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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Pollution Know More

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Greenhouse Effect
In the atmosphere, some gases like CO2 allow sunlight to reach the ground but do not allow the heat to escape out of the atmosphere back into the outer space. This results in increase in temperature of the earth. This is called the green house effect.

Air Pollutants and their Sources




Oxides of carbon
(CO2 and CO)

Homes, industries, automobiles

Oxides of sulphur
(SO2 and SO3)

Automobiles, industries

Oxides of nitrogen
(NO and NO2)

Automobiles, industries


Automobiles, industries


Aerosol spray, refrigerators, air conditioners

Particulate matter
(mercury, soot)

Construction activities, Industries

Water Pollutants and their Sources




Organic waste

Sewage from hospitals, homes, etc.

Inorganic waste


Insecticides and pesticides

Agriculture, industries

Polychlorinated biphenyls (PCB),
chloroform, etc


Radioactive chemicals

Laboratories, hospitals, atomic reactors

Biological Oxygen Demand (BOD)
BOD is measured by placing a sample of water containing known amount of oxygen for five days at 20C in the dusk. After five days, oxygen content of the sample is measured. A high BOD indicates high level of microbial pollution.


  • The range of normal human hearing is between 50Hz to 15,000 Hz frequencies.
  • Frequencies below 50Hz are called infrasound and above 15,000 Hz are ultrasound.
  • Prolonged exposure to noise level of 80 dB or more gradually leads to permanent loss of hearing ability.

Effect of Acid Rain on Human Life

1.      Sulphur dioxide and nitrous oxide from industries and automobile exhauts combine with rain water in the air to form acidic water called acid rains.

2.      Effects of acid rain on human life;

3.      Acid rain changes the level of hydrogen ion concenteration of soil water, and thereby affects the life of plants and aquatic organisms.

4.      Acid rain affects agricultural crops and forests.

5.      Acid rain affects the buildings, leading to their gradual collapse.

6.      Acid rain causes decolourising effects in plants, which in turn reduces their rate of photosynthesis.

7.      Acid rain produces harmful ecological imbalance.

8.      This is followed by disruption of food chain on which man depends for his liveliblood.

Effect of Water Pollution of Human Life

1.      Water polluted with domestic sewage causes a number of epidemic diseases like cholera, dysentery, typhoid, jaundice, etc.

2.      Depletion of oxygen supply in water due to industrial wastes kills fishes and other aquatic organisms.

3.      The toxic substances present in industrial wastes kill microorganisms and other aquatic organisms, which are responsible for biopurification of water.

4.      The waste from factories endangers the lives of fish, cattle and even human beings through the food chain.

5.      Thermal pollution resulting from the industrial wastes leads to cause harmful effects on the fishes and other aquatic animals, and in turn on human too.

6.      Eutrophication resulting from the water pollution reduces the oxygen content in water, rendering it unfit for fishes and other animals.

Photochemical Smog
Natural and artificially emitted hydrocarbons, in the presence of oxides of nitrogen, undergo photochemical reactions, which produce a cloud of toxic chemicals, including ozone and a variety of caustic agents. This process is powered by sunlight and some of the products, such as ozone, reach a peak soon after photon flux from the sun reaches a maximum around
midday. The thermal inversions often associated with some cities can lead to a dangerous buildup of smog in urban areas. Human deaths have been attributed to photochemical smog since the industrial revolution in cities such as London and New York.


Para-dichlorodiphenyltrichloroethane was commonly used during the Second World War. It was used to kill mosquitoes that carried malaria and yellow fever. It was also used to kill body lice that can transmit typhus. Many problems have been associated with the use of DDT. Some of these problems are its bioaccumulation in the food chain, decline of smaller animals, and softening of birds eggs. In 1973, the EPA banned all use of DPT, except those essential to public health. DDT is still used in developing countries.


It is naturally occurring fibrous mineral found in certain types of rock formations. The primary use of asbestos was as a fireproofing material, applied to structural steel members in multistory commercial buildings to attain proper fire protection. With its resistance to heat, asbestos was able to keep the building structure from bending and warping, if exposed to fire. After widespread use of asbestos over a 15 to 25 years time span, a pattern of illness gradually surfaced inin asbestos workers. Three diseases linked to asbestos exposure are asbestosis, a fibrous scarring of the lungs, lung cancer, and mesothelioma, a cancer of the lining of the chest or abdominal cavity.


O3, is a molecule that consists of three oxygen atoms bonded together. The ozone layer in the stratosphere absorbs UV radiation and creates a warm layer of air in the stratosphere, and is, therefore, responsible for the thermal structure of the stratosphere. Ozone that is present in the troposphere is mostly a result of anthropogenic pollution, and therefore, higher concentrations are found in urban areas.

PAN (Peroxyacetyl nitrate)

A class of chemical substances found as a pollutant in the troposphere, formed by photolysis of natural and manufactured organic chemicals. These chemicals act as irritants and mutagens in mammals and are toxic to many plants.


The negative logarithm of the hydrogen ion concentration of a solution. It is the quantitative expression of the acidity and alkalinity of a solution and has a scale that ranges from about 0 to 14. pH 7 is neutral; <7 is acidic; <7 is alkaline.

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