CBSE Class 10 Science Our Environment Notes

Chapter 15: Our environment

Chapter Notes

Key learning:

1) Our environment is composed of various biotic and abiotic factors which interact with each other.

2) Human activities have a great impact on the functioning of the environment.

3) The wastes generated by the various human activities may be biodegradable or non- biodegradable.

4) The enzymes present in the body of decomposers are capable of breaking down the biodegradable substances, but not the non- biodegradable materials.

5) The non-biodegradable materials like plastic and synthetic pesticides persist in the environment for a long duration and may harm its biotic factors.

6) In an ecosystem, the abiotic and biotic factors interact to form a stable unit.

7) The size of an ecosystem ranges in size from as small as a pond or a backyard garden to as large as an entire rain forest.

8) An ecosystem may be natural (like lakes and forests) or artificial (like crop- fields and aquarium).

9) The biotic factors may be classified as producers, consumers and decomposers depending on their mode of nutrition.

10) The food manufactured by the producers from simple inorganic substances is utilized directly or indirectly by the consumers.

11) Herbivores, carnivores, omnivores and parasites are the various types of consumers.

12) The decomposers break down the dead bodies and wastes of organisms and help in nutrient recycling. 

13) Food chains are present in every ecosystem. Each food chain is composed of three to five trophic levels. Trophic level Organisms comprising the trophic level

First Autotrophs / Producers

Second Herbivores / Primary consumers

Third Small carnivores / Secondary consumers 

Fourth Large carnivores / Tertiary consumers

14) There is flow of energy between the various trophic levels.

15) Producers convert solar energy into chemical energy, which is then utilized by the consumers and decomposers.

16) About 1% of solar energy falling on leaves is utilized by plants in photosynthesis to produce food.

17) A large amount of energy loss occurs when the organisms of the higher trophic level feeds on the lower trophic level organisms.

18) There is only 10% flow of energy from one trophic level to the next higher level. Due to this energy loss, only 4

19) The number of individuals in a trophic level decreases as we go up the food chain.

20) Food webs, consisting of several interconnected food chains, are more common in mature.

21) Flow of energy is unidirectional and cannot be utilized by the previous trophic levels.

22) The non-biodegradable chemicals like pesticides and insecticides enter the food chains in land and aquatic ecosystems and then accumulate progressively at each trophic level. This is known as biological magnification.

23) Human activities can cause several environmental problems like ozone layer depletion and waste disposal.

24) Ozone, composed of three oxygen atoms, is a toxic chemical. It is formed by the combination of free oxygen atom with molecular oxygen.

25) The atmospheric ozone layer prevents the entry of solar ultraviolet rays and thus protects all organisms on Earth.

26) Use of chemicals like chlorofluorocarbons has greatly depleted the atmospheric ozone layer, which could endanger the environment.

27) The disposal of large amounts of garbage produced in any human settlement, especially in cities and towns is causing major environmental problems.

28) Changes in our lifestyle and attitude have created many disposable items, many of which are non-biodegradable.

29) Effective methods of waste disposal should be found in order to reduce the harmful effects on our environment.

Top definitions

1) Biodegradable substances – Substances that are broken down by biological processes.

2) Non- biodegradable substances – Substances that are not broken down by biological processes.

3) Ecosystem – A unit formed by all the interacting organisms in an area together with their physical environment.

4) Biotic factors – The living components of the environment such as plants, animals, which interact with each other as well as with the abiotic factors of the ecosystem.

5) Abiotic factors - The nonliving components of the environment such as water, temperature, soil and light that influence the composition and growth of an ecosystem.

6) Producers- Organisms like plants and blue green algae that produce complex organic compounds from simple inorganic molecules using energy from sunlight in presence of chlorophyll. 7) Consumers - Organisms that feed directly or indirectly on producers and cannot synthesize their own food from inorganic sources.

8) Decomposers – Organisms that feed on the dead remains and waste products of organisms and carry out nutrient cycling by breaking down the complex organic materials into simple inorganic ones.

9) Herbivore - An animal that feeds chiefly on plants.

10) Carnivores – Organisms that mainly feed on the flesh or meat of animals.

11) Omnivore - An animal that feeds on both animal and vegetable substances.

12) Parasite - An organism that lives off or in another organism, obtaining nourishment and protection while offering no benefit in return

13) Food chain - A succession of organisms in an ecological community that constitutes a continuation of food energy from one organism to another as each consumes a lower member and in turn is preyed upon by a higher member

14) Trophic level – Each step or level of the food chain.

15) Food web - Complex network of many interconnected food chains and feeding relationships.

16) Biological magnification – A cumulative increase in the concentrations of a persistent substance in successively higher levels of the food chain.

OUR ENVIRONMENT

15.1 ECOSYSTEM :

1. The term Ecosystem was coined by Tansley. According to him Ecosystem is a symbol of structure and function of nature.
2. The term Ecology was coined by Reiter.
3. The term Ecology was first of all described y  E.Haeckel.
4. Father of India Ecology - Prof. Ramdas Mishra.
5. The boundaries of ecosystem are indistinct and have an overlapping character with each other.
6. “The total group of living things and environment of factors present in a particular place is called as ecosystem/”
7. It means any structural and functional unit of the environment that can be identified and studied is called as ecosystem.
8. Ecosystem may be natural or artificial, permanent or temporary. Large ecosystem is called as biome such as desert, forest etc.
9. Homeostasis : Self maintainable characteristic is found in ecosystem. It means an ecosystem maintains the balance between the different trophic levels. Each trophic level controls the other trophic level in an ecosystem.
10. Cybernetics : A science of self control [homeostasis] in an ecosystem is called as “cybernetics” 

15.1 (a) Types of Ecosystem :

Natural (e.g. lake, forest, grassland etc.) or man made (e.g. an aquarium crop field etc.)

(i)  Temporary     :    e.g. rain-fed pond etc.

(ii) Permanent     :    e.g. lake, forest etc.

An ecosystem may be as small as a drop of pond water. Such small ecosystem is called as micro ecosystem. Human activities may modify or convert natural ecosystem into man made ecosystem. Cutting tree or forests and the conversion of land for tree plantation or agriculture etc. are some of the examples of conversion of natural ecosystem to man made ecosystem. 

15.1 (b) Components of Ecosystem :

Ecosystem consists of two components :

(i) Biotic component   ii)  Abiotic component (environment, soil etc.

(i) Biotic components : Different biotic components are connected, through food chain or other relations. That is why it is said that all the living organisms comes under biotic components. Food available for biotic components can be synthesized, from inorganic raw material by the autrophs only.

Biotic components are of thee types which are essential for ecosystem.

(A) Producers : All the autotrophs of ecosystem are called as producers. The green plants are the main producers. Green plants absorb solar energy and convert it into chemical energy. It means energy enters into the ecosystem through the produces. The solar energy is the only ultimate source of energy in ecosystem. This energy is available to the remaining living organisms through the medium of food.

(B)  Consumers: All the heterotrophy of the ecosystem are known as consumers. Animals are the main consumers. They directly (herbivorous) or indirectly (carnivorous) depend upon the producers. There are various types of consumer which are as follows :

1. Primary consumers : They are also known as secondary producers because they synthesize complex materials in the cells by the digestion of food which they obtain from the plants. Such living organisms which obtain food form the producers are known as primary consumers. Such as all the herbivores of ecosystem.
2. Secondary consumers : Animals which feed upon primary consumers and obtain their food. It means those carnivorous which kill and eat the herbivorous. So that they are called as predators e.g. Dog, Cat, Snake etc. In aquatic system whale fish is a secondary consumer.
3. Top consumers : Those animals which kill other animals and earth them by they are not eaten by other animals in the nature .e.g Lion, Vulture, Peacock and Man (human) in our ecosystem. Man and peacock may be omnivorous.

(C) Decomposers or Microconsumer : Those living organisms which decompose the dead bodies of producers and consumers and release mineral substances again into the soil which are present in the dead bodies. So that decomposers help in mineral into the soil which are present in the dead bodies. So that decomposers help in mineral cycle. Only because of this land is the main source of minerals. The main decomposers in ecosystem are - bacteria and fungi which decompose continuously dead animals and dead plants.

