MONTHLY TEST (NOVEMBER) SCIENCE CLASS 7 27.11.20

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CONSERVATION OF PLANTS AND ANIMALS Class 8 Chapter 7

Key Learning Points-Deforestation, Drought, Desertification, Protected areas- Biosphere Reserves, National parks, wildlife centuries, Flora, Fauna, Endemic Species, Red Data Book, Migration, recycling of Paper and afforestation.

Introduction-Different varieties of plant, animals and microorganisms are found on the earth. They are different from each other in many ways. Their geographical distributions as like in tropical, subtropical, temperate and polar region is also different. There are about 1.7 million known species. There are 1.2 million species of animals and 0.5 million species of plants. The different varieties of plants, animals and micro-organisms are together called as ‘biodiversity’. Out of 12 mega-biodiversity regions of the world, India is one among them. Due to climate change, natural and man-made causes the biodiversity is under threat. The sphere of the earth where living organisms are found is called biosphere. 

Deforestation- Forest is a natural resource.  The clearing of forests on large scale and using that cleared land for other purposes is called deforestation.

 Causes for deforestation-

  1. Encroaching forest land for cultivation and other purposes.

  2. Making houses, developing colonies, road, airport and factories.

  3. Using wood as fuel or making furniture.

  4. For mining, ores extraction, petroleum extraction etc.

  5. Some natural causes of deforestation are forest fires and drought.

 Consequences of deforestation-The consequences of deforestation are

   1. Soil erosion and decrease in soil fertility leading to desertification.

   2. Rise in the temperature and pollution level

   3. Increase in the level of carbon dioxide in the atmosphere leading to global warming.

   4. Climate change

   5. Lowering of ground water level.

   6. Disturbs the biodiversity.

   7. Decrease in rainfall and water cycle leading to drought.

   8. Shortage of forest products

   9.  Decrease in the water holding capacity of soil causing floods.

Drought- When number of trees will be less then less carbon dioxide will be used up resulting in its increased amount in the atmosphere. This will lead to global warming because CO₂ traps the heat rays reflected by the earth.  The increase  in  temperature  on  the  earth  disturbs  the water  cycle  and  may  reduce  rainfall.  This may cause droughts.

Desertification-Removal of top layer of soil exposes the hard and rocky lower layers, which have very less humus and air. As they are less fertile, soil becomes like desert. It is termed as desertification.

Forest- A vast area covered with numerous trees and wild animals is called forest. Forests have ecological, economic and aesthetic value. Forest is beneficial for us in many ways as they provide-food, fodder, gum, resin, tannin, rubber, latex, animal products like horn, fur, skin, drugs, medicines, habitat for wild animals including birds, habitat of different varieties of plants, paramount role in climate control, water cycle, controlling flood, oxygen-carbon id-oxide cycle, nutrients recycling etc. But, due to climate change, natural and man-made causes the forests are under threat. So, their conservation is essential to conserve wildlife. As per norms forest should be more than 33% of total area but it’s about 22 % only.

 Conservation of forest and wildlife- Forest and wildlife can be conserved by setting up areas like

  Biosphere reserves, Wildlife sanctuaries, National parks, etc.

  i) Biosphere reserves- They are large areas of protected land for conservation of biodiversity and the traditional life of the tribals living there. There are 18 biosphere reserves in India. e. g- Panchmarhi The Panchmarhi Biosphere Reserve consists of a National Park called Satpura National Park and two wildlife sanctuaries called Bori and Pachmarhi.

