Chapter 13 · Our Environment

NCERT Class 10 Science Chapter 13 Intext Questions (Page 216)

All 2 questions of NCERT Class 10 Science Chapter 13 Intext Questions (Page 216) — Our Environment — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   What is ozone and ​how ​does ​it affect any ​ecosystem?
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   Ozone is ${\text{O}}_3$; its layer shields ecosystems from ultraviolet radiation, but CFC thinning harms humans, plants and plankton, passing the damage up food chains.

   Ozone is a molecule formed by three atoms of oxygen, written ${\mathrm{O}}_3$. It is not the oxygen we breathe, which is ${\mathrm{O}}_2$ and is essential for all aerobic forms of life. At the higher levels of the atmosphere ozone is a product of ultraviolet radiation acting on oxygen: the higher energy ultraviolet radiations split molecular oxygen into free oxygen atoms, ${\mathrm{O}}_2\to \mathrm{O}+\mathrm{O}$, and these atoms then combine with molecular oxygen to give ozone, $\mathrm{O}+{\mathrm{O}}_2\to {\mathrm{O}}_3$. Its effect on an ecosystem depends entirely on where it is. Near the ground ozone is a deadly poison and harms living organisms directly. High in the atmosphere it performs an essential function: it forms a layer that shields the surface of the earth from the ultraviolet radiation of the Sun, which is highly damaging to organisms and is known to cause skin cancer in human beings, so this layer protects every ecosystem on the earth. Since the 1980s the amount of ozone has been dropping sharply because of synthetic chemicals such as chlorofluorocarbons, the CFCs used as refrigerants and in fire extinguishers. A thinner layer lets more ultraviolet radiation reach the ground, where it causes skin cancer, cataract and weakened immunity in human beings and other animals, reduces the growth and yield of green plants and kills the plankton of the sea; and since green plants and plankton are the producers at the first trophic level, the damage passes up to every level above them. In 1987 the United Nations Environment Programme forged an agreement to freeze CFC production at 1986 levels, and CFC-free refrigerators are now mandatory the world over.

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2. Q2
   How ​can you ​help in reducing the ​problem ​of waste disposal? ​Give any two ​methods.
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   Segregate waste and compost the biodegradable part; reduce and reuse so that less waste is created.

   Any two genuine methods are acceptable; the two strongest are these. (i) Segregate the waste at home and compost the biodegradable part. Keep two bins and put the waste into the right one as it is thrown, kitchen waste, peels, leftover food, dead leaves and paper in one, and plastic, polythene, glass and metal in the other. Put the biodegradable waste into a compost pit or bin, keep it moist, and the decomposers turn it into manure in a few weeks, so that this waste never reaches a dump and its nutrients return to the soil; the other bin, kept clean and dry, can be given to a recycler, because mixed waste can be neither composted nor recycled. (ii) Reduce and reuse, so that less waste is created at all. Carry a cloth or jute bag for shopping instead of taking a plastic bag, refuse disposable cups, plates, spoons and straws and use steel or china that can be washed, use both sides of every sheet of paper, refill and reuse bottles and jars, and repair or pass on clothes, books and toys instead of throwing them away. Waste that is never generated needs no disposal at all. Other acceptable methods are giving newspapers, bottles, tins and old metal to a recycler, returning batteries and old electronic items to a proper collection point instead of the dustbin, never littering, and persuading others at home and at school to do the same.

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