Our Environment Class 10 Science Exam Questions

Please refer to Our Environment Class 10 Science Exam Questions provided below. These questions and answers for Class 10 Science have been designed based on the past trend of questions and important topics in your class 10 Science books. You should go through all Class 10 Science Important Questions provided by our teachers which will help you to get more marks in upcoming exams.

Class 10 Science Exam Questions Our Environment

Class 10 Science students should read and understand the important questions and answers provided below for Our Environment which will help them to understand all important and difficult topics.

Very Short Answer:

Question: What are various steps in the food chain called? 
Answer: Trophic level.

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. 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 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. 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. Write the name of the main constituent of biogas. Also state its percentage.
Answer : Methane is the main constituent of biogas. Its formula is CH4. Its percentage is approximately 50–75%.

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 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. List any two abiotic components of an ecosystem.
Answer : Air, water, minerals, sunlight are the abiotic 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. What is a biodegradable substance ?
Answer : Biodegradable substances are the substances that can be broken down by biological processes.

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

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

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

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

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 or 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. 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 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.

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 : Plant → Deer → Lion
According to 10% law,
10% of x = 100
x = 1000 J in deer.
10 % of y = 1000
y = 10,000 J in plant.

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

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. 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: Why do producers always occupy first trophic level of food chain?
                                                         Or
The first trophic level in a food chain are always occupied by green plants, why?
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: 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: List two natural ecosystems. 
Answer:(i) Oceans, (ii) forests are two natural ecosystems.

Question: List two biotic components of environment. 
Answer:Plants, animals, micro-organisms (any two) are biotic components.

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 × 10/100 = 1000 J
Energy available to secondary consumer trophic level = 1000 × 10/100 = 100 J

Question: In the following food chain, 20,000 J of energy was available to the plants. How much energy will be available to man in this chain?
Plants → Sheep → Man
Answer:Plants have 20,000 J of energy available to them. Sheep will get 10% of 20000 J
20000 × 10/100 = 2000 J
Humans will get 10% of 2000 J.
2000 × 10/100
= 200 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: Define ecosystem.
                   OR
What is an ecosystem? 
Answer: All living organisms and abiotic components of surroundings forms an ecosystem.

Question: Draw a food chain which operates in forest ecosystem. 
Answer: Grass → Deer → Tiger.

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: In the following food chain, 10 J is energy available to the hawks. How much energy would have been present for the rats? Plants → Rats → Snakes → Hawks
Answer: 1000 J.

Question: List two steps that should be taken for the maintenance of healthy environment.
Answer: (i) Controlling pollution (ii) Afforestation (iii) Proper Waste Disposal

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 × 1/100 = 100 J
Dear will get 10% of 100 J = 100 × 10/100
 = 10 J
Out of this 10 J of energy, only 1 J of energy can be transferred to lion.

Question: What will be the amount of energy available to the organisms of 2nd trophic level of food chain if energy available at the first trophic level is 1000 J. 
Answer: 10000 × 1/10

Question: Write the appropriate names of trophic level ‘Z’ and ‘X’ in the figure given below.

Answer: ‘X’ is primary consumer, ‘Z’ is tertiary consumer in the given figure.

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: What is the functional unit of environment?
Answer: Ecosystem is the functional unit of environment.

Question: Crop fields are called artificial ecosystem, Justify.
Answer: Crop field ecosystem is created by man and needs care like watering, supply of manure, protection from diseases. Therefore, it is an artificial ecosystem.

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: Which will get more energy, secondary consumers or tertiary consumers?
Answer: Secondary consumers will get more energy.

Question: What is depicted in the below mentioned scheme?

Answer:It depicts 10% law in food chain for energy transfer from one trophic level to another.

Question: List two man-made ecosystem. 
Answer: Aquarium, crop land, park. (Any two)

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: “Save the Tiger” campaign is being over emphasised these days by our government. What may be possible reason?
Answer: It helps to maintain ecological balance in nature and also to preserve gene pool of a particular species.

Question: Why are plastics non-biodegradable substances? 
Answer: It is because plastics are not decomposed by micro-organisms. (Note: Now, plastic eating enzymes has been discovered).

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, 100/10 × 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,100/10 × y = 1,000 J
Therefore, y = 10,000 J
So, we have found that energy available to the producer is 10,000 J.

Question: In a food chain of frog, grass, insect and snake, assign trophic level to frog.
Answer: Grass → Insect → Frog → Snake
Frog is a secondary consumer and belongs to 3rd trophic level.

