Our Environment Notes And Questions | Chapter 15 Class 10

Our Environment Notes And Questions

Below are some of the very important NCERT Class 10 Science chapter 15 our environment notes and questions. These Class 10 our environment notes and questions have been prepared by expert teachers and subject experts based on the latest syllabus and pattern of term 2. Questions with Answers to help students understand the concept.

These Questions for Class 10 Science our environment notes and questions are very important for the latest CBSE term 2 pattern. These class 10 notes and Q and A are very important for students who want to score high in CBSE Board.

We have put together these NCERT  Questions of Class 10 Science chapter 15 our environment notes and questions for practice on a regular basis to score high in exams. Refer to these Questions with Answers here along with a detailed explanation.

All those things and set of conditions that influence the life of an organism like their growth, survival, development and reproduction, constitute the environment.

It is composed of physical surroundings (e.g. air, water), living beings (e.g. plants, animals) and climatic conditions (e.g. rainfall, temperature) of the region.

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Ecosystem

It is the structural and functional unit of the biosphere. It is a stable ecological unit where regular input of energy and circulation of matter takes place. The term ecosystem was coined by AG Tansley (in 1935).

All the interacting or living organisms (biotic components) in an area together with the non-living constituents (abiotic components) of the environment form an ecosystem, e.g. a lake, a field or a forest.  

Types of Ecosystem

There are two types of ecosystem, i.e. natural and artificial ecosystem,

1. Natural Ecosystem

The naturally existing ecosystem without any human support is called a natural ecosystem. Depending upon the habitats, natural ecosystems may be terrestrial (desert, grassland and forest) and aquatic (ponds, lakes, estuaries and marine).

2. Artificial Ecosystem

An ecosystem which is created and maintained by humans is called an artificial or man-made ecosystem. It relies on human efforts to sustain. It does not possess a self-regulating mechanism.

e.g. Aquariums, botanical gardens, field crops, etc. Agro-ecosystem is the largest man-made ecosystem.

Components of Ecosystem 

The ecosystem encompasses both living (biotic) and non-living (abiotic) components of the earth.

1.Biotic Components

These include all the living organisms present in the ecosystem, i.e. plants, animals and microorganisms.

On the basis of food, the different living organisms can be categorized into three groups. These are as follows

(i) Producers. All green plants and certain blue-green algae which can produce food by the process of photosynthesis are producers. These are also called autotrophs. These are the source of nutrition for the rest Of ecosystem.

(ii) Consumers. These are dependent on producers for their nutritional requirement and consume food prepared by producers. These are also called heterotrophs.

Consumers can be further divided into the following three categories:

Herbivores. These are primary consumers which feed directly on the producers, i.e. plants. e.g. Grazing animals.

Carnivores. The carnivores which feed on herbivores are called secondary consumers.

Some are predators which attack and kill their prey and feed on their bodies. Some are scavengers that feed on dead animals that they find. These are called tertiary consumers.

Omnivores. These are animals that feed on both plants and animals, e.g. humans and bears.

(iii) Decomposers. These are microorganisms which feed on decaying and dead organic matter. They break down the remains of dead animals and plants, to release simpler inorganic materials, making nutrients available to producers. 

e.g. Bacteria and fungi.

2. Abiotic Components 

The abiotic components of an ecosystem are the non-living components on which living organisms depends. These components are light, temperature, water, atmospheric gases, wind, etc. 

Food Chain

It is a linear network of living organisms in a community through which energy is transferred in the form of food.

It describes the relationship between organisms about ‘who eats whom’.

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On the basis of choice of habitat, food    chains are of two  

(i) Terrestrial food chain. It is the (bod chain present ou land,

e.g. Grass — Insects — Snake — Hawk.

(ii) Aquatic food chain. It is the chain present in different water bodies.

e.g. Phytoplankton — Zooplankton — Fish — Shark

Trophic Levels

The transfer of food or energy takes place through various steps or levels in the food chain known as trophic levels. 

The producers (autotrophs) are present at the first trophic level. They fix solar energy, making it available for consumers (heterotrophs). The herbivores or 9the primary consumers are found at the second trophic level.

Small carnivores or secondary consumers are present at the third trophic level. The large or the tertiary consumers form the fourth trophic level.

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Energy Flow

  • The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight (light energy). They convert  it into food (chemical energy).
  • When green plants are eaten by primary consumers, a great deal of energy is lost as heat and an average of 10%  of the energy of food eaten by an organism is turned back into its own body and made available for the next level of consumers. This is known as the 10% law (Lindemann in 1942).