(D) Scavengers : Vulture never kills any animal so that vulture is a scavenger, not a decomposer. The process of decomposition takes place outside the body of bacteria. The break down of the food materials takes place in the body of vulture and minerals are released into the soil in the form faecal material. They are also called as reducers because they decomposes and remove the dead bodies of the organism. 

15.1 (c) Structure of an Ecosystem :

The structure of an ecosystem is characterized by the physical organization of biotic & abiotic components. The major structural features of an ecosystem are species composition, stratification, trophic organization and nutrients.

(i) Species composition : Each ecosystem has its own type of species composition. Different ecosystems have different species composition. A great variety of species is found in forest ecosystem, whereas a few species occur in a desert ecosystem.

(ii) Stratification : The organisms in each ecosystem from one or more layers or strata, each comprising the population of particular kind of a species.

(iii)  Trophic organization : Food relationship of producers and consumers is another way to predict ecosystem structure. In an ecosystem there an be only 4 - 5 successive trophic levels because

(A) All the food available in one tropic level is not being eaten by another animal in the next trophic level.

(B) All the food eaten by an animal is not useful, thus a part of energy containing food is passed out as waste products.

(C) A large amount of energy is lost in respiration to drive organisms metabolism and thus, there is not much energy left to support higher trophic levels.

The amount of nutrients such as nitrogen, phosphorus and calcium present in the oil at any given time is termed as standing state.

15.1 (d) Functions of an Ecosystem :

(i) Productivity : Ecosystem helps of maintain the productivity, of the system. The rate of organic matter or biomass production is called as productivity. The study of biomass production in the ecosystem is called as production ecology.

(ii) Energy flow : Energy flow in an ecosystem is a key function of an ecosystem. It determines the following two laws of Thermodynamics :

(A) First law : It states, that energy can neither be created nor destroyed, but can be transferred from one from to other.

(B) Second law : It states, that every energy change involves the degradation or dissipation of energy,

from concentrated to the dispersed form due to metabolic functions, so that only a small part of energy is stored in the biomass.

(iii)  Nutrient cycles : All living organisms get matter from the biosphere component i.e. lithosphere, hydrosphere and atmosphere. Essential elements or inorganic substances are provided by earth and are required by organisms for their body building and metabolism, they are known as biogeochemical  or biogenetic nutrients.

(iv)  Development and stabilization : This function is necessary for the development and giving stability to various life form’s by undergoing certain modifications.

15.2 FOOD CHAIN :

1. The chain of organisms which involves transfer of energy from one trophic level to next trophic level is called as food chain.
2. The flow of food or energy is an ecosystem  is called Food chain. Those organisms which join with the food chain are termed as Trophic levels.
3. Usually, there are four trophic levels present in the ecosystem because level of energy decreases during the flow of energy from one trophic level to the another trophic level.

First trophic level [T1]                            :               Producers

Second trophic level [T2]                      :               Primary consumers

Third trophic level [T3]                         :               Secondary consumers

Fourth trophic level [T4]                        :               Top consumers

The flow of energy occurs in an ecosystem from the first trophic level to the fourth trophic level in the food chain. These are five trophic levels also found in a highly complex ecosystem in which tertiary consumers are present in between the secondary consumer and top consumers, then fifth trophic level (T5) formed by the top consumers.

15.2  (a) Types of food Chain :

 There are three types of food chains which are found in nature.

(i) Predator food chain (ii) Parasitic food chain   (iii) Saprophytic food chain

Predator food chain extends from producers through herbivores to carnivores, parasitic food chain stat from producers but ends with parasites and saprophytic food chain starts with decomposers. Producers are autotrophic organisms which synthesize organic food from simple inorganic raw material through photosynthesis by utilizing solar energy. A part of food synthesized by the producers is used in their body building, while the rest is utilized in providing energy for various life activities.

Some common predator food chains are given below :

1. Vegetation → Grasshopper → Shrew → Hawk
2. Vegetation → Rabbit → Wolf →Tiger    
3. Vegetation →Frog→  Snake → Peacock
4. Plant→  Rat→  Snake→  Hawk.

Aquatic food chains :

1. Phytoplanktons→  Zooplanktons → Small crustacians →Predator insect  →Small fish→  Large fish→  Crocodile
2. Phytoplanktons→  Zooplanktons → Small fish  →Large fish Shark
3. Phytoplanktons→  Zooplanktons → Fish → Crane → Hawk. 

15.3 FOOD WEB :

In nature, the food chins are not isolated sequences but are rather interconnected with one another. “A network of food chains which are interconnected at various trophic levels, so as to form a number o feeding connection amongst different organisms of a biotic community is called as food web. The food web opens several alternate pathways fro the flow of energy. Generally, food web operates according to test and food performances of the organisms at each trophic level, yet availability of food source and other compulsions are equally important. The concept of food web appears to be more real than that of simple food chain. The food web increases the stability of an ecosystem by providing alternate source of the food and allowing endangered population to grow in size. Many food chains are interlinked together to form  food web in a big ecosystem in which flow of food takes place through many directions such as forest. A food web which is present in forest ecosystem is a highly complex and permanent (stable) type of food web.

As much as food web complexes are there as much ecosystem is permanent or stable, such type of ecosystem does not degenerate naturally and continues for longer time period.

The ecosystems which have simple food webs are not more stable. It means that this type of food web can be finished at nay time. Any attack or cutting of plants can causes the destruction of while ecosystem e.g. Gondwana forest is converted into the desert by the activity of men. this is the example of desertification by men.

15.4 ECOLOGICAL PYRAMIDS :

An ecological pyramid is a graphical representation of an ecological parameter like number of individuals or amount of biomass or amount of energy present in various trophic levels of a food chain with producers forming the base and top carnivores from the tip. Ecological pyramids could be upright, inverted or spindle shaped. There are three important parameters of each trophic level in a food chain i.e. number of individual, amount of biomass and amount of energy. 

15.4 (a) Pyramid of Number :

In this type of pyramid the number of individual organisms in various trophic levels is shown. These pyramids may be upright or inverted. The number of organisms of any trophic level depends upon the availability of organisms which are used as food on lower level so that availability of food is the main factor. These producers are of two types :

(i) Phytoplanktons : They are the inactive floating plant, because hey do not have locomotors organs e.g. Diatoms.

(ii) Phytonektons : These plants swim actively in water, because in them locomotary organs are present. Usually flagella are preset in these plants. e.g. Chamydomonas and dinoflagellates. The number of phytoplanktons and phytonketons are higher per unit area of water because they are unicellular.

In a tree ecosystem the pyramid of number is inverted. This is called as parasitic ecosystem because bird depend upon tree and parasites depend upon birds. Therefore with the increase in the number of trophic levels, the number of the organisms increases sequentially.

1. Pyramid of number shows biotic potential of an ecosystem.
2. The number of members of any particular species in a favorable condition is called as their biotic  potential.
3. When the number of the members of any species increases then it is called as population explosion. 

15.4 (d) Pyramid of Biomass :

The biomass of each trophic level is shown by this pyramid. Mostly these pyramids are also upright (erect). e.g. Tree ecosystem.

1. Pyramid of biomass in aquatic ecosystem is inverted, because in this producers are micro organisms and their biomass is lesser than other trophic levels.
2. Pyramids of biomass show the standing crop of ecosystem. It means total amount of living matter at a particular time in an ecosystem is called as standing crop.
3. Total amount of nonliving matter in an ecosystem is called as standing state. 

15.4 (c) Pyramid of Energy :

It always remains erect, because flow of energy is not cyclic. i.e. during the flow of energy at each trophic level goes on decreasing.

1. According to the 10% law of Linderman the 90% part of obtained energy of each organism is utilized in their various metabolic activities and only 10% energy  transferred to the next trophic level. So that 90% energy is lost at each trophic level therefore, top consumers like lion etc., are weakest ecologically.
2. Pyramids of energy show the productivity of any ecosystem.
3. Plant community : All types of plants present at a particular place to form a community, is called as plant community. The distribution of any species at a place depends upon social nature of the species which indicates cooperation between them.
4. Synecology : The ecological study of any plant community is called as “gynecology”.
5. Phytosociology : The study of structure of plant community is known as “phytosociology”
6. Phytogeography : The study of distribution of the plants on the earth is called as “phytogeography”. Some characteristics of plant community are as follows :

(i) Species diversity : There are many verities of organisms found in a community. The total number of species of plants called as population. The ecological study of population is called as Autecology’s. The maximum species diversity is found in tropical forest. The plants are called as flora and animals are termed as fauna. The lowest species diversity is found in Tundra biome or Arctic desert.

