Class 10 Science - Previous Year Questions - Our Environment

Ans: (c)
A food chain shows a sequence of organisms where each is eaten by the next one.
In options (ii) and (iii), the order of organisms is incorrect — they do not represent a proper feeding relationship (for example, man does not eat grasshopper or fish directly, and grass cannot be eaten by a hawk).
Hence, (ii) and (iii) do not constitute a food chain.

Ans: (d)
Only about 1% of the sunlight that falls on green plants is converted into food energy, so 99% of solar energy remains unutilised.

Ans: (b)

Ans: Excessive use of pesticides and chemicals in agriculture leads to their accumulation in soil and water. These chemicals enter the food chain through plants and aquatic organisms and are not degradable. They get progressively accumulated at each trophic level, a process called biological magnification, causing harmful effects on living organisms and the environment.

Ans: (c)
DDT, polyester, and glass cannot be broken down by biological processes; hence, they are non-biodegradable substances.

Ans: (a)

Animals cannot get energy from coal because enzymes are specific and only break down particular biological substances. Since coal cannot be broken down by these enzymes, it cannot provide energy.

Ans: This phenomenon is called biological magnification.

Harmful chemicals such as pesticides and fertilizers enter the food chain through soil and water. These chemicals are not degradable and thus accumulate in the tissues of organisms.At each successive trophic level, their concentration increases because they are passed on through food. Since human beings occupy the top level in the food chain, the maximum concentration of these chemicals accumulates in our bodies.

Ans: (d)

A self-sustaining aquarium needs aquatic plants (producers), small herbivorous fishes (consumers), and decomposers. Terrestrial plants/animals and large consumers like sea urchins are not required in such an aquatic ecosystem.

(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.

Ans: (a)

• Using jute bags helps reduce pollution because jute is biodegradable and such bags can be reused, reducing non-biodegradable plastic waste.

Ans: (c)

The shorter the food chain, the less energy is lost between trophic levels. Since this chain has only two trophic levels, it is the most efficient in terms of energy transfer.

Ans: Decomposers are microorganisms that break down dead plants, animals, and waste materialsinto simple inorganic substances. 

Examples: Bacteria and fungi. 

Role in maintaining balance:

• They recycle nutrients by converting complex organic matter into simple substances that return to the soil and are used again by plants. 
• This process helps in the natural replenishment of the soil and maintains the balance in the ecosystem.

Ans: (c)

Ans: (b)

Using disposable cups and plates increases non-biodegradable waste, leading to environmental pollution and harming ecosystems.

Ans:
(a) The organisms of the first trophic level, known as producers, are very important because they absorb solar energy and convert it into chemical energy through photosynthesis. This stored energy in food becomes the source of energy for all other organisms in the food chain such as herbivores, carnivores, and decomposers. Without producers, no other organisms could survive, as they depend directly or indirectly on them for food. 

(b) The flow of energy in an ecosystem is unidirectional, meaning it moves in one direction only — from the Sun → producers → consumers → decomposers. The energy captured by producers does not return to the Sun, nor can it go backward in the chain. At each trophic level, some energy is lost as heat, so the energy available to the next level keeps decreasing, making the flow one-way and non-cyclic.

Ans:

(a) The gas ‘X’ is ozone (O₃). It is getting depleted mainly due to synthetic chemicals like chlorofluorocarbons (CFCs) used in refrigerants and fire extinguishers. 

(b) In the upper atmosphere, ozone is formed when ultraviolet (UV) radiations split some molecules of oxygen (O₂) into free oxygen atoms (O), which then combine with molecular oxygen to form ozone (O₃).

Ans:

(a) The food chain in which the eagle receives the highest energy from producers is:
Grass → Mouse → Eagle.
This is because the chain is shortest, involving fewer trophic levels, so there is less energy loss between steps, and the eagle receives more energy from the producers.

(b) The organism in which a non-biodegradable pesticide will be found in maximum concentration is the Eagle.
This is due to biological magnification, where harmful chemicals accumulate progressively at each trophic level, reaching the highest concentration in top consumers.

Ans: (d)

According to the 10% law, only 10% of energy is transferred from one trophic level to the next.
If the third trophic level (frog) has 50 kJ, then:
Producer → 1st → 2nd → 3rd
Energy at producer level = 50 × 10 × 10 × 10 = 50,000 kJ.

