Class 12 Biology

Solid Waste

Sanitary landfills were preferred over open dumps with an aim at better management of solid waste. But, generation of huge amounts of garbage in cities has turned many landfill sites into hills of garbage.

Solid waste can be segregated into biodegradable, recyclable and non-biodegradable wastes. Proper segregation can help in better management of solid waste.

Biodegradable waste should be converted into compost so that it can find better use. Biodegradation also helps in power generation. Recyclable waste should be sent for recycling; to make new products.

Hospital Waste: Waste from hospital contains many harmful chemicals and pathogenic microbes. Incineration is the best way to dispose hospital waste.

e-waste: Irreparable computers and other electronic goods comprise e-waste. It can be buried in landfills or incinerated. Primitive methods of recycling of e-waste produce many toxic substances in the air. Workers who are involved in such methods of recycling are always at risk of exposure to harmful substances.

Agrochemicals and Their Effects

Pesticides, herbicides, fungicides, etc. are toxic to non-target organisms. Such organisms are important components of the soil ecosystem. Addition of excess amount of synthetic fertilizers results in eutrophication of the aquatic ecosystems.

Organic Farming: Organic farming involves recycling of waste products from one process for other processes. This helps in minimizing the problem of pollution. Farm waste is converted into compost which is utilized to enhance soil fertility.

Radioactive Waste

Waste from nuclear power plants generate radiation which is extremely damaging to living beings because it causes mutations at a very high rate. Radiation at lower doses causes various disorders; including cancer. Nuclear waste should ideally be buried in shielded containers about 500 m deep below the earth’s surface. But this method is meeting with stiff resistance from public.

Greenhouse Effect and Global Warming

Some gases help in trapping the heat inside an enclosure. This effect is called greenhouse effect. Presence of greenhouse gases in earth’s atmosphere helps in maintaining the earth’s temperature within a comfortable range. However, excess of these gases causes a general rise in earth’s temperature. This is called global warming. Global warming is causing massive changes in the environment and resulting in odd climatic changes.

Ozone Depletion

Ozone is present in abundance in the stratosphere. Ozone layer (or stratosphere) prevents the harmful UV rays from reaching the troposphere and thus saves the living beings from it. The thickness of the ozone in atmosphere is measured in terms of Dobson units (DU).

Ozone is continuously formed by the action of UV rays on molecular oxygen. It is also degraded into molecular oxygen in the stratosphere. In ideal conditions, there is a balance between production and degradation of ozone. But excess use of chlorofluorocarbons (CFC) has disturbed this balance. UV rays act on CFCs to release chlorine atoms. Chlorine degrades ozone to release molecular oxygen. But chlorine atoms are not consumed in this process. So, whatever CFCs are added to the atmosphere, they permanently remain there and continue to affect the ozone levels. Depletion of ozone layer is quite marked over the Antarctic region. Large area of thinner ozone layer is called the ozone hole.

Montreal Protocol: The Montreal Protocol was signed at Montreal (Canada) in 1987 to control emission of ozone depleting substances. Adherence to this protocol by most of the countries has helped immensely in controlling the emission of CFCs. This has indeed helped in controlling the menace of thinning of the ozone layer.

Degradation By Improper Resource Utilisation And Maintenance

Soil erosion and desertification: It takes many centuries to form the fertile topsoil. But over-cultivation, overgrazing, deforestation and poor irrigation practices can easily remove the topsoil. Soil erosion can result in desertification in the long run.

Waterlogging and soil salinity: Irrigation without proper drainage results in waterlogging. Apart from being harmful for the crops, waterlogging draws salt to the surface of the soil. This salt gets deposited as a thin crust on the surface, or starts collecting at the roots of the plants. This is highly damaging to plants.


Conversion of forested areas to non-forested areas is called deforestation. The forest cover in India was about 30% of the total land area at the beginning of the 20th century. By the end of the century, it reduced to 19.4%.

One of the major effects of deforestation is the increased percentage of carbon dioxide in the atmosphere. Deforestation also results in loss of biodiversity due to habitat destruction. Deforestation also results in disturbance of hydrologic cycle, soil erosion, and may eventually lead to desertification.

People’s Participation in Conservation of Forests

The Bishnois of Rajasthan have been conserving forests since a long time. The government has instituted the Amrita Devi Bishnoi Wildlife Protection Award to commemorate the sacrifice of Amrita Devi and many other Bishnoi men and women to protect forest in an incident which happened in 1731.

Chipko Movement is another example of people’s participation in conservation of forests. This movement began in the 1970s in the Garhwal Himalayas.

In the 1980s, the government introduced the concept of Joint Forest Management (JFM) so that the forest department could work closely with the local communities towards conservation of forests.