(ii) Dominant species : The highest number of plants of a species present in a community is called as dominant species and whole plant community is knows as the name of the species. Such as Prosop is community on Aravali hills and Aravali hills and Pinus community on Himalaya. 

B.O.D. It shows the deficiency of oxygen in the water. Daphnia is the indicator of B.O.D.

15.5  OZONE LAYER DEPLETION :

Between 20 and 26 km above the sea level ozone layer is present and the part of atmosphere containing it is called ozonosphere (Stratosphere). This layer is established due to an equilibrium between photo dissociation of ozone by UV - radiations and regeneration of ozone. The thickness of this ozonosphere averages 5 km. The ozone layer acts as an ozone shield and absorbs the harmful UV - radiations of the sunlight so protect the earth’s biota form the harmful effects of strong UV - radiations. So this layer is very important for the survival and existence of life on earth. 

15.5 (a) Causes of Thinning of Ozone Layer :

The decline in spring - layer thickness is called ozone hole. Ozone hole is largest over Antarctica and was just short of 27 million sq. km. during September 2003. Main chemicals to be responsible for destruction of ozone - layer are : chlorofluorocarbons (CFCs), halogens (used in fire extinguishers), methane and nitrous oxide. Out of these, most damaging is the effect of CFCs which  are a group of synthetic chemicals and are used as collants in refrigenratorsare a group of synthetic chemicals and are used as collants in refrigerators and air conditioners; as cleaning solvents, propellants and sterilant etc. These CFCs produce “active chlorine” in the presence of UV - radiations. These active chlorine radicals catalytically destroy ozone and convert it into oxygen. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown -

In 1987, the United National Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.,

Nitrous oxide: is produced in industrial processes, forest fires, solid waste disposal, spraying of insecticides and pesticides, etc. Methane and nitrous oxide also cause ozone destruction. 

15.5 (b) Effects of Ozone Layer Depletion :

The thinning of ozone layer results in increase in the UV radiation (in the rage of 290 - 320 nm) reaching the earth’s surface. It is estimated that 5 percent loss of ozone results in 10 per cent increase in UV - radiations. These UV - radiations can :

(i)  Increases in incidences of cataract and skin cancer.

(ii) Decrease in the functioning of immune system.

(iii) Inhibit photosynthesis in most of phytoplankton so adversely affecting the food chains of aquatic  ecosystems.

(iv) Damage nucleic acids of the living organisms. 

15.6 MANAGEMENT OF NATURAL RESOURCES :

15.6 (a) Introduction :

We often hear or read about environmental problems. These are often global-level problems and we feel helpless to make any changes. There are international laws and regulations, and then there are our own national laws and acts for environmental protection. There are national and international organisations also working towards protecting our environment. The multi crore project of Ganga Action Plan came about in 1985 because the quality of water in the ganga was so poor.

15.6 (b)Pollution of the Ganga:

The Ganga runs its course of over 2500 km from Gangotri in the Himalayas to Ganga Sagar in the Bay of Bengal. It is being turned into a drain by more than a hundred towns and cities in Utter Pradesh, Bihar and West Bengal that pour their garbage and excreta into it. Largely untreated sewage is dumped into the Ganga every day. In addition pollution is caused by other human activities like bathing, washing of clothes and immersion of ashes or unburnt matter also. And then, industries contribute chemical effluents to the Ganga’s pollution load and the toxicity kills fishes in large section of the river.

Three R’s to save the environment :

(i) Reduce : This means ‘to use less’. We van save electricity by switching off unnecessary lights and fans. We can save water by repairing leaky taps.

(ii) Recycle : This means that we can collect plastic, paper, glass and metal items and recycle these materials to make required things instead of synthesizing or extracting fresh plastic, paper, glass or metal. In order to recycle, we first need to segregate our waste so that the material that can be recycled is not dumped along with other waste.

(iii) Reuse : This is actually even better than recycling because the process of recycling uses some energy. In the ‘reuse’ strategy, we can simply use things again and again. 

15.6 (c) need of Manage Our Resources :

Our natural resources are limited with the rapid increase in human population. Due to improvement in health care, the demand for all resources is also increasing. Management of natural resources requires long term perspective to meet the needs and aspirations of future generations. Natural resources should be managed in such a way that every one of the society is benefited from its development. The waste generated from exploration of natural resources should be disposed off safely. For instance, mining causes pollution due to discard of large amount of slag during metal extraction. 

15.7 SUSTAINABLE DEVELOPMENT :

It is the development which can be maintained for a long time without undue damage to the environment. The objective of sustainable development is to provide the economic well being of the present and the future generations and to maintain a healthy environment and life support system. It encourage forms of growth that meet current basic human needs, thus sustainable development implies a change in all aspects of life. It depend upon the willingness of the people to change their perceptions of the socio economic environmental conditions and use of natural resources. 

15.8  BIODIVERSITY :

It is the existence of a wide variety of species of plants, animals and microorganism in a natural habitant within a particular environment. Biodiversity of an area is the number of species or range of different life forms found there. Forests are ‘biodiversity hotspots’. 

15.9 PRACTICES FOR CONSERVATION AND PROTECTION OF ENVIRONMENT :

Conservation means ‘to keep safe’ whereas preservation means ‘to maintain the environment at it is’. Various practices which can help in conserving and protecting our environment are as follows :

1. The practice of crop rotation helps in conserving soil.
2. Judicious use of fertilizers, intensive cropping, proper irrigating and drainage help in the conservation of soil.
3. The treatment of sewage prevents pollution of water bodies and helps in conserving fishes and other aquatic life forms.
4. National parks and wildlife sanctuaries should e established throughout the country in order to protect and conserve will animals, birds and plant species.
5. New trees should be planted in place of those cut for various purposes, which will protect the earth from excessive heating.
6. Harvesting of rain helps in the conservation of groundwater.
7. Composting of solid organic waste for biogas and manure.

15.10 WILDLIFE :

It means all those naturally occurring animals, plants and their species which are not cultivated, domesticated and tamed. 

15.10 (a)Conservation :

It is the sensible use of the earth’s natural resources in order to avoid excessive degradation and betterment of the environment. It includes - the search for alternative food and fuel supplies when these are endangered, an awareness of the dangers of pollution and the maintenance and preservation of habitats and its biodiversity.

(i) Steps for conservation of wildlife :

(A)  Laws should be imposed to ban poaching or capturing of any animal or bird belonging to an endangered species.

(B)  The natural habitats of wild animals and birds should be preserved by establishing National Parks, Sanctuaries and Biosphere reserves throughout the country.

(C)  The Government Department should conduct periodic surveys of National Parks, Sanctuaries and Biosphere Reserves to have a knowledge of all the species of wild animals and birds.

(D)  More attention should be given to conserve the endangered species of wild animals and birds to prevent their extinction.

(E)   Unauthorized cutting of forest trees should be stopped. 

15.11 STAKEHOLDERS OF FORESTS :

 The conservation of forests depend on its forest resources or its various stakeholder, who are as follows : 

15.11 (a) People Who Live in or Around Forests :

(i)  They depend on forest produce, for various aspects of their life.

(ii) The local people need large quantities of firewood, small timber.

(iii) Bamboo is used to make slats for huts and baskets for collecting and storing food.

(iv) Implements for agriculture, fishing and hunting are largely made of wood.

(v) People collect fruits, nuts and medicines from forests, their cattle  also graze in forest.

15.11 (b) Forest Department of the Government :

(i) Which owns the land and controls the forest resources.

(ii) People develop practices to ensure that forest resources are used in a sustainable manner.

(iii) The forest resources were overexploited after the British took control of the forest.

(iv)  Forest department of independent India then owned the land and control the resources of the forest but local needs such as herbs, fruits and fodder were ignored.

(v) Monoculture of pine, teak or eucalyptus have been started which can destroy the bio-diversity of the area. 

15.11 (c) Industrialist :

(i) Industries consider the forest as a source of raw material for its factories.