Therefore, 10% can be taken as the average value for the  amount of organic matter that is present at each step and reaches to the next trophic level.

  • The loss of energy at each step is very large. Only a little energy is available for the next level of consumers, food chains generally consist of three or four steps.
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  • The flow of energy is unidirectional, i.e. the energy which passes to the next trophic level, does not come back to the lower trophic level.

Food Web

It is the interconnection of different food chains, which correlate at various trophic levels operating in an ecosystem, Each organism is generally eaten by two or more other kinds of organisms. They in turn are eaten by several other organisms.

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Environmental Problems

Human are an integral part of the environment. Various human activities pollute the environment in various ways. Serious environmental problems such as biomagnification, ozone layer depletion, waste accumulation are as follows:

Biological Magnification or Biomagnification

It is the phenomenon of progressive increase in the concentration of non-biodegradable toxicants in organisms at each successive trophic level. It is also called bioconcentration. These toxic chemicals enter the food chain through pesticides like DDT.

The maximum concentration of these chemicals gets accumulated in humans as they occupy the topmost place in any food chain.

Depletion of Ozone Layer

Ozone (O3 ) is a molecule formed by three atoms of oxygen. It is found in the stratosphere. It shields the surface of the Earth fli)m harmful ultraviolet (UV) radiations of the Sun.

Formation of Ozone Layer

Ozone is a product of UV radiations acting on oxygen (0 2 ) molecules. The high energy UV radiations split apart some tuoleeulav oxygen (0 2) into free oxygen (O) atoms. These are very reactive and combine with the molecular oxygen to form ozone.

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Ozone Depleting Substance

The increasing use of synthetic chemicals like Chlorofluorocarbons (CFCs) which are used in refrigerants as coolant and in fire extinguishers are responsible for ozone layer depletion.

In the atmosphere UV radiation break down CFCs molecules and release chlorine atom these atoms on reacting with Ozone, disassociate Ozone molecule into oxygen. 

Thus, it leads to depletion of Ozone layer

Managing the garbage we produce

The household waste is called garbage.  Every household produces a lot of garbage on a daily basis. Improvement in our Lifestyle have resulted in Greater amount of waste material generation. 

These way substances can be divided into two main groups:

(i) Biodegradable substances. The substances which can be disposed off naturally by the action of

micro organizations1 like bacteria, fungi, etc., arc called biodegradable substances.

e.g. Tea leaves, waste paper, left over food, etc.

(ii) Non-Biodegradable substances. The substances that cannot be converted into harmless simpler forms by the action of Microorganisms are called non-biodegradable substances. These are toxic, harmful, may be inert and accumulate in the environment or food chain.

e.g. Plastics, insecticides, heavy metals, etc.

Methods of Waste Disposal

Various methods of waste disposal are as given below

(i) Recycling. It is the processing of waste materials to form new products.

(ii) Composting. Biodegradable domestic wastes can be buried in a pit, dug into ground and are converted into compost and used as manure.

(iii) Incineration. It is the burning of a substance at high temperature to form ash. It is commonly used to dispose hospital waste.

(iv) Landfills. Solid waste is dumped into a low lying area and covered with soil.

(v) Sewage treatment. Organic ‘material in the sewage is allowed to settle down and decompose in large tanks. The water from these tanks is cleaned and is released into water bodies.

(vi) Biogas production. In some places, sewage is decomposed anaerobically to yield biogas and manure.

Note: Disposable paper cups which are biodegradable in nature are now being used in trains instead of plastic cups and kulhads.

As the production of kulhads at a large scale resulted in the loss of top fertile layer of soil which leads to soil erosion, whereas, plastic cups are non-biodegradable in nature, therefore cause environmental problems.

Frequently Asked Questions

Short Answer Type Questions

1. Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem.    (CBSE 2019)

2. (i) What do you understand about the term ecosystem?

(ii) Autotrophs are at the first level of the food chain. Give a reason.

(iii) In a food chain of frogs, grass, insects and snakes, assign trophic level to frogs. To which category of consumers do they belong to? (CBSE 2020) 

3. What is the role of decomposers in the ecosystem? (NCERT)

4. Natural water bodies are not regularly cleaned whereas an aquarium needs regular cleaning. hv? (CBSE 21)19)

5. How does studying the food chain in an area or habitat help us? Give an example of four steps of a food chain operating in a large lake.

