CBSE Class 10 Science Our Environment Worksheet Set C

Multiple Choice Questions

Question. Several factories were pouring their wastes in rivers A and B. Water samples were collected from these two rivers. It was observed that sample collected from river A was acidic while that of river B was basic. The factories located near A and B are :
(a) Soaps and detergents factories near A and alcohol distillery near B.
(b) Soaps and detergents factories near B and alcohol distillery near A.
(c) Lead storage battery manufacturing factories near A and soaps and detergents factories near B.
(d) Lead storage bettery manufacturing factories near B and soaps and detergents factories near A.
Answer: (c)

Question. Disposable plastic plates should not be used because :
(a) They are made of materials with light weight.
(b) They are made of toxic materials.
(c) They are made of biodegradable materials.
(d) They are made of non-biodegradable materials.
Answer: (d)

Question. Which of the following constitute a food chain ?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer: (b)

Question. What will happen if dear is missing in the food chain given below ?
Grass → Dear → Tiger
(a) The population of tiger increases
(b) Tiger will start eating grass
(c) The population of grass decreases
(d) The population of tiger decreases and the population of grass increases
Answer: (d)

Question. Which of the following statement is incorrect ?
(a) All green plants and blue green algae are producers.
(b) Green plants get their food from organic compounds.
(c) Producers prepare their own food from inorganic compounds.
(d) Plants convert solar energy into chemical energy.
Answer: (b)

Question. The % of solar radiation absorbed by all the green plants for the process of photosynthesis is about
(a) 1%
(b) 5%
(c) 8%
(d) 10%
Answer: (a)

Question. Match the following
Column I
(a) Secondary consumer
(b) Primary consumer
(c) Producer
(d) Tertiary consumer
Column II
(i) Herbivore
(ii) Autotroph
(iii) Carnivore
(iv) Large carnivore
Answer: (a) (iii), (b) (i), (c) (ii), (d) (iv).

Fill in the blanks

Question. (a) Decomposer organisms are ............................... in their action.
(b) In nature, all green plants are ............................... whereas animals are consumer.
(c) A series of organisms, each of which feeds on the next organism, the beginning of which is a green plant, is called a ............................... .
Answer: (a) Specific, (b) Producers, (c) Food chain

Very Short Answers Type Questions

Question. Why is biogas considered an excellent fuel ?
Answer: Biogas is considered as an excellent fuel because :
(a) It causes no pollution, as it is environmental friendly and burns completely.
(b) Biogas plant from which biogas is produced serves as an excellent way of waste disposal and burns without smoke.
(c) It is economical and produces a large amount of heat per unit mass.

Question. Write the name of the main constituent of biogas. Also state its percentage.
Answer: Methane is the main constituent of biogas. Its formula is \( \text{CH}_4 \). Its percentage is approximately 50–75%.

Question. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer ?
Plant → Deer → Lion
Answer: According to 10% law,
10% of \( x = 100 \)
\( x = 1000\ \text{J} \) in deer.
10% of \( y = 1000 \)
\( y = 10,000\ \text{J} \) in plant.

Question. In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes ?
Plants → Rats → Snakes → Hawks
Answer: 500 J of energy is available to the rats thus according to 10% law, 50 J energy will be available to snakes and 5 J energy will be available to hawk.

Question. What is an ecosystem ?
Answer: An ecosystem is a self sustaining system where biotic and abiotic organisms of various communities interact with each other. Ponds, forests, grasslands etc., are a few examples of ecosystem.

Question. Why is forest considered a natural ecosystem ?
Answer: Forests are considered as natural ecosystem because of the following reasons :
(a) They have species of plants and animals that grow without human intervention.
(b) All these species interact with each other and are interdependent on each other.
(c) These are naturally sustainable.

Question. Why is lake considered to be a natural ecosystem ?
Answer: A lake is considered as a natural ecosystem as it consists of both biotic and abiotic components, both these components in a lake are interdependent and do not require any human interference for their sustenance.

