Please refer to below Exam Question for Class 10 Science Chapter 15 Our Environment These questions and answers have been prepared by expert Class 10 Science teachers based on the latest NCERT Book for Class 10 Science and examination guidelines issued by CBSE, NCERT, and KVS. We have provided Class 10 Science exam questions for all chapters in your textbooks. You will be able to easily learn problems and solutions which are expected to come in the upcoming class tests and exams for standard 10th.

Chapter 15 Our Environment Class 10 Science Exam Question

All questions and answers provided below for Exam Question Class 10 Science Chapter 15 Our Environment are very important and should be revised daily.

Exam Question Class 10 Science Chapter 15 Our Environment

Very  Short Answer Type Questions

Question: What is meant by ‘biological magnification’?
Answer: Biological Magnification is the process by which the harmful and toxic substances enter the food chain and get concentrated in the body of living organisms at each successive level in food chain.

Question: In a food chain of frog, grass, insect and snake, assign trophic level to frog. 
Answer: Grass → Insect → Frog → Snake
Frog is a secondary consumer and belongs to 3rd trophic level.

Question: Give one protective function of forests. 
Answer: Forests help to reduce air pollution.

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 X 1/10 = 100 J.

Question: Draw a food chain which operates in forest ecosystem. 
Answer: Grass → Deer → Tiger.

Question: List two man-made ecosystem. 
Answer: Aquarium, crop land, park. 

Question: “Save the Tiger” campaign is being over emphasised these days by our government. What may be possible reason?
Answer: It helps to maintain ecological balance in nature and also to preserve gene pool of a particular species.

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

Question: In the following food chain, 20,000 J of energy was available to the plants. How much energy will be available to man in this chain? Plants → Sheep → Man
Answer: Plants have 20,000 J of energy available to them. Sheep will get 10% of 20000 J
20000 X 10/100 = 2000 J
2000 × 10/100 = 200 J

Question: Which will get more energy, secondary consumers or tertiary consumers? 
Answer: Secondary consumers will get more energy.

Question: List two natural ecosystems. 
Answer: (i) Oceans, (ii) forests are two natural ecosystems.

Question: Give 2 examples of each:
(A) Organisms occupying the first trophic level
(B) Abiotic factors of an ecosystem
Answer: (A) Organisms occupying the first trophic level:
trees, shrubs, grass.

Question: List two main components of an ecosystem.
Answer: Two main components of an ecosystem are
(1) Biotic Component
(2) Abiotic component

Question: Name two natural ecosystems.
Answer: Examples of natural ecosystems are rivers, forests, ponds, lakes and oceans.

Question: What is an ecosystem?
Answer: An ecosystem is a self-sustained unit which comprises of all the interacting living things together with their non-living environment.

Question: Name any two man-made ecosystems.
Answer: Examples of man-made ecosystems are aquarium, crop-fields, zoo, botanical garden,Greenhouse.

Question: Name the organisms belonging to the second and fourth trophic levels in the food chain comprising the following:
Frogs, Plants, Snakes, Hawks, Insects
Answer: Plants → Insects → Frogs → Snakes → Hawks 
The organism belonging to the second and fourth trophic levels are insects and snakes respectively.

Question: Why do producers always occupy the first trophic level on every food chain?
Answer: Producers always occupy the first trophic level on every food chain because only producers (green plants) have the ability to trap solar energy with the help of chlorophyll (Processknown as photosynthesis).

Question: What will be the amount of energy available to the organisms of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules?
Answer: 1000 j

Question: Why are some substances biodegradable and some non-biodegradable?
Answer: Substances which can be decomposed and broken down to simpler substances by micro-organisms acting on it is called bio-degradable and those substances which cannot be acted upon by micro-organisms and are not broken down into simpler substances are called non-biodegradable substances.

Question: Give any two ways in which non-biodegradable substances would affect the environment.
Answer: (i) The non-biodegradable substances get accumulated and doesn’t get decomposed hence it remains in the ecosystem and causes pollution, chokes the system of many animals and kill them.
(ii) These substances due to accumulation cause water and soil pollution e.g., pesticides, detergents, polythene.

