CBSE Class 10 Science HOTs Our Environment Set 03

Question. We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest ways to make people realize that the improper disposal of waste is harmful to the environment. 
Answer: (i) Residents Welfare Associations should hold meetings regarding the ill-effects of decomposing domestic waste in the bylanes of colonies.
(ii) Slogans could be written down or posters could be put at the places where people generally throw their domestic waste.

Question. Suppose you find a heap of domestic waste, in a nearby park, which is decomposing. What would you do to make the people of the surrounding area realise that such type of disposal of domestic waste is harmful to the environment? 
Answer: (i) By writing slogans or putting posters at the places where people generally throw their domestic waste.
(ii) By motivating the people about proper disposal of waste which prevents pollution that could otherwise endanger human health and environment.
(iii) Banners and signboards educating people about the ill-effects of improper disposal of wastes can be erected/ hanged in residential colonies.
(iv) Street plays highlighting the ill effects of improper disposal of wastes can be organized.

Question. “To discard the household waste we should have two separate dustbins, one for the biodegradable waste and the other for the non-biodegradable waste.” Justify this statement suggesting the proper way of disposal of these wastes. 
Answer: Biodegradable waste can be recycled for future use. If we discard biodegradable and non-biodegradable waste in the same dustbin, then biodegradable waste will become unfit for recycling. The proper way of disposal of these wastes are:
(i) Biodegradable waste can be converted into compost which can be used as manure.
(ii) Non-biodegradable waste should first be treated and then disposed.

Question. Government of India is imposing ban on the use of polythene bags for shopping. List four advantages of using cloth or jute bags over polythene bags. 
Answer: Advantages of jute and cloth bags are:
(i) They are re-usable.
(ii) They are biodegradable.
(iii) They are stronger than polythene bags and can carry more load.
(iv) They can be repaired at home if torn.

Question. State two problems caused by the non-biodegradable waste that we generate in our daily life. 
Answer: Two problems caused by non-biodegradable waste that we generate in our daily life are:
(i) Waste like plastic, cans etc., if falls on drains causes clogging of drains. Clogged drains causes artificial flood in cities.
(ii) Non-biodegradable waste like polythene when gets buried in soil increases soil temperature making the soil unfit for agriculture.

Question. Mention three harmful effects of using polythene bags on the environment. Suggest an effective alternative to these bags. 
Answer: Harmful effects:
(a) They are non-biodegradable and persist in the environment for long periods.
(b) Burning them produces poisonous gases that pollute the air.
(c) When ingested by the animals, it cannot be digested and the animals suffer from in digestion and some may die.
Alternatives: Jute bags/cloth bags.

Question. How can we help in reducing the problem of waste disposal? Give any two methods. 
Answer: Problem of waste disposal can be solved by following methods:
(i) by disposing biodegradable and non-biodegradable waster separately.
(ii) by reusing materials as much as possible.

Question. Mention the basis of classifying substances as biodegradable and non-biodegradable. Give two examples of each.
Answer: Substances which can be broken down into simpler harmless substances in nature by the action of microorganisms are called biodegradable substances. Non-biodegradable substances cannot be broken down into simpler harmless substances in nature.
Examples.
(i) Biodegradable: Agricultural waste and cloth.
(ii) Non-biodegradable: DDT and polythene bags.

Question. We can get electric energy from coal. Does human being get energy from eating coal? Give reason. 
Answer: Enzymes are specific in their action. Specific enzymes are needed for break down of a particular substance. Human body does not contain the enzyme which can break coal to get energy. Hence, we do not get any energy if we try to eat coal.

Question. (a) What is meant by garbage? List two classes into which garbage is classified.
(b) What do we actually mean when we say that the “enzymes are specific in their action”? 
Answer: (a) Garbage: A waste or rubbish produced from a household is known as garbage. It includes spoilt food, vegetable peels, leaves, paper, cattle dung, etc.
Two classes in which garbage is classified as:
(i) Biodegradable garbage
(ii) Non-biodegradable garbage
(b) All enzymes are specific for the type of chemical reaction they catalyse. Specific enzymes are needed for the break down of a particular substance. Biodegradable substances are broken down by biological processes. Microorganisms such as fungi and bacteria break down all living things whereas non-biodegradable substances do not break down by biological processes or by the action of enzymes.

