CBSE - Our Environment

Substances are classified as biodegradable and non-biodegradable because some substances can be decomposed by microorganisms and some cannot.
Substances that are broken down into simple soluble forms are called biodegradable substances and the substances that are not decomposed by microorganisms into harmless substances are called non biodegradable substances.

Biodegradable substances affect the environment by:
→ The biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. This will enhance the soil fertility.
→ The biodegradable substances mainly contain carbon. These substances after decomposition release that carbon back into the atmosphere.

Non-biodegradable substances affect the environment by:
→ They contaminate soil and water resources as they cannot be decomposed by micro-organisms.
→ These substances, when accidentally eaten by stray animals, can harm them and can even cause their death.

The various links or steps in a food chain at which the transfer of food and energy takes place are called trophic levels.
The producers form the first trophic level as they manufacture food. The primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.

food-chain
In the above fig. Grass is the producer which is eaten by the grasshooper known as primary consumer. Then the grasshooper is eaten by shrew, secondary consumer and lastly shrew eaten up by owl, tertiary conusmer.

Various role played by decomposers in the ecosystem are:
→ They clean the environment.
→ They decompose biodegradable substances into useful substances.
→ They release nutrients into soil by decomposing dead and decaying matter, thus making the soil fertile.
→ They maintain the nutrient pool by returning back the nutrients in the pool.

Ozone (O₃) is a molecule, made up of three atoms of oxygen.
Ozone (O₃) forms a layer in the upper atmosphere. It is very essential for the life on this planet. It shields the surface of the earth from ultra-violet radiation (UV) coming from sun as these radiations are very harmful causing skin cancer and cataract in humans. It also does harm to the crops.

We can help in reducing the problem of waste disposal by these methods:
→ By separating biodegradable substances from non-biodegradable substances.
→ By reducing, reusing and recycling non-biodegradable substances.

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

ANS (c) Fruit-peels, cake and lime-juice

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

ANS (b) Grass, goat and human

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

ANS (d) All of the above

If we kill all the organisms of one trophic level it will create an imbalance in the ecosystem. As an Example, In a food chain Grass → Dear → Lion, If we remove all lions then population of deer will increase which will cause over-grazing. This will lead to deforestation. It may even lead to soil erosion causing further conversion of fertile land into barren desert.

Impact of removing all organisms of a trophic level is different for different trophic levels.
For example, if we remove producers from a food chain, no organism will get food, if we remove herbivores from a food chain then carnivores will die and producers will also die due to competition for space and nutrients. No, we can’t remove any trophic level without causing damage to the ecosystem as one is dependent on other for their survival. If we remove any one this will create imbalnce in the ecosystem.

Biological magnification is defined as the phenomena of accumulation or increase in the concentration of some toxic substances at each trophic level.

The levels of biomagnification will be different at different trophic levels. For example, in a pond of water, DDT was sprayed and the producers were found to have 0.04 ppm concentration of DDT. Since many types of planktons are eaten by some fishes and clams, their body accumulates 0.23 ppm of DDT. Sea gull that feeds on clams accumulates more DDT as one sea gull eats many clams. Hawk, the top carnivore, has the highest concentration of DDT.

The problems caused by non-biodegradable wastes are:
→ The cause biomagnification.
→ They increase pollution.
→ They make environment unclean.
→ They kill useful microorganisms.

If all the waste generated would be biodegradable this will also create problem. As the numbers of decomposers will be quite low so wastes cannot be broken down into harmless simpler substance at right time. It will became breeding ground for flies causing spread of diseases. It will also emits foul smell which makes the life of people miserable.

The damage to the ozone layer a cause for concern because:
→ It causes skin darkening, skin cancer, ageing, and corneal cataracts in human beings.
→ It can result in the death of many phytoplanktons that leads to increased global warming.

To limit the damage to the ozone layer, the release of CFCs into the atmosphere must be reduced. CFCs used as refrigerants and in fire extinguishers should be replaced with environmentally-safe alternatives. Also, the release of CFCs through industrial activities should be controlled.