Question: Give one protective function of forests. 
Answer: Forests help to reduce air pollution.

Question: Consider a food chain consisting of wheat, rat, snakes, peacock. What will happen if all snakes are killed?
Answer: The peacock will also die. The population of rats will increase.

Question: Change one consumer each that belongs to the second and third trophic levels from the following organisms : Eagle, frog, tiger, rabbit, fox 
Answer: (i) Second trophic level → Rabbit (ii) Third trophic level → Frog and fox.

Question: What is meant by biological magnification?
Answer: Biomagnification or biological magnification refers to the process of accumulation of non bio degradable chemicals (pesticides, etc.) into the body of organisms through the food chain which go on increasing in its concentration at each trophic level.

Question: In a food chain, if 10,000 joules of energy is available to the producer, how much energy will be available to the secondary consumer to transfer it to the tertiary consumer? 
Answer: According to ten percent law, 10% of the energy of producer will be available to primary consumer, and 10% of this energy will be available to secondary consumer and so on.

Hence, 100 J of energy will be available to the secondary consumer.

Question: What are the two main components of our environment?
Answer: The two main components of our environment are biotic components (living) and abiotic components (non-living). 

Question: The depletion of ozone layer is a cause of concern. Why? 
Answer: Ozone layer is the ozone rich area in the stratospheric layer of atmosphere which acts as a protective shield by preventing harmful UV radiations from entering the Earth surface. Hence, the depletion of ozone layer is a cause of concern.

Question: Why is excessive use of CFCs a cause of concern? 
Answer: CFCs or Chlorofluorocarbons are potent compounds that release active chlorine in the atmosphere which reacts with ozone molecules present there to convert them to oxygen. This results in thinning of ozone layer. Hence, excessive use of CFCs is a cause of concern.

Question: Write one negative effect on the environment, of auent life style of few persons of a society. 
Answer: Affuent lifestyle of few persons leads to exploitation and over consumption of resources leading to their scarcity and generation of greater amount of waste materials which causes imbalance in environment.

Question: What is the function of ozone in the upper atmosphere? 
Answer: Ozone (O₃) gas forms a protective shield in the upper atmosphere that absorbs most of the harmful ultraviolet radiations coming from Sun that can harm human beings, animals and plants. It protects us from various health hazards.

Question: Write the full name of the group of compounds mainly responsible for the depletion of ozone layer. 
Answer: Chlorofluorocarbons (CFCs) are the group of compounds mainly responsible for ozone depletion.

Question: Which class of chemical is linked to the decrease in the amount of ozone in the upper atmosphere of the Earth? 
Answer: The decrease in the amount of ozone in the atmosphere has been linked to synthetic chemicals like chlorofiuorocarbons (CFCs) which are used as coolant and in fire extinguishers, etc.

Question: Why should biodegradable and nonbiodegradable wastes be discarded in two separate dustbins? 
Answer: Biodegradable wastes are decomposed naturally by the action of microbes which degrade them to their simple constituents enabling their nutrients to recycle among the biotic and abiotic components of ecosystem. However, non-biodegradable wastes cannot be disposed off naturally since they cannot be decomposed by microbes. Such wastes are either recycled, incinerated or put in landfills, etc. As the disposal methods of the two types of waste is different, it is advisable to discard the two types of waste in two separate dustbins.

Question: Why did United Nations act to control the production of chlorofluorocarbons (CFCs) used in refrigerators? 
Answer: United Nations act to control the production of CFCs as they are the main chemicals responsible for ozone depletion.

Question: What happens when higher energy ultraviolet radiations act on the oxygen at the higher level of the atmosphere? 
Answer: When high energy ultraviolet radiations react with oxygen present in stratosphere (the higher level of atmosphere) it splits into its constituent atoms. Since these atoms produced are very reactive they react with molecular oxygen (O₂) to form ozone (O₃).

Question: Which disease is caused in human beings due to depletion of ozone layer in the atmosphere? 
Answer: Ozone depletion allows harmful UV radiations to reach Earth which cause skin cancers, sunburns, cataract etc., and malfunctioning of immune system in humans

Short Answer: I

Question: (a) From the following group of organisms create a food chain which is the most advantageous for Human beings in terms of energy.