Question. What is the role of decomposers in the ecosystem ?
Answer: Decomposers act upon dead and decay organisms to convert them into simpler forms. These simple substances get mixed up in the soil and are used as nutrients by the producers. From producers it goes to consumers and so on. They maintain the balance in the ecosystem and provide space for new life in ecosystem.

Question. How can you help in reducing the problem of waste disposal ? Give any two methods.
Answer: We can reduce the use of non-biodegradable wastes. These wastes can be recycled by following various recycling techniques.
(a) Biodegradable wastes can be used to make compost or manure.
(b) Biodegradable wastes can be used in the production of biogas.

Question. What will happen if we kill all the organisms in one trophic level ?
Answer: If we will kill all the organisms in one trophic level the transfer of food energy to the next trophic level will stop i.e., the organisms which are placed higher than this trophic level will die due to lack of food. Similarly the trophic level lower than this one will increase their number. Thus an imbalance would be created in the ecosystem.

Question. Write the common food chain of a pond ecosystem.
Answer: Phytoplanktons → Zooplanktons → Fish → Bird.

Question. Why are some substances biodegradable and some non-biodegradable ?
Answer: There are various types of waste substances released into our environment. Those substances which are degraded into simpler form naturally by the action of microbes like bacteria or fungi are called biodegradable substances. Examples–Vegetables and fruits peels, paper, agricultural wastes etc. Those substances which cannot be degraded into simpler forms naturally by the action of microbes are called non-biodegradable substances. Examples–Aluminium foils, plastic bottles, glass apparatus etc.

Question. Why is it necessary to conserve the environment ?
Answer: It is necessary to conserve the environment to prevent the damage to the environment and to protect the endangered species.

Question. Mention three harmful effects of using polythene bags on the environment. Suggest an effective alternative to these bags.
Answer: (a) Increases soil temperature.
(b) Adverse effect on agricultural products.
(c) Land and animals die after consumption.
Alternative to polythene bags are Jute bags, Paper bags, Cloth bags and Biodegradable bags.

Question. List two biotic components of an eco-system.
Answer: Plants, animals, microorganisms are the biotic components of an ecosystem.

Question. Why is depletion of ozone layer a cause of concern ?
Answer: Ozone layer shields the earth’s surface from harmful ultraviolet (UV) radiations from the sun. UV radiations are damaging to organisms and may cause skin cancer.

Question. Name two natural ecosystems.
Answer: River, pond, forest, ocean etc., natural are ecosystems.

Question. What is ozone ? Name the chemicals that damage the ozone layer.
Answer: Ozone is a molecule formed by three atoms of oxygen. Ozone is a gas present in the outer atmosphere which protects us from harmful ultraviolet (UV) radiations. Chlorofluorocarbons (CFCs) damage the ozone layer.

Question. What is a biodegradable substance ?
Answer: Biodegradable substances are the substances that can be broken down by biological processes.

Question. Give two examples of decomposers ? State their important role in nature.
Answer: Bacteria and fungi are the examples of decomposers. Decomposers help in the replenishment of soil and in the recycling of nutrients back into the soil.

Question. State the essential function performed by ozone at the higher levels of the atmosphere.
Answer: It shields the surface of the earth from the harmful ultraviolet (UV) radiations of the sun.

Question. Why are bacteria and fungi called decomposers ? List any two advantages of decomposers to the environment.
Answer: Bacteria and fungi break down or decompose the dead remains and waste products of organisms. Thus, they are called decomposers. Advantages of decomposers to the environment are :
(a) Natural replenishment of soil.
(b) Recycling of nutrients in the soil.

Question. List any two abiotic components of an ecosystem.
Answer: Air, water, minerals, sunlight are the abiotic components of an ecosystem.

