# Bihar Board Class 10 Science Solutions Chapter 15 Our Environment

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

## Bihar Board Class 10 Science Solutions Chapter 15 Our Environment

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

In-text Questions (Page 257)

Question 1.
The bacterial and fungal enzymes degrade the complex organic compounds present in the dead remains of plants and animals into simpler substances, so such wastes are called biodegradable. However, some wastes like glass, plastics, etc. cannot be degraded by these enzymes due to which they are persistent in the environment for many years. These are called non-biodegradable substances.

Question 2.
Give any two ways in which biodegradable substances would affect the environment.
The biodegradable wastes can affect the environment as:

• Their huge heaps act as breeding grounds for flies and mosquitoes which lead to spread of diseases like typhoid, tuberculosis, cholera, etc.
• During decomposition of these biodegradable wastes, foul smell is produced which makes people feel uncomfortable.

Question 3.
Give any two ways in which non-biodegradable substances would affect the environment.
The non-biodegradable substances would affect the environment as:

• Some of the harmful pesticides and chemicals lead to loss of soil fertility and creates imbalance in the food chains.
• Their increased volumes in the garbage dumps due to non-decomposition create problems for many animals. For example, plastics eaten by cows can choke them to death.

In-text Questions (Page 261)

Question 1.
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Each step or level in the food chain where transfer of energy takes place is called a trophic level. Example: Grass → Insect → Frog → Snake
First Trophic Level : Grass is Producer;
Second Trophic Level : Insect is Primary consumer;
Third Trophic Level : Frog is Secondary consumer;
Fourth Trophic Level : Snake is Tertiary consumer

Question 2.
What is the role of decomposers in the ecosystem?
The complex organic substances present in the dead remains of plants and animals are broken down and converted into simpler inorganic substances by the decomposers. Thus they help in recycling of nutrients and cleansing the environment.

In-text Questions (Page 264)

Question 1.
What is ozone and how does it affect any ecosystem?
Ozone (O3) is a molecule formed by three atoms of oxygen. The ozone present in the lower parts of the atmosphere is a deadly poison and harmful to organisms. But, the ozone present in the higher levels of the atmosphere is good ozone as it shields the organisms against the harmful ultraviolet rays of the Sun (that cause skin cancer) by absorbing them. It is formed by the action of ultraviolet radiation on oxygen molecule to convert it into free oxygen atom. These free oxygen atoms combine with molecular oxygen to form ozone.
$$\mathrm{O}_{2} \stackrel{\mathrm{UV}}{\longrightarrow} \mathrm{O}+\mathrm{O}$$
$$\mathrm{O}+\mathrm{O}_{2} \longrightarrow \underset{(\mathrm{Ozone})}{\mathrm{O}_{3}}$$

Question 2.
How can you help in reducing the problem of waste disposal? Give any two methods.
A collective effort by all the people can be very instrumental in reducing the problem of waste disposal. This can be done by:

• Recycling and reusing the wastes before disposing them off completely in the garbage bins.
• Segregate the various wastes as bio-degradable, non-biodegradable and hazardous wastes by using separate bins for each kind of waste.

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

Question 1.
Which of the following groups contain 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
(a) Grass, flowers and leather

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

Question 4.
What will happen if we kill all the organisms in one trophic level?
If we kill all the organisms in one trophic level, then it will cause imbalance in the ecosystem as transfer of food energy to the next level will stop. An overpopulation of the organisms in the previous trophic level will also take place. This will disturb the ecological balance.

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?
The impact of removing all the organisms in a trophic level will be same as the impact for different trophic levels because it would lead to

• Starvation and death of organisms in the next trophic level as energy transfer to the next level would stop. For example, if all producers are killed, herbivores will be affected as no food will be available for them.
• Overpopulation in the previous level as no organism will be available in the next trophic level to feed on them.

Since all the organisms are interdependent on each other in an ecosystem, it will result in an imbalance in the ecosystem if organisms of any trophic level are removed.

Question 6.
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
The harmful chemicals like pesticides are neither metabolised nor excreted by the organisms. They get accumulated in the body of the organisms due to which their concentration goes on increasing in the successive trophic levels. This phenomenon is called biological magnification.

The level of this magnification goes on increasing as we move up the trophic levels. So, the concentration of these chemicals is highest in the human beings as they occupy the topmost trophic level.

Question 7.
What are the problems caused by the non-biodegradable wastes that we generate?
The following problems are caused by the non-biodegradable wastes:

• They are not decomposed and get accumulated in the environment. They contaminate the soil and water resources.
• Their increased volumes in the garbage dumps due to non-decomposition create problems for many animals. Plastics eaten by cows or other stray animals can choke them to death.
• Their accumulation makes the land unfit for other purposes, makes it infertile.
• The rag pickers are exposed to harmful chemicals and toxins present in these kinds of wastes.
• They enter the food chain and become harmful to human beings and other animals.

Question 8.
If all the waste we generate is biodegradable, will this have no impact on the environment?
Even the biodegradable wastes have an impact on the environment in the following ways:

• A foul smell is released during their decomposition. Also, some harmful gases are released which cause air pollution.
• The heaps of such biodegradable wastes act as a breeding ground for disease causing organisms like flies and mosquitoes.

Question 9.
Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Ozone present in stratosphere acts as a shield which absorbs the harmful ultraviolet rays of the Sun. Damage to the ozone or its depletion will lead to non absorption of UV rays which cause skin cancer, ageing, cataract, etc. Damage to ozone is most prominent in Antarctica region where it’s visible as a ozone hole.