Question: What is the role of decomposers in the ecosystem?
Answer: Decomposers breakdown the complex organic substances like plant’s and animal’s dead body and convert them into simpler inorganic substances.
All the elements that are present in the body on which decomposers act is released back to the nature. Decomposers maintain balance in the nature and plays an important role in the environment.

Question: How can you help in reducing the problem of waste disposal? Give any two methods.
Answer: To reduce the problem of waste disposal we can
(i) Segregate the bio-degradable waste from non-biodegradable waste before dumping it.
(ii) Remove all materials which can be recycled and send it for recycling. e.g., paper, glass, metal, rubber.

  Short Answer Type Questions

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: 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: 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: (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: (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 1/2 shown in diagram.
(ii) According to the 10% law, the amount of energy available will not be sufficient for the survival of the organisms in 1/2 + 1/2 + 1/2 the 5th trophic level.
(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: 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: 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 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: 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: 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: (A) Create a food chain of the following organisms:
Insect, Hawk, Grass, Snake, Frog
(B) Name the organism at the third trophic level of the created food chain.
(C) Which organism of this food chain will have the highest concentration of non- biodegradable chemicals?
(D) Name the phenomenon associated with it.
(E) If 10,000 joules of energy is available to frogs, how much energy will be available to snakes in this food chain.
Answer: (A) Food chain
Grass → Insect → Frog → Snake → Hawk
(B) The organism at the third trophic level of the created food chain is frog.
(C) The organism which will have the highest concentration of non-biodegradable chemicals is Hawk.
(D) The phenomenon associated with it is Biological Magnification.
(E) If 10,000 joules of energy is available to frogs, 1000 joules of energy will be available to snakes in this food chain as per 10% law of energy.
Explanation: The sequence of living organisms in a community in which one organism consumes another organism to transfer food energy is called a food chain.
(1) The starting point of a food chain is a category of organisms called producers, so all food chains begin with producers. In the above food chain grass is producers.
(2) Grass is eaten by insects; the insects are eaten by frog; the frog is eaten by snake and the snake is eaten by hawk. This is a five step food chain.
(3) This food chain has five trophic levels.

(4) The concentration of non-biodegradable chemicals get accumulated at each trophic level. Since hawk occupies the top level in this food chain, so the maximum amount of non-biodegradable chemicals is present in hawk.
(5) The increase in concentration of harmful chemicals in the body of living organisms at each trophic level of a food chain is called biological magnification.
(6) According to 10% law, only 10 percent of energy entering a particular trophic level
of organisms is available for transfer to next higher trophic level. It means the energy
available at each successive trophic level is 10% of previous level. Frogs have 10,000 j of energy, the next level is snakes, so only 10% of 10,000 j of energy is available i.e.1000 j to the snakes.

Question: Why is improper disposal of waste a curse to environment? 
Answer: Disposal of waste means getting rid of waste.
Improper disposal of waste can cause significant harm to human health, safety and can develop causing serious environmental problems.
(1) The accumulation of biodegradable wastes causes an obnoxious smell, which is created during the process of decomposition.
(2) There can also be a possibility of sparking an epidemic if the waste is dumped near a residential area or is allowed to contaminate the water bodies. People living in areas near old and abandoned waste disposal sites are in a particularly vulnerable position.
(3) Improper waste storage or disposal frequently contaminates surface and groundwater supplies.
In case of non- biodegradable substances, for example, chemical fertilizers, the nutrients in the soil are destroyed which thus affects health and reduces the longevity of the people who consume the food cooked with the produce grown in such a soil.
(4) Improper disposal of plastics prevents the seepage of rainwater underground and lead to water scarcity.

Question: What are the advantages of cloth bags over plastic bags during shopping?
Answer: Advantages of cloth bags over plastic bags during shopping are as follows:
(1) Cloth bags are more durable and thus can be used again and again.
(2) They are strong and thus capable of carrying more things.
(3) They are biodegradable in nature.

