NCERT Class 7 Science Chapter 18 Question Answers cover the book exercise in a simplified and precise way. NCERT Class 7 Science Chapter 18 Question Answers are easy to understand and learn for exams.
NCERT Class 7 Science Chapter 18 Question Answers
1. Fill in the blanks:
(a) Cleaning of water is a process of removing pollutants.
(b) Wastewater released by houses is called Sewage.
(c) Dried sludge is used as manure.
(d) Drains get blocked by chemicals and kitchen waste.
2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Wastewater from households, industries, and agricultural activities is called sewage.
It is harmful because –
> It can pollute the whole source of water.
> It contains toxic substances and organisms that cause diseases.
3. Why should oils and fats not be released in the drain? Explain.
> Oils and fats can harden and block pipes.
> In open drains, fats clog the soil pores and block the water flow.
4. Describe the steps involved in getting clarified water from wastewater.
(i) Removal of large objects (rags, sticks, cans, plastic bags, etc.) by passing water through bar screens.
(ii) Removal of impurities (sand, grit, pebbles, etc.) by sedimentation.
(iii) Collection of sludge by scrapper and skimmer to get clarified water.
(iv) Removal of Bacteria by Chlorination.
5. What is sludge? Explain how it is treated.
Sludge is the solid waste collected from wastewater during the treatment of water.
Sludge is decomposed in a separate tank by anaerobic bacteria. Decomposed sludge is used as manure.
6. Untreated human excreta is a health hazard. Explain.
Untreated human excreta causes a lot of health-related issues. It pollutes water, air, and soil. The polluted water also spread diseases like cholera, meningitis, etc.
7. Name two chemicals used to disinfect water.
Ozone and Chlorine.
8. Explain the function of bar screens in a wastewater treatment plant.
Large size waste like rags, sticks, cans, napkins, plastics, etc. are removed from the wastewater through the bar screens.
9. Explain the relationship between sanitation and disease.
Sanitation and disease are related to each other. Sanitation involves proper disposal of sewage received from houe and public places. Sanitation prevents spread of diseases. Hence, sanitation keeps us away from diseases.
10. Outline your role as an active citizen in relation to sanitation.
As active citizen, we should keep our environment clean and sanitized. We should help municipal corporation in garbage collection. We should also spread awareness about the benefits of sanitation.