Bihar Board Class 10 Science Solutions Chapter 15 Our Environment

 

Bihar Board Class 10 Science Chapter 15 Our Environment InText Questions and Answers

Intext Questions (Page 257)

Question 1.
Why are some substances biodegradable and some non-biodegradable ?
Answer:
Some substances can be acted upon by the microorganisms and broken down into simple substances. Such substances are called biodegradable. Some substances are inert and cannot be acted upon by the microorganisms and do not breakdown into simple substances. Such substances are called non-biodegradable.

Question 2.
Give any two ways in which biodegradable substances would affect the environment.
Answer:
Biodegradable substances affect the environment in the following ways :
(a) Thes.e substances are decomposed by the action of microorganisms. This causes fowl smell.
(b) During the process of decaying of bio-degradable substances, various types of gases are released which cause air pollution.

Question 3.
Give any two ways in which non-biodegradable substances would affect the environment.
Answer:
The non-biodegradable substances affect the environment in the following ways:
(i) They persist in the environment for a long time and thus damage the environment.
(ii) Such substances cause land pollution and water pollution.

Intext Questions (Page 261)

Question 1.
What are trophic levels ? Give an example of a food chain and state the different trophic levels in it.
Answer:
There are various series of organisms feeding on one another. These series of organisms taking part in various biotic levels form food chain. The steps or levels of the food chain are called trophic levels.
An example of food chain :
Grass → Deer → Lion.
Various trophic levels are :

• First trophic level is grass. It is producer.
• Second trophic level is deer. It is primary consumers (or. herbivores)
• Third trophic level is lion. It is larger carnivores.

Question 2.
What is the role of decomposers in the ecosystem ?
Answer:
Decomposers are called natural cleaning agent. They act on biodegradable substances and break them into simple substances. In this way, decomposers create a balance in the environment and play an important role in the environment.

Intext Questions (Page 264)

Question 1.
What is ozone and how does it affect any ecosystem ?
Answer:
Ozone is a molecule formed by three atoms of oxygen. Ozone is formed by the reaction of three molecules of oxygen in presence of ultraviolet (UV) rays.

Ozone performs an essential function. It shields the surface of the earth from ultraviolet radiation of the sun. If this radiation enters in the atmosphere, it could cause various disorders. So, ozone protects the ecosystem from damaging.

Question 2.
How can you help in reducing the problem of waste disposal ? Give any two methods.
Answer:
1. There are two types of wastes; biodegradable and non-biodegradable. We should use more and more substances that leave biodegradable wastes.
2. Biodegradable wastes are converted into manure. Non- biodegradable wastes should be sent to the factories for recycling.

Bihar Board Class 10 Science Chapter 15 Our Environment Textbook Questions and Answers

Question 1.
Which of the following groups contains only biodegradable items ?
(a) Grass flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass.
Answer:
(a) Grass, flowers and leather
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass.

Question 2.
Which of the following constitute a food chain ?
(а) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat.
Answer:
(b) Grass, goat and human.

Question 3.
Which of the following are environment-friendly practices ?
(a) Carrying cloth-bags to put purchases in while shopping.
(b) Switching off unnecessary lights and fans.
(c) Walking to school instead of getting your mother to drop you on her scooter.
(d) All of the above.
Answer:
(d) All of the above.

Question 4.
What will happen if we kill all the organisms in one trophic level ?
Answer:
Each and every trophic level depends for its energy needs on its previous trophic level. If all organisms of any of the trophic levels in a food chain are damaged, the organisms of other trophic levels will also be destroyed because Energy flow is stopped from one trophic level to other trophic level.

Question 5.
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:
No, the impact of removing all the organisms in a trophic level is same for different trophic levels. The removal of organisms of any trophic level is damaging and it causes various disorder in ecosystem.

Question 6.
What is biological magnification? Will the levels of this magni-fication be different at different levels of the ecosystem ?
Answer:
When any harmful chemical like DDT enters in a food chain, its concentration increases gradually at each trophic level. This phenomenon is called biological magnification. The levels of this magnification will be different at different levels of the ecosystem.

