Please refer to Chapter 15 Our Environment Class 10 Science Important Questions with solutions provided below. These questions and answers have been provided for Class 10 Science based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 10 Science for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 10.
Class 10 Science Important Questions Our Environment Chapter 15
Very Short Answer:
Question. What is meant by ‘biological magnification’?
Answer : Biological Magnification is the process by which the harmful and toxic substances enter the food chain and get concentrated in the body of living organisms at each successive level in food chain.
Question. Name any two man-made ecosystems.
Answer : Examples of man-made ecosystems are aquarium, crop-fields, zoo, botanical garden, Greenhouse.
Question. In a food chain of frog, grass, insect and snake, assign trophic level to frog.
Answer : Grass → insect → frog → smoke
Frock comes in the third traffic level
Question. Why should biodegradable and nonbiodegradable wastes be discarded in two different dustbins?
Answer : Biodegradable and non-biodegradable wastes should be discarded in two different dustbins because of following reasons:
(1) The biodegradable wastes kept in a separate bin can be dumped directly in a pit for composting or for dumping in landfills.
(2) The useful part of non-biodegradable wastes kept in a different bin can be separated for recycling or reusing them.
(3) Non-useful part of wastes can be disposed off in such a way that it does not harm the people or pollute the environment in anyway.
(4) Segregated waste is cheaper to dispose of because it does not require as much manual or mechanical sorting as mixed waste.
Question. Name two natural ecosystems.
Answer : Examples of natural ecosystems are rivers, forests, ponds, lakes and ocean
Question. List two biotic components of environment.
Answer: Plants, animals, micro-organisms (any two) are biotic components.
Question. Why are green plants called producers?
Answer: Green plants prepare their own food by photosynthesis with the help of CO2, H2O, sunlight and chlorophyll.
Question. Why do producers always occupy first trophic level of food chain?
Answer: They prepare their own food from CO2, H2O and sunlight from environment. They are consumed by herbivores, therefore they always occupy first trophic level.
Question. State a way to prevent accumulation of harmful chemicals in our bodies.
Answer: Minimum use of fertilizers, insecticides and pesticides, can prevent the accumulation of harmful chemicals in our body.
Question. During heavy rain in a village the rain water carried excessive fertilizer to a pond. How will it affect the fish production in pond in the long run?
Answer: Fish production will decrease due to formation of excess of algae.
Question. “Flow of energy is unidirectional”. Name the first two components of the environment involved in flow of energy from the Sun.
Answer: Producers and primary consumers are first two components in the flow of energy.
Question. Define ecosystem.
Answer: All living organisms and abiotic components of surroundings forms an ecosystem.
Question. Which of the following are always at second trophic level of food chains?
Carnivores, Autotrophs, Herbivores.
Answer: Herbivores will always be at second trophic level.
Question. What will be the amount of energy available to the organisms of secondary consumer trophic level of food chain, if the energy available to producer level is 10000 Joules.
Answer: Energy available to primary consumers level is 10000 X 10/100 = 1000 J
Energy available to secondary consumer trophic level = 1000 X 10/100 = 100 J
Question. The following organisms form a food chain. Which of these will have the highest concentration of nonbiodegradable chemicals? Name the phenomenon.
Insects, Hawk, Grass, Snake, Frog.
Answer: Hawk is a decomposer and have maximum concentration of non-biodegradable chemicals.
The phenomenon is called Biomagnification.
Question. Select two non-biodegradable substances from the following waste generated in the kitchen:
Spoil food, Paper bags, Milk, Tea bags, vegetable peels, tin cans, used tea leaves.
Answer: Tea bags and tin cans.
Question. What are various steps in the food chain called?
Answer: Trophic level.
Question. Why are bacteria and fungi called decomposer?
Answer: Bacteria and fungi are called decomposer because they breakdown complex organic matter as remains of plants and animals into CO2, methane and other simple molecules which go into atmosphere and as nutrients to soil.
Question. Consider the following food chain which occurs in forest: Grass → Deer → Lion
If 10000 J of solar energy is available to grass, how much energy would be available to deer to transfer to lion.
Answer: Grass will absorb 1% solar energy i.e. 10000 X 1/100 = 100 J
Dear will get 10% of 100 J = 100 X 10/100 = 10 J
Out of this 10 J of energy, only 1 J of energy can be transferred to lion.
Question: What is an ecosystem?
Answer: 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 selfsupporting system.
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: In an ecosystem, only 10% of energy is transferred from one trophic level to next, i.e., 10 percent law and rest is dissipated into the environment. erefore, if plants (being producers- 1st trophic level)-transfer 500 J of energy to rats (2nd trophic level) then rats would transfer 50 J of energy to snakes (3rd trophic level) which in turn will transfer only 5 J of energy to hawks (4th or last trophic level) in a food chain.