1. Which one of the following is an artificial ecosystem?
(a) Pond
(b) Crop field
(c) Lake
(d) Forest
Ans. (b) Crop field
Explanation: This ecosystem is created by humans.

2. In a food chain, the third trophic level is always occupied by
(a) carnivores
(b) herbivores
(c) decomposers
(d) producers
Ans. (a) carnivores
Explanation: First trophic level is occupied by producers and second is occupied by herbivores.

3. An ecosystem includes
(a) all living organisms
(b) non-living objects
(c) both living organisms and non-living objects
(d) sometimes living organisms and sometimes non-living objects
Ans. (c) both living organisms and non-living objects
Explanation: Both biotic and abiotic factors are present in an ecosystem.

4. In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass →Grasshopper →Frog →Snake →Hawk
(a) 5 kJ
(b) 50 kJ
(c) 500 kJ
(d) 5000 kJ
Ans. (d) 5000 kJ
Explanation: Energy level available at a particular trophic level is 10 times the energy level at the next trophic level. Hence, third trophic level has 50 kJ, 2nd has 500 kJ and 1st has 5000 kJ.

5. Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as
(a) eutrophication
(b) pollution
(c) biomagnifications
(d) accumulation
Ans. (c) biomagnifications

6. Depletion of ozone is mainly due to
(a) chlorofluorocarbon compounds
(b) carbon monoxide
(c) methane
(d) pesticides
Ans. (a) chlorofluorocarbon compounds

7. Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called
(a) decomposers
(b) producers
(c) herbivores
(d) carnivores
Ans. (b) producers
Explanation: Producers use solar energy to make carbohydrates from water and carbon dioxides.

8. In an ecosystem, the 10% of energy available for transfer from one trophic level to
the next is in the form of
(a) heat energy
(b) light energy
(c) chemical energy
(d) mechanical energy
Ans. (c) Chemical energy
Explanation: Energy for the next trophic level is available in the form of food. Food contains chemical energy.

9. Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the
(a) food web
(b) ecological pyramid
(c) ecosystem
(d) food chain
Ans. (b) ecological pyramid
Explanation: In ecological pyramid, number of organisms at higher tropic level is always less than number of organisms at lower trophic level. An organism at higher trophic level usually feeds on more than one type of organisms.

10. Flow of energy in an ecosystem is always
(a) unidirectional
(b) bidirectional
(c) multi directional
(d) no specific direction
Ans. (a) unidirectional
Explanation: Flow of energy in an ecosystem is always from prey to predator and is never in the opposite direction.

11. Excessive exposure of humans to U V-rays results in
(i) damage to immune system
(ii) damage to lungs
(iii) skin cancer
(iv) peptic ulcers
(a) (i) and (ii)
(b) (ii) and (iv)
(c) (i) and (iii)
(d) (iii) and (iv)
Ans. (c) (i) and (iii)

12. In the following groups of materials, which group (s) contains only nonbiodegradable items?
(i) Wood, paper, leather
(ii) Polythene, detergent, PVC
(iii) Plastic, detergent, grass
(iv) Plastic, bakelite, DDT
(a) (iii)
(b) (iv)
(c) (i) and (iii)
(d) (ii) and (iv)
Ans. (d) (ii) and (iv)

13. Which of the following limits the number of trophic levels in a food chain?
(a) Decrease in energy at higher trophic levels
(b) Deficient food supply
(c) Polluted air
(d) Water
Ans. (a) Decrease in energy at higher trophic levels

Explanation: Only 10% of the energy consumed by an organism at a particular trophic level is available for the organism at next trophic level. Hence by the time we reach the fourth trophic level; a minute portion of the energy from producer is available.

14. Which of the statement is incorrect?
(a) All green plants and blue green algae are producers
(b) Green plants get their food from organic compounds
(c) Producers prepare their own food from inorganic compounds
(d) Plants convert solar energy into chemical energy
Ans. (b) Green plants get their food from organic compounds

Explanation: Producers use solar energy to make carbohydrates from water and carbon dioxides. Water and carbon dioxide are inorganic compounds.

