

organisms cannot survive without drinking water. Also, we would need to find out more ways to convert sea water to potable form.

iv. All the trees on the earth are cut. Ans: Trees contribute to the environment in many ways. a. Roots of the trees hold the soil particles firmly, thereby protecting the top fertile soil from

getting eroded, washed off by wind or by heavy rains. b. Also, roots of trees absorb the ground water, which then evaporates in the form of water

vapour through the openings on leaves of the trees. By this the ground water enters the water cycle.

c. Trees/plants take in carbon dioxide for photosynthesis and give out oxygen as a by-product (essential for animals and humans to respire). Thus, the percentage of carbon dioxide from the air is reduced by the tress, thereby making the air pure (free from pollutants).

Thus if all the trees on earth are cut it will lead to environmental imbalance, soil erosion, imbalance of water cycle and poor air quality.

v. Resources are not used judiciously. Ans: a. Resources if not used judiciously, would make existence of life on earth difficult as the

important resources are formed/recycled by natural processes, which are usually slow. b. For eg: It takes about 1000 years to form a 2.5 cm thick fertile layer of soil. c. Hence if we do not use resources judiciously, resources will get depleted and would take

many years to refill/balance the loss, which would thus degrade quality of life on earth. 1. Observe and Discuss (Textbook page no. 1) Observe the figure 1.1 on page 1 of your textbook and answer the following questions: i. Where do we see the birds? Ans:. Birds are seen in the sky. ii. Where is the cow grazing? Ans: Cow is grazing on the land (grassland). iii. Locate the trees and the road. Ans: In the figure, we can see a red colour car near the hills, the car is running on the road. Trees can

be observed near the cow grazing grass. iv. Where does the river come from? How does it flow? Ans: River flows from the mountains. It flows down the hill and finally merges into the sea. v. Where is the aeroplane? Ans: Aeroplane is flying in the sky. vi. Where are the fish seen? Ans: Fishes are seen in the river water. vii. On what is the sail boat floating? Ans:. The sail boat is floating on water.

Formative Evaluation

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2. Can you recall? (Textbook page no. 2) What are the five layers of the atmosphere? Ans: The five layers of atmosphere are: i. Troposphere ii. Stratosphere iii. Mesosphere iv. Ionosphere v. Exosphere 3. Observe and Discuss (Textbook page no. 3) Observe the figure 1.4 on page 3 of your textbook. What is the similarity in the three pictures? Ans: All the three pictures depict “air pollution”, but from different sources such as industrial emissions,

automobile exhausts and forest fire. 4. Use your brain power! (Textbook page no. 3) What would have happened if there were no air on the earth? Ans: Air on earth forms the atmosphere. Air as a whole is made up of many constituents essential for life on

earth. For example: oxygen, nitrogen, carbon dioxide, inert gases, water vapours etc., The atmosphere shields the earth’s surface from harmful UV rays of sun and other harmful radiations. If there is no air on the earth, following effects will be seen: i. Atmosphere will vanish. Thus, all the harmful ultraviolet rays will reach the earth’s surface,

which will cause adverse effects like cancer, eye disorders etc. ii. The earth’s temperature will increase which will disturb the seasonal cycle. iii. Animals and humans will not be able to respire due to lack of oxygen, thus they won’t survive. iv. Plants will die due to lack of carbon dioxide, as plants need carbon dioxide to produce food, i.e.

photosynthesis. v. As plants are the primary producers of the food chain, if all plants will die then entire food chain

will collapse. Hence, air is the basis of life on earth, without which no living form can exist. 5. Lets try this (Textbook page no. 4) Observe how much water is used and for what purposes in your house for a whole day. Record it

in a chart like the one shown below. Divide the total amount of water used in your house by the number of persons to find out how much water each person needs. Purpose for which water is used Amount of water (approx in litres) Bath Brushing teeth Washing clothes and utensils Mopping the floor Drinking Cooking Total use of water

Ans: Purpose for which water is used Amount of water (approx in litres) Bath 50 Brushing teeth 5 Washing clothes and utensils 20 Mopping the floor 10 Drinking 20 Cooking 15 Total use of water 120

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Our family consists of 4 members.

Thus, the amount of water utilized by each person = Totaluse of waterTotal members in family

= 1204

= 30 Litres 6. Find out In what ways is the water in sea and oceans useful even though it is salty? (Textbook page no. 4) Ans: Even though sea water is unfit for drinking as it is salty, there are many ways by which sea water can be

used: i. The water from sea/oceans evaporate due to sun’s heat (in the form of water vapour) and thereby

enters the water-cycle. Without sea water, water cycle would get disturbed. ii. Tidal energy: The water level in the sea increases and falls due to the pull of the moon. The

difference in the energy of rise and fall (high and low tides respectively) is known as the tidal energy. This energy can be used by building a dam near a narrow opening to the sea.