6. Based on their feeding habits, differentiate between parasites and decomposers. 

7. What are trophic levels? Give an example of a food chain and state the different trophic levels in it, (NCERT)

8. Number of trophic levels is limited to 3-4 in a chain. Give a reason.

9. What will happen if we kill all the organisms in one trophic level?

10. State 10% law. Explain with an example how energy flows through different trophic levels.

11. Indicate the flow of energy in an ecosystem. Why is it unidirectional? (NCERT Exemplar) 

12. What do you mean by biological magnification?

13. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem? (NCERT Exemplar)

14. Write the major cause of ozone depletion. What steps should be taken to limit the damage to the ozone layer?

15. Explain how ozone being a deadly poison can still perform an essential function for our environment. (CBSE 2020)

16. Give a reason why a food chain cannot have more than four trophic levels? (CBSE 2020)

17. (i) Explain the role of UV radiation in producing ozone layer.

(ii) Mention the reaction involved.

(iii) Why is excessive use of CFCs a cause of concern?

18. How is ozone formed in the upper atmosphere? State its importance. What is responsible for its depletion? Write one harmful effect of ozone depletion. (CBSE 2019)

19. Give some Diethocls that could be applied to reduce accumulation of pesticides in our.

20. How can you help in reducing Ille prol)letn ol’ waste disposal? Give any two methods.

21. If all the waste we generate is biodegradable, will this have no impact on the environment?

22. Give any two ways ‘in which non-biodegradable substances would aflbet the environment.

23. Why should non-biodegradable wastes be discarded in two separate dustbins?

24. ‘Effective segregation of wastes at the point of generation is very important’. Justify this statement.

25. Sheenu went to a picnic where she saw a pond. Her teacher gives her an assignment to draw the pond ecosystem and show its different components. Help her to complete the assignment.

26. Name the wastes which are generated in your house daily. What measures would you take for their disposal?  (NCERT Exemplar)

27. A modern insecticide has been introduced with  certain new properties like accumulation in the bodies  of predators, broken down by soil bacteria, easily  washed into lakes and rivers and taken up by plant roots. Among all these properties, which one will help in reducing or keeping the level of environment pollution  to lowest?

28. Mona eats curd and yogurt and follows a vegetarian diet. For this food intake, what should be the trophic level occupied by her in a food chain ? 

Long Answer Type Questions

29. What are decomposers? What will be the consequence of their absence in an ecosystem?    (NCERT Exemplar)

30. (i) What are consumers? What will be the consequence of the absence of primary consumers in an ecosystem?

(ii) What will be the direction of energy transfer in each of the following cases?

  1. Grasshopper eaten by a frog
  2. Deer feeds on grass
  3. Deer eaten by a lion

31. (i) Will the impact of removing all the organisms in a trophic level be different for different trophic  levels ?

(ii) Can the organisms of any trophic level be removed  without causing any damage to the ecosystem? (NCERT Exemplar)

32. (i) ‘Energy flow in a food chain is unidirectional’. Justify this statement.

(ii) Explain how the pesticides enter a food chain and subsequently get into our body. (CBSE 2014)

33. (i) How do food chains get shortened? How does the shortening of food chain aflöct the biosphere?

(ii) How will you justify that vegetarian food habits give us more calories?  

34. Explain some harmful effects of agricultural pracåces on the environment. (NCERT Exemplar)

35. What is Ozone and how does it affect any ecosystem? (NCERT Exemplar) 

36. i) What is environmental pollution ?

(ii) Distinguish between biodegradable and non-biodegradable pollutants.

(iii) Choose the non-biodegradable pollutants from the list given below

Paper, DDT, Radioactive waste, Plastic, Insecticides.

37. Suggest any five activities in daily life, which are eco-friendly. (NCERT Exemplar)

38. What are the reasons for the shift from plastic to kulhads and then finally to paper cups? (CBSE 2020)

Case Based Questions

39. Read the following and answer the questions from (i) to (v) given below

Food web is the interconnection of different food chains, which correlate at various trophic levels operating in an ecosystem.

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(i) How many food chains are present in the  food web?

(ii) Name the primary consumer in the given food web.

(iii) How much percentage of energy is less at each trophic level?

(iv) If all the foxes are killed due to a disease, what will be your observations about food sveb?

(v) Name the organism in which accumulation of toxic Non Biodegradable substances is the lowest.

40. Read the following and answer the questions from (i) to (v) given below

Food chains are very important for the survival of most species. When only one element is removed from the food chain it can result in extinction of a species in some cases.