Ans: (c)

Ozone itself is not used as a refrigerant or in fire extinguishers; CFCs (chlorofluorocarbons) are.
Ozone protects the Earth from harmful UV radiation.

Ans: (c)

• A food web is indeed a network of many interconnected food chains, but it actually increases the stability of an ecosystem, not decreases it.

Ans: Natural ponds and lakes are self-sustaining ecosystems that contain producers, consumers, and decomposers. These components interact and maintain a natural balance by recycling nutrients and cleaning the system on their own.

An aquarium or swimming pool, however, is a human-made system that lacks sufficient decomposers and natural processes of purification. Hence, it needs to be cleaned regularly to remove waste and maintain a healthy environment. 

Ans: (d)

Green plants are producers; they make their own food from inorganic substances using sunlight through photosynthesis, so they always occupy the first trophic level in a food chain.

Ans: (b)
Harmful chemicals do accumulate in organisms at the highest trophic level due to a process called biomagnification, and these chemicals are often sprayed on crops to protect them. However, the reason does not directly explain why the accumulation is highest at the top of the food chain, so it’s not a correct explanation of the assertion.

Ans: (A)

• Number of plants/organisms of first trophic level will increase. 
• Number of lions/ organisms of third trophic level will decrease.
• No
• As the organisms of that level will find alternative foods and will not starve to death / food web is more stable where other animals as prey may be available.

OR

• Gas ‘X’ is Ozone.
• Ozone shields the surface of the earth from ultra-violet (UV) radiations from the sun. 
• CFCs (Chlorofluorocarbons)
• Succeeded in forging an agreement to freeze CFC production at 1986 levels / Manufacturing of CFC free refrigerators

Ans: 

• Non-biodegradable substances 
• Two ways: 
  (i) They are inert and persist in the environment for long time and cause pollution.
  (ii) Cause Biological magnification
  (iii) Affect the fertility of soil 

Ans: Phenomenon – Biological Magnification /Biomagnification:

• Pesticides are washed down into the soil and water bodies. 
• From the soil pesticides are absorbed by crop plants along with water and minerals  and enter the food chain.
• These chemicals are non-biodegradable and get accumulated progressively at each trophic level. 
• As human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in our bodies.

Ans: (b)
Ozone can be harmful at ground level, making it a poisonous gas. Statement (C) is also correct since ozone is formed when ultraviolet (UV) radiation interacts with oxygen molecules. However, statement (B) is incorrect because ozone protects the Earth from UV radiation, not infrared radiation, and statement (D) is misleading because ozone's essential functions are primarily in the upper atmosphere, not at lower levels.

Ans: (b)

The answer is (b) because both statements are true: waste can be either biodegradable (which can break down naturally) or non-biodegradable (which cannot), and improper disposal of waste can indeed lead to serious environmental issues. However, the reason does not explain why waste is categorized as biodegradable or non-biodegradable, so it’s not a direct explanation of the assertion.

Ans: Decomposers are the microorganisms that break-down the complex organic substances into simple inorganic substances.
Consequences:
(i) No replenishment of soil
(ii) Foul smell
(iii) Breeding of flies
(iv) Accumulation of dead plants and animals in the environment.
(v) No recycling of nutrients

Ans: When water is lost through stomata in the leaves by transpiration, it creates a suction force/transpiration pull, due to which water is pulled up through xylem of the roots to the leaves.

Ans: (b)
Non-biodegradable wastes are those that do not break down naturally in the environment. In the given options, ballpoint pen refills (ii) and empty medicine bottles made of glass (iii) are non-biodegradable because they can persist in the environment for a long time. The other items like garden waste, fruit and vegetable peels, and old cotton shirts decompose naturally and are considered biodegradable.

Ans: (b)
Assertion (A) correctly states that oxygen is essential for aerobic life forms, while Reason (R) explains a process involving oxygen and ozone formation, which is also true. However, Reason (R) does not explain why oxygen is essential for life, so the correct answer is (b): both are true, but Reason (R) does not explain Assertion (A).

Ans: (d)
A natural ecosystem is one that occurs naturally without human interference. Among the options given, a cropland ecosystem (d) is not natural because it is created and managed by humans for farming purposes. In contrast, pond, grassland, and forest ecosystems develop naturally in the environment.

Ans:

• Population of grass/ first trophic level will increase.
• Population of tiger/ third trophic level will decrease.

