CBSE Class 10 Science 2022 · Paper 31/6/1 · Question 7(b)

(i) Biodegradable wastes (vegetable peels, leftover food, paper) are broken down by decomposers such as bacteria and fungi into simple substances and can be turned into compost (manure) or biogas, whereas non-biodegradable wastes (plastics, polythene, glass, metals) are not broken down by biological processes and remain in the environment for a long time, harming soil, water and animals; many of them can be reused or recycled. They should be discarded separately so that each can be dealt with properly - the biodegradable part by composting or biogas, the non-biodegradable part by recycling or safe disposal. When they are mixed, the plastic contaminates the compost and the wet waste spoils the recyclable materials, so neither can be processed and more waste ends up in dumps. (ii) Chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers, rise into the upper atmosphere and break down ozone, so they deplete (thin) the ozone layer. The ozone layer shields the Earth from the harmful ultraviolet (UV) radiation of the Sun. With the layer thinned, more UV radiation reaches the Earth, and this can cause skin cancer in human beings, damage the eyes (cataract) and weaken the immune system, and it also harms plants and animals.