Question: (A) What is an ecosystem?
(B) List any two natural ecosystems.
(C) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly.
Why? 
Answer: (A) Ecosystem: It is a structural and functional unit of the biosphere which comprises living organisms and their non-living environment that interact by means of food chains and chemical cycles in energy flow, biotic diversity and material cycling and form a stable self supporting system.
(B)

Common examples of natural ecosystem
are pond, lake, meadow, desert, forest etc.
(C) We do not clean ponds or lakes because it is a natural ecosystem and is a self-sustaining unit. Aquatic plants act as producers, small aquatic insects (mosquito larvae, beatles etc.) are herbivores and these herbivores are eaten by carnivores (fish). There are microorganisms (bacteria and fungi) present in the soil of the pond which decompose the dead remains and waste products into simpler inorganic substances and clean the pond.
But an aquarium is an artificial ecosystem.
The transfer of energy takes place from producers to herbivores to carnivores but there is no soil in the pond so microorganisms (decomposers) are not present in the aquarium which act as cleaners. So we have to clean the aquarium regularly. 

Question: What is meant by tropic level in a food chain?
Construct a terrestrial food chain with four trophic levels. The energy flow in a food chain is always unidirectional. Why? 
Answer: Trophic level = Each step or level of the food chain forms a trophic level.
Terrestrial food chain
Grass →         Grasshopper             Frog →         Snake
Producer         Herbivore               Primary       Secondary       
(Autotrophs)  (Primary consumer)  carnivore      carnivore
Flow of energy in an ecosystem is unidirectional Each organism needs energy to carry on vital activities and for building up and repairing the body tissues.
(1) The ultimate source of energy used by living organisms is the sun.
(2) Only 1% of solar radiations are captured by green plants in a terrestrial ecosystem and converted into food energy by photo synthesis. This energy is stored as chemical energy of food.
(3) When green plants (producers) are eaten by primary consumers (Herbivores) a lot of heat is lost as heat to the environment and other activities. Only 10% of the food eaten is turned into its new body and is available for the next level of consumers (Primary carnivores).
(4) Only 10% amount of organic matter reaches the next level of consumers (secondary carnivores).
(5) Since, amount of available energy goes on decreasing at each trophic level, food chains usually consists of only 3 to 4 trophic levels.
For example grass receives 6000 j of energy from the sun. It will pass 10% of energy as per 10% law to grasshopper i.e. 600 j and so on.

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) A terrestrial food chain comprising of fourt trophic levels:
Grass → Grasshopper → Frog → Snake
(B) If we kill all the organisms in one trophic level the transfer of food energy to next level will stop.
Organisms of previous trophic level will also increase.
For example: If all herbivores in an ecosystem are killed:
There will be no food available for the carnivores of that area.
Consequently they will also die or will shift to other areas.
Populations of producers will also increase in absence of herbivores causing imbalance in the ecosystem.
(C) Consider the same food chain as we have made in 19 (a):
Grass → Grass hopper → Frog → Snake
In this food chain, second trophic level is grass hopper and the energy available at this trophic level is 2000 j .
According to 10% law, 10% of energy will be available to frog (Third trophic level) which is 200 j.
The energy available to the snakes will be available as 10% of 200 j. Thus, the energy available to the snake is 20 j.
Explanation: 10% law states that during transfer of energy from one trophic level to the next trophic level, only about 10% energy is available to the higher trophic level. 
To summarise:
Grass → Grass hopper ^{10 %} → Frog  ^10% →
                                                   Snakes

First Trophic         Second trophic    Third Trophic    Fourth Trophic
   level                    level                  level                 level
                              2000j                200j                   20j

Question: Complete the following flow chart based on ecosystem and its components.

Answer:(iv) Living components such as plants, animals

Ecosystem: It is a structural and functional unit of the biosphere which comprises living and non-living components that interact by means of food chains and chemical cycles resulting in energy flow, biotic diversity and material cycling to form a stable and self supporting system.