(ii) These industries are not interested for the sustainability of the forest in one area as they go to a different area after cutting down all tree in one area.

15.11 (d) Wildlife and Nature Enthusiasts :

(i) They are not dependent of the forest but conserve nature and take part in its management.

(ii) Conservationists started with conserving large animals but are now preserving biodiversity as a whole.

(iii) The local people, for instance the Bishnoi community in Rajasthan worked for conservation of forest and wildlife as a religious act. Thus management of forest resources has to take the interests of various stakeholder into account.

15.12  TRADITIONAL USE OF FOREST :

1. Alpine grasslands in Himalayas were grazed by sheep in summer.
2. Nomadic shepherd drove their flock every summer in this area. 

15.12 (c) Causes of Damages to Forests :

(i) Local people damage forest to fulfill their daily needs.

(ii) Deforestation caused by industrial needs.

(iii) Deforestation caused for development projects like building roads or dams.

(iv) By tourists or in making arrangements for tourists. 

15.12 (b) Conservation of Forests :

it includes the following methods :

(i)  Afforestation . It is the practice of transforming an area into forest have not grown  there, it involves three types of forestry programmes.

(A) Social and Environmental forestry. It involves raising of trees for firewood, fodder and agricultural implements for the benefit of rural and trial community.

(B) Agro forestry. It is an absolute commercial forestry developed to fulfill the need of various forest based industries. It is done on the fallow land or free-grazing lands.                     

(C)  Urban forestry. In involves growing of ornamental trees along roads, vacant lands and common parts of urban areas.

(ii) People participation in forest management :

(A) The Sal forests in West Bengal got reduced alarmingly in 1972.

(B) Surveillance and policing to protect resulted frequent clash between forest official and the villagers.

(C) The department then changed its strategy and in Asabari forest, villagers were involved in protection of the badly damaged Sal forest.

(D) In return, villagers were given employment and were allowed to collect firewood and fodder at nominal fee.

(E) By 1983, the Asabari forest showed a remarkable recovery.

(iii) Economic growth and Ecological conservation :

(A) Forest resources should be used in an environmentally and developmentally sound manner.

(B) The benefit of controlled exploitation of resources goes to the people and the environment is also preserved.

(C) If the exploitation is too high, economic and social development will be faster but the environment will further deteriorate.

(D) We should use natural resources cautiously so that economic growth and ecological conservation go hand in hand.

(E) Amrtia Devi Bishnoi National Award. In 1731, Amrita Devi Bishnoi sacrificed her life along with  63 persons for the protections of ‘Khejri’ trees in Khejrali village near Jodhpur in Rajasthan. In the memory Government of India have recently instituted this award for Wildlife Conservation.’

(F) Chipko Movement : During 1970, In Reni village of Garhwal, a contractor was allowed to cut trees in a forest near the village. When the contractor’s workers went to the forest to cut trees the woman of the village hug the tree trunks to prevent the workers from cutting trees, Chipko means ‘hug’ and the movement started by the villagers by hugging tees is called Chipko Andolan’. 

15.13 WATER AS A BASIC NATURAL RESOURCE :

1. It is a valuable national asset.
2. It is the main requirement of human being.
3. Water is of two types - salt water and fresh water.
4. Fresh water is an unlimited natural resource, it can be obtained from three natural resources - rain water, surface water and ground water.
5. Human intervention pollutes  water and also changes the availability of water in various regions.

15.13 (a) Water Sources :

(i) Rain in India re due to monsoon.

(ii) Failure to sustain underground water due to loss of vegetative cover, development of water demanding crop and pollution from industrial effluents.

(iii) Small dams, canals and tank were used for irrigation purpose and to fulfill the basic minimum needs.

(iv) Large dams and canals were made by British as well as our own government.

(v) Due to the mega project, local irrigation methods got neglected and the local people lost control over management of local water sources.

(vi) Large dams and canals were made by British as well as our own government.

13.13 (b) Management of Water Resources :

It includes :

(i) Interacted water-shed plan for drinking, irrigation and industrial uses.

(ii) Flood control

(iii) Transfer of surplus water to water deficit basins by inter-linking of rivers.

(iv) Hydro geological survey to identify over-exploited areas.

(v) Artificial recharging of the ground water.

(vi) Mass awareness programmes through public or private agencies.

(vii) Dams : They are massive barriers built across rivers and streams to confine and utilize the flow of water for human purposes such as irrigation and generation of electricity.

1. Large dams can also ensure the storage of adequate water.
2. Canal system leading from dams transfer large quantity of water upto great distances, e.g. Indira Gandhi Canal or Rajasthan brought greenery to considerable areas.
3. Purposes for building a dam :
4. Generation of electricity
5. Irrigation
6. Control of flood which either stops or slows the amount of water in the river.
7. Criticism about large dams :
8. Social problems : They displace large number of farmers and tribals.
9. Economic problems : They consume huge amount of public money without proportionate benefit.
10. Environmental problems. As they cause deforestation and loss of biological diversity.

15.13 (c) Mismanagement of Water Distribution :

Due to mismanagement in distribution of water, the benefit of contracting a dam goes to few people only. For example, people close to the water source grow water intensive crop like sugarcane and rice while people farther downstream do not get any water. This resulted in discontentment among the people who has been displaced by building of dam.               

(i) Watershed management : It means scientific conservation of soil and water to increase the biomass production.

1. Watershed management not only increases the production and income of the watershed community but also overcomes drought and flood.
2. It increases the life of downstream dam and reservoirs.

(ii) Water harvesting : It means capturing rainwater where it falls or capturing the runoff water in a local area and talking measures to keep the water clean by not allowing polluting activities to take place.

(A) Techniques of water harvesting : Water harvesting techniques are mainly location specific. It is an age - old concept in India.

1. Khadins, tanks and nadis in Rajasthan.
2. Bandharas and tals in Maharashtra
3. Ahars and Pynes in Bihar
4. Kulhs in Himanchal Pradesh
5. Ponds in kandi belt of Jammu.
6. Eris (tanks) in Tamilnadu.
7. Suragams in kerala.
8. Kattas in Karnataka.
9. Due to own control of the local population over exploitation of the local water resources in reduced.

(B) Some of the water harvesting techniques are :

1. Capturing of runoff water roof tops.
2. Capturing of runoff water from local catchments.
3. Capturing seasonal flood water from local streams.

(C) Benefits of water harvesting :

1. Provide drinking water.
2. Provide irrigation water.
3. Increase in ground water resources.
4. Reduces storm water discharge, urban flood and overloading of sewage treatment plants.

(D) Advantages of ground water :

1. It does not evaporate.
2. It spreads out to recharge wells.
3. It provides moisture for vegetation.
4. It does not provide breeding grounds for mosquitoes.
5. It is relatively protected from contamination by human and animal waste.

(E) Traditional water harvesting system :

1. The water harvesting structures are mainly crescent shaped.
2. Monsoon rains fill ponds behind the structures.
3. The large structure hold water throughout the year while most dry up after monsoon.
4. The main purpose of this system is to recharge the ground water and not to hold surface water.

15.14   FOSSIL FUELS :

These fuels are obtained from the remain of plants and animals, which got buried beneath the earth millions of years ago, changed into coal, petroleum and natural gas due to excessive heat and high pressure inside the earth. 

15.14 (a) Non-Renewable Energy Sources :

These are energy sources which cannot be replaced easily when the get exhausted and are also called conventional sources of energy. They are used traditionally for many years and take millions of years to form e.g. Fossil fuels.

(i) Coal : It contains carbon and its compound mainly with nitrogen, oxygen, sulphur and hydrogen. It also consists of inorganic matter.

(ii) Petroleum : ‘Petro’ means rocks and ‘oleum’ means oil, petroleum is therefore the oil found in rocks. It is a complex mixture of solid, liquid and gaseous hydrocarbons. It also contains small amounts of other compounds of carbon, hydrogen, oxygen, nitrogen and sulphur. Large reservoirs of petroleum have been preserved by nature for millions of years between porous rocks beneath the earth.

15.14 (b) Formation of Non-Renewable Energy Sources :

(i) Formation of coal. Coal is formed organic matter which got buried under the earth 300 million years ago. Due to high pressure and temperature inside the earth, this organic matter changed into coal, that is why, coal is called fossil fuel.