The foundation of the food chain consists of primary producers. Primary producers or autotrophs can use either solar energy or chemical energy to create complex organic compounds, whereas species at higher trophic levels cannot and so must consume producers or other life that itself consumes producers.

Because the Sun’s light is necessary for photosynthesis, most life could not exist if the Sun disappeared.

Even so, it has recently been discovered that there are some forms of life, chemotrophs that appear to gain all their metabolic energy from chemosynthesis driven by hydrothermal vents, thus showing that some life may not require solar energy to thrive.

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(i) If 10,000 J solar energy falls on green plants in a terrestrial ecosystem, what percentage of solar energy will be converted into food energy?

(ii) Why are decomposers not included in the food chain?

(iii) How are primary consumers different from primary carnivores?

(iv) State one reason that limits the number of trophic levels in a food chain.

(v) In the given food web, name the organism in which the highest accumulation of toxic substances is found.

41. Read the following and answer the questions from (i) to (v) given below

Each organism is generally eaten by two or more other lands of organisms. They in turn are eaten by several other organisms.

Study the figure which shows the similar relationship between various organisms of the ecosystem through a food web.

Analyze the populations and their effects on each other.

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(i) How many trophic levels are there in the longest food chain?

(ii) What is the role of rabbits in the given food web?

(iii) Give the significance of the food web.

(iv) Why do all food chains start with plants?

(v) What leads an organism to increase in number? 

42. Read the following and answer the questions from (i) to (v) given below

To study the ozone layer depletion, Mrs. Sharma, a science teacher, drew the given flow chart on the blackboard. She asked students to fill the bubbles labeled as 1-5 in the flow chart.

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(i) What are ozone depleting substances?

(ji) How is ozone formed?

(iii) Ravi wants to draw an ozone ‘layer in a diagram showing different layers of atmosphere, where should he label it?

(iv) What is the difference between good ozone and bad ozone?

(v) What could be the effect of ozone depletion?

Answers

1. Ecosystem is defined as the structural and functional unit of the biosphere. It is a stable ecological unit where continuous input of energy and circulation of matter occurs.

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2. (i) Ecosystem is the structural and functional unit of the biosphere and is a stable ecological unit where regular input of energy  and circulation matter takes place. 

(ii) Autotrophs can make their own food in the presence of sunlight. They are the ultimate source of energy for each and every organism of a food chain. Hence, every chain always starts with producers (autotrophs) that is why they are placed at the first trophic level of the food chain. 

(iii) In given food chain, Grass — Insects — Frogs — Snakes

Frogs assign at third trophic level. They acts as secondary consumers who feeds of primary consumers (i.e. insects).

3. Organisms that feed on dead plants and animals are called decomposers, e.g. bacteria, fungi, etc. They break down the complex organic compounds present in the dead remains into simpler substances and obtain nutrition from them. These substances are released into the soil and to the atmosphere.

Thus, they play the following roles

(i) They help in recycling of materials, replenishment of the soil’s nutrients, etc.

(ii) They clean our surroundings by decomposing dead organisms and organic wastes,

4. Natural water bodies are examples of natural ecosystems. They  exist naturally without any human support, whereas an aquarium is an artificial ecosystem which is created and maintained by humans. It rely on human efforts to sustain. It does not possess a self-regulating mechanism.

5. The study of food chain in an area or habitat helps in

(i) understanding the energy transfor through organisms

(ii) understanding the ecological balance in a habitat or ecosystem.

(iii) understanding harmful human activities and disruption of ecological balance, if any.

An example of four steps of food chain operating in a large lake is as follows

Algae —Protozoa —Small fish—Big fish.

6. Parasites are organisms (animals or plants) that live in or an  other organism (host) and take benefits by deriving nutrients from it, i.e. they get food or protection from host organism, e.g. Cuscuta

On the other hands, decomposers are organisms that break down dead or decaying organisms into simple inorganic substances. e.g.  Fungi

7. The transfer of food or energy takes place through various levels in the food chain, which are known as trophic levels. e.g.

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8. In a food chain, about 80-90% of the energy available at a trophic level is lost during its transfer to the next trophic level. Hence, the amount of energy available goes on decreasing at each successive trophic level.

If a plant fixes 4000 J energy, then the next three successive trophic levels will get 400 J, 40 J and 4 J, respectively (according to 10% law). If another level is added in a food chain then it will get only 0.4 J energy. Thus, usually food chains remain shorter and limited to 3-4 trophic levels only.