Question. A lot of waste is generated in neighborhood. However, almost all of it is biodegradable. What impact will it have on the environment or human health?
Answer: Excess generation of biodegradable wastes can be harmful as Its decomposition is a slow process leading to production of foul smell and gases. It can be the breeding ground for germs that create unhygienic conditions.

Question. Write one difference between biodegradable and non-biodegradable wastes. List two impacts of each type of the accumulated waste on environment if not disposed off properly. 
Answer: Differences:
• Biodegradable wastes: These wastes can be broken down into simpler harmless substances in nature by the action of microorganisms.
• Non-Biodegradable wastes: These wastes cannot be broken down into simpler harmless substances in nature.
Two ways in which biodegradable substances affect the environment are:
• Biodegradable substances on decomposing provides a breeding ground for flies, cockroaches and other insects. These insects carry germs and spread various diseases like cholera, diarrhoea, etc.
• During decomposition process of biodegradable substances foul smell and some harmful gases are released which make problem for the nearby living people.
Two ways in which non-biodegradable substances affect the environment are:
(a) Chemical like BHC and DDT are carcinogenic in nature, i.e. cancer causing and induce tumors.
(b) Handling of waste materials may cause skin, respiratory and intestinal infections.
(c) Non-biodegradable substances do not decompose easily so it produces land and water pollution.

Question. Gas A, found in the upper layers of the atmosphere, is a deadly poison but is essential for all living beings. The amount of this gas started declining sharply in the 1980s.
(a) Identify Gas A. How is it formed at higher levels of the atmosphere?
(b) Why is it essential for all living beings? State the cause for the depletion of this gas. 
Answer: (a) Gas A is Ozone. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen \( (O_2) \) molecule. The higher energy UV radiations split apart some molecular oxygen \( (O_2) \) into free oxygen (O) atoms. These atoms then combine with molecular oxygen to form ozone.
\( O_2 \xrightarrow{UV} O + O \)
\( O + O_2 \rightarrow O_3 \)
(b) Ozone shields the surface of the earth / protects living organisms from ultraviolet (UV) radiation released by the sun. Chlorofluorocarbons (CFCs) which are used as refrigerants/ in fire extinguishers lead to depletion of ozone layer.

Question. State in brief two ways in which non-biodegradable substances would affect the environment. List two methods of safe disposal of the non-biodegradable waste. 
Answer: (i) Non-biodegradable waste may accumulate in the environment and concentrate in the food chain, thereby can harm organisms.
(ii) Non-biodegradable substances may pollute the soil and increase soil temperature.
Two methods of safe disposal of non-biodegradable waste are:
(i) Recycling: The wastes are treated and some value materials are extracted for reuse.
(ii) Incineration: Medical and toxic wastes are burnt at high temperature in incinerators. Incinerators transform the waste into ashes.

Question. (a) What is ‘environmental pollution’?
(b) Distinguish between biodegradable and non-biodegradable pollutants.
(c) Choose the biodegradable pollutants from the list given below:
Sewage, DDT, radioactive waste, agricultural waste.
Answer: (a) Environmental pollution is an undesirable change in the physical, chemical or biological characteristics of the natural environment, brought about by man’s activities. This pollution may affect the soil, rivers, seas or the atmosphere.
(b) Differences:
• Biodegradable pollutants: (i) These pollutants can be broken-down into non-poisonous substances in nature by the action of micro-organisms. (ii) They get recycled thus, do not need any dumping sites. (iii) These are obtained from living things. (iv) They cause minimum environmental pollution.
• Non-Biodegradable pollutants: (i) These pollutants cannot be broken-down into non-poisonous substances by microorganisms. (ii) They cannot be recycled thus, require dumping sites. (iii) These are obtained from non-living things. (iv) They cause environmental pollution.
(c) Biodegradable pollutants are sewage and agricultural waste.