(ii) Formation of petroleum. It is formed by the decay of very small (tiny) marine animals and plant buried under the earth about 400 million years ago. Due to excess of heat and pressure it changed into oil called petroleum. It is a fossil fuel.

15.14 (c) Conservation of Coal and Petroleum :

It means more efficient use with regard to economic, social and environmental cost and benefits which result in attainment of higher efficiency, minimisation of wastage and protection of the environment.

We can conserve coal and petroleum by their judicious use and substituting them by other resources wherever feasible. Conservation of coal and petroleum is a joint responsibility of the industries, citizens and government where each one has significant role in Management of Natural Resources.

15.14 (d) Necessity of Judicious Use of Coal and Petroleum :

The fossil fuels, coal and petroleum get exhausted and their combustion pollutes our environment, so a judicious use of these resources is necessary. When combustion take place, oxides of carbon, hydrogen, nitrogen and sulphur are formed. Carbon monoxide is formed instead of carbon dioxide if there is insufficient are. The oxides of sulphur, nitrogen and carbon monoxide are poisonous at high concentrations. Carbon dioxide is a green-house gas which leads to global warming. 

15.14 (e) Uses of Fossil Fuels :

(i) In thermal power plants and steam engines.

(ii) Petroleum products like petrol and diesel are used as fuel in motor vehicles and ships. Other products like kerosene and LPG are used for cooking purpose. 

15.14 (f) Management of Fossil Fuels :

The natural gas is a good alternative to fossil fuels like coal and petroleum. The use of alternative source of non-conventional energy such as solar energy, which energy, biomass energy, etc., should be promoted to save the reserves of fossil fuels. Biogas can also be used for various purposes.

OUR ENVIRONMENT

• Environment means everything which surrounds us. It may include living (biotic) and non-living (abiotic) components. So, it may includes besides all creatures, water & air also.
• Environment affect the life and development of an organism in its natural habitat & vice a versa.
• Substances that are decomposed are called bio-degredable. Eg. organic wastes while some substances like plastics, some chemicals (DDTs & fertilizers) are inert and can’t be decomposed, are called Non-biodegradable
• Actually non-biodegradable persist in the environment for a long time or may harm the various members of the eco system.

1. Ecosystem: It is the structural and functional unit of biosphere which comprises of both biotic and abiotic components that interact with each other to form a stable and self-supporting system.

2. Natural ecosystem: The ecosystems which operate themselves in nature without any interference of human beings are called natural ecosystems.

3. Artificial ecosystem: The ecosystem which is maintained by human beings like croplands, aquarium etc. is called artificial ecosystem.

4. Abiotic components: The non-living physio-chemical factors like soil, humidity, sunlight, rainfall, temperature etc. are the abiotic components.

5. Biotic components: The living organisms like autotrophs, heterotrophs forms the biotic components.

6. Food chain: The sequential interlinking of organisms involving transfer of food energy starting with a producer through a series of organisms where one is eaten by the other is called a food chain.

7. Trophic levels: The distinct sequential steps in the food chain where transfer of energy occurs are referred to as trophic levels.

8. Food web: A network of food chains which are interconnected at various trophic levels to form a number of feeding connections among different organisms is called a food web.

9. Biodegradable wastes: The wastes which get degraded in a natural process by the action of microbes into simpler forms are called biodegradable wastes. Example, food waste, human waste, paper waste, manure, sewage etc.

10. Non-biodegradable wastes: The wastes which cannot be degraded by the action of microbes in a natural way and they persist in environment for a longer period of time are called nonbiodegradable wastes. Examples, Glass, metal, batteries, plastic bottles, tetra packs.

• Environment means everything which surrounds us. It may include living (biotic) and non-living (abiotic) components. So, it may includes besides all creatures, water & air also.
• Environment affect the life and development of an organism in its natural habitat & vice a versa.
• Substances that are decomposed are called bio-degredable. Eg. organic wastes while some substances like plastics, some chemicals (DDTs & fertilizers) are inert and can’t be decomposed, are called Non-biodegradable
• Actually non-biodegradable persist in the environment for a long time or may harm the various members of the eco system.

• All living organisms are classified on the basis of the manner in which they survive in the Ecosystem. These groups include
I Producers– All green plants, blue green algae can produce their food (Sugar & starch) from in organic substance using light energy (Photosynthesis)
II Consumers– Include organisms which depend on the producers either directly or indirectly for their sustenance. In other word consumers consume the food produced by producers.

III DECOMPOSERS– Fungi & Bacterias which break down (decompose) the dead plant, animals complex compounds into the simpler one. Thus decomposers help in the replenishment of the natural resources.
Food chain refers to an arrangement of different biotic groups in a sequence of enery transfer. These biotic groups are producer herbivores, carnivores.

♦ In a food chain, these biotic components where transfer of energy takes place is called a trophic level.
♦ The green plants capture 1% of sunlight falls on their leaves.
♦ The flow of energy is unidirectional in a food chain
♦ There is gradual decrease in the amount of energy transfer from one trophic level to next trophic level in a food chain 

So only 10% of Energy is transferred to next trophic level while 90% of energy is used by present trophic level in its life processes.

♦ While the conc. of harmful chemical increases with every next trophic level in a food chain. It is called Bio-magnification For Eg. 

♦ Maximum concentration of such chemicals accumulated in human bodies.
♦ Naturally the food chains are inter-connected with each other forming a web like pattern, which is known as FOOD WEB.
♦ The loss of energy at each step (trophic level) is very high, so very little amount of energy remains after four trophic levels.
♦ There are gnerally a big population at lower trophic levels of an ecosystem.
For Eg. the population of the producer is higher than the consumer carnivore (lion) population.

ENVIRONMENTAL PROBLEMS

♦ Changes in environment affect us and our activities change the environment around us. This led to the slow degreadation of environment that arose many environmental problems. Eg. depletion of the Ozone Layer and waste disposal. 

I Depletion of Ozone Layer
♦ Ozone (O ) layer is largely found in the stratosphere which is a part of our 3 atmosphere from 12 km – 50km above sea level.
♦ Ozone is a deadly poison at the ground level.
♦ Ozone is formed as a result of a following photochemical reaction. 

♦ Ozone layer is a protective blanket around earth which absorbs most of the harmful U.V. (Ultraviolet) radiation of the Sun, thus protecting the living beings of the earth from health hazards like skin cancer, cataract in eyes, weaken immune system, destruction of plants etc.
♦ The decline of Ozone layer thickness is Antartica was first discovered in 1985 and was termed as OZONE HOLE.

Reason of Ozone Depletion :
Excessive use of CFCs (Chloro Flouro Carbon) a synthetic, inert chemical Eg.
Freon which are used as refrigerants and in fire extinguishers, caused Ozone depletion in the upper atmosphere. A single chlorine atom can destroys 1,00,000 Ozone molecules. U.N.E.P. (United Nation Envrionment Programme) did an excellent job in forging an agreement to freeze CFC production at 1986 levels (KYOTO Protocol) by all countries.

Garbage Disposal
Industrialization and rise in demand of consumer goods have created a major problem in the form of wastes/garbage accumulation and its disposal especially in urban area.
The different methods of solid wastes disposal commonly used around the world are.

1. Open dumping : A conventional method in which solid wastes dumped in selected areas of a town. It actually cause pollution

2. Land fillings : Wastes are dumped in low living area and are compacted by rolling with bulldozers

3. Composting : Organic wastes are filled into a compost pit (2m x 1m x 1m). It is then covered with a thin layer of soil. After about three months the same garbage filled inside the pit changes into organic manure.

4. Recycling : The solid wastes is broken down into its constituent simpler materials. These materials are then used to make new items. Even non-bio degradable solid wastes like plastic, metal can be recycled.

5 Reuse : A very simple conventional technique of using an item again & again.
For Eg. paper can be reused for making envelops etc.

Choose the correct answer from the given options.