9. If we kill all the organisms in one trophic level, the lower trophic level will grow more in number and the higher trophic level will not survive.

Hence, flow of energy from one trophic level to another will not take place.

10. According to 10% law, only 10% of the energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level.

The flow of energy through a food chain is unidirectional and it moves progressively through various trophic levels as follows

(i) Green plants capture 1% of energy of the sunlight that falls on their leaves and convert it into food energy.

(ii) When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment. On an average only 10% of food eaten is turned into its own body and made available for the next level of consumers,

(iii) Thus, 10% can be taken as average value of the amount of organic matter present at each step and reaches the next level of consumers.

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11. The flow of energy in an ecosystem occurs in the following sequence 

Sun — Producer— Herbivore—Carnivore 

                            (Primary)   (Secondary)       

The flow of energy is unidirectional because of the reasons given below

(i) Energy flows progressively from one trophic level to another and cannot revert back. Energy given out as heat is lost to the environment and does not return to be used again.

(ii) The available energy decreases at higher trophic level. Out of the total energy available at a particular trophic level, only 10% is passed on to the next trophic level, making it impossible for energy to flow in the reverse direction.

12. Biological magnification also known as biomagnification is the phenomenon of progressive increase in the concentration of non-biodegradable toxicants in organisms at each successive trophic level.

13. Biological magnification refers to the increase in the concentration of certain toxicants at each successive trophic level.

No, the levels of magnification will not be the same in all trophic levels. When the chemicals do not degrade and accumulate progressively at each trophic level, it leads to biomagnification. Biomagnification is more in organisms of higher trophic levels.

14. Depletion of ozone is mainly caused due to the excessive use of Chlorofluorocarbons (CFCs). These are synthetic chemicals which are used as refrigerants and in fire extinguishers. Steps which should be taken to limit the damage to ozone layer include

(a) Minimizing the use of aerosol spray propellants containing fluorocarbons and chlorofluorocarbons.

(b) Exercising control over large scale nuclear explosions and limited use of supersonic planes.

15. Ozone layers filter the Sun’s ultraviolet radiation (UV-B), thereby protecting the environment from its harmful effects and also play a key role in regulating temperature.

16. The energy and biomass decrease from lower to higher trophic levels, so the length of food chain is restricted and cannot have more than four trophic levels,

17. (i) UV radiation acts on the O2 molecule. Higher energy of UV split apart O2.

(ii)

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(iii) CFCs rise up in the stratosphere where UV radiation splits them releasing molecular chlorine (CI‐). It reacts with O3 and releases oxygen, so O3 gets depleted.

18. Ozone at the higher levels of the atmosphere is a product of UV radiations acting on oxygen (O2 ) molecules. The high energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms are very reactive and combine with the molecular oxygen to form ozone.

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It shields the surface of the Earth from harmful ultraviolet (UV) radiations of the Sun.

Due to environmental pollution, the ozone layer began to deplete in the 1980s.

This was mainly due to the increasing use of synthetic chemicals like Chlorofluorocarbons (CFCs). 

These are used in refrigerants as coolant and in fire extinguishers. Due to depletion of the ozone layer, harmful UV rays can penetrate or enter our atmosphere.

These radiations are highly damaging to organisms. They can cause skin cancer in human beings, damage eyes (cause disease called cataract), decrease crop yield, disturb global rainfall, etc.

19. Following methods could be applied to reduce the accumulation of pesticides in our body.

(i) Minimize the use of pesticides 

(ii) Consuming washed fruits and vegetables

(iii) Developing vegetarian feeding habits

(i.e. feed upon plants as plants belong to lower trophic level so, they have less accumulation of insecticides, whereas organisms of higher trophic level have higher concentration of insecticides and pesticides).

20. We can reduce the problem of waste disposal by the following methods

  • Recycling. The solid wastes such as paper, plastics, glass and metals, etc., are recyclable. So, waste paper can be sent to paper mills for reprocessing to form newspapers. The plastic articles can be melted and remolded again to make new articles.
  • Biodegradable waste. The waste such as leftover food, fruits, animal dung, peels of vegetables can be converted into compost by burying them in a pit dug in ground and can be used as manure.

21. If all the waste is biodegradable, then there will be no accumulation of waste on the Earth and it would be a cleaner place to live.

But if this biodegradable waste is too large in amount then its slow degradation may lead to air pollution (due to release of gasses) as well as water and land pollution.