15. Which group of organisms are not constituents of a food chain?
(i) Grass, lion, rabbit, wolf
(ii) Plankton, man, fish, grasshopper
(iii) Wolf, grass, snake, tiger
(iv) Frog, snake, eagle, grass, grasshopper
(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iii)
(d) (i) and (iv)
Ans. (c) (ii) and (iii)
Explanation: In option (ii) grasshopper does not eat plankton. In option (iii) none of the animals eats grass.

16. The percentage of solar radiation absorbed by all the green plants for the process
of photosynthesis is about
(a) 1 %
(b) 5 %
(c) 8 %
(d) 10 %
Ans. (a) 1%
Explanation: In a terrestrial ecosystem, green plants utilize about 1% of solar energy which falls on their leaves.

17. In the given Figure 15.1 the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

(a) T4
(b) T2
(c) T1
(d) T3
Ans. (c) T1
Explanation: Maximum energy is available at the producer’s level.
18. What will happen if deer is missing in the food chain given below?
Grass →Deer →Tiger
(a) The population of tiger increases
(b) The population of grass decreases
(c) Tiger will start eating grass
(d) The population of tiger decreases and the population of grass increases
Ans. (d) The population of tiger decreases and the population of grass increases
Explanation: Population of tiger will decrease because of lack of food. Population of grass will increase because of lack of predators.

19. The decomposers in an ecosystem
(a) convert inorganic material, to simpler forms
(b) convert organic material to inorganic forms
(c) convert inorganic materials into organic compounds
(d) do not breakdown organic compounds
Ans. (b) convert organic material to inorganic forms

20. If a grasshopper is eaten by a frog, then the energy transfer will be from
(a) producer to decomposer
(b) producer to primary consumer
(c) primary consumer to secondary consumer
(d) secondary consumer to primary consumer
Ans. (c) primary consumer to secondary consumer

Explanation: Grasshopper feeds on grass and hence is a primary consumer. Frogs feed on insects and hence are secondary consumers.
21. Disposable plastic plates should not be used because
(a) they are made of materials with light weight
(b) they are made of toxic materials
(c) they are made of biodegradable materials
(d) they are made of non-biodegradable materials
Ans. (d) they are made of non-biodegradable materials
Explanation: Because of their non-biodegradable nature, plastic keeps on accumulating in the environment.

Wastes pollute our environment, air, soil and water, and cause harmful effects on all living organisms.

Phytoplanktons and aquatic plants → small aquatic animal’s larvae, insects etc) →Fish →bird

Cloth bags are
(a) capable of carrying more things
(b) made of biodegradable material
(c) do not pollute our environment
(d) can be reused 

Crop fields are manmade and some biotic and abiotic components are manipulated by humans

Substances that are broken down into simpler substances by biological processes are said to be biodegradable.

Examples, wood, paper.

Substances that cannot be broken down into simpler ones by biological processes are said to be non-biodegradable. Examples, plastic, DDT.

(a) The physical and biological world where we live in
Ans. Environment/biosphere
(b) Each level of food chain where transfer of energy takes place
Ans. Trophic level
(c) The physical factors like temperature, rainfall, wind and soil of an ecosystem
Ans. Abiotic factors
(d) Organisms which depend on the producers either directly or indirectly for food
Ans. Heterotrophs (consumers) 

Decomposers break down the dead and decaying organic matter and return the nutrients to the soil. Thus, they play a very important role in the nutrient re-cycling in the environment.

