NCERT 8th Class (CBSE) Science: Pollution of Water and Air

Question: Explain circumstances leading to acid rain. How does acid rain affect us?

Answer: When oxides of nitrogen and sulphur mix with rainwater, they form acids. It results in acid rain, i.e. the rainwater becomes acidic. Acid rain is very harmful for living beings. Acid rain also damages buildings and monuments.

Question: Describe the ‘Green House Effect’ in your own words.

Answer: Some gases trap solar radiation which helps in increasing the temperature of the atmosphere. This effect is called greenhouse effect.

Question: Prepare a brief speech on global warming that you have to make in your class.

Answer: Global warming is a serious concern of the modern times. It is one of the greatest challenges that our planet is facing. It is the unequal and continuing rise in the average temperature of the Earth’s climate system. It occurs as a result of an increased concentration of greenhouse gases in the atmosphere. We are using more cars and bikes than past. We are also consuming at a large scale which means more and more factories are coming up to satisfy our greed. All of this has resulted in an increased level of carbon dioxide in the atmosphere. The increased level of carbon dioxide has resulted in global warming.

Due to this weather changes are drastic, the summers have become hotter and winters have become much colder. We are seeing increased instances of flash floods and all this is being attributed to global warming. It would result in total disaster for us. It is high time we should stand up and fight against global warming.

Question: Describe the threat to the beauty of the Taj Mahal.

Answer: Taj Mahal, one of the seven wonders of the world, is made up of white marble. Marble is composed of calcium carbonate. Calcium carbonate reacts with acids to form a powder – like substance that is then washed away by the rain, in other words, gets corroded. This phenomenon is known as marble cancer. This is the reason, acid rain (oxides of nitrogen and sulphur mix with rainwater, form acids) is damaging the Taj Mahal. This wonderful monument has lost its pearly white finish and is looking pale and dull, reason behind this is the soot particles emitted from the Mathura oil refinery located near Agra. If corrective measures are not taken, the future generations may not be able to see the actual beauty of the Taj.

Question: Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer: Increased level of nutrients in water helps in promoting the growth of algae. Algae proliferate quickly to cover the whole water body. This phenomenon is called algal bloom. Finally, when these algae die; many decomposers thrive in the water body to decompose the dead algae. Increased population of decomposers means a lot of oxygen in the water gets utilized by them. This leaves less oxygen for other aquatic plants and animals. Thus, the aquatic plants and animals perish in the process.

Question: How do automobiles pollute air?

Answer: Automobiles usually have internal combustion engines which use petrol or diesel as fuel. Combustion of petrol or diesel results in emission of many polluting gases; like carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide, etc. Moreover, minute particles are also emitted from automobile engines. Thus, automobiles end up polluting the air.

Question: Write a short note on ozone layer.

Answer: Ozone layer is a protective layer in the atmosphere. It contains a higher amount of ozone than any other layer of the atmosphere. However, compared to other gases; ozone still forms a negligible part of air in ozone layer. This layer prevents harmful ultraviolet radiations from the sun from entering our atmosphere. Ultraviolet radiations can cause skin cancer in humans and animals, and is also harmful for plants. Any damage to the ozone layer can be highly detrimental to the living beings.