Chapter 17: OUR ENVIRONMENT

1. Explain : Environment.
   ANS
   
   • DEFINITION: All organisms including plants, animals, micro-organisms and human beings and their physical surroundings with which they interact is called environment.
   • All biotic and abiotic components of the environment are interlinked and interdependent for maintaining environmental balance.
   • Environment varies from place to place due to variation in climate, soil type and topography.
   • All organisms adjust to their environment for survival and any change in any component of the environment may cause discomfort and affect the normal life of the organism.
2. Explain : Ecosystem.
   ANS
   
   • DEFINITION: An interacting system formed by the biotic community together with its physical environment is called ecosystem.
   • An ecosystem may be of small size or large size.
   • There are mainly two types of ecosystem based on the kind of habitat: (i) Aquatic (ii) Terrestrial.
   • Aquatic ecosystems include fresh water ecosystems like rivers, springs, ponds and lakes as well as marine ecosystem formed by oceans.
   • Terrestrial ecosystems include forests, grasslands and deserts.
   • Every ecosystem possesses a specific structure and performs definite functions.
   • Every ecosystem gradually merges into another one.
3. Explain : Components of ecosystem.
   ANS
   
   • An ecosystem consists of mainly two types of components: (A) Biotic components (B) Abiotic components.
   • Biotic components include all living organisms like producers, consumers and decomposers.
   • Abiotic components include non-living factors such as soil, water, light, temperature, wind, humidity, rain, inorganic nutrients and dead organic matter.
   • BIOTIC COMPONENTS:
     (i)Producers:
     • Producers are autotrophic organisms.
     • They possess chlorophyll and produce food througfh the process of photosynthesis.
     • Green plants in terrestrial ecosystem and various algae in aquatic ecosystem act as producers.
     
     (ii)Consumers:
     • Consumers are heterotrophic organisms.
     • They cannot synthesize their food.
     • They consume other organisms and their products as food.
     • They are divided into following four categories.
       1. HERBIVORES (First order consumers): These organisms obtain their food from plants.
       2. CARNIVORES(Secondary/Tertiary level consumers): They predate upon herbivores and other carnivores. If they consume herbivores, they are second order consumers.If they consume other carnivores, they are third (and higher) order consumers.
       3. OMNIVORES: They consume food from both plants and animals.
       4. DECOMPOSERS: They obtain food by decomposing dead bodies of plants and animals. They convert complex organic matter into simple organic molecules and then transform them into inorganic molecules.
   • ABIOTIC COMPONENTS: All nonliving components of an ecosystem are included in abiotic components and divided into two categories.
     1. CLIMATIC factors which include temperature, water, light, wind, mineral elements, and topography of habitat.
     2. EDAPHIC factors which include soil structure and composition.
4. Explain food chain giving suitable example.
   ANS
   
   • DEFINITION: A sequence of living organisms in a community in which one organism consumes another organism is called food chain.
   • Each link of a food chain forms a trophic level.
   • Producers form first trophic level, herbivores form the second level and carnivores form the third level. Thus , a food chain usually starts with producers and ends with carnivores.
   • Food chains are of two types (i) Grazing food chain (ii) Detritus food chain.
   • A grazing food chain begins with chlorophyllous producers and extends through herbivores, carnivores and decomposers.
   • A detritus food chain begins with decomposers and passes through detritus feeding organisms in soil to organisms feeding on detriytus feeders.
   • EXAMPLE : Terrestrial food chain
     
     
   • EXAMPLE : Marine food chain
     
     
   • ENERGY TRANSFER (FLOW) IN A FOOD CHAIN
     • A food chain describes how energy and nutrients move through an ecosystem.
     • Producers (autotrophs) are at the first trophic level. They produce energy.
     • Herbivores (primary consumers) are at the second trophic level. They obtain energy from the producers.
     • Carnivores (secondary and higher level consumers) are at next higher trophic levels. They obtain energy from herbivores or previous level carnivores.
     • Thus, chemical energy produced by autotrophs from sunlight is transferred progressively to next trophic levels.
     • Flow of energy in a food chain is unidirectional and does not revert back to the previous trophic level.
     • For example, energy captured by producers does not go back to sun, energy captured by herbivores does not go back to producers and so on.
5. Explain Food Web with example.
   ANS
   