Here, a turbine (circular structure with blades somewhat fan-like) can be used to convert tidal energy into electricity.

iii. Wave energy: Winds blowing over the sea, form waves. In areas where the waves formed are very high and strong, the energy can be used for rotation of the turbine and by rotating these turbines, energy can be produced.

7. Observe and Discuss (Textbook page no. 5) Observe the figure 1.6 on page 5 of your textbook and answer the following questions. i. For which purposes is water being used? Ans: In the given picture, water is used in various ways: a. Industries are utilising water for their processes. b. Truck drivers are washing their truck. c. Women are washing clothes and utensils. d. Some people are swimming / bathing in the river. e. Water from river is also utilized for farming. In the picture, we can see a pump pulling

water from river and supplying it to a field. f. Apart from all these, a water tank is seen situated near the residential area, which indicates

that the same water, which is polluted with all the effluents and waste from human activities, is used for drinking and other domestic uses.

ii. Do other living things use water like we do? Ans: From the picture, it is clearly evident that only we (humans) extensively use the water resource.

We pollute the water bodies by introducing untreated industrial waste, by washing clothes, utensils and vehicles near it. Unlike humans, other living things like plants and animals, utilize water only according to their needs. They do not pollute the water bodies.

8. Can you tell? (Textbook page no. 5) i. What do you see on land? Ans: We can see many different things on land. a. Natural forms: Living natural forms: Plants, trees, shrubs, animals, insects, worms. Non-living natural forms: Land forms such as valleys, mountains, hills, plateau etc; Water

bodies such as sea, oceans, rivers, lakes, waterfalls; soil, rocks, sand etc. b. Artificial forms: These are made by humans for fulfilling their needs. These include: Houses, buildings, towers, schools, hospitals, industries; besides that

bridges, railways, roads etc. various monuments, places for recreation like gardens, ponds, parks are also seen on the land.

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ii. What has man created on land? Ans: Man-made creations on land are: a. Various architectural forms: Towers, schools, hospitals, industries, houses, dams b. Bridges, roads, tunnels, that make transportation easier. c. Various monuments, ponds, gardens, parks. 9. Use your brain power! (Textbook page no. 7) What are the constituents of soil? Classify them as biotic and abiotic constituents? Ans: Soil is made up of various constituents, which can be classified as follows: i. Living components (Biotic constituents): Plants, worms, insects, rodents (mice and rat). ii. Non-living components (Abiotic constituents): Soil, stones, dry leaves, dead-decomposing

animals and plants, water. 10. Lets try this (Textbook page no. 6) i. Perform the following activity a. Take a transparent plastic bottle, a handful of soil, some stones, sand, some dry leaves and

water. b. Cut off the upper tapering part of the bottle. Put the rest of the materials in the lower part

and add water. c. Stir the mixture thoroughly and put it aside. Observe it the next day and answer the following questions. 1. How does the mixture in the bottle look now? Ans: Unlike the initial day (Day 1), when we had stirred

the mixture, the mixture gets segregated into various layers the next day, depending upon the weight of substances. Lightest substance forms the topmost layer (i.e dry leaves) while the heaviest settle down (i.e. big stones).

2. Do you see layers in it? Ans: Yes, well differentiated layers can be seen. 3. What is seen in the different layers from top to

bottom? Ans: The different layers observed in the bottle are as

follows: i. Dry leaves (lightest of all) ii. Soil iii. Sand

iv. Small stones v. Larger stones (heaviest of all) ii. Obtain specimens of soil from various places in your surroundings such as your own yard, a

garden, hills, river banks, fields and rocky ground. Note the differences in the specimens with respect to colour, feel, texture and the size of the particles. (Textbook page no. 7)

Ans: Type of soil Characteristics

Yard Garden Hills River Bank Fields Rocky

ground

Colour Brown Dark Brown

Light brown

Dark brown

Light brown to Dark brown

Grey

Texture Dry-soft Soft, wet

Dry particulate

Soft, loamy

Dry to soft Hard, Dry

Size of particles Coarse Loamy, clay

Sandy, loamy, small, big stones

Loamy, clay

Coarse Large (small – big stones)

Dry leaves

Soil

Sand

Small stones Big stones

Layers of the mixture in the bottle

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Note: The texture, size and colour of the soil largely depends on the amount of water and amount of

organic matter present in the soil. For example, the garden and the river bank soil is well watered and is rich in organic matter.

Hence, it appears dark in colour. But, the land with rocks has no organic matter and also cannot hold water due to its large pore size. Thus, it appears dry and grey.