22. The two ways in which non-biodegradable substances would affect the environment are

(i) They make the environment poisonous and unfit for survival of living ol’ life.

(ii) They block the transfer of energy and minerals in the ecosystem.

23. Biodegradable materials are broken down by microorganisms present in nature into simple harmless substances. Non-biodegradable materials need a different treatment like heat and temperature for disposal and hence, both should be discarded in two different dustbins.

24. Effective segregation of waste as biodegradable and non-biodegradable is much easier to recycle. Biodegradable waste used to make manure can be made out of compost, whereas non-biodegradable waste could be recycled and reused for various purposes. Also effective segregation of wastes means that less waste goes to landfill, which makes it cheaper and better for people and the environment.

25. A pond ecosystem refers to a freshwater ecosystem where there are various organisms dependent on each other with the prevailing water environment for their nutrients and survival.

Phytoplankton—Zooplankton —Small fish—Big fish

There are two components of the pond ecosystem

(i) Abiotic. It includes water, dissolved minerals, oxygen and carbon dioxide. Sunlight is the main source of energy.

(ii) Biotic. It consists of phytoplanktons, zooplanktons, aquatic insects, fishes and other aquatic animals. These organisms are classified as producers, consumers and decomposers.

26. The waste generated in our house and measures for its disposal are given in the table below

Household Wastes Measures for disposal
Kitchen waste like bottles plastic, foods etc. prepare a compost pit
Paper wastes like newspaper, envelopes, etc.Should be recycled
vegetable fruit pillsCan be placed near
trees / plants so that on decomposition enrich the soil with nutrients
plastic bagsShould be safely dumped in garbage bins for non biodegradable waste
all other wastesSegregation in to biodegradable and nonbiodegradable waste

27. Insecticides are non-biodegradable chemicals added to crop fields to stop the growth of insects infecting the crops. Modern insecticides are being developed keeping in mind the harm they cause to the environment and its components.

Biodegradable insecticides can be decomposed into harmless substances, which will subsequently be dispersed in their specific pathways and cause no pollution.

Non-biodegradable insecticides build up in the fat tissues of the body and pass on to organisms that feed on them. 

Hence, they accumulate along the chain resulting in significant amounts in the tissues of consumers at the highest trophic level.

The property of newly developed insecticide includes that it can easily get decomposed into simpler components by soil bacteria.

28. Mona follows a vegetarian diet along with milk products. She should be considered as occupying the third trophic level because the curd is prepared by the Milk cow/buffalo  by the action of bacteria, but the energy of the milk is getting transferred from cow to Mona, so Mona is at the third trophic level.

Grass      —— Cow (milk)  —— Human 

(First trophic) (Second trophic) (Third trophic)

29. Organisms which break down the complex organic compounds present in dead and decaying matter into simpler inorganic materials are called decomposers, e.g. certain bacteria and fungi.

Decomposers act as cleaning agents of the environment by decomposing dead bodies of plants and animals. They also help in recycling of materials, replenishment of soil’s nutrients, etc.

The consequence of their absence in an ecosystem can be disastrous. The dead bodies would persist for long, leading to their accumulation and thus, polluting the environment. The biogenetic nutrients associated with these remains will not be returned back to the environment.

As a result, all the nutrients present in soil, air and water would soon be exhausted and the whole life cycle of organisms would be disrupted. 

30. (i) Consumers are the organisms who derive energy by eating plants or other organisms as they cannot produce food on their own. Absence of primary consumers in nature would lead to enormous growth of plants and decline in the population of carnivore animals, who eat them. Hence, the whole food web will get distrupted.

(ii) The direction of energy transfer in following cases are as follows

  1. Primary consumer (grasshopper) to secondary consumer (frog).
  2. Producer (grass) to primary constnuer (deer).
  3. Primary consumer (deer) to secondary consumer (lion) 

31. (i) Yes, the impact of removing all the organisms in a  trophic level will be different [or dillörent trophie lex els. The lower trophic level ol’ an ecosystem has a greater number of individuals than the higher trophic levels. 

Removal of producers will affect all the organisms of successive trophic levels and it will threaten their survival. The removal of higher trophic level will lead to increase in organisms’ lower trophic level and the organisms at higher trophic level will die due to  shortage of food. 

(ii) No, removal of all organisms of a trophic   level will disturb the ecosystem. Killing of higher trophic level organisms will cause explosion in the population of lower

trophic level organism. This will adversely affect the ecosystem and the environment.

