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1.It is becoming clear that denitrifying fungi, nitrifying archaea, anammox bacteria, aerobic denitrifying bacteria and heterotrophic nitrifying microorganisms are key players in the nitrogen cycle.
2.(i) By the decomposition of dead organic matter.
(ii) As the product of respiration by both plants and animals.
(iii) As the gaseous waste formed by the combustion of fuels like coal, wood, petrol and gaseous fuels.
3.Atmosphere regulates the average temperature on the earth. Earth and Ocean temperature is widely regulated by atmosphere. Atmosphere acts as a barrier to heat which reach reaches earth surface and hence it creates a shield to protect earth optimum temperature.
(1)Various greenhouse gases like methane, carbon dioxide, water vapour and ozone responsible for protecting the earth atmosphere.
(2)During night the atmosphere minimizes the heat escape to atmosphere hence reduces the excessive cooling on earth.
(3)Atmosphere composition also adjusts with sudden drift in temperature and hence maintain the heat level on earth.
4.(a)Acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.
(b)Presence of smog indicates that there is a lot of smoke present in the air i.e the air is polluted with gaseous pollutants as well as particulate matter. it indicates that the place has a lot of air pollution in it.
5.(a)Soil contamination or soil pollution as part of land degradation is caused by the presence of xenobiotics (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity, agricultural chemicals or improper disposal of waste.
(b)Soil pollution can be prevented by :-
1.Cultivation by natural fertilisers and not using the toxic pesticides and artificial fertilisers.
2. avoid dumping of industrial waste, acidic precipitates etc in to the soil.
3. avoid using detergents.
4.afforestation,use other dustbins for throw biodegradable and non-biodgeradable.
6.Three human activities that would lead to air pollution are:
i) Emission of harmful gases and dust particles from vehicles.
ii) Combustion of fossil fuels like coal, petroleum releasing oxides of nitrogen and sulphur.
iii) Smoke released from industries containing harmful gases like sulphur dioxide, oxides of nitrogen.
7.(¡)Nitrogen fixation is the process by which atmospheric nitrogen is converted by either a natural or an industrial means to a form of nitrogen such as ammonia. ... Commercially produced ammonia is used to make a wide variety of nitrogen compounds, including fertilizer and explosives.
(¡¡)Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil.
(¡¡¡)Denitrification is the microbial process of reducing nitrate and nitrite to gaseous forms of nitrogen, principally nitrous oxide (N2O) and nitrogen (N2). A large range of microorganims can denitrify. Denitrification is a response to changes in the oxygen (O2) concentration of their immediate environment.