(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. 
The extensive use of pesticides in agricultural production can degrade and damage the community of micro-organisms living in the soil, particularly when these chemicals are overused or misused as chemical compounds build up in the soil.

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.

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.

The organism at higher trophic level 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 nonbiodegradable 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.

(a) For example 10,000 J energy is available to producer.
(b) Then 1000 J energy will be available to primary consumer.
(c) 100 J energy will be available to secondary consumer.
(d) 10 J energy will be available to tertiary consumers

Question: Give any two ways in which biodegradable substances would affect the environment.
Answer : The two ways in which biodegradable substances would affect the environment are :
(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 : The two ways in which non-biodegradable substances would affect the environment are :
(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 : The various methods of waste disposal are :
(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 0non-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 :

The above concept explains that
(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 The above concept explains that 
(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 eading to their maximum concentration at the highest trophic level (human beings) is called biological magnification

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: Compare the advantages of cloth bags over polythene bags.
Answer: (i) Cloth is biodegradable, does not pollute environment.
(ii) It can be used again like plastic bag and moreover it is ecofriendly.

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: Accumulation of harmful chemicals in our body can be avoided. Explain how this can be achieved.
Answer: (i) Wash vegetables and fruits with saline water and vinegar.
(ii) Shock the vegetables in salt water for few minutes before cooking.
(iii) Boil the vegetables.
(iv) Organic manure and organic ecofriendly pesticides should be used.

Question: What would happen if number of carnivores decreases in the ecosystem?
Answer:If number of carnivores decreases in the ecosystem, then it will lead to increase in number of herbiores.As a result number of plants will decrease and consequently amount of O₂ will also decrease in the ecosystem.

Question: Why are some substances biodegradable and some are non-biodegradable? 
Answer: Biodegradable substances are those which are broken by micro-organisms and get decomposed. They do not persist in environment for a very long time e.g., paper.
Non-biodegradable substances are those which are not broken by micro-organisms. They persist in environment for long time. e.g. plastic, DDT.

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: 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:(a) What is an ecosystem? List its two main components. 
(b) We do not clean ponds or lakes, but an aquarium needs to be clean regularly, explain.
Answer: (a) Ecosystem is composed of different organisms interdependent upon each other. Biotic and abiotic components are its two main components.
(b) Pond or lake is a natural ecosystem, several organisms present in it maintain a balance in the ecosystem. Aquarium is an artificial ecosystem in which bacteria convert fish food into ammonia which is harmful for fish. Water needs to be changed regularly. Chlorine water should be dechlorinated otherwise fish will not survive. Air pump is needed to provide oxygen. Artificial ecosystem need utmost care to remain stable.

Question: Pesticides like DDT which are sprayed to kill pests on crops are found to be present in soil, ground water, water bodies etc. Explain how do they reach these places.
Answer: (i) Soil. Pesticides get settled on soil when sprayed over plants.
(ii) Groundwater. Pesticides present in soil reach lower layers of soil during irrigation and get mixed with ground water.
(iii) Waterbodies: When agricultural waste as well as waste water get mixed up with water bodies, pesticides enter waterbodies because these are non-biodegradable.

Question: Arrange the following in food chain:
(a) Frogs, Insects, Birds, grass. (b) Fish, algae, small animal, big animal.
Answer: (a) Grass → Insects → Frog → Birds
(b) Algae → Small animal → Fish → Big animal

Question: Will the impact of removing all the organisms in a trophic level be different for different trophic levels?
Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer:The impact of removing all the organisms in a trophic level will be different for different trophic levels. It is not possible to remove organisms of any trophic level without causing damage to ecosystem because organisms of each level are interdependent.

Question: Construct an aquatic food chain showing four trophic levels. 
Answer:

Question: Energy flow is unidirectional in food chain? Explain. 
Answer:The energy of sun is taken by plants and cannot be given back. Herbivore eat plants and cannot give back energy to plants. Carnivores eat herbivores and cannot give back energy to herbivores. It means flow of energy is unidirectional from lower trophic level to higher trophic level.

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: Name the organisms which belong to first and third trophic level in food chain comprising of the following: Insects, birds, frog and grass.
Answer: First trophic level – Grass
Third trophic level – Frog

Question: What does a trophic level represent in a food chain? State the position of autotrophs and herbivores in a food chain.
Answer: Trophic level represents each of several hierarchial levels of a food chain operating in an ecosystem, consisting of organism sharing the same function in the food chain and the same nutritional relationship to the primary sources of energy. The position of producers (or autotrophs) in a food chain constitute the first trophic level.They fix up sun’s energy and make it available for consumers. The herbivores or primary consumers (which feed upon plants) constitute the second trophic level in a food chain.