Ans: (c)

In a food chain, the second trophic level usually consists of primary consumers that eat producers (like plants). In option (c), tiger, grass, snake, frog, there are no primary consumers (like a herbivore) between the grass (producer) and the snake. Instead, the snake directly feeds on frogs, which means the second trophic level is missing.

Ans: (d)
Multiple fission is a type of asexual reproduction where an organism divides into many parts at once. In this case, Plasmodium (d), which causes malaria, reproduces through multiple fission in its life cycle, producing many daughter cells simultaneously. The other options like yeast, Leishmania, and Paramecium reproduce differently.

Ans: (a)
In a food chain, energy is lost at each trophic level due to metabolic processes, typically around 90% of energy is lost as heat, while only about 10% is transferred to the next level. Therefore, a food chain with fewer trophic levels will retain more energy available to the organisms at the higher level.
With 2 trophic levels (e.g., producers and primary consumers), there is minimal energy loss compared to longer chains, making it more advantageous in terms of energy efficiency.
Thus, the correct answer is (a) 2 trophic levels.

Ans: The use of several pesticides results in accumulation of pesticides in rivers and ponds. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals and enters the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies i.e., biological magnification. Our food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues cannot always be removed by washing or other means and causes health hazards.

Ans: Ozone (O₃) is a molecule formed by three atoms of oxygen. It is formed in the stratosphere layer of atmosphere when high energy UV rays act on O₂ molecule splitting it into free oxygen (O) atoms. These atoms then combine with molecular oxygen (O₂) to form ozone (O₃).

Ans: In a garden, various plants like grasses, trees, flower bearing plants such as jasmine, sunflower, rose, and animals like insects, frogs and birds are found. All these living organisms interact with each other and their growth, reproduction and other activities are affected by the abiotic components such as light, water, wind, soil, minerals, etc. of ecosystem. Thus, a garden is considered to be an ecosystem.

Ans: Differences between biodegradable and non-biodegradable substances are as follows :

Domestic waste can be safely disposed off by composting. In composting, biodegradable domestic wastes, such as left-over food, fruit, vegetable peels, etc., can be buried in pit, dug into ground. They are converted into compost and used as manure.
In landfill a huge pit is made in an open low lying area and wastes are dumped into the pits. Once the pits are full, they are covered with soil and left for decomposition.

Ans: The process by which harmful substances enter the food chain and becomes concentrated at each trophic level is known as biomagnification.
Example:Biomagnification of DDT in an Aquatic Food Chain

Ans: (A) Kitchen gardens are referred to as artificial ecosystems because they are man-made and contain adjusted abiotic and biotic components. It is an ecosystem where plants are produced, including fruits and vegetables, whereas a forest is a place where various creatures live in harmony and rely on one another for food and other necessities. As a result, a forest creates an ecosystem that can support itself. 
(B) Two things to keep in mind while designing an artificial ecosystem: 
(1) Balance between biotic and abiotic factors. 
(2) Recycling of nutrients and wastes. 
Reason: Abiotic factors include elements like temperature, light, water, and nutrients, whereas biotic factors are things like plants, animals, fungus, and microorganisms. Due of their interdependence, any changes to one of these components can have an impact on the ecosystem as a whole. To support the development and survival of all organisms within the ecosystem, it is crucial to maintain a balance between various components in the ecosystem. Recycling is essential for maintaining the health and sustainability of the ecosystem.

Ans: (A) The flow of nutrients and energy from one organism to another at different trophic levels forms a food chain. 
Plants → Rat → Snake → Hawk 
(B) Only 10% of energy will be transferred to the next trophic level, according to the 10% law of energy transfer, and 90% will be wasted as heat and incomplete digestion. According to this law, 
(1) Energy is transferred from producers to the second trophic level = 20,000 J. 
(2) Energy moved from the second to the third trophic level: 10% of 20,000 J = 2,000 J. 
(3) Energy moved from the third to the fourth trophic level is equal to: 10% of 2,000 J = 200 J

Ans: 
(i) Crop fields are the artificial ecosystems because in crop fields, both biotic (living) and abiotic (non-living) components are manipulated by human beings. Humans can change edaphic factors by adding fertilisers, water, etc. Biotic components may be changed using biocides or adding useful organisms like earthworms etc.
(ii) A food chain consists of various organism at various trophic levels. In terrestrial ecosystem, a common food chain is
Grass Grasshopper→ Frog→ Snake

Ans: 
(i) The two human made ecosystems are aquarium and garden.
(ii) We do not clean pond as we do in an aquarium because the waste generated in a pond is acted upon by the decomposers which convert them into simple soluble substances, whereas, in aquarium, the waste gets mixed with water and left untreated due to absence of decomposers.