Plants →Rats →Snakes →Hawks
5000 J 500 J 50 J 5 J
Question: Why is a lake considered to be a natural ecosystem?
Answer: Lake is an ecosystem where living organisms grow reproduce and interact among each other as well as with abiotic components and carry out other activities in nature by themselves without any human interference, therefore it is referred to as a natural ecosystem.
Question: We ofen use the word environment. What does it mean?
Answer: Environment can be defined as the physical or biological world where an organism lives. Literally speaking, an organism’s immediate surrounding constitutes its environment which includes both biotic and abiotic components around him.
Question: In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producers? Plants ?? Deer ?? Lion
Answer: As per 10% law of flow of energy in an ecosystem only 10% of energy is received by the next trophic level. Hence, in the given food chain :
If 100 J of energy is availabe to lion, the plants or producers have 10,000 J of energy available to them.
Plants →Deer →Lion
10, 000 J 1000 J 100 J
Question: List two biotic components of a biosphere.
Answer: Two biotic components of a biosphere are:
(i) Producers – Include organisms which can produce their food using simple inorganic compounds, e.g., all green plants, blue green algae (cyanobacteria),
(ii) Consumers – Include organisms which are unable to synthesise their food, therefore, utilise materials and energy stored by the producers or eat other organisms, e.g., all the animals.
Question: In a food chain of frog, grass, insect and snake, assign trophic level to frog.chlorophyll.
Answer: In the given food chain, frog belongs to the third trophic level as shown here :
Grass → Insect→ Frog → Snake
T1 T2 T3 T4
Question: Why do producers always occupy the first trophic level in every food chain?
Answer: Producers are the green plants that can manufacture food using CO2 and H2O in the presence of sunlight, i.e., they are autotrophs. They serve as a source of food for all non-producers orconsumers directly or indirectly. Hence, producers occupy the First trophic level in a food chain.
Question: Why are green plants called producers?
Answer: Green plants are called producers because they manufacture their own food with the help of CO2 and H2O in the presence of sunlight and chlorophyll.
Question: Which of the following are always at the second trophic level of food chains? Carnivores, Autotrophs, Herbivores
Answer: Herbivores always occupy the second trophic level of food chains
Question: List two examples of natural ecosystem.
Answer: The two examples of natural ecosystem are :
(i) Forest ecosystem
(ii) River ecosystem
Question: The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals? Name the phenomenon associated with it.Insects, Hawk, Grass, Snake, Frog
Answer: Among the following organisms of the food chain, hawk being top consumer is present at topmost trophic level, hence will have the highest concentration of non-biodegradable chemicals due to a phenomenon known as biomagnification.
Question: Bacteria and fungi are called decomposers. Why?
Answer: Bacteria and fungi are called decomposers because these microorganisms break down the complex organic matter present in dead plants and animals into simpler substances.
Question. (A) Create a food chain of the following organisms: Insect, Hawk, Grass, Snake, Frog
(B) Name the organism at the third trophic level of the created food chain.
(C) Which organism of this food chain will have the highest concentration of nonbiodegradable chemicals?
(D) Name the phenomenon associated with it.
(E) If 10,000 joules of energy is available to frogs, how much energy will be available to snakes in this food chain.
Answer : (A) Food chain
Grass → Insect → Frog → Snake → Hawk
(B) The organism at the third trophic level of the created food chain is frog.
(C) The organism which will have the highest concentration of non-biodegradable chemicals is Hawk.
(D) The phenomenon associated with it is Biological Magnification.
(E) If 10,000 oules of energy is available to frogs, 1000 Moules of energy will be available to snakes in this food chain as per 10J law of energy.
Question. (A) What is an ecosystem?
(B) List any two natural ecosystems.
(C) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly.Why?
Answer : (A) Ecosystem: It is a structural and functional unit of the biosphere which comprises living organisms and their non-living environment that interact by means of food chains
and chemical cycles in energy flow, biotic diversity and material cycling and form a stable self supporting system.
(B) (Image 370)
Common examples of natural ecosystem are pond, lake, meadow, desert, forest etc.
(C) We do not clean ponds or lakes because it is a natural ecosystem and is a self-sustaining unit. Aquatic plants act as producers, small aquatic insects (mosquito larvae, beatles
etc.) are herbivores and these herbivores are eaten by carnivores (fish). There are microorganisms (bacteria and fungi) present in the soil of the pond which decompose the dead remains and waste products into simpler inorganic substances and clean the pond.