Question. Excessive exposure of humans to UV-rays results in
(i) damage to immune system (ii) damage to lungs
(iii) skin cancer (iv) peptic ulcers
(a) (i) and (ii)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (iii) and (iv)
Answer : C

Question. Choose the incorrect statement from the following:
(a) Ozone is a molecule formed by three atoms of oxygen.
(b) Ozone shields the surface of the Earth from ultraviolet radiations.
(c) Ozone is deadly poisonous.
(d) Ozone gets decomposed by UV radiations
Answer : D

Question. In the following groups of materials, which group(s) contains only non-biodegradable items?
(i) Wood, paper, leather (ii) Polythene, detergent, PVC
(iii) Plastic, detergent, grass (iv) Plastic, bakelite, DDT
(a) (iii)
(b) (iv)
(c) (i) and (iii)
(d) (ii) and (iv)
Answer : D

Question. Depletion of ozone is mainly due to
(a) chlorofluorocarbons
(b) carbon monoxide
(c) methane
(d) pesticides
Answer : A

Question. Which one of the following greenhouse gases is a contributor due to incomplete combustion of coal and petroleum?
(a) Oxides of nitrogen
(b) Methane
(c) Carbon monoxide
(d) Carbon dioxide
Answer : C

Assertion-Reason Type Questions 

For question numbers 2 two statements are given-one labeled as Assertion (A) and the other labeled
Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.

Question. Assertion: Ozone is formed in upper atmosphere by O2 in presence of UV radiations.
Reason: Ozone depletion will lead to UV rays reaching earth which may cause skin cancer.
Answer : B

Question. 2. Assertion: Polythene bags and plastic containers are non-biodegradable substances.
Reason: They can be broken down by microorganisms in natural simple harmless substances.
Answer : C

Case Study Questions

1. Observe the following diagram and answer the questions any four from (i) and (v)

Question. Choose the waste management strategy that is matched with correct example.
(a) Refuse Choose products that use less packaging
(b) Reduce Give unwanted toys and books to hospitals or schools
(c) Reuse Not using single use plastic
(d) Repurpose Making flower pot from used plastic bottle
Answer : D

Question. Effective segregation of wastes at the point of generation is very important. Select the appropriate statements giving the importance of waste segregation.
I. less waste goes to the landfills
II. better for public health and the environment
III. help in reducing the waste
IV. resulting in deterioration of a waste picker’s health
(a) both I and II
(b) both I and III
(c) both II and III
(d) both I and IV
Answer : A

Question. According to the ‘Solid Waste Management Rule 2016’, the waste should be segregated into three categories. Observe the table below and select the row that has correct information

Answer : B

Question. The given graph shows the amount of waste generated, dumped and treated in percentage. Identify
the reason of low success rate of waste management process.

a) only 15% of urban India’s waste is processed
(b) less than 60% of waste is collected from households
(c) more than 60% of waste is collected from households
(d) both (a) and (b)
Answer : A

Question. Recycling of paper is a good practice but recycled paper should not be used as food packaging because
(a) recycled papers may release color /dyes on food items
(b) recycled papers are not absorbent
(c) recycled papers can cause infection due to release of methane
(d) recycled papers are costly
Answer : A

2. Biosphere is a global ecosystem composed of living organisms and abiotic factors from which they derive energy and nutrients. And ecosystem is defined as structural and functional unit of the biosphere comprising of living and non-living environment that interact by means of food chains and chemical cycles resulting in energy flow, biotic diversity and material cycling to form a stable, self-supporting system

Question. The diagram below shows a food web from the sea shore

The mussel can be described as
(a) Producer
(b) Primary consumer
(c) Secondary consumer
(d) Decomposer
Answer : C

Question. Consider the following statements concerning food chains:
(i) Removal of 80% tigers from an area resulted in greatly increased growth of vegetation
(ii) Removal of most of the carnivores resulted in an increased population of herbivores.
(iii) The length of the food chains is generally limited to 3 – 4 trophic levels due to energy loss
(iv) The length of the food chains may vary from 2 to 8 trophic levels Which two of the above statements are correct?
(a) (i), (iv)
(b) (i), (ii)
(c) (ii), (iii)
(d) (ii), (iv)
Answer : C

Question. The given figure best represents

(a) Grassland food chain
(b) Parasitic food chain
(c) Forest food chain
(d) Aquatic food chain
Answer : A

Question. Which trophic level is incorrectly defined?
(a) Carnivores – secondary or tertiary consumers
(b) Decomposers – microbial heterotrophs
(c) Herbivores – primary consumers
(d) Omnivores – molds, yeast and mushrooms
Answer : D

Question. Which of the following group of organisms are not included in ecological food chain?
(a) Carnivores
(b) Saprophytes
(c) Herbivores
(d) Predators
Answer : B

Very Short Answer Type Questions

Question. List two biotic components of environment.
Answer : Plants, animals, micro-organisms (any two) are biotic components.

Question. What will be the amount of energy available to the organisms of 2nd trophic level of food chain if energy available at the first trophic level is 1000 J.
Answer : 1000 × 1/10 = 100 J

Question. What will be the amount of energy available to the organisms of secondary consumer trophic level of food chain, if the energy available to producer level is 10000 Joules.
Answer : Energy available to primary consumers level is 10000 × 10/100 = 1000 J
Energy available to secondary consumer trophic level 1000 × 10/100 = 100 J

Question. State a way to prevent accumulation of harmful chemicals in our bodies.
Answer : Minimum use of fertilizers, insecticides and pesticides, can prevent the accumulation of harmful chemicals in our body.

Question. Compare the advantages of cloth bags over polythene bags.
Answer : (i) Cloth is biodegradable, does not pollute environment.
(ii) It can be used again like plastic bag and moreover it is ecofriendly.

Question. Define trophic level. Name the first trophic level.
Answer : Each level in a food chain is called trophic level. First trophic level is producers

Question. Study the following food chain: Grass → Sheep or Goat → Man; Algae → Fish → Man Who is the ultimate sufferer of using pesticides like DDT on land and in water? Give reason.
Answer : Man is the ultimate sufferer. Food chain in given cases ends on man i.e. last trophic level.

Question. Arrange the following in food chain:
(a) Frogs, Insects, Birds, grass. (b) Fish, algae, small animal, big animal.
Answer : (a) Grass → Insects → Frog → Birds
(b) Algae → Small animal → Fish → Big animal

Question. Name the organisms which belong to first and third trophic level in food chain comprising of the following: Insects, birds, frog and grass.
Answer : First trophic level – Grass
Third trophic level – Frog

Question. What happens during first step of ozone formation in the the atmosphere?
Answer : 

Question. Which compounds are responsible for the depletion of ozone layer?
Answer : (i) CFC, (ii) NO, (iii) Free radicals of chlorine (iv) Aerosols

Short Answer Type Questions

Question. What is the role of decomposers in the ecosystem?
Answer : (i) Decomposers decompose the remains of plants and animals.
(ii) They clean the environment.
(iii) They bring back the raw materials to environment.

Question. Which of the following are not biodegradable: Wool, glass, silver foil, leather? 
Answer : Glass, silver foil.

Question. Name the gases which have replaced CFCs.
Answer : (i) HFCs (Hydrofluorocarbons), (ii) Perfluorocarbons (PFCs) have replaced CFCs.

Question. What is full form of CFC and UNEP? 
Answer : CFC stands for Chloroflurocarbon
UNEP stands for United Nations Environment Programme

Question. Name any two items which can be easily recycled but are generally thrown in the dust-bin by us.
Answer : (i) Bits of paper (ii) Plastic bottles of water or cold drinks

Question. Name the radiations that are absorbed by ozone layer?
Answer : UV radiations (Ultra-Violet radiations) are absorbed by ozone layer

Question. Ozone is deadly poisonous, still it performs an essential function. How?
Answer : It protects earth from harmful UV radiations.

Question. Why is excessive use of CFC a cause of concern? 
Answer : CFC will deplete ozone layer which prevents UV radiation to reach earth. It causes skin cancer.

Question. Why should bio-degradable and non-biodegradable wastes discarded into separate dust bins?
Answer : It saves time and energy by separating them and waste disposal can be done in right way in minimum time.

Question. Your mother always thought that fruit juices are very healthy for everyone. One day, she read in the newspaper that some brands to fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to health.
(a) How would you explain to your mother about fruit juices getting contaminated with pesticides?
(b) It is said that the harmful pesticides enter our body as well as the bodies of other organisms, they get accumulated and beyond a limit causes harm and damage to our organs. Name the phenomenon and write about it.
Answer : (a) Farmers spread pesticides on fruits and it get mixed up with fruits and enter fruit juices.
(b) The process is called bio-magnification. The concentration of toxic substances like pesticides, insecticides increase with each trophic level in food chain.