Question. Where and how did ‘‘Chipko Andolan’’ start in our country ? How did this movement ultimately benefit the local people ?
Answer: ‘Chipko’ means ’hug’ and ‘Andolan’ means’ movement’. This movement was started in Garhwal region of Uttarakhand by hugging tree trunks to prevent the cutting of trees. (a) Forest produce was made available to the local population. (b) It benefitted the environment by conserving the quality of soil and the resources.

Question. We often use the word environment. What does it mean ?
Answer: Environment is the physical, chemical and biological conditions of the region.

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 producers (plants) have the ability to trap solar energy with help of chlorophyll.

Question. Why is excessive use of CFCs a cause of concern ?
Answer: When CFC’s reach upper layers of the atmosphere they cause depletion of ozone layer and allows harmful UV radiations to reach the surface of the earth to create health hazards.

Short Answers Type Questions

Question. (a) From the following group of organisms create a food chain which is the most advantageous for Human beings in terms of energy. [Hawk, Rat, Cereal plant, Goat, Snake, Human Being]
(b) State the possible disadvantage if the cereal plant is growing in soil rich in pesticides.
(c) Construct a food web using the organisms mentioned above.
Answer: (a) Cereal Plant – Human Being. (b) If cereal plants are grown in soil rich in pesticides, it can pose a potential risk to humans and other life forms and can result in unwanted side effects to the environment. Pesticides are lethal to non-targeted species also. Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than their target species, because they are sprayed or spread across entire agricultural fields. (c) [A diagrammatic representation of a food web would be constructed connecting Cereal plant to Rat and Goat; Rat to Snake and Hawk; Goat to Human and Hawk; Snake to Hawk].

Question. (a) Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
(b) List any two practices that can be followed to dispose off the waste produced in our homes.
Answer: (a) The harmful effects of plastics on the environment are : (i) Plastics do not undergo degradation, thus, stay in the soil for many years, which affects the soil fertility and degrades the soil quality. (ii) When plastic artifacts enter the drainage and sewage system, they block the pipes and the drains causing water logging. Alternatives to the usage of plastic bags are : (i) We can reduce the use of plastic bags by carrying jute bags and paper bags to carry items from the market. (ii) We can reduce the use of plastic containers for the storing of food and other items and also use more durable materials like metal boxes. (iii) We can avoid using take away food containers. (b) The practices that can be followed at our homes to dispose off wastes are : (i) We can use discarded bottles and jars to store food items and water. (ii) We can use broken artifacts and create something new with our own creativity, for e.g., discarded water bottles can be used as containers for craft, decorative items etc.

Question. Write the essential function performed by ozone at the higher levels of the Earth’s atmosphere ? How is it produced ? Name the synthetic chemicals mainly responsible for the drop of amount of ozone in the atmosphere. How can the use of these chemicals be reduced ?
Answer: Ozone layer absorbs most of the harmful ultraviolet radiations from the sun to the earth. It is formed high up in the atmosphere by the action of ultraviolet radiation on oxygen gas. Chlorofluorocarbons are the synthetic chemicals responsible for the drop of amount of ozone in the atmosphere.
\( \text{O}_2 \xrightarrow{\text{UV}} \text{O} + \text{O} \)
\( \text{O} + \text{O}_2 \rightarrow \text{O}_3 \)
The use of these chemicals can be reduced by : (a) Replacement of chlorofluorocarbons with hydrochlorofluorocarbons because it breaks down more quickly. (b) Safe disposal of old appliances such as refrigerators and freezers. (c) Finding substitute chemicals that are ozon friendly.

Question. Define a food chain. Design a terrestrial food chain of four trophic levels. If a pollutant enters at the producer level, the organisms of which trophic level will have the maximum concentration of the pollutant in their bodies ? What is this phenomenon called ?
Answer: It is the sequence of arrangement of living organism in a community in which one organism consumes another organism to transfer food energy. Terrestrial food chain: Grass → Insect → Frog → Bird. The organism at higher trophic level (Bird) will have the maximum concentration of pollutants. This phenomenon is called biological magnification.