Question 7.
What are the problems caused by the non- biodegradable wastes that we generate ?
Answer:
The non-biodegradable wastes persist in the environment for a long time and cause various problems. Non bio-degradable wastes cause :

• Water pollution so that water becomes unfit for drinking.
• They cause land pollution and due to it land loses its beauty.
• They cause stoppage of flow of water in drains.
• They also cause air pollution and make the air poisonous.

Question 8.
If all the waste we generate is biodegradable, will this have no impact on the environment ?
Answer:
The biodegradable wastes do not persist for a long time in the environment. However, they also cause harmful effects but these effects are only for sometime. These wastes can be converted into useful substances and broken into simple substances by the action of microorganism. So, there will be impact of biodegradable waste but for a short time.

Question 9.
Why is the damage to the ozone layer a cause for concern ? What steps are being taken to limit this damage?
Answer:
Enlargement of ozone hole will cause more ultraviolet rays to reach on the earth’s surface. This is very harmful for us, animals and microorganisms in the following ways :

• Ultraviolet radiations may cause skin disease, especially skin cancer.
• Plant life will be disturbed due to retarded growth and destruction of pigments.
• UV-rays may kill microorganisms, decomposers and other useful microbes. It may lead to ecological imbalance.

Steps to prevent damage of ozone layer :

• Judicious use of aerosol spray propellants such as fluorocarbon and chlorofluorocarbons which cause depletion or hole in ozone layer.
• Limited use of supersonic planes.
• Control over large scale nuclear explosions,

Bihar Board Class 10 Science Chapter 15 Our Environment Textbook Activities

Activity 15.1 (Page 256)

• Collect waste material from your homes. This could include all the waste generated during a day, like kitchen waste (spoilt food, vegetable peels, used tea leaves, milk packets and empty cartons), waste paper, empty medicine bottles / strips / bubble packs, old and torn clothes and broken footwear.
• Bury this material in a pit in the school garden or if there is no space available, you can collect the material in an old bucket/flower pot and cover with at least 15 cm of soil.
• Keep this material moist and observe at 15-day intervals.

Question 1.
What are the materials that remain unchanged over long periods of time ?
Answer:
Milk packets, empty cartons, empty medicine bottles/ strips,1bubble packs and broken footwear remain unchanged for a long time.

Question 2.
What are the materials which change their form and structure over time ?
Answer:
Spoil food, vegetable peels, used tea leaves, empty cartons, old and torn clothes change their form and structure over time.

Question 3.
Of these materials that are changed which ones change the fastest ?
Answer:
Vegetable peels change fastest.

Activity 15.2 (Page 257)

Use the library or internet to find out more about biodegradable and non-biodegradable substances.

Question 1.
How long are various non-bio-degradable substances expected to last in our environment ?
Answer:
These substances are inert and persist for a long time in the environment. They may last for a decade to a century.

Question 2.
These days, new types of plastics which are said to be biodegradable are available. Find out more about such materials and whether they do or do not harm the environment.
Answer:
Biodegradable plastics or bioplastics are very much in news these days. Other simpler things are polymer fabrics, dental implants, etc.

Activity 15.3 (Page 258)

• You might have seen an aquarium. Let us try to design one.
• What are the things that we need to keep in mind when we create an aquarium? The fishes would need a free space for swimming (it could be a large jar), water, oxygen and food.
• We can provide oxygen through an oxygen pump (aerator) and fish food which is available in the market.

Question 1.
If we add a few aquatic plants and animals, it can become a self-sustaining system. Can you think how this happens ?
Answer:
Plants can do photosynthesis in which they release O2. This O2 is used by both plants and animals for respiration and CO2 is released. This CO2 is used by plants in photosynthesis. So they become self-sustaining system.