11. A little fun! i. Given below is a list of substances, group them as good constituents of air and bad

constituents. Ans:

Good constituents of air Bad constituents of air Nitrogen Carbon monoxide Water vapour Soot Xenon Chlorofluorocarbons Helium Dust particles Argon Nitrogen dioxide Neon Sulphur dioxide Oxygen Carbon-dioxide [beyond 0.03%] Krypton Carbon tetrachloride

Rayon and Nylon are not gases but man- made fibres. Rock and minerals are present in soil and not in air ii. Given below are list of landforms. Arrange them in order of the land best suited for the

growth of plants. For example: The land best suited for growth will come first while the one which is worst

for growth will come at end. Ans: The order of land best suited for growth of plants is as follows: River side Garden

Nitrogen

Humus

Soot

Xenon

Chlorofluorocarbons

Rock Neon

Carbon monoxide

Argon

Nitrogen dioxide

Krypton

Helium

Nylon Rayon

Water vapour

Minerals

Dust particles

Oxygen Sulphur dioxide

Carbon tetrachloride

Carbon dioxide

Seashore Plains

River side

Rocky mountain

Marshy land Garden

Desert

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Plains Marshy land Rocky mountain Seashore Desert The reason for the same is

a. River side soil is rich in organic material and minerals brought down and deposited by the river. Thus, the area is rich in humus which is best for cultivation.

b. Garden and plains are good for cultivation/growth of plants, but they depend on rain as a source of water and also on fertilizers for giving a good yield, unlike the river side which is naturally a fertile land.

c. Marshy land has less percentage of soil and more percentage of water, thus the necessary anchorage provided by the soil for the plants to grow is absent. Thus, only few plants like lotus can survive in such conditions.

d. Rocky mountains are not suited as water cannot seep deep into the rocks. Thus, water flows down the surface. Hence due to lack of water and organic matter, plant growth is not supported in rocky mountains.

e. Seashores, although has plenty of water around, the salty water cannot support growth of plants. Also, the sand lacks capacity to hold water.

f. Desert has sand, lacks water and organic matter as the sand is porous and unable to hold the water. Hence, only few exceptional plants (eg. Cactus) grow in it.

12. Activity (Textbook page no. 8) i. Obtain detailed information about the work of the India Meteorological Department. Ans: Students may attempt this activity on their own. ii. Find a remedy for water scarcity. Ans: Students may attempt this activity on their own. 1. Choose the correct alternative. i. Which of the following constituent of air is not an inert gas? (A) Argon (B) Nitrogen (C) Xenon (D) Neon ii. Which of the following is not a characteristic of water? (A) It is colourless. (B) It is tasteless. (C) It is odourless. (D) Substances cannot dissolve readily in it. iii. Oxygen is important for ______ other than breathing. (A) production of fire extinguisher (B) burning (C) production of ammonia (D) production of proteins iv. Proportion of gases is maximum in ______ layer of atmosphere. (A) mesosphere (B) troposphere (B) stratosphere (D) exosphere v. What is the percentage of oxygen in air? (A) 12% (B) 2.1% (C) 21% (D) 1.2%

Chapter Assessment

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2. Match the words from Group ‘A’ with the related descriptions given in Group ‘B’. Group ‘A’ Group ‘B’

i. Floods a. Soil formation ii. Microbes b. Soil erosion iii. Carbon tetrachloride c. Fossil fuels iv. Crude oil d. Ozone depletion

3. Answer in one word. i. 16th of September is celebrated as which day? ii. Name the two gases that combine to form water. 4. Answer the following in your own words. i. Write two uses of nitrogen. ii. Name some processes that destroy the soil. iii. Give reasons why man is mainly responsible for the serious problem of water scarcity. iv. Explain the components of biosphere. Give their importance in brief for sustainability of life. Answers: 1. i. (B) ii. (D) iii. (B) iv. (B) v. (C) 2. (i − b), (ii − a), (iii − d), (iv − c) 3. i. “Ozone Protection Day” ii. Hydrogen and oxygen. 4. i. Two uses of nitrogen are: a. Building proteins in living things. b. Helps in production of ammonia. c. Helps in airtight packaging of food stuffs. (Students may write any two uses) ii. Processes that destroy the soil are: a. Floods and heavy rains. b. Storms and strong wind. c. Human activities like mining, constructing houses etc. iii. Man uses maximum water as compared to any other living form. Humans pollute the rivers, lakes, ponds by discharging the industrial wastes; household waste,

excreta, washing clothes, vehicles in the water bodies. Humans exploit the ground water to the fullest by digging borewells in the ground. Humans cut trees by which water cycle gets affected. Thus, the increasing population has led to increased uncontrolled use of water, thereby creating

its scarcity. iv. Biosphere is the collective name for atmosphere, lithosphere and hydrosphere and the living

forms occupying it. The components of the biosphere are: Atmosphere (air) envelopes the earth protecting it from harmful elements but allows sunlight and

heat to reach the earth. It contains gases needed for life to sustain, i.e oxygen for animals and humans and carbon dioxide

for plants. The hydrosphere consists of water on the earth’s surface. It is also important for survival on

earth as major proportion of blood of animals and sap of plants is made of water. Thus, water forms the basis of all life processes.

The lithosphere or the land is of importance for existence of life as it fulfills the basic needs of all living forms, i.e food, shelter and clothing. Also, land provides the means for earning a living for man.

Hence air, water and land, the basic components of biosphere are of importance for sustainability of life.

std. 6, general science, maharashtra board€¦ · the biosphere (from greek bios = life, sphaira =...

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