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
Ans. (b) Is not a matching pair
Both biotic and abiotic components of environment constitute an ecosystem

An aquarium is an artificial and incomplete ecosystem in contrast to a pond/lake which are natural, self-sustaining and complete ecosystems

Flow of energy in an ecosystem can be described as follows:
• In the terrestrial environment, green plants utilize about 1% of solar energy that is falling on their leaves. This energy is converted into organic matter by plants.
• But a great portion of energy is utilized by the plants for their own metabolic needs. Just 10% of the total energy is available for primary consumers.
• Similarly, out of total energy consumed by an organism at a particular trophic level, just 10% is available for the organism at next trophic level.
• As a result, a negligible amount of energy is available for the organisms at the topmost trophic level. Due to this, an ecosystem contains at the most four trophic levels.
• There are more organisms at lower trophic than at top trophic levels. This is the general rule but some exceptions may be present.
• The food chain becomes quite complex in real world: making the food web because most of the carnivores eat many organisms.
The flow of energy is unidirectional because of two reasons. Energy always flows from the prey to the predator and not the other way round. Less energy is available as we move towards higher trophic levels. 

Decomposers break down the complex organic substances of garbage, dead animals and plants into simpler inorganic substances that 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.

Following are four activities in daily life which are eco-friendly:
(a) Walking for short distance commute: This activity helps in preventing air pollution.
(b) Using bicycle for going to school: This activity prevents air pollution which can happen when we use car for this purpose.
(c)Reusing water for mopping floor: This helps in conservation of water. Water which is collected after washing clothes and vegetables should be used for mopping the floor.
(d) Using public transport for long distance commute: In a mode of public transport, many people can travel together. This helps in reducing the number of cars and bikes on roads. Thus, it helps in preventing air pollution. 

(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. 

Following are some methods which should be used for waste management in fertilizer industries:
Use of catalytic converters in chimneys: Chimneys of a factory may produce many harmful gases and SPMs (suspended particulate matters). A catalytic converter helps in minimizing the harmful gases in the exhaust fume.

Electrostatic precipitators in chimneys: Electrostatic precipitator helps in minimizing SPMs in exhaust. Thus, it helps in minimizing air pollution.

Effluent treatment: All steps should be taken to prevent direct discharge of effluents into the nearest waterbody. An effluent treatment plant should be installed in the factory. It should have proper facilities for physical, chemical and biological treatment of effluent.

This will help in checking the pollution of waterbodies. It will also help in utilsing the treated water as source for irrigation. This water can also be used as drinking water after further treatment. 

The main byproducts of fertilizer industries are as follows:
Ammonia and ammonium salt, Suspended solids and ash, Acids and alkalis, Oil, Arsenic, MEA and methanol, Nitrates, Urea, Cooling water conditioning chemicals like chromate, Phosphates, biocides, etc, Cyanides and sulphides, Fluorides, Phosphates, etc.
Effect on environment:
• Suspended solids and ash add up to SPM in air. Thus, they increase air pollution. 
• Arsenic and cyanide are lethal substances. They may enter the food chain and cause diseases because of biomagnifications.
• Fluoride in drinking water is highly harmful for teeth.
• Most of the byproducts may reach water bodies and can alter the pH of water. This can be harmful for the aquatic ecosystem. 

Some of the harmful effects of agricultural practices on the environment are as follows:
Climate Change: Farming promotes monoculture because a selected number of species is grown on a large tract of land. This affects the biodiversity of the area. This is not good for the climate.
Deforestation: Large scale farming has been possible because man has cleared vast tracts of forests. Even today, forest is being cleared to make way for agriculture. This has reduced the habitat for most of the wildlife.
Soil Degradation: When farming is done for a long period on a land, its soil is robbed off all the nutrients. This results in soil degradation.
Water shortage: For good harvest, farmers need to use lot of water for irrigation. Most of the crops need plenty of water for proper growth. This has resulted in overexploitation of water resources; especially groundwater. This is the reason; even rural areas are suffering from shortage of drinking water.
Pollution: Farming involves use of synthetic fertilizers and pesticides. These substances cause soil pollution, water pollution and air pollution. Moreover, use of tractors and combine harvesters necessitate burning of fossil fuels. This adds up to air pollution. 

Food chain	Food Web
(a) Food chain is a series of organisms feeding on one another	(a) Food web consists of a number of interlinked food chains.
(b) Members of higher trophic level feed upon a single type of organism of the lower trophic level	(b) Members of higher trophic level can feed upon organisms of the lower trophic levels of other food chain.