Question. What is ozone? How and where is it formed in the atmosphere? Explain how does it affect ecosystem. 
Answer: Ozone is an isotope of oxygen, i.e. it is a molecule formed by 3 atoms of oxygen.
\( O_2 \rightarrow O + O \)
\( O_2 + O \rightarrow O_3 \text{ (Ozone)} \)
Ozone exists in the ozone layer of stratosphere. At higher level of atmosphere, \( O_2 \) molecule breaks down to 2 oxygen atom. The oxygen atom then combines with the oxygen molecule to form ozone.
Ozone layer in the atmosphere prevents UV rays from reaching earth. Exposure to excess UV rays causes skin cancer, cataract and damages eye and immune system. It also decreases crop yield and reduces population of phytoplankton, zooplankton and certain fish larvae which are an important constituent of aquatic food chain. It also disturbs rainfall, causing ecological disturbance and reduces global food production. Thus, it affect the ecosystem.

Question. You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment Day.’
(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment. 
Answer: (a) Ozone layer at the higher levels of the atmosphere, acts as a shield to protect earth from the harmful effects of the ultraviolet (UV) radiations; hence, it should be protected.
(b) (i) Urging the people not to buy aerosol products with CFC that are available in the market. (ii) Conducting poster making competition or street plays presenting the importance of ozone layer on earth.

Question. Why is damage to the ozone layer a cause for concern? What are its causes and what steps are being taken to limit this damage? 
Answer: Damage to the ozone layer is a cause for concern because the ozone layer shields the surface of earth from harmful UV radiations from the sun which cause skin cancer in human beings. Synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in the fire-extinguishers are the main reason for the depletion of the ozone layer. Steps taken to limit this damage - Many developing and developed countries have signed and are obeying the directions of UNEP (United Nations Environment Programme) to freeze or limit the production and usage of CFCs at 1986 levels.

Question. (a) How can we help in reducing the problem of waste disposal? Suggest any three methods. 
(b) Distinguish between biodegradable and non-biodegradable wastes.
Answer: (a) The three methods for reducing the problem of waste disposal are:
(i) Recycling: solid, wastes like paper, plastics, metals can be sent to processing factories where they are remoulded or reprocessed to new materials.
(ii) Production of compost: Biodegradable wastes like fruit and vegetable peels, plant products, left over food, grass clippings, human and animal waste can be converted into compost by burying this waste into ground and can be used as manure.
(iii) Incineration: Burning down many household waste, chemical waste and biological waste into ash is known as incineration. A large amount of waste can be easily converted into ash which can be disposed off in landfill.
(b) Differences:
• Biodegradable wastes: (i) These wastes can be broken-down into non-poisonous substances in nature by the action of micro-organisms. (ii) They get recycled thus, do not need any dumping sites.
• Non-Biodegradable wastes: (i) These wastes cannot be broken-down into non-poisonous substances by microorganisms. (ii) They cannot be recycled thus, require dumping sites.

Question. What are chlorofluorocarbons? How are they responsible for causing ozone hole in atmosphere? What will be the consequences of ozone hole?
Answer: Carbon compounds which contain chlorine and fluorine are called CFCs (Chlorofluorocarbons). For example, \( CCl_2F_2 \) (Dichlorodifluoromethane). CFCs are available in aerosol sprays. They lead to depletion of ozone layer causing ozone hole. CFCs (Chlorofluorocarbons) react with ozone in stratosphere and deplete ozone.
Consequences of ozone hole:
Ozone layer in the atmosphere prevents UV rays from reaching earth. Due to occurence of ozone hole, UV rays reach earth. Exposure to excess UV rays cause skin cancer, cataract and damages eyes and immune system. It also decreases crop yield and reduces population of phyto and zoo planktons and certain fish larvae, which are important constituent of aquatic food chain. It also disturbs rainfall causing ecological disturbance and reducing global food production.