Ans: In the given food chain, 20,000 J of energy must have been present in grass. This is because, as per the 10% law of energy transfer, only 10% of energy is transferred to the next trophic level.

Ans:  Artificial ecosystems area unit human-made structures wherever organic phenomena and abiotic elements area unit created to act with one another for survival. it's not self-sufficient and might decrease while not human facilitated. samples of artificial ecosystems embrace aquariums, agriculture fields, zoos, etc.

• A system, that is formed and maintained by mortals, is named synthetic | a synthetic} or man-made system. Some samples of artificial ecosystems area unit aquariums, gardens, agriculture, apiary, poultry, piggery, etc.
• Man-made ecosystems don't seem to be self-sufficient as a result they rely on naturally created ecosystems just like the water bodies. just like the crop fields that could be an artificial system that depends on water bodies like rivers, and groundwater for water and life. Same approach gardens conjointly rely on nature for their property.
• All organisms like plants, animals, microorganisms, and mortals further because the physical surroundings act with one another and maintain a balance in nature. All interacting organisms in a locality in conjunction with the non-living constitute the setting kind associate degree system.
• All the organic phenomenon elements comprising living organisms and abiotic elements comprising physical factors like temperature, rainfall, soil, etc create an associate degree system.
• An artificial system could be a variety of systems created by man by artificial means and not present sort of a forest, ponds, lakes, etc. samples of artificial ecosystems area unit crop fields and gardens.
• Man-made ecosystems don't seem to be self-sufficient as a result they rely on naturally created ecosystems just like the water bodies. just like the crop fields that could be an artificial system that depends on water bodies like rivers, and groundwater for water and life. Same approach gardens conjointly rely on nature for their property.

Hence, artificial ecosystems don't seem to be self-sufficient.

Ans: (a) Producers form the first trophic level of all food chains. They are called producers because they are autotrophic organisms which alone are able to manufacture organic food from inorganic raw materials by the process of photosynthesis. They capture sun’s energy and convert it into chemical energy. The chemical energy is used in combining raw materials into organic food. This food is used up by themselves and rest enters the food chains as food for consumers.
(b) Human beings are most adversely affected by biomagnification because they occupy the highest trophic level in any food chain. As in biomagnification, successive concentration of non-biodegradable substances increases in the trophic level of food chains, so, it leads to most toxicity at highest trophic level. Hence, maximum concentration of chemicals get accumulated most in their body.
(c) Absence of decomposers will lead to the accumulation of dead remains and waste products of organisms in our natural ecosystem. The decomposers breakdown complex organic substances into simple inorganic substances, so, that it can go into the soil and can be used up by plants.

Ans: Ozone (O₃) is a molecule formed by three atoms of oxygen. It is formed in the stratosphere layer of atmosphere when high energy U V rays act on O₂ molecule splitting it into free oxygen (O) atoms. These atoms then combine with molecular oxygen (O₂) to form ozone (O₃).

Ozone shields the surface of the earth from U V radiations from the sun. The depletion of ozone layer will lead to global warming and some serious health issues such as damage of skin cells that leads to skin cancer, snow blindness or inflammation of cornea, increased fatality of young animals, mutations and reduced immunity.

Ans: (a) We do not clean pond as we do in an aquarium because the waste generated in a pond is acted upon by the decomposers which convert them into simple soluble substances, whereas, in aquarium, the waste gets mixed with water and left untreated due to absence of decomposers.
(b) The ozone layer is getting depleted at the higher levels of the atmosphere due to use of chlorofluorocarbons (CFCs) which are used in refrigerator. Other ozone depleting substances include carbon tetrachloride, hydrofluorocarbons used in fire extinguisher, air i conditioners, etc.
Due to the ozone layer depletion, humans will be directly exposed to the ultraviolet radiations of sun. This will result in serious health issues like skin cancer, sunburns, quick ageing, mutations and weak immune system.

