10 Chp 15 Prvs Aprd Qsns

                  Class 10 Science               

       Chapter 15 Our Environment    

 Previous Years Appeared Questions

       MULTIPLE CHOICE QUESTIONS        

1. Observe the food chain given below :Grass → Grass hopper → Frog → Snake → Eagle. If the energy available at first tropic level is 5000 J, then the amount of energy available for snake is (June 2019)

(A) 500J   (B) 5J    (C) 0·5J  (d) 50j

Ans: (B) 5J

2. The correct statement with respect to biodegradable substances among the following. These substances (July 2021)

(A) undergo recycling naturally in the environment

(B) harm various organisms in the ecosystem

(C) increase the density of harmful chemicals in different tropic levels

(D) remain inert in the environment for a long time

Ans: (A) undergo recycling naturally in the environment

3. The materials that change slowly their form and structure in the environment are (Sep 2021)

(A) Plant fibres

(B) Peels of vegetables

(C) Waste papers

(D) Used tea leaves

Ans: (A) Plant fibres

4. Atmospheric layer that absorbs ultraviolet radiations coming from the sunlight is made up of this molecule. (April 2020)

(A) N2       (B) H2      (C) O3   (D) O2

Ans:  (C) O3 

5. Primary consumers in any food chain are always (June 2022)

(A) carnivores

(B) herbivores

(C) higher carnivores

(D) producers.

Ans: (B) herbivores

6. The materials that take more time to change their forms and structure are (State level preparatory 2023)

(A) DDT, BHC, Insecticide

(B) Waste paper, torn cotton clothes

(C) Vegetable peels, used tea leaves

(D) Medicine bottle, milk pocket 

Ans: (A) DDT ,BHC ,insecticides

7. Algae → Small insects → Large insects → Small fish → Large fish → Human. The arrangement of trophic levels in this food chain are in the (MQP 2023)

(A) increasing order of energy availability.

(B) increasing order of both energy availability and storage of harmful chemicals.

(C) increasing order of storage of harmful chemicals.

(D) decreasing order of both energy availability and storage of harmful chemicals. 

Ans: (C) increasing order of storage of harmful chemicals.

8. Producers of aquatic eco-system are (June 2023)

(A) algae         (B) small fishes       

C) larvae        (D) protozoa.

Ans. :  (A) algae

                ONE MARKS QUESTIONS            

1. Micro-organisms like bacteria are called decomposers. Why? (June 2019)

Ans : Bacteria and fungi are called decomposers because they break down the dead and decaying organic matter into simpler substances and provide the nutrients back to the soil.

2. What is the role of decomposers in an ecosystem ?. (April 2022)

Ans. : Decompose dead wastes ( organic ) of plants and animals thus keep surroundings clean and maintain ecological balance. 

3. Nowadays Chlorofluorocarbon ( CFC ) free refrigerators are being manufactured. Why ? (June 2022)

Ans. : CFC‘s are responsible for the decrease in the amount of ozone layer which protects the earth from ultraviolet rays of sun.

4. What is biological magnification‘ ? (June 2022) (June 2023)

Ans. : Process that involves magnification ( increase ) of the harmful chemicals at different trophic levels of ecosystem.

5. What is the function of ozone layer? (MQP 2023)

Ans : Ozone protects the earth from harmful UV-radiation. 

                TWO MARKS QUESTIONS            

1. A food chain in a polluted aquatic ecosystem is given. Observe it and answer the following questions. Fresh water → Algae → Fishes → Birds.

(i) Which organisms are disturbed more due to bio-magnification ? Why?

(ii) This ecosystem will be destroyed gradually due to bio-magnification. Why? (April 2019)

Ans :

(i) Birds get affected more due to bio-magnification. As the birds occupy the top most level in the given food chain, the maximum concentration of harmful chemicals causing bio-magnification get accumulated in their body.

(ii) Bio-magnification is the process of accumulation of non-degradable chemicals in the various tropic levels of food chains. As the chemicals are non-degradable or cannot be washed. they cannot be removed from the organisms of the food chain. This leads to gradual destruction of the ecosystem. 

2. A student places a piece of cucumber, a glass piece, a banana peel and a plastic pen in a pit and closes it. What changes can be observed in these materials after a month? Give scientific reason for these changes. (April 2019)

Ans :

★ Cucumber piece and banana peel are organic substances.

★ They are biodegradable substances, and are eco-friendly.

★ Glass piece and plastic pen are inorganic/synthetic substances.

★ They are non-biodegradable substances and cause soil pollution.

3. As energy moves progressively through various tropic levels of food chain it is no longer available to the previous level. Give reasons. (June 2020)

Ans :

★ The flow of energy is unidirectional. 

★ At every tropic level, large amount of energy is lost in form of heat for maintaining metabolic activities.

★ The amount of heat lost is generally 90 % and only 10 % of energy is retained and is available from previous tropic level to the next

★ Thus it is said that no energy is available for the previous tropic level.

4. Mention any two effects of non-biodegradable substances on the environment. (June 2022)

Ans. :

★ These substances do not undergo natural recycling and remain inert in the environment.

★ May harm the various members by adding into different stages of ecosystem / cause ‗Biological magnification‘.

★ Cause environmental pollution.

5. Mention any two methods that reduce the problems caused while disposing the wastes. (June 2022)

Ans:

★ By adopting following methods :  Segregation of dry wastes and wet wastes.

★ Reusing of wet wastes by converting them into manures.  Recycling dry wastes

★ Limiting the use of disposable materials

★ Following eco-friendly packagings.