32. (i) The producers convert solar energy into chemical energy in the form of organic compounds. The primary consumers (herbivores) derive their nutrition from the producers. According to the energy transfer law, only 10% of energy is transferred from one trophic level to the other.

So, the energy that is captured by the producer does not revert back to the Sun and the energy transferred to the herbivores does not come back to the producers. It  just keeps on moving to the next trophic level in one direction. That is why the flow of energy in the food chain is always unidirectional 

(ii) A large number of pesticides and chemicals are used to protect our crops     pests and diseases. Sorne of these chemicals are washed clown from the soil, while some enter the water bodies. 

From the soil, they are absorbed by plants along with water and minerals and from the  water bodies, they are taken up by aquatic plants and animals. This is how these chemicals enter the food chain.

As these chemicals cannot decompose, they accumulate progressively at each trophic level. This increase in the concentration of harmful chemicals with each step of the food chain is called biomagnification. As human beings occupy the top level in any food chain, these chemicals get accumulated in our bodies in considerably high amounts causing diseases.

33. (i) Undesirable activities of man eliminate growth of organisms belonging to one or more trophic levels in a food chain. Thus, the food chain gets shortened, e.g. hunting tigers for their skin, etc. 

It causes imbalance in the functioning of the ecosystem and biosphere. If organisms of one trophic level are eliminated, the organisms prior to that trophic level will flourish and increase in number. Also, the organisms of the subsequent trophic level will sharply decrease, thereby creating an imbalance.

(ii) Vegetarian food chain is advantageous in terms of energy because it has less number of trophic levels. As we know, only 10% of the energy is transferred to the next trophie level in a food chain, so if a person is vegetarian then, he would have a maximum amount of energy by consuming producers or plants in a food chain.

34. Some harmful effects of agricultural practices on the environment are as follows

(i) Soil degradation. Extensive cropping causes loss of soil fertility. Also, over time it can lead to soil erosion and finally to desertification.

(ii) Pollution. Use of synthetic chemical fertilizers and nucl  pesticides leads to soil, water and air pollution.

(iii) Water shortage. Excess use of groundwater for agriculture lowers the water level. This results in acute water shortage at many places.

(iv) Biomagnification. The chemical pesticides, being  accumulate in organisms in increasing amount of each trophic level 

(v) Deforestation. Indiscriminate cutting of trees of agriculture has resulted in loss of habitat for wildlife.

Thus, it also causes damage to natural ecosystem.

35. Ozone is a triatomic molecule, i.e. made up of three atoms of oxygen joined together. Its molecular formula is O3. It can affect any ecosystem in the following ways

(i) It protects against ultraviolet rays if present in the stratosphere.

(ii) Ozone dissipates the energy of UV rays by undergoing dissociation followed by reassociation.

our environment notes and questions

(iii) In the atmosphere, it is highly toxic and causes injury to mucous membranes, eye irritation and internal hemorrhages in animals and humans.

36, (i) Environmental pollution is an undesirable change in the physical, chemical or biological characteristics of the natural environment, brought about by man’s activities. This pollution may affect the soil, water or air. 

(ii) Differences between biodegradable and non-biodegradable pollutants are as follows:

BiodegradableNon-biodegradable
These pollutants can be broken down into non toxic substances in nature by the action of microorganisms these pollutants cannot be broken down into non toxic substances by microorganisms
They get recycled thus, do not need any dumping sitesThey cannot be recycled thus, required dumping sites
They cause minimum environmental pollutionThey cause maximum environmental pollution

37. Some daily life eco-friendly activities are

(i) Save a tree, use less paper. You can buy ‘tree-free’ 100% post-consumer recycled paper for everything from greeting cards to toilet paper. Paper with a high post-consumer waste content uses less pulp and keeps more waste paper out of landfills.

(ii) Opt bamboo for hardwood floors Bamboo is considered as an environmentally-friendly flooring material due to its high yield and the relatively fast rate at which it replenishes itself. It takes just 4-6 years for bamboo to mature, compared to 50-100 years for typical hardwoods. Also look for sources that use formaldehyde-free glues.

(iii) Reduce plastics, reduce global warming Unfortunately, plastics are made from petroleum, the processing and burning of which is considered one of (he main contributors to global warming, according to the EPA. In addition, sending plastics to the landfill also increases greenhouse gasses. 

Reduce, reuse and recycle our plastics are one of the best ways to combat global warming.