Question. How can we help in reducing the problem of waste disposal ? Suggest any three methods.
Answer: The three methods by which we can reduce the problem of waste disposal are : (a) Adopting the 3R approach i.e., Reduce, Reuse, Recycle. (b) Segregation of waste into biodegradable and non-biodegradable waste. (c) Conversion of waste into useful components like biogas and then using compost as a fertiliser.

Question. Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem.
Answer: Ecosystem refers to the interaction of all the biotic and abiotic components present in a particular area. Energy flows across the trophic levels following the 10% law. Only 10% of the energy available to a trophic level is passed on to the next trophic level. [Block diagram showing: Producers (10,000J) → Primary Consumer (1000J) → Secondary Consumer (100J) → Tertiary Consumer (10J)].

Question. Students in a school listened to news read in the morning assembly that the mountains of garbage in Delhi, suddenly exploded and various vehicles got buried under it. Several people were also injured and there was traffic jam all around. In the brain storming session the teacher also discussed this issue and asked the students to find out a solution to the problem of garbage. Finally they arrived at two main points—one is self management of the garbage we produce and second is to generate less garbage at individual level.
(a) Suggest two measures to manage the garbage we produce.
(b) As an individual what can we do to generate the least garbage? Give two points.
(c) List two values the teacher instilled in his students in this episode.**
Answer: (a) (i) For managing garbage, first we must segregate it into biodegradable & non-biodegradable substances. Biodegradable substances like vegetable peels, domestic waste, animal excreta, cow dung etc. must be converted into manure. This not only helps in enriched growth of plants but also prevents dumping of it in open production of foul smell etc. (ii) For non-biodegradable substances, we must further segregate as recyclable & non-recyclable. All recyclable metals, plastic, glass must be sent to differ factories which after proper cleaning, process them into new products. (iii) For rest over garbage, practices like filling it into landfills which can be converted into playground for children or incineration at places with proper management for it can be done. (b) (i) We must follow the policy of ‘reduce’. We should try to switch off lights when unnecessary for our resources & for garbage, try using same sheet of blank paper not used from other side, try making registers with utilising all the pages to reduce our demand for rough copies, reducing usage of plastic disposable cups. (ii) We must follow the policy of ‘reuse’. Using jam bottles, milk cartons, packaging boxes, ketchup bottles is a good way to use resources already once used. (c) The teacher instilled environmental responsibility and proactive civic behavior.

Question. Give any two ways in which biodegradable substances would affect the environment.
Answer: (a) Decomposition of biodegradable substances results in production of foul smell. (b) The area where biodegradable wastes are accumulated serves as a good breeding place for mosquitoes, flies etc, which are the main carriers of germs for diseases like cholera, jaundice, typhoid etc.

Question. Give any two ways in which non-biodegradable substances would affect the environment.
Answer: (a) Non-biodegradable substances like pesticides [DDT] enter the food chain and leads to biomagnification. (b) As non-biodegradable substances cannot be degraded naturally so they accumulate in the soil causing pollution and also reduces the fertility of the soil.

Question. Give any two examples of each : (a) Organisms occupying the first trophic level, (b) Carnivores, (c) Biodegradable wastes of humans, (d) Ecosystem, (e) Abiotic factors of an ecosystem.
Answer: (a) Grass, green plants. (b) Tiger, Eagle. (c) Kitchen waste like peels of vegetables, fruits, left over foods and old newspaper. (d) Natural ecosystem includes forest, pond and artificial ecosystem which include garden, parks, crop fields. (e) Physical factors like temperature, sunlight and Edaphic factors like soil.