Question 2.
Can you leave the aquarium as such after we set it up ? Why does it have to be cleaned once in a while ? Do we have to clean ponds or lakes in the same manner ? Why or why not ?
Answer:
We cannot leave the aquarium as such as we set it up. It should be cleaned once in a while because it becomes polluted due to the life processes of plants and animals. Yes, we have to clean ponds or lakes because ponds and lakes are also natural aquarium. They are also polluted by natural and animal activities.

Activity 15.4 (Page 259)

Question 1.
While creating an aquarium did you take care not to put an aquatic animal which would eat others ? What would have happened otherwise ?
Answer:
If we put an aquatic animal which eats others, then it eats other animals in the aquarium and ultimately it also dies.

Question 2.
Write the aquatic organisms in order of who eats whom and form a chain of at least three steps
Answer:

Question 3.
Would you consider any one group of organisms to be of primary importance ? Why or why not ?
Answer:
First- trophic level (plants) are considered to be of primary importance. It is due to plants that there are producers. So there should be producers for sustaining life of other trophic levels in a food chain.

Activity 15.5 (Page 261)

• Newspaper reports about pesticide levels in ready-made food items are often seen these days and some states have banned these products. Debate in groups the need for such bans.

Question 1.
What do you think would be source of pesticides in these items ? Could pesticides get into our bodies from this source through other food products too ?
Answer:
The pesticides enters in food items through food chain. The pesticides also get into our bodies through other food products. It is because the pesticides are stored in them through by the process of biological magnification.

Question 2.
Discuss what methods could be applied to reduce our intake of pesticides ?
Answer:

• Excessive use of pesticides on crops, vegetables and fruits should be avoided.
• Cereals, fruits and vegetable should be thoroughly washed with clean water before use.
• Drinking water should be filtered using lastest techniques.

Activity 15.6 (Page 262)

Question 1.
Find out from the library, internet or newspaper reports, which chemicals are responsible for the depletion of the ozone layer.
Answer:
The main chemical responsible for the depletion of ozone layer is chlorofluoro-carbon (CFG). Besides chemicals such as nitric oxide (NO), hydroxyl (OH), free radicles of chlorine (Cl), bromine (Br) also have damaged the ozone layer.

Question 2.
Find out if the regulations put iii place to control the emission of these chemicals have succeeded in reducing the damage to the ozone layer. Has the size of the hole in the ozone layer changed in recent years ?
Answer:
After the Montreal Protocol, CFC production was sharply limited beginning in 1987 and phased out completely by 1996. This resulted in improvement in the situation. In 2003, scientists announced that the depletion of the ozone layer may be slowing down. Satellite reports and the ground stations, confirmed that the upper atmosphere ozone depletion rate has slowed down significantly during the past decade. However, CFCs have very long atmospheric lifetimes, ranging from 50 to over 100 years, so the final recovery of the ozone layer is expected to require several lifetimes.

Activity 15.7 (Page 262)

Question 1.
Find out,what happens to the waste generated at home. Is there a system in place to collect this waste ?
Answer:
The waste generated at home is dumped into the garbage homes. Usually there is a system of collecting these wastes provided by the local authority.

Question 2.
Find out how the local body (panchayat, municipal corporation, resident welfare association) deals with the waste. Are there mechanisms in place to treat the biodegradable and non-biodegradable waste separately ?
Answer:
The local bodies have an organised system to deal with the wastes – from collection to their safe disposal. Yes, there are separate mechanisms to treat biodegradable and ^non-bio-degradable wastes. Biodegradable wastes are converted into manure while non- biodegradable wastes are sent to the industries for recycling.

Activity 15.8 (Page 263)

Question 1.
How much waste is generated at home in a day ?
Answer:
Usually it is between 2 kg to 4 kg per day.

Question 2.
How match of this waste is biodegradable ?
Answer:
2 kg to 3 kg per day.

Question 3.
How much waste is generated in the classroom in a day ?
Answer:
llA kg to 2 kg per day.

Question 4.
How much of this waste is biodegradable ?
Answer:
1 kg to IV2 kg per day.