Ans: Kulhad:

• Kulhad is a cup that is made using clay or soil.
• This is usually used for serving tea/coffee.
• This was brought in use to replace the plastic cup in trains.
• Plastic is a nonbiodegradable harmful substance that does not decompose in nature and affects the ecosystem or environment negatively.
• Kulhads are made of biodegradable soil, therefore, this was used to replace the plastic and protect the environment and health of humans.

Discontinuation of kulhads:

• Since kulhads are made using clay, it is a practice of harming the environment too.
• The clay is fertile soil and kulhads were discontinued to avoid its reduction.
• Making of kulhad on a large scale to serve tea passengers in the train was leading to the loss of this top fertile soil.

Ans: (a) Garbage is the waste material (rubbish) especially of domestic refuse. The two classes into which garbage is classified are
(i) Biodegradable
(ii) Non-biodegradable.
(b) Enzymes are specific in their action. For example, enzyme maltase acts on sugar maltose but not on lactose or sucrose. Different enzymes may act on the same substrate but give rise to different products. Similarly an enzyme may act on different substrates producing different end products.

Ans: Consumers are the organisms which are unable to synthesise their own food. Therefore, they utilise materials and energy stored by the producers or eat other organisms. They are known as the heterotrophs. The consumers are of following categories:
(i) Primary or first-order consumers: These include the animals which eat plants or plant products. They are called herbivores or primary (first order) consumers. E.g., Cattle, deer, goat, rabbit, hare, rats, mice, grasshoppers etc
(ii) Secondary or second order consumers: These include the animals which depend on primary consumers for their food. They are called primary carnivores or secondary (second order) consumers. Secondary consumers can be carnivores or omnivores. E.g., Cats, dogs, foxes, small fish, etc.
(iii) Tertiary or third order consumers: These are large carnivores (or top carnivores) which feed on primary and secondary consumers. These are termed as secondary carnivores or tertiary (third order) consumers. Common examples include shark and crocodile, wolves, lion, etc. (iv) Quaternary or fourth order consumers: These are even larger carnivores which feed on secondary carnivores (tertiary consumers). E.g., Tigers, lions and eagles/hawks etc.

Ans: When high energy ultraviolet radiations react with oxygen present in stratosphere (the higher level of atmosphere) it splits into its constituent atoms. Since these atoms produced are very reactive, they react with molecular oxygen (O₂) to form ozone (O₃).

Ozone shields the surface of the earth from UV radiations from the sun. The depletion of ozone layer will lead to global warming and some serious health issues such as damage of skin cells that leads to skin cancer, snow blindness or inflammation of cornea, increased fatality of young animals, mutations and reduced immunity. In 1980s, the production of CFCs increased which releases active chlorine in the atmosphere. The active chlorine then reacts with ozone molecules present there to convert them to oxygen. This results in thinning of ozone layer. CFCs are used as refrigerants and in fire extinguishers. That is why, amount of ozone in the atmosphere dropped sharply.

Ans: 
(a) Two harmful effects of using plastic bags on the environment: 
(i) Plastic bags are non-biodegradable substances which are not acted upon by microbes. So, they cannot be decomposed and therefore persist in the environment for a long time causing harm to the soil fertility and quality.
(ii) Plastic bags choke drains which result in waterlogging, that allows breeding of mosquitoes and hence leads to various diseases. Jute bags and cloth bags are the alternatives to the polyethene bags.
(b) Practices that can be followed to dispose off the waste produced in our homes: 
(i) Separation of biodegradable and non-biodegradable wastes.
(ii) The biodegradable waste can be converted to manure.
(iii) Non-biodegradable waste should be disposed off at suitable places from where municipal authorities can pick them up and dispose properly and scientifically.
(iv) Use discarded bottles and jars to store food items.

Ans: (A) A terrestrial food chain comprising of four trophic levels: 
Grass → Grasshopper → Frog → Snake 
(B) If we kill all the organisms in one trophic level then 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 an imbalance in the ecosystem. 
(C) Consider the same food chain that we have made i.e., (A), 
Grass → Grasshopper → Frog → Snake 
In this food chain, organism at the second trophic level is grasshopper 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. 
The 10% law states that during transfer of energy from one trophic level to the next trophic level, only about 10% of energy is available to the higher trophic level.
To summarise:

Ans: 
(a) The number of trophic levels in a food chain are limited because at each trophic level only 10% of energy is utilised for the maintenance of organism which occur at that trophic level and the remaining large portion is lost as heat. As a result, organisms at each trophic level pass on lesser energy to the next trophic level, than they receive. The longer the food chain, the lesser is the energy available to the final member of food chain.
(b) Biological magnification is characterised by the increase in the non-biodegradable substances (DDT, Hg, etc.) in successive trophic levels of a food chain. The level of such toxic substances will be different in different trophic levels of a food chain because these substances are accumulated more in higher trophic levels.