Question. Why do most food chains have 3-5 steps only?
Answer : Following 10% rule of energy flow, very little energy is left at the trophic levels beyond 3-5 levels that may not be enough to sustain life of a big carnivore, hence most food chains are short and have 3-5 steps only. Longer ones will have very small carnivores at the top

Question. Pesticides like DDT which are sprayed to kill pests on crops are found to be present in soil, ground water, water bodies etc. Explain how do they reach these places.
Answer : (i) Soil. Pesticides get settled on soil when sprayed over plants.
(ii) Groundwater. Pesticides present in soil reach lower layers of soil during irrigation and get mixed with ground water.
(iii) Waterbodies: When agricultural waste as well as waste water get mixed up with water bodies, pesticides enter waterbodies because these are non-biodegradable 

Question. What would happen if number of carnivores decreases in the ecosystem?
Answer : If number of carnivores decreases in the ecosystem, then it will lead to increase in number of herbiores.
As a result number of plants will decrease and consequently amount of O2 will also decrease in the ecosystem.

Question. Differentiate between autotrophs, heterotrophs and decomposers and give one example of each.
Answer : (i) Autotrophs. Those organisms which prepare their own food with the help of CO2, H2O and sunlight in presence of chlorophyll e.g. green plants.
(ii) Heterotrophs. Those organisms which do not prepare their own food but dependent on the other food. e.g. animals and human beings.
(iii) Decomposers. Those organisms which decompose the complex molecules present in the dead remains of plants and animals e.g. bacteria, fungi, earthworm.

Question. Will the impact of removing all the organisms in a trophic level be different for different trophic levels?
Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer : The impact of removing all the organisms in a trophic level will be different for different trophic levels. It is not possible to remove organisms of any trophic level without causing damage to ecosystem because organisms of each level are interdependent.

Question. What will happen if we kill all the organisms in one trophic level?
Answer : If we kill the organisms in one trophic level.
(i) The population of organisms in previous trophic level will increase.
(ii) The population of organisms in next trophic level may decrease.
(iii) It will cause an ecological imbalance in the food chain.

Question. Energy flow is unidirectional in food chain? Explain.
Answer : The energy of sun is taken by plants and cannot be given back. Herbivore eat plants and cannot give back energy to plants. Carnivores eat herbivores and cannot give back energy to herbivores. It means flow of energy is unidirectional from lower trophic level to higher trophic level.

Question. (a) What is an ecosystem? List its two main components. 
(b) We do not clean ponds or lakes, but an aquarium needs to be clean regularly, explain.
Answer : (a) Ecosystem is composed of different organisms interdependent upon each other. Biotic and abiotic components are its two main components.
(b) Pond or lake is a natural ecosystem, several organisms present in it maintain a balance in the ecosystem. Aquarium is an artificial ecosystem in which bacteria convert fish food into ammonia which is harmful for fish. Water needs to be changed regularly. Chlorine water should be dechlorinated otherwise fish will not survive. Air pump is needed to provide oxygen. Artificial ecosystem need utmost care to remain stable.

Question. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer : The process in which harmful chemicals like pesticides enter the food chain and get accumulated in each trophic level is called biomagnification. The level of biomagnification will be different from different trophic level. Primary consumers will have higher concentration of pesticides than producers and secondary consumers will get pesticides by eating primary consumers and will have even higher concentration.

Question. Accumulation of harmful chemicals in our body can be avoided. Explain how this can be achieved.
Answer : (i) Wash vegetables and fruits with saline water and vinegar.
(ii) Shock the vegetables in salt water for few minutes before cooking.
(iii) Boil the vegetables.
(iv) Organic manure and organic ecofriendly pesticides should be used.

Question. What is meant by food chain? ‘The number of trophic levels in food chain is limited.’ Give reason to justify the statement. 
Answer : Food chain is a sequence in which nutrients, food and energy is transferred in systematic way. Lower trophic level have maximum population because energy is available in more extent. Primary consumers get 10% of energy of producers.
Secondary consumers get 10% of energy of primary consumers.
Tertiary consumers get 10% of energy of secondary consumers i.e. very less energy is available, that is why the trophic levels are limited. Tiger population is decreasing day by day as food is not easily available for them and forests are decreasing due to cutting of trees 

Question. What term do you use for trophic levels comprising of
(a) the organisms which make their own food
(b) animals feeding on plant matter only
(c) organisms breaking down dead plants and animals
Answer : (a) Producers (b) Herbivores (c) Decomposers

Question. List three characteristics of energy flow in an ecosystem.
Answer : (i) The sun is the main source of energy on earth. About 1% of incident solar energy is utilized by plants during photosynthesis.
(ii) Producers [plants] convert solar energy to chemical energy of food, and then it is passed on to the consumers and to decomposers back to soil. This is in accordance with law of conservation of energy.
(iii) The energy flow is unidirectional, that is, it flows from producers through herbivores to carnivores; it cannot be transferred in the reverse direction.
(iv) The amount of energy flow decreases with successive trophic levels.

Question. How will you create an artificial aquatic ecosystem, which is self-sustainable?
Answer : • Take a large jar filled with water, oxygen, food and aquatic plants and animals.
• Oxygen/oxygen pump.
• Fish food.
• Aquatic plants/Producers provide O₂ during photosynthesis.
• Aquatic animals/Consumers release CO₂ for the process of photosynthesis.
• Decomposers are also important for natural cleaning of the aquarium

7. (a) Complete the following table

(b) How is ozone formed at the higher levels of atmosphere?
Answer : 

Question. Why are some substances biodegradable and some are non-biodegradable?
Answer : Biodegradable substances are those which are broken by micro-organisms and get decomposed. They do not persist in environment for a very long time e.g., paper.
Non-biodegradable substances are those which are not broken by micro-organisms. They persist in environment for long time. e.g. plastic, DDT.

Question. What is ozone and how does it affect any ecosystem?
Answer : Ozone is a triatomic (O3) gas formed in upper atmosphere by action of UV light on oxygen. It protects earth from harmful UV radiations

Question. (a) What do you understand by ‘watershed management’? List any two advantages of watershed management.
(b) Human beings occupy the top level in any food chain. What are the consequences of this on our body?
Answer : (a) Soil and water conservation in a scientific way is called ‘watershed management’.
Advantages: (i) Increase in production and income of watershed communities,
(ii) Mitigate draughts and floods, (iii) Increase the life of downstream dam reservoir.
(b) Maximum level of biomagnification occurs in human beings because of progressive accumulation.
We get very small amount of energy as only 10% of previous energy gets transferred to each trophic level.

Question. Mention three methods to reduce amount of wastes produced.
Answer : (i) Recycling of non-biodegradable waste.
(ii) Reuse of waste such as newspapers can be used for making carry bags and envelopes
(iii) Biodegradable domestic waste should be disposed in pits to form manure.
(iv) Biogas plants should be used for disposal of waste in rural areas.

Question. When the government banned the use of polybags in Delhi, the vegetable grocers found it difficult as it affected their sales. The market committee held a meeting and decided to spread awareness about harmful effect of polybags.
(i) How will you convince people that plastics are harmful to the environment?
(ii) What alternatives of polythene bags do we have, which are environment friendly?
(iii) Not many people in Delhi have stopped using polythene bags even though they are officially banned. How can schools enaculate environmental values in students?
Answer : (a) They need to be told that cows and other animals eat polythene which is fatal for them. Coloured polythene is also very harmful for vegetables and fruits.
(ii) Paper bags, jute bags, bags of biodegradable materials are ecofriendly and carrying your own shopping bag is also more convenient.
(iii) Schools must teach students to protect environment. They should make paper bags and distribute to small shopkeepers regularly so that gradually their habits will change

Question. (a) Why is it necessary to conserve our environment?
(b) State the importance of green and blue dustbins in the safe disposal of the household waste.
Answer : (a) It is necessary to conserve our environment because
(i) It helps in protecting the ozone layer.
(ii) It helps in maintaining animal and human food chains.
(iii) It provides us with many useful products such as medicines and wood.
(b) Disposal of household waste is carried out in green and blue bins, respectively. It will be very useful in the separate disposal of biodegradable and non-biodegradable wastes. This will also ensure the application of 3 R’s— Reduce, Reuse and Recycle 

Question. List two causes of depletion of ozone layer. Mention any two harmful effects of depletion of this layer.
Answer : Two causes of depletion of ozone layer are: (i) CFCs (ii) Aerosols
Two harmful effects of depletion of this layer are:
(i) UV radiations can reach the earth and causes skin cancer, harmful to eyes and immune system will be disturbed.
(ii) It may lead to variations in rainfall, ecological disturbance

Question. (i) What is the height of ozone from the equator?
(ii) Name the rays against which ozone layer provides protection.
(iii) Name one effect of depletion of ozone layer. 
Answer : (i) 10 to 16 km (ii) UV rays (iii) Global warming.

