Our Environment Class 10 Worksheet Science Chapter 13

Fill in the blanks.
Q1: Producers always contain __________pigments.
Ans: chlorophyll
Producers, like plants, always contain chlorophyll because it's a pigment that absorbs light energy for photosynthesis. This energy is used to convert carbon dioxide and water into glucose, which is a form of chemical energy.

Q2: A position in a food chain is called a __________ .
Ans: trophic level
A position in a food chain is called a trophic level. Each trophic level represents a step in the transfer of energy and matter within a food chain that starts with producers and ends with carnivores.

Q3: __________constitute the first trophic level.
Ans: Autotrophs
Autotrophs, such as plants, constitute the first trophic level. They are organisms that can produce their own food by using sunlight, water, and carbon dioxide.

Q4: A series of interconnected food chains representing the feeding relationship of the organisms within an ecosystem is called__________ .
Ans: food web
A food web is a series of interconnected food chains representing the feeding relationships of organisms within an ecosystem. It shows how energy and nutrients are passed from one organism to another.

Q5: Autotrophs capture the energy present in sunlight and convert it into__________ .
Ans: chemical energy
Autotrophs like plants capture the energy present in sunlight and convert it into chemical energy through a process called photosynthesis. This chemical energy is stored in the form of carbohydrates which are used for growth and development.

Q6: In a grassland ecosystem a hawk represents the __________.
Ans: top carnivore
In a grassland ecosystem, a hawk represents the top carnivore. This means it is at the top of the food chain and has no natural predators within that ecosystem.

Mark the statements true (T) or false(F).
Q1: The frog that eats the grasshopper is a secondary consumer.
Ans: true
The frog that eats the grasshopper is a secondary consumer. It is a carnivore that eats primary consumers (like the grasshopper), which eat producers (plants).

Q2: Sewage may be used to produce biogas.
Ans: true
Sewage can indeed be used to produce biogas. Biogas is produced by the anaerobic digestion or fermentation of biodegradable materials such as sewage.

Q3: Decomposers are also called saprotrophs.
Ans: true
Decomposers are also called saprotrophs. They are organisms that break down dead or decaying organisms, and in doing so, they carry out the natural process of decomposition.

Q4: All green plants and blue-green algae are producers.
Ans: true
All green plants and blue-green algae are producers. They are capable of photosynthesis, a process that converts light energy, usually from the Sun, into chemical energy in the form of glucose or other sugars.

Assertion and Reason Type Questions

Q1: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Polythene bags and plastic containers are non-biodegradable substances.
Reason: They can be broken down by microorganisms in natural simple harmless substances.
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: C
The assertion is correct because polythene bags and plastic containers are non-biodegradable substances, meaning they cannot be broken down naturally by biological processes. However, the reason statement is false as it contradicts the assertion. They cannot be broken down by microorganisms into harmless substances, which is why they persist in the environment for long periods.

Q2: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Ozone is formed in upper atmosphere by O2 in presence of UV radiations.
Reason: Ozone depletion will lead to UV rays reaching earth which may cause skin cancer.
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: D
The assertion is true as ozone is indeed formed in the upper atmosphere by the interaction of O2 molecules with UV radiations. However, the reason statement is also true but not related to the assertion. While it's correct that ozone layer depletion allows more UV rays to reach Earth's surface, causing skin cancer, it does not explain how ozone is formed.

Q3: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Tropical rain forests are disappearing fast from developing countries such as India
Reason: No value is attached to these forests because these are poor in biodiversity.
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: C
The assertion is true because tropical rain forests are being rapidly cut down and destroyed in many developing countries, including India. The reason statement, however, is false. Tropical rain forests are in fact rich in biodiversity, and their loss is a serious environmental concern.

Q4: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Aquarium needs regular cleaning
Reason: There are no microbes to clean water in aquarium, therefore, it needs to be regularly cleaned
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: A
The assertion and reason are true and directly related. Aquariums do require regular cleaning because unlike natural bodies of water, they lack the presence of certain microorganisms that help keep the water clean.

Q5: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Biotic components of ecosystem continuously require energy to carry on life processes.
Reason: Biotic components are the nonliving components of the ecosystem
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: C
The assertion is true as biotic components (living organisms) of an ecosystem do require continuous energy for life processes. But the reason statement is incorrect. Biotic components refer to living organisms, not non-living components of the ecosystem.

Q6: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Aquariums are known as the man made ecosystems
Reason: Aquariums are created and maintained by humans
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: A
The assertion and reason are both true and directly related. Aquariums are indeed man-made ecosystems since they are created and maintained by humans to mimic a natural aquatic environment.

Q7: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: First trophic level in a food chain is always a green plant
Reason: Green plants are called producers
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: A
The assertion is that the first trophic level in a food chain is always a green plant. The reason is that green plants are called producers. Both these statements are correct. Green plants are the primary producers as they have the ability to produce their own food through photosynthesis. Therefore, they form the first level in a food chain. Hence, the reason correctly explains the assertion.