But an aquarium is an artificial ecosystem.
The transfer of energy takes place from producers to herbivores to carnivores but there is no soil in the pond so microorganisms (decomposers) are not present in the aquarium which act as cleaners. So we have to clean the aquarium regularly.
Question. What is meant by tropic level in a food chain?
Construct a terrestrial food chain with four trophic levels. The energy flow in a food chain is always unidirectional. Why?
Answer : Trophic level = Each step or level of the food chain forms a trophic level.
Terrestrial food chain
Grass → Grasshopper → Frog → Snake
Producer Herbivore Primary Secondary (Autotrophs) (Primary consumer) carnivore carnivore Flow of energy in an ecosystem is unidirectional Each organism needs energy to carry on vital activities and for building up and repairing the body tissues.
(1) The ultimate source of energy used by living organisms is the sun.
(2) Only 1% of solar radiations are captured by green plants in a terrestrial ecosystem and converted into food energy by photo synthesis. This energy is stored as chemical energy of food.
(3) When green plants (producers) are eaten by primary consumers (Herbivores) a lot of heat is lost as heat to the environment and other activities. Only 10% of the food eaten
is turned into its new body and is available for the next level of consumers (Primary carnivores).
(4) Only 10% amount of organic matter reaches the next level of consumers (secondary carnivores).
(5) Since, amount of available energy goes on decreasing at each trophic level, food chains usually consists of only 3 to 4 trophic levels.
For example grass receives 6000J of energy from the sun. It will pass 10% of energy as per 10% law to grasshopper i.e. 600 J and so on. (Image 371)
Question. List four problems caused by non-biodegradable wastes.
Answer : Lot of Problems are caused by non- biodegradable wastes. Four Problems are as follow:
(1) Soil Pollution
(2) Water Pollution
(3) Ecological imbalance
Question. Complete the following flow chart based on ecosystem and its components. (Image 371)
Ecosystem: It is a structural and functional unit of the biosphere which comprises living and non-living components that interact by means of food chains and chemical cycles
resulting in energy flow, biotic diversity and material cycling to form a stable and self supporting system.
Question. (A) Complete the following table: (Image 371)
(B) How is ozone formed at the higher levels of atmosphere?
Answer : (A) O2
(C) Benefits of Oxygen to biotic component.
Breathing: All biotic components inhale oxygen from the atmosphere and exhale CO2.
Question. What is ozone? Name the chemicals that damage the ozone layer.
Answer : Ozone is a molecule formed by three atoms of oxygen.
Synthetic chemicals such as chlorofluorocarbons (CFC) and aerosols are the chemicals that damage the ozone layer in the atmosphere.
Question. Why are crop fields known as artificial ecosystems?
Answer : An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. Artificial ecosystems are those ecosystems which have been modified by human beings for their own benefit. Crop fields are man made and some biotic and abiotic components are manipulated by humAnswer :
(1) In a crop field, plants do not grow naturally.
They are mostly grown by humans, hence, they are considered as artificial ecosystems.
(2) It usually consists of a major crop (monoculture).
(3) Unwanted plants are removed using weedicides.
(4) Pests and unwanted insects are killed using pesticides and insecticides.
(5) Artificial fertilisers, manures and nutrients are externally supplied to the soil by man.
These activities of man alter the biotic and abiotic components of the ecosystem. Therefore,crop fields are known as artificial ecosystems.
Question. (1) Create a terrestrial food chain depicting four trophic levels.
(2) Why do we not find food chains of more than four trophic levels in nature?
Answer : A food chain showing I tropic level
II tropic level, III tropic level and IV tropic level .
A flow chart or a diagrammtic representation showing all the four tropic levels would also be accepted.
Question. What are the advantages of cloth bags over plastic bags during shopping?
Answer : Advantages of cloth bags over plastic bags during shopping are as follows:
(1) Cloth bags are more durable and thus can be used again and again.
(2) They are strong and thus capable of carrying more things.
(3) They are biodegradable in nature.
Question. Define Ecosystem. Briefly describe the two types of ecosystem.
Answer : Ecosystem: An Ecosystem is a self contained unit of living things (plants, animals and decomposers) and their non-living environment (soil, air and water). It needs only the input of sunlight energy for its functioning.
Types of Ecosystem: There are two types of ecosystem:
Natural ecosystem: These ecosystems operate in the nature by themselves without any human interference. They can be terrestrial or aquatic.
The common examples of terrestrial ecosystem are forest, grassland and desert. The common examples of aquatic ecosystem are ponds, lakes, rivers, sea.