 

 

ii) National parks are areas reserved for wildlife where they can freely use the habitats and natural resources. There are 101 National parks in India. They cover more than 40 thousand square kilometre of area. It is 1.23 % of total area of India. Satpura National Park is the First Reserve Forest in India. e.g.- Jim Corbett National park, Uttarakhand, Kanha National Park, Keoladev national park, Bhartpur etc 

 

For further reference visit on www.examstocks.com

iii) Wildlife sanctuaries-They are areas where animals are protected from any disturbance to them or their habitat. There are 553 wildlife sanctuaries in till date. They are about 3.64 % of total area and cover about one lakh twenty thousand square kilometres. e.g.- Black buck sanctuary , Buxar, Bihar

Flora and fauna

Flora and fauna are natural resources. They are members of different species. They are found in different regions of the biosphere. Some are exclusively located to a particular area. Others are wide spreaded globally. Biodiversity is the variety of plants, animals and microorganisms found in the area. The biodiversity consist of different verities of plants and animals. All the different varieties of plants are called as flora and all the different verities of animals are called as fauna.

The flora of Panchmarhi consists of sal, teak, wild mango, jamun, silver ferns etc.

 The fauna of Panchmarhi consists of wild dog, cheetal, wolf, leopard, blue bull, barking deer etc.

SPECIES-

A group of population capable of interbreeding is called a species.

 e. g. - Cats, Tigers, Deer, Tomato, Mango etc.

The animal species reproduce to form young ones of their own kind only.

But, when breeding occurs in between members of different species, any different kind of individual is formed.

e. g.- Hinny, is the infertile hybrid organism of reproduction between male horse (Stud/Stallion) and female donkey.

e. g.- Mule, is the infertile hybrid offspring of am male donkey and female horse (mare).

Endemic Species -Endemic species are those species of plants and animals found only in a particular area and not found anywhere else. Those species of organisms which are exclusively found in any particular area are called endemic species.

e. g.- Sal Trees and Wild Mango are two endemic flora species of the Panchmarhi Biosphere reserve.

e. g.- Bison, Indian Giant Squirrel and Flying Squirrel are the endemic fauna species of Panchmarhi Biosphere reserve.

 

                                    

A particular type of species is endemic to a zone, state or a country. Destruction of their habits, introduction of new species, introduction of new species and diseases are some reasons why endemic species are in greater danger of becoming extinct.

 

 

Project Tiger

Project Tiger was launched on 1st April 1973 by the government of India. The project aimed at ensuring a viable population of tiger in their natural habitats and also to protect them from extinction and preserving areas of biological importance as a natural heritage. The project's  task  force  visualized  these tiger reserves as  breeding  nuclei,  from  which  surplus  animals would migrate to adjacent forests.

Red Data Book- The book provides a central information source in organizing studies and monitoring programs on rare and endangered species and their habitats. It is regularly consulted when developing and implementing special measures for the protection and rehabilitation of such species. Red Data Books are books which keeps a record of all endangered plants and animals. These volumes of red data book are maintained by World Conservation Union (W.C.U.). It was earlier called as International Union of Conservation of Nature and Natural resources (I.U.C.N.).The indiscriminate hunting, killing and destroying of forest are main causes for loss of animals.  There are three main categories of animals- vulnerable, endangered and extinct.   

 

Vulnerable Animals- Those animals which are low in number and may become endangered if exploitation and deforestation continues are called vulnerable animals. e.g.- Red panda, One- horned Rhino, Olive Ridley Turtle etc.

Endangered Animals –Those animals which are extremely low in number and not protected will become extinct. e.g.– Tiger, Musk deer, Indian bustard etc. It is a record of endangered species of plants and animals.

Extinct Animals- Those animals which were once alive but now not found on the earth are called extinct. e.g.- Dodo, Dinosaur, Cheetah,  Pink headed duck, mountain quail etc.

Ecosystem -An ecosystem consists of all the plants, animals and microorganisms living in an area along with the non living components like climate, water, soil, river deltas etc. An ecosystem consists of biotic and abiotic factors.

   

Biotic/ Living factors like plants, animals and micro-organisms

Abiotic/ Non-living/ Physical factors like water, sunlight, temperature, soil, air, humidity, rainfall and heat.