Question: (A) Complete the following table:

(B) How is ozone formed at the higher levels of atmosphere?
Answer: (A) O2
(B) O3
(C) Benefits of Oxygen to biotic component. Breathing: All biotic components inhale oxygen from the atmosphere and exhale CO₂.

Question: Why are crop fields known as artificial ecosystems? 
Answer: An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. Artificial ecosystems are those ecosystems which have been modified by human beings for their own benefit. Crop fields are man made and some biotic and abiotic components are manipulated by humans.
(1) In a crop field, plants do not grow naturally.
They are mostly grown by humans, hence, they are considered as artificial ecosystems.
(2) It usually consists of a major crop (monoculture).
(3) Unwanted plants are removed using weedicides.
(4) Pests and unwanted insects are killed using pesticides and insecticides.
(5) Artificial fertilisers, manures and nutrients are externally supplied to the soil by man.
These activities of man alter the biotic and abiotic components of the ecosystem. Therefore,
crop fields are known as artificial ecosystems.

Question: What are decomposers? State the role of decomposers in the environment.
Answer: The decomposers are the various organisms in the ecosystem which help in decomposing the dead bodies of plants and animals by breaking down the complex organic substances into simpler inorganic substances.
Role of decomposers in the environment:
(1) They decompose the wastes of organisms, dead plants and animals in the absence of which these would pile up leading to foul gases, diseases and deaths.
(2) They help in recycling of nutrients and thus maintain fertility of the soil.
(3) They play a major role in various biogeochemical cycles which are natural ways of nutrient cycling.

Question: mention three harmful effects of using polythene bags on the environment. Suggest an effective alternative to these bags.
Answer: Harmful effects of using polythene bags on the environment are listed below:
(1) Plastic causes land pollution and water pollution as it is a non-biodegradable substance.
(2) Burning of plastic releases toxic gases and causes air pollution.
(3) Plastic bags cause harm to the life of animals when they consume it along with food.
(4) Plastic bags can cause blocking in sewage line.
(5) The surfaces of tiny fragments of plastic may carry disease-causing organisms and act as a vector for diseases in the environment.
An effective alternative to these bags is the use of jute bags, paper bags or other bags made of cloth.

Question: List four problems caused by non-biode- gradable wastes. 
Answer: Lot of Problems are caused by non- biodegrad- able wastes. Four Problems are as follow:
(1) Soil Pollution
(2) Water Pollution
(3) Ecological imbalance
(4) Biomagnification

Question: (1) Create a terrestrial food chain depicting four trophic levels.
(2) Why do we not find food chains of more than four trophic levels in nature?
Answer: A food chain showing I tropic level (1/2 mark),
II tropic level (1/2 mark), III tropic level (1/2 mark)
and IV tropic level (1/2 mark).
A flow chart or a diagrammtic representation showing all the four tropic levels would also be accepted According to the 10% law, the amount of energy available will not be suffcientforthe survival of the organism in the 5th trophic level.

Question: What is ozone? Name the chemicals that damage the ozone layer.
Answer: Ozone is a molecule formed by three atoms of oxygen.
Synthetic chemicals such as chlorofluoro- carbons (CFC) and aerosols are the chemicals that damage the ozone layer in the atmosphere.

Question: How will you create an artificial aquatic eco-system, which is self-sustainable?
Answer: • 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.