Question. Briefly describe different methods of wastes disposal ?
Answer: (a) Land-fills : In urban areas wastes are filled or deposited in low lying areas. These are also known as dumping grounds where wastes are buried. (b) Recycling of wastes : Some wastes like papers, plastics, metals etc., which can be recycled are send to special recycling treatment plants so that new substances can be made from them. (c) Preparation of compost : Biodegradable wastes like kitchen wastes, peels of fruits and vegetables etc., can be used to prepare compost which serves as a good manure to the plants. (d) Incineration : Some wastes like medical wastes, chemical wastes are burnt at very high temperature in an incinerator and the ashes left behind are disposed by land-fills. (e) Production of biogas : Biodegradable wastes can be used in biogas plants to produce biogas which is used for several purposes like as a fuel.

Question. Why is damage to the ozone layer a cause of concern ? What steps are being taken to limit this damage ?
Answer: Ozone layer is found in stratosphere which prevents the harmful UV rays of sun from entering earth‘s surface. Various ozone depleting substances like CFCs cause a great damage to ozone layer thus leading to its depletion. So harmful UV rays from sun can easily pass through this layer and cause various genetic disorders, mutations, cancer, eye diseases etc., in humans. UV rays also affect plants and animals. In 1987, UNEP [United Nations Environment Programme] succeeded in forging an agreement called Montreal protocol which states that to reduce the use of CFCs and replace CFCs with other alternatives.

Question. Why have been kulhads banned for serving tea on platforms ? What types of cups are used in trains and platforms ?
Answer: Kulhads are made from the top fertile layer of soil. Use of this soil to make kulhads on a large scale would lead to loss of fertile top soil. This fertile top soil is of great use for the growth of plants as it contains many useful nutrients. Hence, kulhads have been banned for serving tea on platforms. Nowadays disposable paper cups are used in trains and platforms.

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 ?
(c) How the students would have motivated each other for the success of their decision ?
Answer: (a) The use of polythene and plastic be reduced in daily life because they are non-biodegradable. (b) (i) by carrying tiffin and water in steel containers. (ii) Encourage the use of ink pens. (c) By spreading awareness in the form of Nukkad Natak, speeches in morning assembly, class discussions, display boards etc. The students can be motivated for the success of their decision.

Question. With the help of an example of a food chain, prove that the flow of energy in the biosphere is unidirectional.
Answer: Sun → Producer/Plant → Primary Consumer/Herbivore → Secondary Consumer/Carnivore → Top Carnivore. (a) At each trophic level only 10% of the energy is passed on to the next and the rest is either utilised for its own metabolic activities or is lost in the environment as heat. (b) Lost energy is not returned to the previous level or solar input. Thus the flow of energy in the biosphere is unidirectional.

Question. Your mother always thought that fruit juices are very healthy for everyone. One day she read 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 organs. Name the phenomenon and write about it.
Answer: (a) (i) During growing of fruit crops, pesticides are often used which may contaminate the fruit and hence the fruit juices. (ii) By using contaminated ground water for making fruit juices. (b) The phenomenon is known as bio-magnification or Biological magnification. The progressive accumulation of non biodegradable toxic substances or chemicals at each trophic level leading to their maximum concentration at the highest trophic level (human beings) is called biological magnification.

Long Answers Type Questions

Question. Distinguish between producers and consumers.
Answer: 1. Producers prepare their own food; Consumers depend on producers for their food. 2. Producers prepare food from inorganic material by photosynthesis; Consumers depend on readymade food. 3. Producers always constitute the first trophic level; Consumers are placed at second or higher trophic levels. 4. Producers possess chlorophyll; Consumers do not possess chlorophyll pigments. 5. Producers trap solar energy and convert it to chemical energy; Consumers eat producers to get chemical energy. Examples: Producers–Green plants, algae; Consumers–Humans, animals.

Question. What is a food chain? Why is the flow of energy in an ecosystem unidirectional? Explain briefly.
Answer: Food Chain is a sequence of organisms in which one consumes the other to transfer energy. for eg. Plant (Producer) → Cow (Herbivore) → Lion (Carnivore). The flow of energy in an ecosystem is always unidirectional as they cannot revert back the energy consumed or lost in environment. 3. for example, plants cannot revert back the chemical energy into solar energy. 4. Since they move progressively from one trophic level to the other, the energy content goes on decreasing according to 10% law. 5. They do not have that much energy to reverse the flow even if they want to.