Steps to limit ozone damage:

• The use of substances called CFCs (Chlorofluorocarbons) as refrigerants and in fire extinguishers should be reduced and these should be replaced by environment friendly substances.
• UNEP (United Nations Environment Programme) has forged an agreement to freeze CFCs production at 1986 levels by all countries.

### Bihar Board Class 10 Science Chapter 15 Our Environment Textbook Activities

Activity 15.1 (Textbook page 256)

The materials like metallic containers, plastic bottles, bubble packs, broken footwear, etc. remain unchanged for longer periods of time. The materials which change their form and structure overtime are the empty cartons, kitchen wastes, torn clothes etc.

The fastest change is seen in spoilt food, vegetable peels, used tea leaves.

Activity 15.2 (Textbook page 257)

The non-biodegradable substances last from a few years to several million years. Biodegradable plastics are plastics that can be decomposed by the action of living organisms like bacteria. Under proper conditions, some biodegradable plastics can degrade to the point where microorganisms can completely metabolise them. They do not harm the environment in the way the non-biodegradable plastics harm because they are decomposed at a faster rate by the microorganisms and once decomposed they are no more a problem.

Activity 15.3 (Textbook page 258)

An aquarium becomes a self sustaining system once the above essential materials are provided in it. The water, oxygen and food are the resources which help in the life processes of organisms present in the aquarium. The aerator keeps providing fresh supply of oxygen in it. The biotic and the abiotic components interact among themselves to sustain the artificial ecosystem. We cannot leave the aquarium as such for a longer time as the growth of microorganisms like bacteria and fungi occurs which need to be removed in order to avoid infection of the fishes. Lakes and ponds are large ecosystems which do not need to be cleaned so frequently. But sometimes they need to be cleaned in order to avoid siltation or excessive growth of aquatic plants. Example is the recent cleaning of the Pushkar lake in Ajmer.

Activity 15.4 (Textbook page 259)

Yes, we have to take care not to put an aquatic animal which would eat others. Otherwise the ecosystem will not remain self-sustaining and can lead to imbalances in the processes and the whole ecosystem (aquarium).

The food chain present in the ecosystem would also consist of primary producers, primary consumers, secondary consumers, etc. Primary producers will be the phytoplanktons and the algae. Primary consumers will be zooplanktons. Secondary consumers will be small fishes followed by the larger fishes as the tertiary consumers. These groups are dependent on each other as the energy produced by the organisms at one level gets transferred from the lower level to the higher level. The aquatic organisms in the chain would be will be:
Phytoplanktons (producers) → zooplanktons (primary consumers) → small fishes (secondary consumers) → large fishes(tertiary consumers)

The producers can be considered of primary importance in an ecosystem. But, an aquarium being an artificial ecosystem, the role of human being is more in maintaining the supply of nutrients, aeration, energy, etc. to keep the ecosystem self sustaining type.

Activity 15.5 (Textbook page 261)

There is a big debate going on regarding the use of chemical pesticides as most of them like DDT once taken in by animals through the food products they consume, can neither be excreted nor metabolised. It starts accumulating in the body of the organism and as we go higher up the food chain, the concentration of harmful toxicant reaches higher levels. This phenomenon is called as biological magnification which is harmful for the health of human beings and other organisms too. Source of pesticides in the food items are the pesticides sprayed on plants or crops by humans to increase their levels of agricultural production. Yes, pesticides can enter our body from this source through other food products too as the various organisms are dependent upon each other for their survival.

The methods which can be applied are

• use of bio-control agents to protect loss of crop
• development and use pest resistant crops
• practice of organic farming

Activity 15.6 (Textbook page 262)

The chemical which has been highly detrimental to the ozone layer is the use of chlorofluorocarbons in the refrigerator, deo-sprays, etc. The harmful effect of these chemical was highlighted in 1985 when the ozone hole was detected in Antarctica. The various countries of the world met and signed the Montreal protocol in 1987 which laid down the roadmap to control the emission of ozone depleting substances.

Activity 15.7 (Textbook page 262)

The wastes generated in our homes are segregated in the various bins designated for keeping biodegradable, recyclable, non-biodegradable and hazardous wastes separately. The scavengers take away the wastes from the homes and dispose it off properly at the places meant for them so that they do not cause harm to other living organisms. The resident welfare association have designated scavengers who take the wastes away from the home. The recyclable materials are either recycled or sent to units which recycle the wastes for various other processes. The non-biodegradable and hazardous substances are disposed off by sending them to the landfill sites or by incineration.

Activity 15.8 (Textbook page 263)

Approximately 2-3 kg of waste is generated at home in a day. Approximately half of it is biodegradable. The waste generated per day in a classroom is approximately 1 kg. Almost all the waste generated in the classroom is biodegradable. The biodegradable waste can be put in compost pits and converted to compost or the recyclable ones can be recycled.

Activity 15.9 (Textbook page 263)

The sewage is treated in the sewage treatment plants. The plans are being made to ensure that no untreated sewage is discarded in the local water bodies. The local industries send their wastes to the sewage treatment plants where the harmful chemical and constituents are removed from it, before discharging it into the water bodies. Though some mechanisms are there to prevent soil and water from getting polluted by such wastes, other advanced systems are being implemented to control such pollution.

Activity 15.10 (Textbook page 263)

The electronic items thrown as e-wastes contain many harmful and hazardous substances like lead, cadmium, chromium, brominated flame retardants or polychlorinated biphenyls (PCBs).
Refer- http://ewasteguide.info/hazardous-substances
http://listverse.com/2013/01/27/10-ways-recycling-hurts-the-environment/http://www.livestrong.com article/181103-the-effect-of-recycling-plastic-water-bottles-on-the-environment/