 

Migration -Migration  is  the  movement  of  animals  from  its  own habitat  to  some  other  habitat  for  a  particular  time period  due  to  climatic  changes, in search of food or  for breeding. Those birds which fly very long distances to reach another land are called migratory birds.

e.g- Arctic tern, Siberian Crane etc

Recycling of Paper -About  seventeen  full  grown  trees  are  required  to produce  one  tonne  of  paper.  Paper can be recycled about five to seven times for next use.  We  should  save, reuse  and  recycle  paper  to  save  not  only  trees  but also to save the energy, water and chemicals used to make paper.

3R- Reduce, Reuse and Recycle

Reforestation - Reforestation is the restoring of destroyed forests by planting new trees. We should plant at least as many trees as we cut. We have already caused a lot of damage to our forests.  If we have to regain our green wealth, reforestation is the only option.

 

SOIL Class 7 Chapter 9

 

                                                        SOIL Class 7 Chapter 9

LEARNING OBJECTIVES-

-Knowledge about soil and soil formation

- Soil Profile

-Types of soil

-Properties of soil

-Moisture content in the soil

-Absorption of water by soil

-Soil and Crops

Soil erosion and soil conservation-

SOIL-

The natural covering of broken rock particles and humus of the surface of the earth that supports life is called soil. Soil is the outer layer of the earth crust.

Soil supports plants and animals. The sources of food are grown in soil. Fuels, fodder, medicines and fibres are grown in soil. Water for drinking is mainly obtained as underground water. Soil is a habitat for many living organisms like, earthworm, ants, bacteria, fungi, wound worms etc. various kinds of minerals are obtained from the soil like gold, copper, manganese etc.

FORMATION OF SOIL-Soil is a mixture of sand, small rock particles and humus. The sand and small rock particles are formed by physical, chemical and biological weathering of rocks. The humus is formed by humification of dead organic matters. The process of soil formation is called pedogenesis. The study of soil and its properties is called pedology.

Pedogenesis = Weathering of Rocks + Humification

The wind, water, ice, temperature etc help in breaking of rocks. It is physical weathering of rocks. The water, organic acid like carbonic acid formed by decomposition of organic matter, chemical reactions in rocks and acid rain causes the weathering of rock by chemical methods. The animals and roots of plants are the biological agents for causing weathering of rocks.

SOIL PROFILE-

The vertical section of soil which shows differently coloured and textured layers is called soil profile. The chemical composition and depth of different layers of a soil profile also differ from each other. The layers of soil profile are as following-

1. A-Horizon or top soil layer - It is the upper most layer of the soil. It is dark in colour than other layers due to presence of humus (decomposed organic matter). It is soft and porous. It allows water to move inside the soil (water percolation) easily. It is rich in minerals, so plants grow easily. The water holding capacity of this layer is also more due to presence of humus. In this layer various kinds of insects, worms and roots of plants are found in this layer. 

2. B-Horizon or Subsoil layer – It is just below the A-horizon. It has very less amount of humus. It is less fertile than A-horizon. It has very less population of microorganisms. It is rich in minerals, harder and compact than top layer. It is slightly light in colour because of more minerals and less humus.

3. C- Horizon – It is just below the B-horizon. It has small rocks formed due to weathering of bedrocks. The roots of trees do not rich to this layer. Very little humus may be found somewhere in it.

4. R-Horizon or Bedrock or Parent rock- The bedrock undergoes weathering to add rocks, sand and minerals to the soil layers. It is very hard and does not allow the water to move down it.     

              

           

                               Fig: Soil Profile

TYPES OF SOIL-The size of rock particles are different in different soils. The colour of soil varies according to the presence of minerals and their characteristics. The chemical nature of soil classifies the soil also.

A. SOIL TYPES ON THE BASIS OF PARTICLE SIZE-

Following types of particles are found in the soil.