Question: Answer the following questions:
(A) To discard the household waste, we should have two separate dustbins, one for the biodegradable waste and the other for non-biodegradable waste. Justify the
given statement and suggest the proper ways of disposal of such wastes.
(B) Classify the given waste into biodegradable and non-biodegradable waste used tea
leaves, leather bag, plastic bag, jute bag.
Answer: (A) First identify the waste as bioderadable and non-bioderable waste and use two different dustbins according to being biodegrable or not we can take blue for non-biodegradable and green for biodegradable. Biodegradable waste can be composted, turned into manure and decompose by micro organisms easily.
Non-biodegradable waste should be collected and disposed off at right place so that it can be recycled.
(B)

Question: What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: Biological magnification: The increase in concentration of harmful chemical substances like pesticides in the body of living organisms at each trophic level of a food chain is called Biological magnification.
Several pesticides and harmful chemicals enter our body through food chain and remain there without being decomposed. The accumulation of these harmful chemicals increases towards the higher side of the food chain that is the level or concentration of the harmful chemicals increases with increasing trophic level. So, it is different at different levels of the ecosystem.
Explanation: There are different ways in which poisnous chemicals enter different food chaine at producer level.
For example:
DDT in water → DDT in phytopauktone and zooplanktons → DDT in eagret
→ DDT in fish 0.02 ppm
5 ppm 1600 ppm 240 ppm
Biological magnification in food chain
If water bodies were found to contain 0.02 pm (parts per million) of DDT (use of DDT is now banned). The phytoplanktone and zooplanktone which consume this water were found to contain 5 ppm concenration of DDT in their body. Fish feeding on such plank tone had 240 ppm DDT in there body tissue. The level of DDT concentration reacted to 1600 ppm in birds feeding on there fish.
Humans which perhaps occupy the highest point in the food chain will face highest accumulation.

Question: Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer: Ozone prevents the passage of harmful ultraviolet radiations through the atmosphere to the earth. The damage to the ozone layer is a cause of concern since in the absence of the ozone layer harmful ultraviolet radiation will reach the earth and harm organisms on the earth.
Depletion of ozone layer has been linked to chloro-floro-carbons or CFCs which are used as refrigerants. To prevent depletion of the ozone layer, use of CFCs is being restricted and replaced by more eco-friendly refrigerants
under a UNEP (United Nations Environment Programme) initiative agreed upon in 1986.

Question: List two main causes of the pollution of water of the river Ganga. State how pollution and contamination of river water prove harmful for the health of the people of neighbouring areas.
Answer: Causes:
• Disposal of industrial effluents
• Human activities like bathing, washing,
immersion of ashes, etc.
• Disposal of untreated sewage
Harmful effects on health:
• Spreads water borne diseases,
• Consumptions of contaminated fishes
(or any other relevant affect)

Question: Define Ecosystem. Briefly describe the two types of ecosystem.
Answer: Ecosystem: An Ecosystem is a self contained unit of living things (plants, animals and decomposers) and their non-living environment (soil, air and water). It needs only the input of sunlight energy for its functioning.
Types of Ecosystem: There are two types of ecosystem:
Natural ecosystem: These ecosystems operate in the nature by themselves without any human interference. They can be terrestrial or aquatic.
The common examples of terrestrial ecosystem are forest, grassland and desert. The common examples of aquatic ecosystem are ponds, lakes, rivers, sea.
man-made or artificial ecosystem: These are maintained by man and hence are called Man- made ecosystems or artificial ecosystem. Man maintains the natural balance by the addition of energy and planned manipulations. Example:
crop field, aquarium, garden.

Long Answer Type Questions

Question: (A) Natural water bodies are not regularly cleaned whereas an aquarium needs regular cleaning. Why?
(B) What are decomposers? What will be the consequence if the decomposers
are completely eradicated from an ecosystem? Give justification in support of your answer.
Answer: (A) Natural water bodies are natural ecosystems in which the diversity of organisms is balanced and the wastes produced are naturally eliminated from water as they are decomposed by the ecomposers present.
Whereas an aquarium is a man made ecosystem in which selective organisms have been kept and maintained in a restricted and artificial environment. As there are no decomposers, the uneaten food and wastes produced by the fishes keeps accumulating and hence requires regular cleaning.
(B) The decomposers are the various organisms in the ecosystem which help in decomposing the dead bodies of plants and animals by breaking down the complex organic substances into simpler inorganic substances.
If decomposers are completely eradicated from our ecosystem:
(1) The ecological balance would be disturbed.
(2) Wastes of organisms and dead plants and animals would pile up leading to foul gases,diseases and deaths.
(3) The soil would lose its fertility as there will be no recycling of nutrients.
(4) The bio geo chemical cycles which are natural ways of nutrient cycling would be affected leading to insuffcientnutrients.

