Environmental Issues - CBSE Class 12th NCERT Solution

Get, detailed solutions to the questions of the chapter Environmental Issues from NCERT class 12th Biology textbooks

Chapter 16 - Environmental Issues- Class 12th Biology NCERT Solutions

Get, detailed solutions to the questions of the chapter Environmental Issues from NCERT textbooks. The objective is to helping students regarding the pattern of answering the question as per the cbse latest marking scheme. Cbse.jagranjosh.com provided you NCERT solutions for classes 12th math and science subjects.





Some questions of this chapter are given here.

Q. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.


Since domestic sewage mainly contains impurities (biodegradable wastes) such as suspended solid (sand, salt, clay), colloidal material (fecal matter, bacteria, plastic and cloth fiber), dissolved materials (nitrate, phosphate, calcium, sodium, ammonia), and disease-causing microbes. The organic wastes from the sewage enter the water bodies; it serves as a food source for micro- organisms such as algae and bacteria. As a result, the population of these micro- organisms in the water body increases. Here, they utilize most of the dissolved oxygen for their metabolism. This results in an increase in the levels of Biological oxygen demand (BOD) in river water and results in the death of aquatic microorganism. 

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Q. Why ozone hole forms over Antarctica? How will enhanced ultraviolet Radiations affect us?


The ozone formed in the troposphere is called “bad zone” as it harms plants and animals. The ozone formed in the stratosphere is called “good zone” as it acts as shield and absorbs ultraviolet radiation from the sun. The ozone hole is more prominent over the region of Antarctica.

 Increased concentration of chlorine in the atmosphere is the main cause of formation of ozone hole. The main source of Chlorine is chlorofluorocarbons (CFC’s) widely used as refrigerants. The release of Chlorine atoms causes the conversion of ozone into molecular oxygen.

 Around 10,000 molecules of ozone are destroyed by one atom of chlorine which causes ozone depletion. The huge amounts of UV rays reached on the earth because of ozone depletion.

UV -B damages DNA and mutation occurs. It also causes skin darkening and skin cancer. .It is lethal for microorganism High levels of UV-B cause corneal cataract in human beings.

Q. List all the wastes that you generate, at home, school or during your Trips to other places, could you very easily reduce? Which would be Difficult or rather impossible to reduce?


Wastes Generated at Home: It include plastic bags, paper napkin, toiletries, kitchen wastes (such as peelings of vegetables and fruits, tea leaves), domestic sewage, glass, etc.

Wastes Generated at Schools It includes waste paper, plastics, vegetable and fruit peels, food wrappings, sewage etc.

Wastes Generated at Trips: It include plastic, paper, vegetable and fruit peels, disposable cups, plates, spoons etc.

All the above categories of waste generated be easily reduced by the judicious use of the above materials. Wastage of paper can be minimized by writing on both sides of the paper and by using recycled paper. Plastic and glass waste can also be reduced by recycling and re-using. Also, substituting plastics bags with biodegradable jute bags can reduce wastes generated at home, school, or during trips. Domestic sewage can be reduced by optimizing the use of water while bathing, cooking and other household activities.
Micro-organisms do not have the ability to decompose non- biodegradable wastes such as plastic, metal and broken glass





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