S.N.	Soil Particle	Particle size
1	Clay	Less than 0.2 mm
2	Silt	More than 0.2 mm
3	Sand	0.2 – 2.0 mm
4	Gravel	2.0 – 50 mm

So, soil types are-

1. Sandy soil- The soil which is mainly made up of large sand particles is called sandy soil. Clay and silt may be found very less in such a soil. It is mainly the desert area soil like Thar desert, Rajsthan, Haryana, Gujrat and Punjab. The soil is well aerated due to presence of quite large air-spaces in between soil particles. It has fewer nutrients. Its water holding capacity is less. It can be ploughed easily. It dries easily.

 

2. Clayey Soil- This soil has very small size clay particles. It smooth and its water holding capacity is very good. The aeration of this soil is not so good. The mineral nutrients are good in this soil. The ploughing of clayey soil is difficult. Sometimes water logging is seen in this soil.

3. Loamy soil- It is one of the best quality of soil for agriculture. It is made up of sand(40%), silt (40%) and Clay (20%). Its water holding capacity is good. It' minerals content is also optimum. It is suitable for all types of crops but wheat, pulses are mainly grown in this soil. 

B. SOIL TYPES ON THE BASIS OF PLACE OF FORMATION

1. Red soil

2. Black Soil

3. Alluvial Soil

4. Laterite soil

5. Mountain Soil

6. Desert Soil

C.SOIL TYPES ON THE BASIS OF CHEMICAL NATURE

1. Acidic soil- pH= 0-7

2. Basic (Alkaline Soil) - pH= 7-14

3. Neutral Soil – pH=0

Properties of Soil-

1. Colour of Soil- The colour of soil is due to mineral contents and organic matters present in it. Red, brown and yellow colours are due to different types of iron oxides in the soil. The black soil is due to certain other minerals, mountain lava and humus present in it.

2. Soil Structure- The soil texture/ structure is different for different kind of soil. Many soils are sticky while others do not stick with each other.

3. Percolation rate- The movement of water down the soil layers is called as percolation or seepage. It helps in recharging the underground water. Sandy soil has more water percolation rate while clayey soil has least water percolation rate.

     Percolation rate =Volume of water (in ml.)/Percolation time (in minute)

4. Absorption of water by soil- The water holding / absorption capacity of the soil is different for different soil. It is estimated by the formula as-

     Percentage Absorption of water by soil = Volume of water absorbed by the soil/    X 100

                                                                                                                                 Weight of soil

5. Moisture content in the soil- The little amount of water adhered to the soil particles is called soil moisture. In summer season, the dry soil has negligible moisture. In rainy season, the soil moisture will be high. When a little amount of soil is warmed in a test-tube, little water vapour can be seen on inner wall of beaker.

Activity 1- To find out the Percolation Rate of soil

Requirements- Clan ground of soil, hollow glass pipe, measuring cylinder, 250 ml water and a Stopwatch.

Procedure-Clean the ground and dig a small hole. Place a glass pipe in that hole and fill it up with soil. Now pour 250 ml of water and start noting down the time take in percolation of water with the help of a stop watch.

Observation- Approximately in 25 minutes 250 ml of water percolated through the soil.

So, we can calculate the percolation rate by the following formula-

Percolation rate =Volume of water (in ml.)/Percolation time (in minute)

                             = 250 ml/25 minutes

                             =10 ml/min.

Repeat this activity with sandy and clayey soil also. The sandy soil will have more percolation rate and clayey soil will show comparatively less percolation rate.

Activity 2- To calculate water absorption/water holding capacity of the soil-

Requirements- 100 gm dry powered Soil, a funnel, measuring cylinder, dropper, filter paper, 100 ml water and calibrated conical flask.

Procedure- The filter paper was folded as like a cup and place in the funnel. This was then placed in the mouth of conical flask. The 100 ml water was very slowly poured with the help of dropper.

Observation- The water that came down in the conical flask was 45 ml. It means 55 ml water was absorbed by the dry soil. So, the water absorption capacity of soil was calculated by the formula-

Percentage Absorption of water by soil = Volume of water absorbed by the soil/Weight of soil X 100

                                                                    =55 ml/100 gm X 100

                                                                     =55 %

Repeat this activity with sandy and clayey soil also. The sandy soil will have less water holding capacity and clayey soil will show comparatively more water absorption capacity.