Question: Why is Government of India imposing a ban on the use of polythene bags? Suggest two alternatives to these bags and explain how this ban is likely to improve the environment.
Answer: Government of India is imposing a ban on the use of polythene bags because these are non-biodegradable substances which are not acted upon by the microbes. So, they cannot be decomposed and therefore persist in the environment for a long time thereby causing harm to the ecosystem. Polybags choke drains which results in water logging, that allows breeding of mosquitoes and hence leads to various diseases like malaria, dengue, etc. Jute bags and cloth bags are the alternatives to the polythene bags. 

Question: “Affluent life style has a negative effect on the environment.” Justify this statement with the help of an example. 
Answer: With the advancement in technology over time, there has been improvement in lifestyle of people. Such changes in peoples, lives have also changed their attitudes. When people have more resources at their end they tend to overuse and misuse it thereby generating huge amounts of waste material. For example, the affuent life style has forced people to start using more of disposable articles, e.g., plastic cups, bags, etc., which keep on accumulating in the environment and lie undecomposed, thereby negatively affecting the environment.
Similarly, excessive use of refrigerators and air conditioners, plastic foams, etc., also releases high quantities of CFCs which are responsible for ozone depletion.

Question: We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest ways to make the residents realise that the improper disposal of their waste is harmful to the environment. 
Answer: Some of the ways to make people realise that the improper disposal of waste is harmful to the environment includes making people aware of negative impacts of waste disposal.
(a) Improper disposal of waste will release harmful gases in the environment that make it unclean and unhygienic for the living organisms.
(b) The waste will flow to water bodies along with rain water and become a threat to aquatic life and pollute the water bodies.
(c) It provides space for breeding of the mosquitoes and which results in spread of malaria,filariasis, dengue, etc.
(d) Hazardous chemicals from wastes get into the soil and can harm the plants when they take up the contamination through their roots. This will affect the health of other animals and humans and will have negative impact on environment. 

Question: Give one example each from your daily life where the domestic waste can be effectively reused and recycled.
Answer: We can reuse plastic and glass jars of jams and pickles, etc, for the purpose of storage of things like salt, sugar, tea etc., whereas we can recycle newspapers, plastic of some types, broken glass and metal wares for making fresh paper, plastic, glass and metal objects. 

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  non-biodegradable waste, for saving the environment.
Answer: Differences between biodegradable and nonbiodegradable wastes are as follows:

People should adopt the following changes in their habit to dispose off non-biodegradable waste, so as to save the environment.
(i) Non-biodegradable household waste should be disposed in separate dustbins and should not be mixed with biodegradable waste.
(ii) Recyclable non-biodegradable wastes like glass, paper, metal, various types of plastics etc., can be sent to local recycling units.
(iii) People should try to reuse items as much as possible instead of disposing them as this reduces need of new materials and keeps ecological impact down.
(iv) Use of cloth bags/gunny bags/paper bags instead of polythene /plastic bags.
(v) Use of compost, vermicompost instead of fertilisers. 

Question. The activities of man has adverse effect on all forms of living organisms in the biosphere. Unlimited exploitation of nature by man disturbed the delicate ecological balance between the living and non-living components of the biosphere. The unfavourable conditions created by man himself threatened the survival of not only of himself but also of the entire living organisms on the mother earth. One of your classmate is an active member of ‘Eco Club’ of your school which is creating environmental awareness amongst the school students, spreading the same in society and working hard for preventing environmentalde gradation of the surroundings.
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 the Eco-club of your school.
Answer : a. Conservation of our environment is necessary to leave it in good condition for our future generations.
b. Green and blue dustbins should be used to segregate wet and dry waste so that according to their nature they can be sent for the safe disposal to compost pits/ biogas plant and recycling in factories.
c. Two values: He is concerned about environment, problem solving attitude.

Question. Differentiate between autotrophs, heterotrophs and decomposers and give one example of each.
Answer : a. Autotrophs are the organisms that can make theirown foo d from carbon dioxide and water under the action of sunlight and in the presence of chlorophyll. Example: All green plants.
b. Heterotrophs are the organisms which cannot make their own food by the process of photosynthesis and are dependent on others for food. Example: All animals.
c. Decomposers are the organisms that decompose the complex molecules present in the dead remains of plants and animals. Example: Bacteria, Fungi.