Question. Explain energy relationships with trophic levels.
Answer: Each step or level of the food chain where transfer of food or energy takes place is referred to as a trophic level. The energy relationship within trophic levels is shown in a form of pyramid. Grass : They are the producers so are placed in first trophic level. They transfer energy to grasshopper, but only 10% is available according to Lindeman’s 10% Law. If grass has 10,000 kcal, only 1000 kcal transfers to grasshopper. Similarly grasshopper is placed at second trophic level; frog in third, snake in fourth and hawk is fifth. At each trophic level the energy goes on decreasing i.e., frog will receive 100 kcal, snake 10 kcal and hawk only 1 kcal. Thus a food chain can be only up to maximum 5 trophic levels.

Assertion and Reasoning Based Questions

Question. Assertion : Arctic’s ozone depletion tends to be milder and short lived than the Antarctic’s.
Reason : CFCs, frigid temperatures and sunlight are not present at the Arctic at the same time.
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If assertion is false but reason is true.
Answer: (a)

Question. Assertion : The flow of energy is unidirectional.
Reason : Energy as it progresses through the various trophic levels it is no longer available to the previous level.
(a) A
(b) B
(c) C
(d) D
Answer: (a)

Question. Assertion : Plastics are non- biodegradable.
Reason : Enzymes cannot degrade plastics.
(a) A
(b) B
(c) C
(d) D
Answer: (a)

Question. Assertion : Energy available at each trophic level gets diminished progressively.
Reason : Little usable energy remains after four trophic levels.
(a) A
(b) B
(c) C
(d) D
Answer: (c)

Question. Assertion : Chemicals and toxins accumulate more and more as you move up the food chain.
Reason : Anything that gets into biological tissue, that is not normally there, has the potential to accumulate and magnify.
(a) A
(b) B
(c) C
(d) D
Answer: (a)

Creating Based Questions

Question. Suggest an alternative coolant that can be used instead of CFCs.
Answer: HFCs have replaced CFCs and HCFCs as coolant for refrigerators. HFCs pose no harm to the ozone layer. They are potent green house gases. HFCs are generated during the manufacturing of HCFCs.

Question. Rita wants to have an aquarium at home. What are the things that she needs to keep in mind in designing an aquarium ?
Answer: The fish would need a free space for swimming, water, oxygen and food. Thus, she need a good aquarium tank, oxygen can be provided through an oxygen pump (aerator) and fish food is available in the market. Water parameters for nitrate, nitrite, ammonia and pH levels are to be maintained. To condition water properly, use a de-chlorinating and biological aquarium supplement. It is recommended to change 25 percent of the aquarium water at least once a month.

Question. Shyam was very upset after reading the news of a whale shark that was found dead. Suggest some measures that can be taken to reduce plastic waste.
Answer: Cloth bags can be used instead of using plastic bags as they are washable, strong and more durable. They are made of biodegradable material and do not pollute the environment. They can be recycled and reused. These days, new types of plastics which are said to be biodegradable, are available.

Question. Using the following information, form a pathway which shows the flow of energy at each trophic level. And also include information that is not mentioned below to complete it. light energy, organic products, first trophic level, herbivores, second trophic level, energy.
Answer: Light energy → green surfaces of plants → chemical energy stored in various → organic products in the plants → first trophic level → herbivores consume plants as food → second trophic level → convert chemical energy into kinetic energy → herbivores are consumed by carnivores of the first order (secondary consumers) → third trophic level → primary carnivores are consumed by top carnivores (last level) → energy will be degraded.