Question. (a) Improvement in our lifestyle has resulted in greater amount of waste generation. Suggest one change we can incorporate in our lifestyle in order to reduce non-biodegradable waste.
(b) The following organisms form a food chain: Insect, Hawk, Grass, Snake, Frog
Which of these will have highest concentration of non-biodegradable chemicals? Name the phenomenon.
Answer : (a) (i) More use of disposable items like paper plates, plastic and polythene which are recyclable.
(ii) Change in packaging Suggestion. Reuse of plastic containers
(b) Hawk will have highest concentration of non-biodegradable chemicals. This process is called biomagnification

Question. Mention the negative effect of our lifestyle on the environment.
Answer : (i) Global warming occurs due to increase in number of vehicles and over use of fossil fuels.
(ii) Due to excessive use of deodrants, perfumes, CFCs, etc. ozone layer is getting depleted.
(iii) Air pollution occurs due to industralisation.
(iv) Wastes causes pollution due to release of sewage in water bodies.
(v) Pollution of soil occurs due to overuse of chemicals is agriculture.

Question. How is ozone both beneficial and damaging? How can we prevent the damaging effect of ozone? List one way.
Answer : Damaging as it is a deadly poison.
Beneficial as it shields the surface of the earth from UV radiations of the Sun.
By not using synthetic chemicals like CFCs, that depletes O₃ layer.

Question. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer : If all waste we generate is biodegradable, the adverse effect on environment will be minimum. They will produce CO2, methane which is released in atmosphere.
Nutrients will be mixed in soil to increase the fertility of soil

Long Short Answer Type Questions

Question. (i) Create a terrestrial food chain depicting four trophic levels.
(ii) Why do we not find food chains of more than four trophic levels in nature?
Answer : (i) A terrestrial food chain depicting four tropic levels is shown in diagram. ½
(ii) According to the 10% law, the amount of energy available will not be sufficient for the survival of the organisms in the 5th trophic level. ½+½+½
(A flow chart or a diagrammatic representation showing all the four tropic levels would also be accepted).
According to the 10% law, the amount of energy available will not be sufficient for the survival of the organism in the 5th trophic level

Question. Give an example of food chain and state the different trophic levels in it.
Answer : An example of food chain is grassland food chain. Its different trophic levels are shown in the given figures.

Question. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer? Plants → Deer → Lion
Answer : Plants → Deer → Lion
It is given that 100 J of energy is available to lion.
Let the amount of energy available to deer be x Joules.
According to 10% law, 10% energy from deer must have been transfered to lion. So, energy available to deer can be calculated as, 10/100 × x = 100 J, Therefore, x = 1,000 J
Now, let the amount of energy available to plants be y Joules.
According to 10% law, 10% energy from plants must have been transfered to deer. So, energy available to plant can be calculated as, 10/100 × y = 1,000 J
Therefore, y = 10,000 J
So, we have found that energy available to the producer is 10,000 J.

Question. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose of non-biodegradable waste for saving the environment.
Answer : Biodegradable substances
Can be broken down into simpler substances by nature / decomposers/ bacteria/ saprophytes
Eg. – Human Excreta/ Vegetable peels, etc. (any one)
Non-biodegradable substances
Can’t be broken down into simpler substances by nature / decomposers.
Eg. – Plastic/ glass (any one)
Two habits to dispose of non-biodegradable wastes are:
(i) Use of separate dustbins for biodegradable and non-biodegradable wastes,
(ii) Reuse of things such as polybags, etc.,
(iii) Recycling of wastes
(iv) Use of cotton /jute bags for carrying vegetables etc.

Question. Construct an aquatic food chain showing four trophic levels.
Answer : 

Question. (a) Construct a terrestrial food chain comprising four trophic levels.
(b) What will happen if we kill all the organisms in one trophic level?
(c) Calculate the amount of energy available to the organisms at the fourth trophic level if the energy available to the organisms at the second trophic level is 2000 J.
Answer : (a) Level 1 Plants and algae
Level 2 Herbivores like goat, cow
Level 3 Carnivores like fox, wild cat, mongoose
Level 4 large carnivores, lion, tiger
(b) If we kill all organisms in one trophic level, then transfer of energy as well as matter to next higher level will stop, it will lead to overpopulation at one particular level, disturb the food chain and cause collapse of ecosystem.
(c) Energy available at second trophic level of 2000 J
Energy available at third trophic level is 2000 × 1/10 = 200 J
Energy available at fourth trophic level is 200 × 1/10 = 2 J

Question. (a) Water is an elixir of life, a very important natural resource. Your Science teacher wants you to prepare a plan for a formative assessment activity, “How to save water, the vital natural resource”. Write any two ways that you will suggest to bring awareness in your neighbourhood, on ‘how to save water’.
(b) Name and explain any one way by which underground water table does not go down further.
Answer : (a) Water is one of the most precious natural resources that has vital importance in our lives. It is an essential component of the human body and is used almost everywhere in our day-to-day activities, such as cooking, washing, in agriculture and industries. It is an indispensable part of our life,
without which the life on earth is not possible. However, the amount of fresh water available for sustaining life is very less. So, it is very important to conserve water. For creating awareness among people, we can adopt the following two ways.
(i) Door to door campaigning. (ii) Nukkad Nataks
(b) Underground water table can be recharged through rainwater harvesting. Rainwater harvesting is a process by which rain water is collected and stored for the purpose of recharging the ground water or for future use like for irrigation and agriculture, for livestock, etc. In India, rainwater harvesting is an old tradition, which is followed till now in many parts of India. For example, bawris are traditional architectural rainwater harvesters that were built for collecting water, in the state of Rajasthan.
There are two ways of rainwater harvesting:
(i) Surface runoff harvesting: In urban areas, rain water that flows away from the surface can be collected and used for various purposes.
(ii) Rooftop rainwater harvesting: The rainwater on the roofs of the buildings is collected through canals that drains the water into ground water reservoirs. This stored water can later be utilised 

Question. What is ozone? How and where is it formed in the atmosphere? Explain how it affects an ecosystem.
                                    OR
What is ozone and how does it affect any ecosystem?
Answer : Ozone is a molecule containing three atoms of oxygen (O3). It is a highly poisonous gas present in the
upper layers of the atmosphere.
Formation of ozone: The UV radiations from Sun split some molecules of oxygen (O2) apart into free
oxygen atoms (O + O). These atoms then combine with oxygen molecules to form ozone.

Ozone layer shields the surface of the earth against damaging UV radiations of the Sun.

Question. You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment Day’.
(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.
Answer : (a) Ozone layer is a rich zone of ozone found in upper atmosphere. It helps in shielding the Earth from the harmful UV radiations coming from the Sun. If ozone layer gets depleted, UV radiations can directly reach the Earth’s surface and drastically affect the life on Earth. For instance, UV radiations coming from the Sun causes skin cancer. So, it is very important to protect the ozone layer so as to save our environment and the planet Earth.
(b) Some of the ways to help protect and stop the depletion of the ozone layer include: Not buying products in aerosol cans, maintaining air-conditioning filters and units.
In order to halt the depletion of the ozone layer, countries around the world have banned the use of chlorofluorocarbons and other ozone-depleting substances. These compounds produce chlorine and bromine atoms high in the atmosphere, and these atoms react with ozone, destroying it.
By reducing the use of fluorescent lights.
By minimising the use of vehicles to limit the emission of harmful gases that cause damage to the ozone layer, we can contribute to its protection.