Man-made or artificial ecosystem: These are maintained by man and hence are called Manmade ecosystems or artificial ecosystem. Man maintains the natural balance by the addition
of energy and planned manipulations. Example: crop field, aquarium, garden.
Question. List two causes of depletion of ozone layer. Mention any two harmful effects of depletion of this layer.
Answer: Two causes of depletion of ozone layer are: (i) CFCs (ii) Aerosols
Two harmful effects of depletion of this layer are:
(i) UV radiations can reach the earth and causes skin cancer, harmful to eyes and immune system will be disturbed.
(ii) It may lead to variations in rainfall, ecological disturbance.
Question. (i) What is the height of ozone from the equator?
(ii) Name the rays against which ozone layer provides protection.
(iii) Name one effect of depletion of ozone layer.
Answer: (i) 10 to 16 km (ii) UV rays (iii) Global warming.
Question. You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment Day’.
(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.
Answer: (a) Ozone layer is a rich zone of ozone found in upper atmosphere. It helps in shielding the Earth from the harmful UV radiations coming from the Sun. If ozone layer gets depleted, UV radiations can directly reach the Earth’s surface and drastically affect the life on Earth. For instance, UV radiations coming from the Sun causes skin cancer. So, it is very important to protect the ozone layer so as to save our environment and the planet Earth.
(b) Some of the ways to help protect and stop the depletion of the ozone layer include: Not buying products in aerosol cans, maintaining air-conditioning filters and units.
In order to halt the depletion of the ozone layer, countries around the world have banned the use of chlorofluorocarbons and other ozone-depleting substances. These compounds produce chlorine and bromine atoms high in the atmosphere, and these atoms react with ozone, destroying it.
By reducing the use of fluorescent lights.
By minimising the use of vehicles to limit the emission of harmful gases that cause damage to the ozone layer, we can contribute to its protection.
Question. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer? Plants → Deer → Lion
Answer: Plants → Deer → Lion
It is given that 100 J of energy is available to lion.
Let the amount of energy available to deer be x Joules.
According to 10% law, 10% energy from deer must have been transfered to lion. So, energy available to deer can be calculated as, 10/100 × X = 100 J, Therefore, x = 1,000 J
Now, let the amount of energy available to plants be y Joules.
According to 10% law, 10% energy from plants must have been transfered to deer. So, energy available to plant can be calculated as,
10/100 × y = 1,000 J
Therefore, y = 10,000 J
So, we have found that energy available to the producer is 10,000 J.
Question. (a) Water is an elixir of life, a very important natural resource. Your Science teacher wants you to prepare a plan for a formative assessment activity, “How to save water, the vital natural resource”.
Write any two ways that you will suggest to bring awareness in your neighbourhood, on ‘how to save water’.
(b) Name and explain any one way by which underground water table does not go down further.
Answer: (a) Water is one of the most precious natural resources that has vital importance in our lives. It is an essential component of the human body and is used almost everywhere in our day-to-day activities, such as cooking, washing, in agriculture and industries. It is an indispensable part of our life, without which the life on earth is not possible. However, the amount of fresh water available for sustaining life is very less. So, it is very important to conserve water. For creating awareness among people, we can adopt the following two ways.
(i) Door to door campaigning. (ii) Nukkad Nataks
(b) Underground water table can be recharged through rainwater harvesting. Rainwater harvesting is a process by which rain water is collected and stored for the purpose of recharging the ground water or for future use like for irrigation and agriculture, for livestock, etc. In India, rainwater harvesting is an old tradition, which is followed till now in many parts of India. For example, bawris are traditional architectural rainwater harvesters that were built for collecting water, in the state of Rajasthan.
There are two ways of rainwater harvesting:
(i) Surface runoff harvesting: In urban areas, rain water that flows away from the surface can be collected and used for various purposes.
(ii) Rooftop rainwater harvesting: The rainwater on the roofs of the buildings is collected through canals that drains the water into ground water reservoirs. This stored water can later be utilised.
Question. How is ozone both beneficial and damaging? How can we prevent the damaging effect of ozone? List one way.
Answer: 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 depletes O3 layer.
Question. (a) Complete the following table:
(b) How is ozone formed at the higher levels of atmosphere?
(b) It is formed by action of UV light on oxygen. 3O2(g) UV ⇌ 2O3 (g)
Question. Define trophic level. Name the first trophic level.
Answer: Each level in a food chain is called trophic level. First trophic level is producers.
Question. Give an example of food chain and state the different trophic levels in it.
Answer: An example of food chain is grassland food chain. Its different trophic levels are shown in the given figures.
Question. What is the role of decomposers in the ecosystem?
Answer: (i) Decomposers decompose the remains of plants and animals.