Question. Using the following information form a pathway showing the formation of ozone at higher levels. [Ozone, UV, Molecular oxygen]
Answer: Ozone production → UV radiation acting on oxygen (\( \text{O}_2 \)) molecule → the higher energy UV radiation split apart some molecular oxygen (\( \text{O}_2 \)) → \( \text{O}_2 \xrightarrow{\text{UV}} \text{O} + \text{O} \) → free oxygen (O) atoms then combine with molecular oxygen ozone \( \text{O} + \text{O}_2 \rightarrow \text{O}_3 \) (Ozone).

Paragraph/Table and Case Study Based Questions

The energy flow in the ecosystem is one of the major factors that support the survival of such a great number of organisms. For almost all organisms on earth, the primary source of energy is solar energy. It is amusing to find that we receive less than 50 per cent of the sun’s effective radiation on earth. When we say effective radiation, we mean the radiation, which can be used by plants to carry out photosynthesis.

Question. Green plants utilise ............... percent of sun’s energy to prepare their food by the process of photosynthesis.
(a) 1 percent
(b) 10 percent
(c) 20 percent
(d) 99 percent
Answer: (a)

Question. If 100 J energy is available at the producer level in a food chain then the energy available to the secondary consumer will be:
(a) 10 J
(b) 0.1 J
(c) 1 J
(d) 0.01 J
Answer: (c)

Question. The ____________ is the functional unit of environment.
(a) Genus
(b) Ecosystem
(c) Class
(d) Biome
Answer: (b)

Question. Which of the two sets belong to the same trophic level?
(a) Frog: Lizard
(b) Rabbit: Tiger
(c) Vulture: crow
(d) Deer: Hawk
Answer: (a)

Question. A food chain comprising birds, green plants, fish and man. The concentration of harmful chemical entering the food chain will be maximum in:
(a) plant
(b) man
(c) birds
(d) fish
Answer: (b)

The amount of ozone in the atmosphere has begun to drop sharply from 1980s. This decrease has been linked to synthetic chemicals. In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze harmful chemicals production at 1986 levels. Based on the paragraph answer the following questions:

Question. At what level of atmosphere ozone layer is found?
(a) Troposphere
(b) Stratosphere
(c) Biosphere
(d) Ionosphere
Answer: (b)

Question. At higher level of atmosphere radiations act upon oxygen molecule to form:
(a) Oxygen
(b) Ozone
(c) Carbon monoxide
(d) All of these
Answer: (b)

Question. What is the major cause of ozone depletion?
(a) Chlorofluorocarbons
(b) Hydrochlorofluorocarbons
(c) Carbon tetrachloride and methyl chloroform
(d) All of these
Answer: (d)

Question. Which of the following source is responsible for the depletion of ozone layer?
(a) Fire extinguisher
(b) Aerosol sprays
(c) Refrigerators
(d) All of these
Answer: (d)

Question. In which of the following country Ozone hole has appeared?
(a) Africa
(b) North America
(c) Japan
(d) Antarctica
Answer: (d)

Archives

Question. The activities of man had adverse effects on all forms of living organisms in the biosphere. (a) Why is it necessary to conserve our environment ? (b) State the importance of green and blue dustbins in the safe disposal of the household waste. (c) List two values exhibited by your classmate who is an active member of Eco club of your school.
Answer: (a) To prevent ecological imbalance and protect life. (b) Green dustbins are for biodegradable waste; Blue dustbins are for non-biodegradable waste. (c) Environmental awareness and social responsibility.

Question. In a food chain of frog, grass, insect and snake, assign trophic level to frog.
Answer: Grass (1st) → Insect (2nd) → Frog (3rd).

Question. List four advantages of properly managed watershed management.
Answer: (i) Conserves soil and water, (ii) Increases biomass production, (iii) Recharges groundwater, (iv) Mitigates floods and droughts.

Question. “Reuse is better than recycling of materials”. Give reason to justify this statement.
Answer: Reuse saves energy used in the recycling process and avoids additional waste generation.

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: 1,000 J.