Question: Suggest any four activities in daily life which are eco-friendly. 
Answer: Four activities in daily life which are eco-friendly:
(1) Separation of biodegradable and non- biodegradable substances.
(2) Gardening
(3) Use of gunny bags/paper bags in place of polythene/plastic bags.
(4) Use of compost and vermicompost in place of fertilizers.
(5) Harvesting rain water.
(6) Using public transport, cycling or walking to travel.
(7) Switch off fans and lights when not in use.
(8) Use of compost and vermicompost in place of fertilizers.

Question: What are the by-products of fertilizer industries? How do they affect theenvironment?  
Answer: The harmful by-products are gases such as SO₂ and NO. They cause extensive air pollution and are responsible for acid rain.
The harmful by-products of the fertilizer industries are:
(1) Gases – SO₂, NO, CO, CO₂, and H₂S.
(2) Solids – Pyrite ashes, calcium carbonate, sand and plastic bag.
Effect on environment: The majority of the gaseous by-products like carbon dioxide, and methane are green house gases which contribute to global warming. The rest of the gases like sulphur dioxide and nitrous oxide are air pollutants and lead to acid rain. These gaseous by-products cause breathing and respiratory problems.
The solid waste and waste water discharges into the water body. When these wastes are discharged into the water body, they increase the nutrient content of the water and cause algal bloom (increase in the number of algae).
Due to algal bloom, algae form a layer on the surface of the water and hence, the oxygen does not reach the water body. Thus affecting the aquatic life.
Also, these wastes are non-biodegradable, so they get accumulated at each trophic level by entering the food chain at the producer level and in the process of the transfer of food through food chains, these harmful chemicals such as pesticides , industrial effluents, heavy metals and radioactive substances get concentrated at each trophic level. This is called bio- magnification.

Question: How can we help in reducing the problem of waste disposal? Suggest any three methods.
Answer: Methods to reduce the problem of waste disposal:
(1) Segregation of waste should be done by separating biodegradable waste substances from non-biodegradable substances.
(2) By recycling solid wastes like paper, plastic and metals etc, i.e., they are reprocessed or melted and remoulded to make new articles.
(3) By composting biodegradable domestic wastes such as fruit and vegetable peels, leaves of potted plants can be converted into compost and used as a manure.
(4) By reducing and reusing of Non Biodegradable substances.
(5) By minimizing the use of disposable items which are non-biodegradable.

Question: How is ozone formed in the upper atmosphere?
State its importance.
What is responsible for its depletion? Write one harmful effect of ozone depletion.
Answer: Ozone is produced by the action of UV radiations on oxygen molecule.
First, the energy of UV radiations splits some molecular oxygen, O₂, into free oxygen, O.
O2 ^uv→ O + O
The free oxygen O combines with molecular oxygen O₂ to form Ozone, O₃.
O + O₂ → O3
Importance of ozone: Ozone shields the earth’s surface from the harmful ultraviolet (UV) radiations from sun.
Synthetic chemicals such as Chlorofluorocarbons (CFC) and aerosols are mainly responsible for depletion of ozone in the atmosphere.
Harmful effect of ozone depletion:
(1) Ozone layer depletion causes increased UV radiation levels at the Earth’s surface, which is damaging to human health as it causes certain types of skin cancers, eye cataracts and immune deficiency disorders.
(2) UV radiation also affects terrestrial and aquatic ecosystems, altering growth, food chains and biochemical cycles.
(3) UV rays also affect plant growth, reducing agricultural productivity.