 Soil and Crops- The crop to be grown in a particular soil depends on the following factors-

a. The type of soil.  

b. The climate of that region.

c. The mineral and humus contents of the soil.

1. Sandy Soil- It has low water holding capacity. The humus content is also low. The crops that grow well are wheat and legumes like gram, pea, vegetables, chili etc. Coconut grows in sandy soil of coastal areas.

2. Clayey Soil- Its water holding capacity is maximum. It is well for growing paddy, sugarcane, jute etc.

3. Loamy Soil- Its moderate water holding capacity, optimum humus and minerals content make loamy soil good for almost all type of crops. Paddy, Wheat, Legumes, Vegetables, Cotton, etc. grow well in loamy soil.

Soil Erosion- The top soil is very fertile. The carrying away of fertile topsoil by river water, heavy rain, strong wind, animals etc. from one place to another is called soil erosion. The grasses and roots of trees bind the soil and prevent soil erosion. 

Impacts of Soil erosion-

A. Soil erosion causes flood.

B. Soil erosion results into famine.

C. Soil erosion causes landslide in hilly areas.

Causes of soil erosion-

1. Overgrazing

2. Deforestation

3. Excess ploughing of cop fields

Soil Conservation- The judicious and economic use of soil is called soil conservation. Soil conservation is done to make soil usable for coming generations. Following are the common methods of soil conservation-

1. Afforestation-Plantation of trees on large scale.

2. Contour/step farming in hilly areas.

3. Avoiding overgrazing and excess ploughing of fields.

4. Construction of dams and river embankments.

Soil Pollution- The adding of harmful toxic substances which make the soil unfit for use is called soil pollution. Chemicals like paints, chemical fertilizers, polythene, plastic, salts, radioactive wastes, oil, grease, dye, acids, industrial wastes etc are some harmful substances which harm the soil.

The soil quality, percolation rate, fertility and water holding capacity are affected due to it.

 EXERCISE QUESTIONS-

Q.1

FRICTION Class VIII Chapter 12

                                                  FRICTION      Class VIII     Chapter 12

INTRODUCTION -

When we go somewhere by a bicycle we often apply brakes to slow or stop the bicycle. When we are running or walking and unknowingly under our feet some banana peel comes, we often fall and get injured. 

Look at the tyres of bicycle, bus; truck etc. like vehicles there is special design to help in its stopping on applying brakes. The rough surfaces help in stopping of vehicle unlike the smooth slippery surfaces. It is due to presence of friction in between the road or surface and the tyres of the vehicle the helps in stopping the vehicle on applying the brakes.

The force that comes in between two surfaces in contact due to their relative motion is called friction or frictional force.

SALIENT FEATURES OF FRICTION-

Following are the salient features of frictional force-

1. The force of friction opposes the applied force. e.g.- If you push a wooden box on a surface, the frictional force will come into action. It opposes the push force and reduces the net force.

2. The force of friction results in between two surfaces in contact. The nature of surfaces (rough or smooth) or irregularities, inter-molecular force of attraction (Adhesion or Cohesion) and deformation of surface due to weight are factors which come in action during friction.

3. Friction can be reduced by using lubricants, polishing, using ball bearings and making the streamlined body.

4. Friction can be increased by making the surfaces in contact rough and increasing the weight of moving object.

5. Friction is necessary evil. It has many advantages as well as many disadvantages. It plays crucial role in our day to day life.

FACTORS AFFECTING FRICTION- The force of friction results in between two surfaces in contact. The nature of surfaces (rough or smooth), inter-molecular force of attraction (Adhesion or Cohesion) and deformation of surface due to weight are factors which come in action during friction.

