Environmental Issues, Class 12, Biology, CBSE

Environmental Issues, Class 12, Biology, CBSE

post image


post image

Environmental Issues

Causes of air pollution

The main causes of air pollution are as follows:
(a) Exhaust from Automobiles: Most of the automobiles use fossil fuels. Burning of fossil fuel releases carbon dioxide and carbon monoxide. Carbon dioxide is a greenhouse gas. Carbon monoxide is a poisonous gas even at low concentrations.
(b) Exhaust from Factories and Power Plants: Coal is the main fuel being used in factories. Burning of coal produces carbon dioxide and oxides of sulphur. Oxides of sulphur and nitrogen form acid rain when they mix with rainwater. Acid rain is harmful for living beings and also for buildings and monuments.
(c) Chlorofluorocarbons (CFCs): These are compounds of carbon and halogens and are used as refrigerant. These are also used in pressurized cans. Excess level of CFCs in the atmosphere damages the ozone layer. Ozone layer works like a shield and prevents the harmful ultraviolet radiations from reaching up to the living beings. Any damage in the ozone layer can be very harmful.
(d) Suspended Particulate Matters (SPMs): Some fine particles remain suspended in the air. These are called suspended particulate matters. Stone quarries and various other factories contribute to SPMs.

Electrostatic precipitators

  • In electrostatic precipitators, the polluted gas is passed through electrodes by the virtue of their behaviour in an electrical field and the particulate matter is eliminated.

Vehicular standards

  • Government of India has adopted auto fuel policy to effectively cut down sulphur and nitrogen oxides in the automobile exhausts.

Noise pollution

Source includes:

1. Household
2. Social
3. Commercial 
4. Industrial 
5. Transportation

Harmful effects

1. Hypertension
2. High-stress levels
3. Hearing loss
4. Sleep disturbances

Measures to minimise noise pollution

1. Avoid burning crackers
2. Planting trees on the roadside

Sources of water pollution

Sources of water pollution are as follows:

1. Household detergents
2. Industrial wastes
3. Sewage
4. Thermal pollution
5. Oil spills
6. Agricultural runoff
7. Radioactive wastes

Effects of sewage discharged in river

1. When organic wastes from the sewage enter the water bodies, it serves as a food source for micro-organisms such as algae and bacteria, which leads to an increase in the population of microorganisms.
2. They utilize the dissolved oxygen for their metabolism. This leads to an increase in BOD in rivers and results in the death of aquatic organisms.


  • Biochemical oxygen demand or Biological oxygen demand, is a measurement of the amount of dissolved oxygen (DO) that is used by aerobic microorganisms when decomposing organic matter in water.

Eutrophication or nutritional enrichments

1. Eutrophication is the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen, phosphorus, or both. 
2. Eutrophication can be a natural process in lakes, occurring as they age through geological time.

E-waste (generation, disposal and recycling)

E-waste is a popular, informal name for electronic products nearing the end of their useful life. Computers, televisions, VCRs, stereos, copiers, and fax machines are common electronic products.

1. Generation: Mostly, in large cities.
2. Disposal of e-waste: Burn the waste which gives out harmful fumes
3. Recycling: Many of these products can be reused, refurbished, or recycled under skilled supervision.

Global warming (effects and control measures)

Effects of global warming are as follows:

1.Climate change
2. Sea level change
3. Water balance
4. Human health

Control measures of global warming are as follows:

1. Laws
2. Reduction in thermal power station
3. Planting trees
4. Use of public means of transport instead of private motorized vehicles

Ozone depletion

1. Ozone layer is found in the upper part of the atmosphere called stratosphere.
2. Ozone layer surrounding the earth acts as a shield for earth as it absorbs ultraviolet radiation coming from sun.
3. Ozone is continuously formed in the atmosphere by the action of UV rays on molecular oxygen and also degraded into molecular oxygen by the stratosphere.
4. There should be a balance between production and degradation of ozone in the stratosphere, but the balance is being disturbed by the chlorofluorocarbons.

Sustainable management (e.g., chipko movement)

1. The Chipko Movement began in 1974 from a small village; Reni in Garhwal district.
2. The women of the village began hugging a tree to prevent the cutting of trees by the contractors.
3. The Chipko movement later spread to other parts of India. It had been instrumental in stopping deforestation to a large extent.

Effects of deforestation

Deforestation is the disappearance or removal of forest. The effect of deforestation are as follows:
1) The amount of carbon dioxide in the air will increase, resulting in the increase of the earth’s temperature.
2) In the absence of trees and plants, the animals will not get food and shelter.
3) In the absence of trees, the soil will not hold water, which will cause floods.
4) Deforestation may harm health as the forest is the noise absorber.

Leave a Reply

Your email address will not be published. Required fields are marked *

error: Content is protected !!