(ii) They clean the environment.
(iii) They bring back the raw materials to environment.
Question. Study the following food chain: Grass → Sheep or Goat → Man; Algae → Fish → Man
Who is the ultimate sufferer of using pesticides like DDT on land and in water? Give reason.
Answer: Man is the ultimate sufferer. Food chain in given cases ends on man i.e. last trophic level.
Question. Why do most food chains have 3-5 steps only?
Answer: Following 10% rule of energy flow, very little energy is left at the trophic levels beyond 3-5 levels that may not be enough to sustain life of a big carnivore, hence most food chains are short and have 3-5 steps only. Longer ones will have very small carnivores at the top.
Question. Which compounds are responsible for the depletion of ozone layer?
Answer: (i) CFC, (ii) NO, (iii) Free radicals of chlorine (iv) Aerosols
Question. When the government banned the use of polybags in Delhi, the vegetable grocers found it difficult as it affected their sales. The market committee held a meeting and decided to spread awareness about harmful effect of polybags.
(i) How will you convince people that plastics are harmful to the environment?
(ii) What alternatives of polythene bags do we have, which are environment friendly?
(iii) Not many people in Delhi have stopped using polythene bags even though they are officially banned. How can schools enaculate environmental values in students?
Answer: (a) They need to be told that cows and other animals eat polythene which is fatal for them. Coloured polythene is also very harmful for vegetables and fruits.
(ii) Paper bags, jute bags, bags of biodegradable materials are ecofriendly and carrying your own shopping bag is also more convenient.
(iii) Schools must teach students to protect environment. They should make paper bags and distribute to small shopkeepers regularly so that gradually their habits will change.
Question. (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.
Answer: (a) It is necessary to conserve our environment because
(i) It helps in protecting the ozone layer.
(ii) It helps in maintaining animal and human food chains.
(iii) It provides us with many useful products such as medicines and wood.
(b) Disposal of household waste is carried out in green and blue bins, respectively. It will be very useful in the separate disposal of biodegradable and non-biodegradable wastes. This will also ensure the application of 3 R’s— Reduce, Reuse and Recycle.
Question: What are decomposers? List two important roles they play in the environment.
Answer: Decomposers are microorganisms including bacteria and fungi which decompose or breakdown the complex organic compound present in dead plants and animals into simpler substances. Role of decomposers in environment are –
(i) They help in decomposing dead bodies of plants and animals, and hence act as cleansing agents of environment.
(ii) They help in recycling of materials in the ecosystem to maintain its stability.
Question: “To discard the household waste we should have two separate dust-bins, one for the biodegradable waste and the other for the non-biodegradable waste.” Justify this statement suggesting the proper way of disposal of these wastes.
Answer: “To discard the household waste we should have two separate dust-bins, one for the biodegradable waste and the other for the non-biodegradable waste.” Segregation of biodegradable and nonbiodegradable waste is utmost important for their proper disposal, as different methods are adopted for their disposal. Biodegradable wastes can be composted whereas non-biodegradable wastes can be recycled, incinerated or land filled.
Question: List two reasons to show that the existence of decomposers is essential in an ecosystem.
Answer:The existence of decomposers in an ecosystem is essential because
(i) If there were no decomposers, then the dead bodies of plants and animals would keep lying as such and the elements constituting plant and animal bodies would never be returned to their original pools like soil, air and water. In such case the organic waste go on accumulating and, the cyclic process of life and death would be disrupted.
(ii) Decomposers make the soil fertile by providing replenishing nutrients to it, thus forming the integral part of ecosystem.
Question: Describe how decomposers facilitate recycling of matter in order to maintain balance in the ecosystem.
Answer: Decomposers or saprotrophs are those microconsumers, which break down the complex organic compounds and release inorganic compounds or nutrients into the environment from where they are reused by the producers.
Decomposers include bacteria and fungi. They help in material and nutrient cycling and thus contribute to maintain balance in the ecosystem.
Question: State with reason any two possible consequences of elimination of decomposers from the Earth.
Answer: Consequences of elimination of decomposers are :
(i) There would be no recycling of nutrients and therefore, raw materials to produce food will not be available to producers. Hence, the food chains will get affected.
(ii) The dead bodies of plants and animals will go on accumulating in the absence of decomposition thereby polluting the environment.
Question: “Industrialisation has adversely deteriorated the environment.” Give four reasons in support of this statement.
Answer: Industrialisation has deteriorated our environment in the following ways :
(i) Rapid industrialisation has increased the demand of more land area for setting up of new factories. This demand is being fulfilled by clearing up of forest area. Deforestation is one of the major causes of ecological imbalance, biodiversity loss and ecosystem unstability.