The nature of surfaces in contact determines the amount of friction. Smooth surfaces cause less friction while rough surfaces cause comparatively more friction. Plane Glass will produce very less friction while plane cemented rough floor will produce more friction. It is due to irregularities in between two surfaces in contact.

e.g.- Drop of rainwater in glass of window remain hang on.

Fig. Water droplets adhered on Glass

There comes an inter-molecular force of attraction between two surfaces in contact. The inter-molecular force between similar molecules of same material is called cohesion. The inter-molecular force between dissimilar molecules of different materials is called adhesion.

The deformation of surface due to weight is also a factor. When weight of moving object is increased and surface on which it is moving becomes changed, the frictional force increases.

e.g.- It is difficult to walk on sand than on plane surface.

 

FRICTION AS A NECESSARY EVIL- There are certain advantages and disadvantages of friction. So, it is called as a necessary evil.

Advantages-

1. Friction develops between our feet or shoes and the ground. So, it helps in walking and running.

2. Friction helps in writing with pen, pencil on paper and on blackboard with chalk.

3. Friction helps to light the matchstick when rubbed on the side of the matchbox.

4. Friction that develops between tyres and the road helps the vehicles to run on the road.

5. Friction between breaks and tyres help to stop the vehicle on applying the force.

Disadvantages-

1. Friction slows down or stops the motion of the objects.

2. Friction generates heat. So, the running vehicles and machines become hot. It is wastage of energy.

3. Friction causes wear and tear of the soles of shoes and slippers.

INCREASING OF FRICTION- Friction can be increased by –

1. Making the surface more rough-

e. g.- The new tyres with more roughness give better grip than the old weared out tyres.

e. g.- The carpets help in comfortable walking on granite floor.

e. g.- ‘Kabaddi’ players rub their hands with soil for better grip of their opponents.

e. g. –Pens are provided with rubber grip for better holding and comfortable writing.

e. g. – Weight lifters and Gymnasts apply powder on their hand for better grip.

2. Increasing the weight of moving object-

e. g.- The pulling of a mat is comparatively easy than the pulling of mat with more load kept on that.

REDUCING OF FRICTION-

1. By Polishing- due to polishing the roughness of the surface get reduced. So, the irregularities due to contact of two surfaces become less and friction reduces.

2. By using lubricants – A lubricant is a substance which reduces friction. e. g.- Oil, Grease, Talcum powder and Graphite. Lubricant is applied in machines to reduce the friction.

e.g.- The movement of doors and windows become smooth when oil is applied on the hinges.

e.g.- The moving parts of a machine or vehicle are made smooth by using grease.

e.g.-The coins of carom-board move faster easily on striking due to spreading of talcum powder.   

3. By using ball-bearings – The ball bearing change the sliding friction into rolling friction. Rolling friction is less than sliding friction so it is easy to move the vehicles, fans etc where it is found.

4. By making streamlined body design- The streamlined bodies are narrow from front and back. It reduces the friction on moving body in air and water.

 

TYPES OF FRICTION-

 A. STATIC FRICTION- The friction which develops and balances a force applied on an object and do not allow its motion upto a threshold level is called static friction.

The static friction is exactly equal to the applied maximum force until the object does not start moving.

B. SLIDING FRICTION- The friction that develops when an object slides over other is called as sliding friction.

C. ROLLING FRICTION- The friction that develops when an object rolls over the other object is called rolling friction.

D. FLUID FRICTION (DRAG)- (Daniel Bernoulli) The liquids and gases are commonly called as fluids. The resistance or friction that develops when a solid object travelling in liquid or gaseous medium is called fluid friction. It is also called as drag.

Fig. Four types of forces on flying Aeroplane

Four types of forces on a flying aeroplane are-

1.Fluid friction /Drag 

2. Thrust  

3. Weight due to gravity 

4. Lift or Upthrust 

The viscosity (thickness) of fluid, surface texture i.e. roughness or smoothness and shape of moving object are factors that affect the fluid friction.

 

EXERCISE QUESTIONS-