Question. a. What is an ecosystem? List its two main components.
b. We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain.
Answer : a. A self-sustaining functional unit consisting of living (biotic) and nonliving (abiotic) components, is called an ecosystem.
1. Biotic components: Plants and animals.
2. Abiotic components: Light, soil, temperature, humidity, wind, air, etc.
b. An aquarium is an artificial and incomplete ecosystem in contrast to a pond or lake which is natural, self- sustaining and complete ecosystem.
In natural ecosystem, decomposers help in recycling waste. So, an aquarium needs to be cleaned regularly.

Question. What is ozone? How and where is it formed in the atmosphere? Explain how it affects an ecosystem?
Answer : Ozone is a molecule containing three atoms of oxygen (O3), a highly poisonous gas present in the upper layers of the atmosphere.
Formation of ozone – The UV radiations split some molecular oxygen (O2) apart into free oxygen atoms (O + O). These atoms then combine with molecular oxygen to form ozone.
Affects of an ecosystems are:
i. Due to depletion of ozone layer, UV radiations reach the earth. These UV radiations cause skin cancer, damage to eyes and immune system.
ii. This depletion of ozone layer may also lead to variations.

Question. After the examination Rakesh with his friends went on a picnic to a nearby park. All friends carried cooled food packed in plastic bags or plastic cans. After eating the food some friends collected the leftover food and plastic bags etc and planned to dispose them off by burning. Rakesh immediately checked them and suggested to segregate the leftover food and peels of fruits from the plastic materials and respectively dispose them off separately in the green and red dustbins placed in the corner of the park.
a. In your opinion, is burning plastic an eco¬friendly method of waste disposal? Why? State the advantage of method suggested by Rakesh.
b. How can we contribute in maintain the parks and roads neat and clean?
Answer : a. No, it pollutes air.
Advantage: Segregation of wastes into biodegradable and non biodegradable wastes at the initial stage of disposal saves time and energy.
b. By putting wastes in proper dustbins.

Question. ‘Energy flow in a food chain is unidirectional.’ Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Answer : a. Energy moves progressively through the various trophic levels and is no longer available to the previous trophic level. The energy captured by autotrophs does not revert back to the solar input. Therefore flow of energy is unidirectional.
b. Pesticides, used for crop rotation when washed down into the soil/water body, are absorbed by the plant/producer along with water and minerals.
Being non-biodegradable these chemicals get accumulated progressively in the food chain and enter our body.

Question. Pesticides like DDT which are sprayed to kill pests on crops are found to be present in the soil, groundwater, water bodies etc. Explain how do they reach these places?
Answer : a. Soil: Pesticides are sprayed to protect plants from insects and they, consequently, get settled into soil particles, when used on plants.
b. Groundwater: Through irrigation in the fields, these pesticides present in soil pass into lower layers of soil and reaches groundwater.
c. Water bodies: When the waste water or other agricultural waste is thrown in water bodies likeriver , canals, ponds, etc., the pesticides affect water bodies.

Question. Aquariums need to be cleaned once in a while, whereas ponds or lakes do not require any cleaning. Explain.
Answer : A aquarium is not a ‘self-sustained’ ecosystem. Waste in aquarium cannot be decomposed as microorganisms in it are not active.
Whereas ponds and lakes are natural, and selfsustained ecosystem in which microorganisms help in decomposing the waste matters.

Question. Larger animals kill the smaller animals in the forest, eat whatever they can, leave the rest in the forest but the forest is never found full of dead animals. What happens to the bodies of these dead animals?
Answer : Bacteria and fungi have enzymes to break down complex organic substances to simple and smaller ones. They decompose them returning the nutrients back to soil/ humus.

Question. Monika was observing a lizard on the wall which chased an insect and ate it. She felt that lizard is cruel and ugly. Suddenly the lizard fell and was eaten by a cat. She started thinking, how organisms are connected to each other for their food?
a. What is a food chain? Will the world be a better place without lizards?
b. Make a food chain of five organisms.
c. Do you think lizard is cruel and ugly?
d. To which trophic level does the lizard belong?
Answer : a. Food chain is a sequence of ‘who eats whom’ in an ecosystem. No, lizards are a part of many food chains. Without them food chain will be disrupted.
b. Grass $ grass hopper $ frog $ snake $ peacock.
c. No, it is only obtaining food for its survival like all other organisms.
d. Third trophic level/ secondary consumer/ small carnivore.