Ans: An ecosystem is defined as a structural and functional unit of the biosphere. It comprises of living organisms and their non-living environment that interact by means of food chains and biogeochemical cycles resulting in energy-flow, biotic diversity and material cycling to form stable self-supporting system. Green plants capture about 1% of the solar energy incident on the earth to carry out the process of photosynthesis.
A part of this trapped energy is used by plants in performing their metabolic activities and some energy is released as heat into the atmosphere. The remaining energy is chemical energy stored in the plants as photosynthetic products. When these green plants are eaten up by herbivores, the chemical energy stored in the plants is transferred to these animals. These animals (herbivores) utilise some of this energy for metabolic activities and some energy is released as heat while the remaining energy is stored in their body. This process of energy transfer is repeated till top carnivores. In an ecosystem, transfer of energy follows 10 per cent law, i.e., only 10 per cent of the energy is transferred to each trophic level from the lower trophic level. The given block diagram shows unidirectional flow of energy at different trophic levels in a freshwater ecosystem:

Ans: (a) The three methods of waste disposal are:

• Recycling: solid, wastes like paper, plastics, metals can be sent to processing factories where they are remoulded or reprocessed to new materials.
• Production of compost: Biodegradable wastes like fruit and vegetable peels, plant products, left over food, grass clippings, human and animal waste can be converted into compost by burying this waste into grund and can be used as manure.
• Incineration: Burning dawn many household waste, chemical waste and biological waste into ash is known as incineration. A large amount of waste can be easily converted into ash which can be disposed off in landfill.

(b) Differences between:

Ans: 
(a) A self-sustaining functional unit consisting of living and non-living components is called an ecosystem.
Components: Biotic components like plants and animals. Non-biotic components like soil, wind, light etc.
(b) A pond is a complete, natural and self-sustaining ecosystem whereas an aquarium is an artificial and incomplete ecosystem, without decomposers therefore it needs regular cleaning for proper running.

Ans: (a) Ozone layer at the higher levels of the atmosphere, acts as a shield to protect earth from the harmful effects of the ultraviolet (UV) radiations; hence, it should be protected.
(b) 

• Urging the people to not to buy aerosol products with CFC that are available in the market.
• Conducting poster making competition or street plays presenting the importance of ozone layer on earth.

Ans:

(a) 

• Pesticides are the chemicals used to protect our crops from diseases and pests.
• These chemicals are washed down either into the soil or into water bodies.
• From the soil, they are absorbed by the terrestial plants along with water and minerals.
• From the water bodies, they are absorbed by the aquatic plants.
• When the fruits of these plants are used to prepare fruit juices, they are contaminated with the pesticides.

(b)

• The phenomenon is called biomagnification. It is the phenomenon in which certain harmful chemicals enter the food chain and get accumulated and increase in concentration at successive trophic levels.
• It is because they are not degradable.
• The maximum concentration of these chemicals is found in the top level consumers.

Ans: Plants → Deer → Lion
1,000,000 J of energy was available to the producer.

Ans: The biodegradable and non-biodegradable wastes must be discarded in two different dustbins because biodegradable wastes gets decomposed by the microorganisms whereas non-biodegradable wastes can be recycled and reused.

Ans: Agricultural/crop fields, aquaria, gardens,

Ans: Some natural ecosystems are:

• Temperate forest
• Tropical forest
• Grassland
• Ocean
• Lake
  Types of Natural Ecosystem

Ans: Decomposers are microorganisms that derive their nutrition from dead remains and waste products of organisms.
They play a vital role in our environment by breaking down the complex organic substance into simple inorganic substance which is made available for plants and other organisms. Hence they act as scavengers and not only keep the environment clean but also replenish the minerals.

Ans: It is the sum total of all external conditions and influences that affect the life and development of an organism, i.e. the environment includes all the physical or abiotic and biological or biotic factors.

Ans: Green plants can produce their own food by photosynthesis from inorganic compounds and hence are called producers.