(ii) Industries release various harmful gases in the environment which pollute the air.These gases when inhaled by people around, cause various respiratory diseases in them.
(iii) A lot of efiuent and liquid waste is discharged from various industries which is mostly dumped into nearby water bodies. This causes water pollution. Polluted water causes death of various aquatic organisms and consumption of this polluted water causes various diseases in humans.
(iv) The solid waste released from factories is dumped on open land and not treated properly to ensure their proper decomposition. This leads to land pollution that degrades quality of soil and also causes various kinds of diseases in humans and animals.
Question: “Energy flow in food chains is always unidirectional.” Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Answer: A food chain involves a nutritive interaction between the living organisms of ecosystem. There is a unidirectional flow of energy from Sun to producers and subsequently to series of different types of consumers, i.e.,
It cannot pass in reverse direction.There is always a decrease in the flow of energy and content with rise in trophic level. As some energy is lost at each step as heat and is also used up in various metabolic activities.
Some harmful non-biodegradable chemicals (pesticides, e.g., D.D.T.) enter the bodies of organisms through the food chains and get concentrated at each trophic level.This phenomenon is called biomagnification or biological magnification. For example, in a food chain operating in a pond, river or lake, the water contains a small amount — 0.02 ppm (parts per million) of harmful pesticides, i.e., D.D.T. When this water is consumed by phytoplanktons and zooplanktons, the concentration of these chemicals increases to 5 ppm. Fishes feeding on these, accumulate 240 ppm. Birds and humans feeding on these fishes were found to contain 1600 ppm of these chemicals. Thus, there is an increase in the concentration of the chemicals at each trophic level.
Question: What is meant by food chain? “The number of trophic levels in a food chain is limited.” Give reason to justify this statement.
Answer: The sequence of living organisms in a community in which one organism consumesor feeds upon another organism to transfer food energy, is called a food chain. Te various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels. In fact, in a food chain, each step representing an organism forms a trophic level. 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. Food chains generally consist of three or four trophic levels because beyond that the energy available to the next organism will be too small and insuficient to sustain the life of that organism.
Question:“Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues.” State the reason to explain how and why it happens.
Answer: Pesticides are poisonous chemical substances which are sprayed over crop plants to protect them from pests and diseases. These chemical pesticides mix up with soil and water. From soil and water, these pesticides are absorbed by the growing plants along with water and other minerals. When herbivorous animals feed on these plants the poisonous pesticides enter their bodies through the food chain. Similarly, when the carnivorous animals eat these herbivores, the pesticides get transferred to their bodies. Therefore, the plant products such as food grains, vegetables and fruits as well as meat of animals contain varying amounts of pesticide residues in them depending upon the trophic level they occupy in a food chian..
Question: You have been selected to talk on “Ozone layer and its protection” in the school assembly on ‘Environment Day’. (a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.
Answer: (a) The ozone layer is very important for the existence of life on Earth because it forms a protective shield around Earth by absorbing most of the harmful ultraviolet (UV) radiations coming from the Sun and prevents them from reaching the Earth. The UV radiations have extremely harmful effects on human beings, animals and plants as well, i.e., cause mutations, skin cancer, cataract, damage immune system, etc. So, ozone layer must be protected to save the environment.
(b)The two ways which can help in protection of ozone layer and environment are :
(i) The use of chemicals like chlorofluorocarbons (CFCs) which are widely used in refrigerators and air conditioners (as a coolant), in fire extinguishers and in aerosol sprayers destroy the ozone layer gradually. We can protect our ozone layer by avoiding the use of such objects which are releasing CFCs.
(ii) Nitrous oxide is the largest ozone depleting substance as well as greenhouse gas released by human activities, such as from motor vehicles, fertilisers. People should be encouraged to use more public transport, car pooling, using hybrid or electric cars and use of fertiliser formulations to reduce emission of nitrous oxide.
Long Answer type Questions :
Question. (A) A food chain generally has three or four trophic levels. Explain.
(B) What is biological magnification? Explain.
(A) Energy keeps decreasing at every trophic level.
Because the loss of energy at each trophic level is so great that very little usable energy remains after 3-4 trophic levels.
(B) Pesticides/harmful chemicals from the soil/water bodies are absorbed by the plants along with water and minerals.
As these harmful chemicals are nonbiodegradable, They get accumulated/magnified at each trophic level in a food chain.
Question. (A) Natural water bodies are not regularly cleaned whereas an aquarium needs regular cleaning. Why?
(B) What are decomposers? What will be the consequence if the decomposers are completely eradicated from an ecosystem? Give Justification in support of your answer.