Q8: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: The concentration of harmful chemicals is least in human beings.
Reason: Man is at the apex of the food chain.
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: D
The assertion is that the concentration of harmful chemicals is least in human beings. This statement is false as humans are at the top of the food chain and due to bio-magnification, the concentration of harmful chemicals increases at each trophic level. The reason is that man is at the apex of the food chain, which is a true statement.

Q9: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Decomposers keep the environment clean.
Reason: They recycle matter by breaking down the organic remains and waste products of plants and animals.
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: A
The assertion is that decomposers keep the environment clean. This statement is true as decomposers break down dead organic matter, returning nutrients to the soil and keeping the environment clean. The reason is that they recycle matter by breaking down the organic remains and waste products of plants and animals, which is also true and correctly explains the assertion.

Q10: Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion: Man is a herbivore.
Reason: Omnivores eat both plant food and meat of animals.
(a) Both ‘A’ and ‘R’ are true and ‘R’ is correct explanation of the Assertion.
(b) Both ‘A’ and ‘R’ are true but ‘R’ is not correct explanation of the Assertion.
(c) ‘A’ is true but ‘R’ is false.
(d) ‘A’ is false but ‘R’ is true.
Ans: D
The assertion is that man is a herbivore. This statement is false as humans are omnivores, consuming both plant and animal-based foods. The reason is that omnivores eat both plant food and meat of animals. This statement is true and correctly defines an omnivore, but it does not correctly explain the false assertion.

Short Answer Type Questions

Q1: Give any two ways in which biodegradable substances would affect the environment.

Ans: (i) They produce foul smell during decomposition process.
(ii) They may produce harmful gases such as ammonia, methane and carbon dioxide. 

Q2: Differentiate between natural and artificial ecosystem.
Ans:

• Natural ecosystem
• Naturally occurring ecosystem
• E.g., pond, grassland, forest
• Artificial ecosystem
• These are man-made ecosystem
• E.g., garden, aquarium, crop-field.

Q3: List any two advantages of decomposers to the environment?
Ans: Bacteria and fungi are called decomposers because they decompose or consume the dead remains of other organisms.
Advantages :
(i) Decomposers degrade garbage and the organic wastes which would otherwise cause environment problems.
(ii) Decomposers recycle the nutrients through biochemical cycle. 

Q4: Write the harmful effects of using plastic bags, on the environment. Suggest alternatives to plastic bags.
Ans:

• Plastic bags are non-biodegradable wastes, they are not degraded, they begin to stink, emitting foul gases, spoil the beauty of places and contaminate soil, water and air with toxins.
• Cloth bags are used instead of plastic bags because they are stronger, more durable and washable. 

Q5: (a) Define ecosystem.
(b) Autotrophs are at the first level of food chain. Give reason.
(c) In a food chain of frogs, grass, insects and snakes, assign trophic level to frogs. To which category of consumers do they belongs to?
Ans: (a) Ecosystem: It is the functional unit of the environment comprising living and non-living components.
(b) The first trophic level in a food chain is always producers (plants) because they have the ability to trap solar energy with the help of chlorophyll. As a result, they produce food by photosynthesis.
(c) Frogs are secondary consumers. 

Q6: (i) Create a terrestrial food chain depicting four trophic levels.
(ii) Why do we not find food chains of more than four trophic levels in nature?
Ans: (i) Rice (Producers) → Rat (Herbivores) → Snake (Carnivores) → Peacock (Top carnivores)

(ii) This is because according to 10 percent law of energy transfer, only 10 percent of the energy passes from one trophic level to the next. Thus, the amount of energy goes on decreasing with the successive trophic levels. 

Q7: 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?
Ans: Ozone protects the surface of earth from harmful ultraviolet (UV) radiations emitted by the sun. Ozone is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms combine with molecular oxygen to form ozone.
O2 →UV O + O
O + O2 → O3
(zone)
Chlorofluorocarbons (CFCs) are mainly responsible for the drop of amount of ozone in the atmosphere. Use of these chemicals can be reduced by using alternate products that do not harm the ozone layer. Also, safe disposal of old appliances like refrigerators prevents its emission.

Q8: Give reason to justify the following:
The existence of decomposers is essential in a biosphere. 
Ans: The existence of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substances that can be absorbed by the plants.
Thus, decomposer:
(a) replenish the soil naturally,
(b) helps in removing the biodegradable waste. 

Q9: How is ozone both beneficial and damaging? How can we prevent the damaging effect of ozone?
Ans: Damaging as it is a deadly poison. Beneficial as it shields the surface of the earth from UV radiations of the Sun.
By not using synthetic chemicals like CFCs, that deplete layer. 