Question. (a) We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest ways to make people realize that the improper disposal of waste is harmful to the environment. 
(b) Suppose you find a heap of domestic waste, in a nearby park, which is decomposing. What would you do to make the people of the surrounding area realise that such type of disposal of domestic waste is harmful to the environment? 
Answer: (a) (i) Residents Welfare Associations should hold meetings regarding the illeffects of decomposing domestic waste in the bylanes of colonies. (ii) Slogans could be written down or posters could be put at the places where people generally throw their domestic waste.
(b) (i) By writing slogans or putting posters at the places where people generally throw their domestic waste. (ii) By motivating the people about proper disposal of waste which prevents pollution that could otherwise endanger human health and environment. (iii) Banners and signboards educating people about the ill-effects of improper disposal of wastes can be erected/ hanged in residential colonies. (iv) Street plays highlighting the ill effects of improper disposal of wastes can be organized.

QUESTIONS

Question. (a) Using ‘Kulhads’ as disposable cups to serve tea in trains, proved to be a bad idea. Why?
(b) Why is plastic not degraded by bacteria? 
Answer: (a) Using Kulhads on a large scale would result in the loss of top fertile soil, which takes hundreds of years to form.
(b) Bacteria and other decomposers lack the specific enzymes required to break down the long-chain polymers in plastics into simpler substances.

Question. How will accumulation of biodegradable waste effect our environment?
Answer: Accumulation of biodegradable waste causes foul smells, releases harmful greenhouse gases like methane during anaerobic decomposition, and provides breeding grounds for disease-carrying pests like flies and mosquitoes.

INTEGRATED (MIXED) QUESTIONS

Question. (a) Explain ‘biological magnification’ with the help of an example.
(b) Construct an aquatic food chain showing four trophic levels.
(c) What are the advantages of disposable paper cups over disposable plastic cups? 
Answer: (a) Biological magnification is the progressive accumulation of non-biodegradable chemicals like DDT at each successive trophic level. Example: Water (\( 0.02 \text{ ppm} \)) \( \rightarrow \) Phytoplankton (\( 5.0 \text{ ppm} \)) \( \rightarrow \) Fish (\( 240 \text{ ppm} \)) \( \rightarrow \) Bird (\( 1600 \text{ ppm} \)).
(b) Phytoplankton \( \rightarrow \) Zooplankton \( \rightarrow \) Small Fish \( \rightarrow \) Large Fish.
(c) Disposable paper cups are biodegradable and environment-friendly as they decompose naturally, whereas plastic cups are non-biodegradable and cause pollution.

Question. (a) State two problems caused by the non-biodegradable waste that we generate in our daily life. 
(b) What is meant by biodiversity? List two advantages of conserving forests and wildlife.
(c) Draw an energy pyramid showing different trophic level. 
Answer: (a) (i) Clogging of urban drainage systems leading to waterlogging. (ii) Soil pollution and degradation of soil fertility when buried in fields.
(b) Biodiversity refers to the variety and variability of life on Earth. Advantages: (i) Maintenance of ecological balance and stable food webs. (ii) Source of medicines, wood, and other essential resources.
(c) [Description: A pyramid with Producers at the base, followed by Primary Consumers, then Secondary Consumers, and Tertiary Consumers at the apex. 10% energy transfer is indicated between levels.]

Ecosystem - What are its Components?

Question. Consider the following ecosystems:
I. Ponds
II. Forests
III. Aquariums
IV. Crop fields
Out of these, the natural ecosystems are
(a) I, II and III
(b) II, III and IV
(c) I and II only
(d) I, II and IV
Answer: (c) I and II only

Question. What will happen if the deer are missing in the following food chain?
\( \text{Grass} \rightarrow \text{Deer} \rightarrow \text{Tiger} \)
(a) The population of tigers will increase.
(b) The amount of grass will decrease.
(c) The tigers will die.
(d) The tigers will start eating grass.
Answer: (c) The tigers will die.