Answer : (A) Natural water bodies are natural ecosystems in which the diversity of organisms is balanced and the wastes produced are naturally eliminated from water as they are decomposed by the decomposers present. Whereas an aquarium is a man made ecosystem in which selective organisms have been kept and maintained in a restricted and artificial environment. As there are no decomposers, the uneaten food and wastes produced by the fishes keeps accumulating and hence requires regular cleaning.
(B) The decomposers are the various organisms in the ecosystem which help in decomposing the dead bodies of plants and animals by breaking down the complex organic substances into simpler inorganic substances.
If decomposers are completely eradicated from our ecosystem:
(1) The ecological balance would be disturbed.
(2) Wastes of organisms and dead plants and animals would pile up leading to foul gases, diseases and deaths.
(3) The soil would lose its fertility as there will be no recycling of nutrients.
(4) The bio geo chemical cycles which are natural ways of nutrient cycling would be affected leading to insuffcient nutrients.
Question. What are the by-products of fertilizer industries? How do they affect the environment?
Answer : The harmful by-products are gases such as SO2 and NO. They cause extensive air pollution and are responsible for acid rain. The harmful by-products of the fertilizer industries are: (1) Gases – SO2, NO, CO, CO2, and H2S. (2) Solids – Pyrite ashes, calcium carbonate, sand and plastic bag.
Effect on environment: The majority of the gaseous by-products like carbon dioxide, and methane are green house gases which contribute to global warming. The rest of the gases like sulphur dioxide and nitrous oxide are air pollutants and lead to acid rain. These gaseous by-products cause breathing and respiratory problems.
The solid waste and waste water discharges into the water body. When these wastes are discharged into the water body, they increase the nutrient content of the water and cause algal bloom (increase in the number of algae). Due to algal bloom, algae form a layer on the surface of the water and hence, the oxygen does not reach the water body. Thus affecting the aquatic life.
Also, these wastes are non-biodegradable, so they get accumulated at each trophic level by entering the food chain at the producer level and in the process of the transfer of food through food chains, these harmful chemicals such as pesticides , industrial effluents, heavy metals and radioactive substances get concentrated at each trophic level. This is called biomagnification.
Question. Give reason to justify the following:
(A) The flow of energy in every food web is unidirectional.
(B) The decomposers play an important role in an ecosystem.
Answer : (A) The energy in every food web is unidirectional which means that the solar energy utilized by the autotrophs does not revert back to the Sun. The energy moves progressively through various trophic levels and this energy is no longer available to the previous trophic level.
Moreover, the energy available at each trophic level gets diminished due to loss of energy at each level and follows the 10 percent law.
(B) Role of decomposers in the ecosystem:
(1) They play a critical role in the flow of energy through an ecosystem.
(2) They decompose the wastes of organisms, dead plants and animals in the absence of which these would pile up leading to foul gases, diseases and deaths.
(3) They help in recycling of nutrients and thus maintain fertility of the soil.
(4) They play a major role in various biogeochemical cycles which are natural ways of nutrient cycling.
Question. How is ozone formed in the upper atmosphere?
State its importance.
What is responsible for its depletion? Write one harmful effect of ozone depletion.
Answer : Ozone is produced by the action of UV radiations on oxygen molecule.
First, the energy of UV radiations splits some molecular oxygen, O2, into free oxygen, O.
O2 ⎯u⎯v→ O + O
The free oxygen O combines with molecular oxygen O2 to form Ozone, O3.
O + O2 → O3
Importance of ozone: Ozone shields the earth’s surface from the harmful ultraviolet (UV) radiations from sun.
Synthetic chemicals such as Chlorofluorocarbons (CFC) and aerosols are mainly responsible for depletion of ozone in the atmosphere.
Harmful effect of ozone depletion:
(1) Ozone layer depletion causes increased UV radiation levels at the Earth’s surface, which is damaging to human health as it causes certain types of skin cancers, eye cataracts
and immune deficiency disorders.
(2) UV radiation also affects terrestrial and aquatic ecosystems, altering growth, food chains and biochemical cycles.
(3) UV rays also affect plant growth, reducing agricultural productivity.
Question. How can we help in reducing the problem of waste disposal? Suggest any three methods.
Answer : Methods to reduce the problem of waste disposal:
(1) Segregation of waste should be done by separating biodegradable waste substances from non-biodegradable substances.
(2) By recycling solid wastes like paper, plastic and metals etc, i.e., they are reprocessed or melted and remoulded to make new articles.
(3) By composting biodegradable domestic wastes such as fruit and vegetable peels,leaves of potted plants can be converted into compost and used as a manure.