Q10: (a) Explain the role of UV radiation in producing ozone layer.
(b) Mention the reaction involved.
(c) Why is excessive use of CFCs a cause of concern?
Ans: (a) Ozone is formed in the upper atmosphere when solar UV radiation dissociate molecules of oxygen (O) and then this oxygen atom (O) combines with an oxygen molecule.
(b) Reaction involved:
O2 →UV O + O
O + O2 → O3
(c) When CFC's reach upper layers of the atmosphere, they cause depletion of ozone layer, and allow harmful UV radiations to reach the surface of the earth to create health hazards. 

Q11: How will you create an artificial aquatic ecosystem, which is self-sustainable?
Ans: (a) Large jar filled with water, oxygen, food and aquatic plants and animals.
(b) Oxygen/oxygen pump.
(c) Fish food.
(d) Aquatic plants/Producers provide O2 during photosynthesis.
(e) Aquatic animals/Consumers release CO2 for the process of photosynthesis.
(f) Decomposers are also important for natural cleaning of the aquarium.

Long Answer Type Questions
Q1: Suggest suitable mechanisms for waste management in fertiliser industries.
Ans: 

• Effluents and harmful gases are the major pollutants which are generated in a fertiliser, chemical or pesticides factory. Scientific mechanism for reduction in emission of pollutants in environment is :
  For reduction of gaseous pollutants, electro-static precipitators (ESP) are commonly used. ESP works on the principle of "opposite charges attract." When the gaseous emissions containing unburnt pollutants such as coal particles, unburnt carbon, SOx, NOx, etc. enters this field, ash particles gets charged and attracted towards the collecting plates due to the force produced by the electric field. Thereby, reducing the gaseous emissions in the atmosphere. 
• In addition to this, industrial waste water generated from the fertiliser industry contains pollutants that may contaminate our natural water resources. For safe disposal of industrial waste water, effluent treatment plant (ETP) is set up to treat the waste water. An ETP is used to purify water and remove any toxic and non-toxic materials or chemicals from it. They use evaporation and drying methods, and other auxiliary techniques such as centrifuging, filtration, incineration for chemical processing and effluent treatment. The treated water can be used in the industrial process and for irrigation of plantation. 

Q2: Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage? 
Ans:

• Ozone layer is a protective shield around the Earth. It prevents harmful ultraviolet radiation of the Sun from reaching the Earth. Air pollutants, like chlorofluorocarbons (CFCs), are causing depletion of ozone layer.
• Depletion of ozone layer is allowing greater amount of UV radiation to reach the Earth. UV radiation can affect the ecosystem by affecting photosynthesis in plants, destroying planktons and decomposers. In human beings, UV radiation may cause skin cancer, cataract and damage to immune system.
• Many developed as well as developing nations of the world have agreed to sign and obey the directions of UNEP (United Nations Environment Programme) to cease the production of CFCs or to limit their production to some extent.

Q3: Explain some harmful effects of agricultural practices on the environment.
Ans:  Some harmful effects of agricultural practices on the environment are :
(i) Excess use of ground water for agriculture lowers the water level.
(ii) Excessive use of fertilisers affects the soil pH and kills useful microbes.
(iii) Excessive use of chemical pesticides lead to biomagnification.
(iv) Extensive agriculture causes loss of soil fertility.
(v) Burning of agricultural waste like paddy and wheat straw results into the formation of smog that pollutes environment substantially.
(v) It affects our natural eco-system. 

Q4: Suggest any four activities in daily life which are eco-friendly.
Ans:  Activities in daily life which are eco-friendly are given below :
(i) Use of compost and vermicompost in place of fertilisers.
(ii) Separation of biodegradable and non-biodegradable substances.
(iii) Gardening
(iv) Use of gunny bags or paper bags in place of polythene.
(v) Rain water harvesting. 

Q5: Name the wastes which are generated in your house daily. What measures would you take for their disposal?
Ans: The wastes which are generated in our house daily are :
(i) Paper wastes like newspapers, bags, kitchen wastes, etc.
(ii) Plastic bags.
(iii) Vegetable or fruit peels.
Measures taken for proper disposal are:
(i) Prepare a compost pit for kitchen wastes.
(ii) Safe disposal of plastic bags.
(iii) Segregation of biodegradable and non-biodegradable wastes.
(vi) Fruit peels can be placed near trees or plants, which on decomposition will enrich the soil with nutrients.
(v) Recycling of paper wastes.

Q6: (a) Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.
(b) What will happen if decomposers are absent in an ecosystem?
Ans: (a) The flow of energy is generally from Sun → producer → herbivore → carnivore.
Since the flow of energy is progressively from one trophic level to another and does not revert back, it is said to be unidirectional. Further, the available energy decreases in the higher trophic levels making it impossible for energy to flow in the reverse direction.
(b) Decomposers include micro-organisms such as bacteria and fungi that obtain nutrients by breaking down the remains of dead plants and animals.
It breaks down the complex organic substances of garbage, dead animals and plants into simpler inor ganic substances that go into the soil and are used up again by the plants.
In the absence of decomposers, recycling of material in the biosphere will not take place.