Question 5.
Suggest ways of dealing with this waste.
Answer:
Most of the classrooms waste consists of paper, fruits peels, left out vegetable and bread pieces etc. These are all biodegradable and can be used to prepare compost that can be used in school garden. Biodegradable and non-biodegradable wastes should be collected separately in home. They may also be disposed off at municipal disposal centres separately, so that biodegradable wastes can be used to prepare compost/manure.

Activity 15.9 (Page 263)

Question 1.
Find out how the sewage in your locality is treated. Are there mechanisms in place to ensure that local water bodies are not polluted by untreated sewage.
Answer:
Sewage is collected from various points of city and carried to water recycling centres. Sewage collected in big tanks are treated with modern techniques such as grinding, settling, neutralization, biological treatment, disinfection such as chlorination, etc. After proper treatment, water is discharged into river or into other water sources or used for recycling.

Question 2.
Find out how the local industries in your locality treat their waste. Are there mechanisms in place to ensure that the soil and water are not polluted by this waste ?
Answer:
Various industrial units use different techniques to treat their waste before releasing it into river. The method of treatment depends upon the chemicals present in the waste.

Activity 15.10 (Page 263)

Question 1.
Search the internet or library to find out what hazardous materials have to be dealt with while disposing off electronic items. How would these materials affect the environment ?
Answer:
In electronic items lead, silicon and cadmium are present (along with wines, glass pieces, plastics, etc.) which are very poisonous. They affect human population and other animals causing water and land pollution. They cause serious diseases of lungs, circulatory system, kidney, etc. In the environment, biomagnification of these dangerous substances occurs and a very high percentage of these may accumulate in human body. As a result, body metabolism gets badly affected and serious diseases are caused.

Question 2.
Find out how plastics are recycled. Does the recycling process have any impact on the environment ?
Answer:
In recycling of plastic Waste plastic is heated, mixed, with some chemicals like sulphur and then used for moulding or making road surface. In this process, fumes of harmful substances are mixed into the air causing air pollution. Sometimes waste plastic is dissolved into one or more solvent and then decolourised or mixed up with different colours. Finally, plastic is separated for recycling and the solvent is discarded or evaporated. Here again fumes of plastic dyes and solvents cause air pollution.

Bihar Board Class 10 Science Chapter 15 Our Environment NCERT Exemplar Problems

Short Answer Type Questions

Question 1.
Why is improper disposal of waste a curse to environment?
Answer:
Wastes pollute our environment. These pollute, air, soil and water and cause harmful effects on all living organisms. Thus, improper disposal of waste a curse to the enviornment.

Question 2.
Write the common food chain of a pond ecosystem.
Answer:
Phytoplanktons and aquatic plants → small aquatic animals larvae, insects etc. → fish → bird.

Question 3.
What are the advantages of cloth bags over plastic bags during shopping?
Answer:
Cloth bags are –
(a) capable of carrying more things
(b) made of biodegradable material
(c) do not pollute our environment
(d) can be reused
Whereas plastic bags are non-biodegradable and pollute our environment.

Question 4.
Why are crop fields known as artificial ecosystems?
Answer:
Crop fields are man-made and some biotic and abiotic components are manipulated by humans. Different biotic and abiotic components together constitute an ecosystem. Thus, crop fields are known as artificial ecosystem.

Question 5.
Differentiate between bio-degradable and non- biodegradable substances. Cite examples.
Answer:
Substances that are broken down into simpler substances by biological processes are called as biodegradable e.g., wood, paper.
Substances that cannot be broken down into simpler ones by biological processes are called as non-biodegradable g.g., plastic, DDT.

Question 6.
Suggest one word for each of the following statements/definitions
(а) The physical and biological world where we live in
(b) Each level of food chain where transfer of energy takes place
(c) The physical factors like temperature, rainfall, wind and soil of an ecosystem
(d) Organisms which depend on the producers either directly or indirectly for food
Answer:
(a) Environment/biosphere
(b) Trophic level
(c) Abiotic factors
(d) Consumers/heterotrophs

Question 7.
Explain the role of decomposers in the environment.
Answer:
Decomposers break down the dead and decaying organic natter and return the nutrients to the soil. Thus, they play a repy important role in the nutrient recycling in the environment.