6. onstruct below given types of food chains that comprise algae, aquatic birds, large fish, and small fish.

i) Food chain that shows the flow of energy in the increasing order

ii) Food chain that shows the flow of harmful chemicals in the increasing order. (State level preparatory 2023)

Ans:

i) Birds→ Large fish→ small fish→ algae

ii) algae → small fish → large fish → Birds  

7. Give an example for a food chain of grassland ecosystem. If there is an increase in the number of organisms in the second trophic level, how does this affect on that food chain? (April 2023)

Ans. : 

Grass → Grasshopper → Frog → Snake → Eagle ( Any suitable food chain ) 

★ If the number of organisms in the second trophic level increases, then the number of organisms in the first trophic level decreases. 

★ Eventually population of the rest of the organisms in the trophic levels decreases and leads to ecological imbalance. 

              THREE MARKS QUESTIONS           

 1. Give reason :

a) Food chains generally consist of only three or four steps.

b) Decomposers play an important role in an ecosystem.

c) Protecting of ozone layer is necessary. (Sep 2020)

Ans :

a) Food chains generally consist of only three or four steps because, energy is lost in each tropic level. Hence, a shorter food chain is more efficient.

b) Decomposers play an important role in an ecosystem because, they break down the dead and decaying organic matter into simpler substances and provide the nutrients back to the soil.

c) Protecting of ozone layer is necessary because , the ozone layer is a natural layer of gas in the upper atmosphere that protects humans and other living things from harmful ultraviolet (UV) radiation from the sun

2. What is trophic level ? Flow of energy in an ecosystem is always unidirectional. Why? Explain. (April 2022)

Ans. : Different levels or stages of food chain are called trophic level.

Energy flow in an ecosystem is unidirectional because,

★ The energy that is captured by autotrophs does not revert back to the solar input.

★ The energy which passes to the herbivores do not come back to autotrophs.

★ As energy moves progressively through the various trophic levels it is no blonger available to the previous level.

★ At different levels energy is lost in the form of heat.  

                FOUR MARKS QUESTIONS          

              IMPORTANT QUESTIONS               

1. What is ozone and how does it affect any ecosystem?

Ans : Ozone is a molecule formed by three oxygen atoms (O3) Ozone is essential for all kinds of ecosystems on earth as it protects the ecosystem from the harmful effects of ultraviolet radiations cause skin cancer, cataract and affect our immune system.

2. How ozone layer is formed ? Explain with equations

Ans : 

★ Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule.

★ The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O)atoms.

★ These atoms then combine with the molecular oxygen to form ozone

3. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Ans :

★ The damage to the ozone layer is a cause for concern because if the ozone layer in the atmosphere disappears completely, then harmful ultraviolet radiations coming from the sun would reach the earth. These ultraviolet radiations would cause skin cancer and other ailments in human beings, animals and also damage the plants.

★ Ozone layer is damaged by the substance called chloroflourocarbons (CFC) , so we have to avoid using such substances.

★ The United Nations Environment Programme (UNEP) unanimously forged an agreement among its member countries to freeze CFC production .

4. Why are some substances biodegradable and some non-biodegradable?

Ans : Substances that are broken down by biological processes are said to be biodegradable. In our environment, many of the substances are broken easily by decomposers However, there are other substances also which are not broken down in this manner and are known as nonbiodegradable substances. Since these substances are not degraded by decomposers, so they persist for a long time.

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

Ans :

a) They may produce foul smell during decomposition process.

b) They may produce some harmful gases such as ammonia, methane, carbon dioxide, etc., which can further-cause global warming.

c) These substance are the sources for harmful microbes and can spread diseases.

6. Give any two ways in which non-biodegradable substances would affect the environment.

Ans :

a. These inert substances simply persist in the environment. This means that these substances require land area for dumping.

b. Excess of fertilizers, pesticides and other chemicals changes soil chemistry and also affects aquatic life.

c. Most of these chemicals and heavy metal are easily absorbed by the organisms. This causes biological magnification.

7. Which bag will you prefer for shopping and why ? (a) Jute bag (b) Polythene bag

Ans : Jute bag was biodegradable , while polythene bag was non-biodegradable, so I prefer Jute bag for shopping 

8. How can you help in reducing the problem of waste disposal? Give any two methods.

Ans :

(i) Preparing compost : All biodegradable wastes like, kitchen waste , cattle wastes can be dumped in the compost pit.

(ii) By following 3 R‘s : Reduce , reuse and recycle

★ By opting biodegradable substances in our daily life

★ Reusing and recycling of plastics and papers

9. Why only 10% energy is transferred to the next trophic level ?

Ans : At every tropic level, 90% of energy is lost in form of heat for maintaining metabolic activities. Hence , only 10% energy is transferred to the next trophic level

10. Why natural ecosystem is more stable than artificial ecosystem ?

Ans : The natural ecosystem is more stable because it has been evolved naturally by adopting requires changes with the time whereas artificial ecosystem is created by man seeing the natural ecosystem.

11. Study the food chain given below.

★ Grass → Grasshopper → Frog

★ Wheat → Rat → Snake → Hawk

Which of the two consumers frog/hawk will get more available energy and why?

Ans : Frog will get more energy Because , In a food chain only 10% of the energy will be available for the next tropic level. Frog is a secondary consumer while Hawk is a tertiary consumer , Hence Frog will get more energy.

12. What will happen if we kill all the organisms in one tropic level?

Ans : The number of organisms will be increased in lower tropic level and this will leads to scarcity of food. The number of organisms will be decreased in higher tropic level because of unavailability of food. Finally the whole food chain will be destroyed.

13. Why it is an advantage to have a shorter food chain?

Ans : In a food chain only 10% of the energy will be available for the next tropic level. Hence , to get sufficient energy shorter food chain is advantageous.