Question. A system of interdependent food chains represents
(a) food web
(b) trophic levels
(c) ecosystem
(d) community.
Answer: (a) food web

Human body is made up of five important components of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture. Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradable, they get accumulated progressively at each trophic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.

Question. Why is the maximum concentration of pesticides found in human beings?
Answer: Humans occupy the top level in most food chains. Because pesticides are non-biodegradable, they accumulate progressively at each trophic level. This phenomenon, called biological magnification, results in the highest concentration being found in the top consumers, which are humans.

Question. Give one method which could be applied to reduce our intake of pesticides through food to some extent.
Answer: By practicing organic farming, which uses natural fertilizers and bio-pesticides instead of synthetic chemical pesticides, we can reduce the pesticide residue in our food.

Question. Various steps in a food chain represent
(a) food web
(b) trophic level
(c) ecosystem
(d) biomagnification.
Answer: (b) trophic level

Question. With regard to various food chains operating in an ecosystem, man is a
(a) consumer
(b) producer
(c) producer and consumer
(d) producer and decomposer.
Answer: (a) consumer

Question. Food web is constituted by
(a) relationship between the organisms and the environment
(b) relationship between plants and animals
(c) various interlinked food chains in an ecosystem
(d) relationship between animals and environment.
Answer: (c) various interlinked food chains in an ecosystem

Question. What is an ecosystem?
Answer: An ecosystem is a self-supporting unit where living organisms (biotic components) interact among themselves and also with their surrounding non-living (abiotic) environment (like soil, air, and water).

Question. Why is a lake considered to be a natural ecosystem?
Answer: A lake is considered a natural ecosystem because it is self-sustaining and operates in nature by itself without human interference, maintaining its own cycle of biotic and abiotic interactions.

Question. In the following food chain, plants provide \( 500 \text{ J} \) of energy to rats. How much energy will be available to hawks from snakes?
\( \text{Plants} \rightarrow \text{Rats} \rightarrow \text{Snakes} \rightarrow \text{Hawks} \)
Answer: According to the ten percent law, only \( 10\% \) of the energy is transferred to the next trophic level.
Energy available to Rats \( = 500 \text{ J} \)
Energy available to Snakes \( = 10\% \text{ of } 500 \text{ J} = 50 \text{ J} \)
Energy available to Hawks \( = 10\% \text{ of } 50 \text{ J} \)

\( \implies 5 \text{ J} \)

Question. In the following food chain, \( 100 \text{ J} \) of energy is available to the lion. How much energy was available to the producers?
\( \text{Plants} \rightarrow \text{Deer} \rightarrow \text{Lion} \)
Answer: Energy available to Lion \( = 100 \text{ J} \)
This is \( 10\% \) of the energy of the Deer. So, energy of Deer \( = 1000 \text{ J} \).
This is \( 10\% \) of the energy of the Plants. So, energy of Plants (Producers) \( = 10,000 \text{ J} \).

\( \implies 10,000 \text{ J} \)

Question. List two biotic components of a biosphere.
Answer: Plants and Animals.

Question. Why are green plants called producers?
Answer: Green plants are called producers because they can synthesize their own organic food (carbohydrates) from inorganic substances using solar energy through the process of photosynthesis.

Question. In a food chain of frog, grass, insect and snake, assign trophic level to frog.
Answer: The food chain is: \( \text{Grass (1st)} \rightarrow \text{Insect (2nd)} \rightarrow \text{Frog (3rd)} \rightarrow \text{Snake (4th)} \). The frog belongs to the third trophic level.

Question. Why do producers always occupy the first trophic level in every food chain?
Answer: Producers occupy the first trophic level because they are the only organisms that can capture solar energy and convert it into chemical energy (food), which then becomes available to all other consumers in the ecosystem.