Short Answer:  II 

Question: What is ozone ? How and where is it formed in the atmosphere ? Explain how does it affectan ecosystem.
Answer: Ozone is a form of oxygen. It is a made up of three atoms of oxygen. It is highly poisonous. However, good amount of ozone is present in upper part of the atmosphere called stratosphere. In the stratosphere ozone is being photo-dissociated and generated simultaneously by absorption of harmful ultraviolet (UV) radiations coming from Sun. 

The two reactions are in equilibrium thereby maintaining a steady concentration of ozone in the stratosphere. Ozone layer is commonly called ozone blanket. It acts as a protective shield to protect all types of life from the harmful effect of UV radiation.there fore, any thinning or depletion of ozone layer allows entry of high energy UV radiations into the earth’s surface, thereby causing harmful effects on plants, animals and human beings.
The harmful effects of ozone depletion on man, animals and plants includes :
(i) Incidences of skin cancer and herps
(ii) Damage to eye sight, photoburning as well as increased incidences of cataract in eyes
(iii) Damage to immune system and hence lowering the body’s resistance to disease
(iv) Increased embryonic mortality
(v) 10-25% decline of photosynthesis in plants
(vi) Global warming

Question: After the examinations Rakesh with his friends went on a picnic to a nearby park. All friends carried cooked food packed in plastic bags or plastic cans. After eating the food some friends collected the leftover food and plastic bags etc., and planned to dispose them off by burning. Rakesh immediately checked them and suggested to segregate the leftover food and peels of fruits from the plastic materials and respectively dispose them off separately in the green and red dustbins placed in the corner of the park.
(a) In your opinion, is burning plastic an eco-friendly method of waste disposal? Why? State the advantage of method suggested by Rakesh.
(b) How can we contribute in maintaining the parks and roads neat and clean?
Answer: (a) No, burning plastic is not an eco-friendly method of waste disposal. Burning plastics can produce toxic fumes and cause air pollution. Plastic, being non-biodegradable cannot be dumped (land filled), so the best way to dispose plastic items is to recycle them. Recycling is a less polluting and more sustainable option.
Rakesh segregated left over food items, fruit peels, i.e., biodegradable waste and plastic material, i.e. non-biodegradable waste.The biodegradable waste can be converted to manure whereas non-biodegradable waste can be recycled.This contributes in decreasing the level of pollution and easy disposal and treatment of waste.
(b) We can contribute to keep our roads and parks clean by adopting following habits:
(i) We should recycle non-biodegradable waste products instead of dumping it in garbage.
(ii) We should use carry bags made of natural fibre as jute, cloth, instead of plastic bags.
(iii) We should make compost of biomass collected from park such as food waste, leaf litters, etc,.
(iv) We should stop littering, throwing garbage and spitting on road sides, parks, etc.

Question: The activities of man had adverse effects on all forms of living organisms in the biosphere. Unlimited exploitation of natureby man disturbed the delicate ecological balance between the living and nonliving components of the biosphere The unfavourable conditions created by man himself threatened the survival not only of himself but also of the entire living organisms on the mother Earth. One of your classmates is an active member of ‘Eco club’ of your school
which is creating environmental awareness amongst the school students, spreading the same in the society and also working hard for preventing environmental degradation of the surroundings. 
(a) Why is it necessary to conserve our environment? 
(b) State the importance of green and blue dust-bins in the safe disposal of the household wastes.
(c) List two values exhibited by your classmate who is an active member of Eco-club of your school.
Answer: (a) Environment is the physical and biological world where we live. It includes both living and non-living components. Environment affects organisms without becoming an integral part of them. We all depend on our environment for all our needs and any imbalance in it affects both organims and abiotic components. Hence, there is a need to conserve our environment. 
(b) Green dustbins are meant for disposal of biodegradable wastes whereas blue dustbins are meant for disposal of non-biodegradable wastes. Separate disposal of biodegradable and non-biodegradable household waste is more environment friendly as it helps in proper and effective disposal of respective wastes as the two types of waste have separate disposal methods.
(c) The classmate is conscious and aware of the importance of environment. He is a responsible citizen who is making efforts and creating awareness towards the conservation of environment and uplifment of its quality. He also shows leadership qualities actively by engaging other students into these activities.