   • A large number of food chains exist in an ecosystem and many organisms act as a link in more than one food chain.
   • The network formed by the interconnected food chains in an ecosystem is called a food web.
   • This means that the various food chains in an ecosystem do not operate in isolation but they operate in the form of a network of food chains called food web.
   • EXAMPLE:
     
     
6. Write a note on Biological Magnification.
   ANS
   
   • Pesticides like DDT and other chemicals are widely used to protect crops from diseases and pests. Most of these chemicals are non-biodegradable.
   • Due to uncontrolled use of such chemicals, their level increases in the soil and water bodies.
   • These chemicals enter the body of plants and aquatic animals and then they get accumulated progressively at each trophic level.
   • This phenomenon is called Biological Magnification.
7. Mention some global problems.
   ANS
   
   • Global problems are faced not only by individual but by the whole planet and potentially all the people.
   • Some of the major global problems are:
     

     (i) Climate change (ii) Global warming (iii) Deforestation (iv) Depletion of ozone layer
     (v) Loss of biodiversity (vi) Scarcity of water (vii) Problems of waste disposal 
     (viii) Maritime safety (ix) Pollution

8. Write a note on Ozone layer and its depletion.
   ANS
   
   • Ozone layer is located in the stratosphere which is about 50 km high in atmosphere from earth's surface.
   • This layer absorbs UV-radiation from sunlight and prevents it from reaching earth's surface> Ultraviolet rays have harmful effect on living organisms.
   • FORMATION OF OZONE
     
     • Oxygen molecules absorb ultraviolet photons and break down into two oxygen atoms by the process of photo-dissociation or photolysis.
       O₂ ----> O + O
     • The free oxygen atom combines with oxygen molecule to form a molecule of ozone.
       O + O₂ ----> O₃
   • DEPLETION OF OZONE LAYER
     • The phenomenon of depletion of ozone layer was first noticed in the year 1980.
     • It was observed that about 40-50% depletion of ozone layer had occurred over South polar region. Such a large depletion is called 'Ozone Hole'.
     • Later, such ozone holes were also noticed in North polar region.
     • It is probable that ozone holes may develop in other regions with human population.
     • Development of ozone holes depends on the prevalent wind, climatic conditions and suspended particulate matter in the atmosphere.
     • The main factor responsible for the depletion of ozone layer is the addition of chloride ions (Cl^-) in the atmosphere.
     • Chlorine reacts with ozone and removes atoms of oxygen(O) one by one. One chlorine atom can decompose 100,000 molecules of ozone in this manner.
     • Almost 80% of total depletion of ozone layer in the stratosphere is done by chlorofluorocarbons (CFCs). Freon is a CFC used in refrigerators and air-conditioners.
9. Explain : Biodegradable waste and non-biodegradable waste.
   ANS
   
   • BIODEGRADABLE WASTE:
     The waste materials which are broken down by biological processes are called biodegradable. Vegetables, fruits, torn clothes, paper, etc., are examples of biodegradable substances.
   • NON-BIODEGRADABLE WASTE:
     The waste materials which cannot be decomposed by biological processes are called non-biodegradable. Plastic bags, plastic bottles, glass, polythene, etc., are examples of non-biodegradable substances.
10. How the amount of house-hold waste can be reduced?
    ANS
    We can reduce house-hold waste by the following practice:
    • Buy loose fruits and vegetables in order to avoid packaging.
    • Avoid buying disposable items such as razors and pens.
    • Use reusable nappies.
    • Uae reusable carry-bags.
    • Use rechargable batteries.
    • Donate old clothes and shoes to the needy.
    • Reuse the back of papers and envelops.
    • Collect kitchen waste in bags or containers and as soon as they are filled dispose off them properly.
    • Some waste materials can be used to generate extra income if managed properly.