DAV SCIENCE CLASS IV

WATER SCARCITY AND CONSERVATION OF WATER D1.How much of the surface of earth is covered by water? Ans: Three –fourth (3/4 th ) of the earth is covered by water. D2.Name three sources   of fresh water. Ans: Three   sources of water are river, well and lake . D3.State the effect of deforestation on rainfall. Ans: Reckless   cutting of trees is called deforestation. If there will be forest ,then more amount of   water vapor will be released   to atmosphere and that brings rain .Due to deforestation there are less numberof trees   which leads to decrease in rainfall. D4.State two reasons that   are leading to clearing   of forests. Ans: The   reasons for clearing forest are :- i)For construction of building and factories ii)For earning money by selling the wood of the trees. D5. state one utility of dams. Ans: Dams are used for storing a large amount of water   which can be utilized for generating electricity, irrigation of crops and pisciculture (rearing of fish).

SAFE   HANDLING   AND STORAGE OF WATER D1.State the meaning of the term potable water. Ans: Water which is   clean,germ free and fit for drinking is called potable water. D2.Name any two diseases that can be caused by drinking unclean water. Ans:Two diseases that can be caused by drinking unclean water are diarrhea and jaundice D3.Name the diseases which are spread by mosquitoes. Ans:The diseases spread by mosquitoes are malaria, dengue, chikungunya and filaria.   D4. How does boiling help in making water safe   for drinking? Ans:Boiling kills the germ present in water   and make   safe for drinking. D5.Name two methods of purification   of water. Ans:Two methods of purification of water are boiling and chlorination. D6.Name any two    ways of safe handling of drinking water. Ans:Ways of safe handling of drinking water are: i)Water should be stored in clean and covered container. ii)we should not dip our hand in water stored for drinking . iii)We should