(4) By reducing and reusing of Non Biodegradable substances.
(5) By minimizing the use of disposable items which are non-biodegradable.
Question. Explain some harmful effects of agricultural practices on the environment.
Answer : Harmful effects of agricultural practices on the environment:
(1) Fertilizer added to soil not only changes the chemistry of the soil but also kills many useful microbes.
(2) Pesticides sprayed over crops reach water bodies and persistent pesticides undergo bio-magnification proving harmful to higher organisms.
(3) Extensive cropping on a particular piece of land causes the loss of soil fertility.
(4) Continuous use of ground water in agriculture has resulted in lowering of water table at most of the places
(5) Natural ecosystems and habitats have been damaged because of clearing of land for agriculture.
(6) Excessive cutting down of trees for agricultural purposes causes deforestation and can lead to soil erosion.
(7) Synthetic fertilizers and pesticides used in the field during rainfall are washed away to rivers and other bodies, which cause water pollution.
Question. Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem
Answer : Ecosystem: An ecosystem is a self-sustained unit which comprises of all the interacting living things together with their non-living environment. Flow of energy in an eco system: Energy flows through an ecosystem in only one direction. Energy is passed from organisms at one trophic level or energy level to organisms in the next trophic level.
Question. Mention the negative effect of our lifestyle on the environment.
Anawer: (i) Global warming occurs due to increase in number of vehicles and over use of fossil fuels.
(ii) Due to excessive use of deodrants, perfumes, CFCs, etc. ozone layer is getting depleted.
(iii) Air pollution occurs due to industralisation.
(iv) Wastes causes pollution due to release of sewage in water bodies.
(v) Pollution of soil occurs due to overuse of chemicals is agriculture.
Question. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose of non-biodegradable waste for saving the environment.
Two habits to dispose of non-biodegradable wastes are:
(i) Use of separate dustbins for biodegradable and non-biodegradable wastes,
(ii) Reuse of things such as polybags, etc.,
(iii) Recycling of wastes
(iv) Use of cotton /jute bags for carrying vegetables etc.
Question. What is ozone? How and where is it formed in the atmosphere? Explain how it affects an ecosystem.
Anawer: Ozone is a molecule containing three atoms of oxygen (O3). It is a highly poisonous gas present in the upper layers of the atmosphere.
Formation of ozone: The UV radiations from Sun split some molecules of oxygen (O2) apart into free oxygen atoms (O + O). These atoms then combine with oxygen molecules to form ozone.
O2 → UV O + O ; O + O2 → O3
Ozone layer shields the surface of the earth against damaging UV radiations of the Sun.
Question. (a) Construct a terrestrial food chain comprising four trophic levels.
(b) What will happen if we kill all the organisms in one trophic level?
(c) Calculate the amount of energy available to the organisms at the fourth trophic level if the energy available to the organisms at the second trophic level is 2000 J.
Anawer: (a) Level 1 Plants and algae
Level 2 Herbivores like goat, cow
Level 3 Carnivores like fox, wild cat, mongoose
Level 4 large carnivores, lion, tiger
(b) If we kill all organisms in one trophic level, then transfer of energy as well as matter to next higher level will stop, it will lead to overpopulation at one particular level, disturb the food chain and cause collapse of ecosystem.
(c) Energy available at second trophic level of 2000 J Energy available at third trophic level is 2000 X 1/10 = 200 J
Energy available at fourth trophic level is 200 X 1/10 = 2 J
Question. Your mother always thought that fruit juices are very healthy for everyone. One day, she read in the newspaper that some brands to fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to health.
(a) How would you explain to your mother about fruit juices getting contaminated with pesticides?
(b) It is said that the harmful pesticides enter our body as well as the bodies of other organisms, they get accumulated and beyond a limit causes harm and damage to our organs. Name the phenomenon and write about it.
Anawer: (a) Farmers spread pesticides on fruits and it get mixed up with fruits and enter fruit juices.
(b) The process is called bio-magnification. The concentration of toxic substances like pesticides, insecticides increase with each trophic level in food chain.
Question. (a) What do you understand by ‘watershed management’? List any two advantages of watershed management.
(b) Human beings occupy the top level in any food chain. What are the consequences of this on our body?
Anawer: (a) Soil and water conservation in a scientific way is called ‘watershed management’.
Advantages: (i) Increase in production and income of watershed communities,
(ii) Mitigate draughts and floods, (iii) Increase the life of downstream dam reservoir.
(b) Maximum level of biomagnification occurs in human beings because of progressive accumulation.
We get very small amount of energy as only 10% of previous energy gets transferred to each trophic level.