Question: Explain some harmful effects of agricultural practices on the environment.
Answer: Harmful effects of agricultural practices on the environment:
(1) Fertilizer added to soil not only changes the chemistry of the soil but also kills many useful microbes.
(2) Pesticides sprayed over crops reach water bodies and persistent pesticides undergo bio-magnification proving harmful to higher organisms.
(3) Extensive cropping on a particular piece of land causes the loss of soil fertility.
(4) Continuous use of ground water in agriculture has resulted in lowering of water table at most of the places
(5) Natural ecosystems and habitats have been damaged because of clearing of land for agriculture.
(6) Excessive cutting down of trees for agricultural purposes causes deforestation and can lead to soil erosion.
(7) Synthetic fertilizers and pesticides used in the field during rainfall are washed away to rivers and other bodies, which cause water pollution.

Question: Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem 
Answer: Ecosystem: An ecosystem is a self-sustained unit which comprises of all the interacting living things together with their non-living environment.
Flow of energy in an eco system:
Energy flows through an ecosystem in only one direction. Energy is passed from organisms at one trophic level or energy level to organisms in the next trophic level.

Question: Monika was observing a lizard on the wall which chased an insect and ate it. She felt that the lizard was cruel and ugly. Suddenly, the lizard fell and was eaten by a cat. She started  thinking, how are organisms connected to each other for their food?
What is a food chain? Will the world be a better place without lizards?
make a food chain of five organisms.
To which trophic level does the lizard belong? 
Answer: A lizard eats an insect. When the lizard falls, it is eaten by a cat. Hence, the lizard depends on the insect for food, while the cat depends on the lizard for food. This interdependence of organisms on one another for their food is called food chain. It is very important to have a food chain in the ecosystem for maintaining the balance of nature. Hence, even though the lizard is an ugly creature, it is important for maintaining the balance of nature.
The food chain of five organisms is as follows:
Sun → Plants → Insect → Lizard → Cat
We can see that the lizard belongs to the fourth tropic level.

Question: Give reason to justify the following:
(A) The flow of energy in every food web is unidirectional.
(B) The decomposers play an important role in an ecosystem.
Answer: (A) The energy in every food web is unidirectional which means that the solar energy utilized by the autotrophs does not revert back to the Sun. The energy moves progressively through various trophic levels and this energy is no longer available to the previous trophic level.
Moreover, the energy available at each trophic level gets diminished due to loss of energy at each level and follows the 10 percent law.
(B) Role of decomposers in the ecosystem:
(1) They play a critical role in the flow of energy through an ecosystem.
(2) They decompose the wastes of organisms, dead plants and animals in the absence of which these would pile up leading to foul gases, diseases and deaths.
(3) They help in recycling of nutrients and thus maintain fertility of the soil.
(4) They play a major role in various biogeochemical cycles which are natural ways of nutrient cycling.

Question: Mr. Kumar, the incharge of ‘‘Eco-Club’’ of a school felt the need of organising an
‘‘Awareness Campaign’’ for the residents of the nearby areas to make them realise the
necessity of segregating the biodegradable and non-biodegradable wastes. He went
from door-to-door with his students and gave arguments to explain the people about
the importance of disposal of their household waste judiciously. He also informed them about the prosecutional provisions in the cases where garbage is thrown at places other than the specified bins.
List two advantages of disposing the waste after segregating it in two categories.
Answer: The two advantages of disposing the waste after segregating it in two categories:
(1) The biodegradable wastes kept in a separate bin can be dumped directly in a pit for composting or for dumping in landfills.
(2) The useful part of non-biodegradable wastes kept in a different bin can be separated for recycling or reusing them.
(3) Non-useful part of wastes can be disposed off in such a way that it does not harm the people or pollute the environment in anyway.
(4) Segregated waste is cheaper to dispose of because it does not require as much manual or mechanical sorting as mixed waste.