Ans: Energy available at each successive trophic level of food chain is ten per cent of that at the previous level.
This is called ten per cent law. Thus, 90 per cent energy is lost to the surroundings at each trophic level. However, plants absorb only one per cent of radiant energy of the Sun during photosynthesis. This is explained as under :

Ans: Ozone is an isotope of oxygen, i.e. it is a molecule formed by 3 atoms of oxygen.

Ozone exists in the ozone layer of stratosphere. At higher level o f atmosphere, O₂ molecule breaks down to 2 oxygen atom. The oxygen atom then combines with the oxygen molecule to form ozone.
Ozone layer in the atmosphere prevents UV rays from reaching earth. Exposure to excess UV rays causes skin cancer, cataract and damages eye and immune system. It also decreases crop yield and reduces population of phytoplankton, zooplankton and certain fish larvae which are an important constituent of aquatic food chain. It also disturbs rainfall, causing ecological disturbance and reduces global food production. Thus, it affect the ecosystem.

Ans: The energy flow through different steps in the food chain is unidirectional. The energy captured by autotrophs does not revert back to the solar input and it passes to the herbivores, i.e. it moves progressively through various trophic levels. Thus energy flow from sun through producers to omnivores is in single direction only.
Pesticides are sprayed to kill pests on food plants. The food plants are eaten by herbivores and alongwith the food, pesticides are also eaten by the herbivores. Herbivores are eaten by carnivores and alongwith the herbivore animal, pesticide also enters the body of the carnivore. Man eat both plants and animals and pesticide alongwith food enters the body of human. Concentration of pesticides increases as we move upward in the food chain and the process is called bio-magnification.

Ans: Ecosystem: It is the structural and functional unit of biosphere, comprising of all the interacting organisms in an area together with the non-living constituents of the environment. Thus, an ecosystem is a self-sustaining system where energy and matter are exchanged between living and non-living components.
Main components of ecosystem:
(i) Biotic Component: It means the living organisms of the environment-plants, animals, human beings and microorganisms like bacteria and fungi, which are distinguished on the basis of their nutritional relationship.
(ii) Abiotic Component: It means the non-living part of the environment-air, water, soil and minerals. The climatic or physical factors such as sunlight, temperature, rainfall, humidity, pressure and wind are a part of the abiotic environment.
An aquarium is an artificial and incomplete ecosystem compared to ponds or lakes which are natural, self-sustaining and complete ecosystems where there is a perfect recycling of materials. An aquarium therefore needs regular cleaning.

Ans: CFC → Chloroflurocarbon

Ans: Herbivores are always at the 2^nd trophic level.

Ans: Hawk will have highest concentration of non-biodegradable chemicals. The phenomenon is called biomagnification.

Ans: Only green plants can make their own food from sunlight. Green plants, therefore, always occupy the 1^st trophic level in a food chain.

Ans: 100 Joules of energy will be available to the organism of the 2^nd trophic level.

Ans: (a) Biodiversity is the existence of a wide variety of species of plants, animals and microorganisms in a natural habitat within a particular environment or existence of genetic variation within a species. Biodiversity of an area is the number of species or range of different life forms found there. Forests are ‘biodiversity hotspots’. Every living being is dependent on another living being. It is a chain. If biodiversity is not maintained, the links of the chain go missing. If one organism goes missing, this will affect all the living beings who are dependent on it.
(b) A garden comprises of different kind of flora and fauna such as grasses, flowering and nonflowering plants, trees, frogs, insects, birds, etc. All these living organisms depend and interact with each other and their growth, reproduction and other vital biological activities depend upon the abiotic component comprising of physical factors like temperature, rainfall, wind, soil and minerals. Therefore, we can say that a garden is an ecosystem.
(c) Only 10% energy is transferred to the next trophic level because other 90 per cent is used for things like respiration, digestion, running away from predators.

Ans: Biodegradable substances: 
These can be broken down into simpler substances by nature/ decomposers/bacteria/saprophytes/ saprobionts. 
Example: Human Excreta/Vegetable peels, etc. 
Non-biodegradable substances: 
These can’t be broken down into simpler substances by nature/decomposers. 
Example: Plastic/glass (or any other) (Any one) 
Habits: 
(1) Use of separate dustbins for iodegradable and non-biodegradable waste. 
(2) Recycling of waste. 
(3) Use of cotton/jute bags for carrying vegetables etc.