Question: What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: The process in which harmful chemicals like pesticides enter the food chain and get accumulated in each trophic level is called biomagnification. The level of biomagnification will be different from different trophic level. Primary consumers will have higher concentration of pesticides than producers and secondary consumers will get pesticides by eating primary consumers and will have even higher concentration.

Question: What term do you use for trophic levels comprising of
(a) the organisms which make their own food
(b) animals feeding on plant matter only
(c) organisms breaking down dead plants and animals
Answer: (a) Producers (b) Herbivores (c) Decomposers

Question: What is meant by food chain? ‘The number of trophic levels in food chain is limited.’ Give reason to justify the statement. 
Answer: Food chain is a sequence in which nutrients, food and energy is transferred in systematic way. Lower trophic level have maximum population because energy is available in more extent. Primary consumers get 10% of energy of producers. Secondary consumers get 10% of energy of primary consumers.
Tertiary consumers get 10% of energy of secondary consumers i.e. very less energy is available, that is why the trophic levels are limited. Tiger population is decreasing day by day as food is not easily available for them and forests are decreasing due to cutting of trees.

Question: How will you create an artificial aquatic ecosystem, which is self-sustainable?
Answer: • Take a large jar filled with water, oxygen, food and aquatic plants and animals.
• Oxygen/oxygen pump.
• Fish food.
• Aquatic plants/Producers provide O₂ during photosynthesis.
• Aquatic animals/Consumers release CO₂ for the process of photosynthesis.
• Decomposers are also important for natural cleaning of the aquarium.

Question: What will happen if we kill all the organisms in one trophic level? 
Answer: If we kill the organisms in one trophic level.
(i) The population of organisms in previous trophic level will increase.
(ii) The population of organisms in next trophic level may decrease.
(iii) It will cause an ecological imbalance in the food chain.

Question: Differentiate between autotrophs, heterotrophs and decomposers and give one example of each.
Answer: (i) Autotrophs. Those organisms which prepare their own food with the help of CO₂, H₂O and sunlight in presence of chlorophyll e.g. green plants.
(ii) Heterotrophs. Those organisms which do not prepare their own food but dependent on the other food. e.g. animals and human beings.
(iii) Decomposers. Those organisms which decompose the complex molecules present in the dead

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.
Answer: (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) 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.
Answer: (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 × 1/10 = 200 J
Energy available at fourth trophic level is 200 × 1/10 = 2 J

Question: List three characteristics of energy flow in an ecosystem.
Answer:(i) The sun is the main source of energy on earth. About 1% of incident solar energy is utilized by plants during photosynthesis.
(ii) Producers [plants] convert solar energy to chemical energy of food, and then it is passed on to the consumers and to decomposers back to soil. This is in accordance with law of conservation of energy.
(iii) The energy flow is unidirectional, that is, it flows from producers through herbivores to carnivores; it cannot be transferred in the reverse direction.
(iv) The amount of energy flow decreases with successive trophic levels.

Question: (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?
Answer: (i) A terrestrial food chain depicting four tropic levels is shown in diagram. ½
(ii) According to the 10% law, the amount of energy available will not be sufficient for the survival of the organisms in the 5th trophic level. ½+½+½
(A flow chart or a diagrammatic representation showing all the four tropic levels would also be accepted).
According to the 10% law, the amount of energy available will not be sufficient for the survival of the organism in the 5th trophic level.

Long Answers Type Questions

Question: Distinguish between producers and consumers.
Answer :

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. Consider a food chain Grass → Grasshopper → Frog → Snake → Hawk. This food chain can also be considered as energy chain. We can place these animals in different trophic levels, for example :
Grass : They are the producers so are placed in first trophic level. They utilize solar energy to prepare food. They transfer this energy to grasshopper, but only 10% of the energy is available to grasshopper according to Lindeman’s 10% Law. If grass has 10,000 kcal of energy only 1000 kcal will be transferred to grasshopper. So energy at next trophic level is reduced.

Similarly grasshopper is placed at second trophic level; frog in third, snake in fourth and fifth trophic level is occupied by hawk. At each trophic level the energy goes on decreasing i.e., frog will receive 100 kcal of energy, snake 10 kcal and finally hawk only 1 kcal. Thus, energy at each trophic level goes on decreasing and the animal placed at apex will receive lowest energy. Thus a food chain can be only up to maximum 5 trophic levels. In this way there exists a relationship between trophic levels and energy.

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