(iv) Use healthier paints Conventional paints contain solvents, toxic metals and Volatile organic compounds (VOCs) that can cause smog, ozone pollution and indoor air quality problems with negative health effects, according to the EPA. These unhealthy ingredients are released into the air, while we are painting, drying of paint and even after the paints are completely dry.

(v) Use compost Instead of using synthetic fertilizers, compost provides a full complement of soil organisms and the balance of nutrients needed to maintain the soil’s health. Healthy soil mininii.ses the population of  weeds.

38. Materials that retain for a long time in the environment, without getting by any natural agents, also causing harm to the environment are called non-biodegradable. 

Plastic cups are non-biodegradable and raised the concern towards hygiene, thus they were replaced by kulhads.

Kulhads are made up of clay on a large scale resulting in the loss of top fertile soil. It is replaced by disposable paper cups because the paper can be recycled, it is biodegradable and is eco-friendly material which does not cause environment pollution.

39. (i) There are 6 food chains that constitute the given food web. These are as follows

  1. Seeds— Mice — Foxes  
  2. Young trees — Mice — Foxes 
  3. Young trees — Rabbits — Foxes
  4. Grass — Rabbits — Foxes
  5. Grass — Rabbits — Snake
  6. Young trees — Rabbits — Snake

(ii) The primary consumers are the organisms who directly feed on the producers. In the given food web, rabbits and mice are the primary consumers, whereas foxes and snakes are the secondary consumers.

(iii) About 90% of energy is loss at each trophic level.

(iv) The foxes feed on the rabbits and mice. If all the foxes are killed then there will be no direct predator of rabbits and mice, hence the number of rabbits and mice (i.e. both are primary consumers) will increase in the given ecosystem, which will disturb its balance.

(v) Accumulation of toxic non-biodegradable substances increases at each trophic level. It is least in organisms of first trophic level (i.e. seeds), young trees and grass and highest in organisms of third trophic level (i.e. foxes and snakes).

40. (i) The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight (light energy). They convert it into food energy (chemical energy).

Therefore, if 10,000 J solar energy falls on green plants in a terrestrial ecosystem, only 1% of solar energy, i.e. 100 J will be converted into energy.

(ii) Decomposers are not included in the food chain as they act at every trophic level of the food chain.

(iii) Primary consumer are those organisms who directly feed on plants; e.g. herbivores 

Primary carnivores are those organisms who feed on plant-eating animals e.g. snakes.

(iv) Decrease in energy at higher trophic levels (according to 10% law) is one of the reasons that limits the trophic levels in a food chain.

(v) Owl is placed at the highest trophic level in the given food web, therefore the accumulation of non-biodegradable toxic materials are found to be highest in them due to biomagnification.

41. (i) The longest food chain consists of a maximum five trophic levels.     

(ii) Rabbit is a herbivore as it feeds on plants directly. Its role in the given food web is to transfer the energy from  producers to carnivores.

(iii) The significance of food web is as follows 

  1. Food chains provide pathways for availability of food. 
  2. It allows endangered populations to grow in size. 

(iv) Sun or solar energy is the ultimate source of energy for the Earth. Only plants can utilize this energy to make their on food.

(v) When a predator for a particular organism decreases in number, the organisms start increasing in number.

As the animals which used to feed on them decrease in number, therefore, the population of those organisms increases.

42. (i) Substances that are responsible for depletion of the ozone layer or breakdown of ozone molecules are known as ozone depleting substances.

e.g. CFCs, halogens, nitrous oxide, CCl4 and CH4 are ozone depleting substances responsible for ozone layer depletion.

(ii) Atomic oxygen is highly reactive. It combines with molecular oxygen to form ozone.

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(iii) Ozone layer is found in the stratosphere around 15-30 km above the Earth’s surface.

(iv) Ozone is a triatomic molecule made up of three atoms of oxygen (03). It is present in the atmosphere as an ozone layer shield that protects us from high energy UV radiations. 

So, it is known as good ozone whereas near the surface of earth ozone act as a highly poisonous gas. Hence,  bad ozone.

(v) Cancers, mutations, effects on eyesight, global warming, weakening of the immune system, etc., are some adverse effects of ozone depletion.


Final Words

From the above article, you have practiced Class 10 chapter 15 our environment notes and questions. We hope that the above-mentioned notes and Q & A for term 2 will surely help you in your exam. 

If you have any doubts or queries regarding Class 10 chapter 15 our environment notes and questions, feel free to reach us and we will get back to you as early as possible.

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