Question 8.
Select the mis-matched pair in the following and correct it.
(a) Biomagnification-Accumulation of chemicals at the successive trophic levels of a food chain
(b) Ecosystem-Biotic components of environment
(c) Aquarium-A man-made ecosystem
(d) Parasites – Organisms which obtain food from other living organisms
Answer:
(b) Is not a matching pair
Both biotic and abî4tic component’óf environment constitute an ecosystem.

Question 9.
We do hot cjean ponds or lakes, but an aquarium needs to be , cleaned. Why?
Answer:
An aquarium is an artificial and incomplete ecosystem in contrast to a pond/lake which are natural, self-sustaining and complete ecosystems.

Long Answer Type Questions

Question 10.
Indicate the flow of energy in an ecosystem, Why is it unidirectional? Justify.
Answer:
The energy transfer process can be described in terms of the following steps :

• Green plants called producers absorb solar energy arid convert CO₂ and water into carbohydrates.
• A major part of this energy is used up by the plants for their metabolic activities and also for their growth. :
• Herbivores eat these plants and the chemical energy stored in plants gets transferred to them. A part of this energy is utilise  by herbivores for their own requirements.
• When carnivores eat.herbivores, the energy gets transferred to them.

At every step of energy transfer, only a part of the total energy is passed to the next trophic level. The unutilised energy is lost to the surroundings as heat energy. Since the flow is progressively from one trophic level to another and does not revert back, it is said to be unidirectional. Further, the available energy decreases in the higher trophic levels making it impossible for energy to flow in the reverse direction.

Question 11.
What are decomposers? What will be the consequence of their absence in an ecosystem?
Answer:
Decomposers are the organisms that break down the complex organic substances of garbage, dead animals and plants into simpler inorganic substances. These substances go into the soil and are used up again by the plants. In the absence of decomposers recycling of material in the biosphere will not take place. Thus, decomposers are called natural cleaning agent. They create a balance in the environment and play an important role in the environment.

Question 12.
Suggest any four activities in daily life which are eco-friendly.
Answer:

• Separation of biodegradable and non-biodegradable substances.
• Gardening.
• Use of gunny bags/paper bags in place of polythene/ plastic bags.
• Use of compost and vermicompost in place of fertilisers.

Question 13.
Give two differences between food chain and food web.
Ans.
Food chain :
(а) Food chain is a series of organisms feeding on one another.
(b) Members of higher trophic level feed upon a single type of organism of the lower trophic level.

Food Web :
(a) Food web consists of a number of interlinked food chains.
(b) Members of higher trophic level can feed upon organisms of the lower trophic levels of other food chain.

Question 14.
Name the wastes which are generated in your house daily. What measures would you take for their disposal?
Answer:
Wastes generated in my house :
(a) Kitchen wastes
(b) Paper wastes like newspapers, bags, envelopes
(c) plastic bags
(d) Vegetable/fruit peels/rind

Measures for disposal
(a) Segregation of biodegradable and non-biodegradable  wastes.
(b) Safe disposal of plastic bags.
(c) Vegetable/fruit peels can be placed near trees/plants, which on decomposition will enrich the soil with nutrients.
(d) Give paper wastes for recycling.
(e) Prepare a compost pit for kitchen wastes

Question 15.
Explain some harmful effects of agricultural practices on the environment.
Answer:
(a) Excessive use of fertilisers changes the chemistry of soil and kills useful microbes.
(b) Excessive use of non-biodegradable chemical pesticides leads to biological magnification.
(c) Extensive cropping causes loss of soil fertility.
(d) Excess use of ground water for agriculture lowers the water table.
(e) Damage to natural ecosystem/habitat.