Question: Your mother always thought that fruit juices are very healthy for everyone. One day she ead in the newspaper that some brands of fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to our health.
(A) How would you explain to your mother about fruit juices getting contaminated with pesticides?
(B) It is said that when these harmful pesticides enter our body as well as in
the bodies of other organisms they get accumulated and beyond a limit cause
harm and damage to our orgAnswer: Name the phenomenon and write about it.
Answer: (A) Pesticides and other chemicals are sprayed on crops to protect them from diseases
and pests. These chemicals are non- biodegradable and can stick to the surfaces
of fruits and vegetables. If these fruits are not washed or disinfected thoroughly before use, they will contaminate the fruit juice.
(B) The phenomenon is Biological Magnification, which refers to the process where toxic substances move up the food chain and become more concentrated at each trophic level. The pesticides and chemicals or industrial effluents are washed down into the soil or water bodies from where they are absorbed by the plants, aquatic plants or animals.
This is how they enter our food chain and being non-biodegradable, their concentration increases at each trophic level. As human beings are at the top of the trophic level in any food chain, aximum concentration of these harmful chemicals get accumulated in our bodies.

Question: While teaching the chapter “Our Environment” the teacher stressed upon the harmful effects of burning of fossil fuels, plastic, paper etc.
The students noticed the extensive use of plastic and polythene in daily life, which can
be avoided and the surroundings can be kept clean. They decided to make their school “plastic and polythene” free and motivated each other for its minimum use.
(A) Why should the use of polythene and plastic be reduced in daily life?
(B) In what ways the students would have avoided the use of plastic and polythene in their school? 
Answer: (A) The use of polythene and plastic should be reduced in daily life because of the following reasons:
(1) They cause land pollution and water pollution as they are non-biodegradable substances.
(2) Burning of plastic and polythene releases toxic gases and causes air pollution.
(3) Plastic and polythene bags cause harm to the life of animals when they consume it along with food.
(4) Plastic and polythene bags can cause blocking in sewage line.
(5) The surfaces of tiny fragments of plastic and polythene may carry disease- causing organisms and act as a vector for diseases in the environment.
(B) Students would have avoided use of plastic and polythene in following ways:
(1) By carrying tiffnandwaterinsteel containers thereby avoiding the use of plastic.
(2) By carrying their items in cloth bags, jute bags or paper bags instead of using polythene bags.
(3) By boycotting all such items such as plastic plates and spoons, juices served
in plastic cans and stationery items etc made of plastic or polythene which are sold in school canteen.

Question: (A) A food chain generally has three or four trophic levels. Explain.
(B) What is biological magnification? Explain.
Answer: (A) Energy keeps decreasing at every trophic level.
Because the loss of energy at each trophic level is so great that very little usable
energy remains after 3-4 trophic levels.
(B) Pesticides/harmful chemicals from the soil/water bodies are absorbed by the plants along with water and minerals.
As these harmful chemicals are non- biodegradable, They get accumulated/magnified at each trophic level in a food chain.

Question: Differentiate between biodegradable and non-biodegradable substances with the
elp of one example each. List two changes in habit that people must adopt to dispose non-biodegradable waste, for saving the environment.
Answer: Biodegradable substances: can be broken down into simpler substances by nature /decomposers / bacteria / saprophytes / saprobionts.
Ex.- Human Excreta/Vegetable peels, etc.
Non-biodegradable substances : can’t be broken down into simpler substances by nature / ecomposers.
Ex.- Plastic/ glass (or any other) (any one)
Habits:
• Use of separate dustbins for biodegradable and non biodegradable waste,
• Reuse of things such as poly-bags, etc.,
• Recycle of waste
• Use of cotton /jute bags for carrying
vegetables etc. (any two)

Question: Give reason to justify the following:
(A) The existence of decomposers is essential in a biosphere.
(B) Flow of energy in a food chain is unidirectional. 
Answer: (A) The existance of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substances that can be absorbed by the plants. Thus, decomposers help in the recycling of the minerals, and also helps in removing the biodegradable waste.
(B) The flow of energy is unidirectional. The energy captured by the autotrophs does not return to the solar input and the energy which passes to the herbivores does not come back to autotrophs. Only 10% of the energy is passed on to the next level.
As it moves progressively through the previous level. Hence, the energy flow is unidirectional. For Example: