The Class 7 is an important year in a student’s life and Science is one of the subjects that require dedication, hard work, and practice. It’s a subject where you can score well if you are well-versed with the concepts, remember the important formulas and solving methods, and have done an ample amount of practice. Worry not! Home Revise is here to make your Class 7 journey even easier. It’s essential for students to have the right study material and notes to prepare for their board examinations, and through Home Revise, you can cover all the fundamental topics in the subject and the complete NCERT Class 7 Science Book syllabus.
Exercise Questions
1. Fill in the blanks:
(a) Cleaning of water is a process of removing ____________.
(b) Wastewater released by houses is called ____________.
(c) Dried ____________ is used as manure.
(d) Drains get blocked by ____________ and ____________.
Solution:
(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 cooking oil and fats .
2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Wastewater released by houses is called sewage. Untreated sewage should not be discharged into the sea because sewage consists of pollutants and harmful microorganisms, which will contaminate water, causing disease in people using contaminated water.
3. Why should oils and fats not be released in the drain? Explain.
Solution:
Oils and fats should not be released into the drain because drains get blocked by cooking oil and fats.
4. Describe the steps involved in getting clarified water from wastewater.
Solution:
Use an aerator from an aquarium to bubble air through the sample in the glass jar. Allow several hours for aeration; leave the aerator attached overnight. If you do not have an aerator, use a mechanical stirrer or a mixer. This reduces the foul smell of wastewater.
Then, the water is filtered through the layers of sand, fine gravel and medium gravel. Filtration makes the wastewater clean from various types of pollutants. The water is filtered continuously until it becomes clear.
Water is disinfected by using a chlorine tablet.
5. What is sludge? Explain how it is treated.
Solution:
Solids like faeces settle at the bottom while treating sewage, and this material is called sludge. Sludge can be treated as follows:
Sludge is removed using a skimmer and then transferred to a tank where it is decomposed by anaerobic bacteria to produce biogas.
6. Untreated human excreta is a health hazard. Explain.
Solution:
Untreated human excreta is a health hazard because it consists of various disease-causing microorganisms and pollutants that will contaminate the soil and water resource from where people draw water for drinking and domestic purposes. When people use water contaminated with human excreta, they get diseases like Cholera, Typhoid, Dysentry and Hepatitis.
7. Name two chemicals used to disinfect water.
Solution:
Chlorine and Ozone are used to disinfect water.
8. Explain the function of bar screens in a wastewater treatment plant.
Solution:
Bar screens remove large objects like rags, sticks, cans, plastic packets and napkins.
9. Explain the relationship between sanitation and disease.
Solution:
Sanitation and disease are interrelated as lack of sanitation leads to illness, and good sanitation practices prevent diseases.
10. Outline your role as an active citizen in relation to sanitation.
Solution:
Every citizen has a role to play in maintaining proper sanitisation. Following are the things we should follow to play an active role.
11. Here is a crossword puzzle: Good luck!
Across
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from human body
Down
1. Used water
2. A pipe carrying sewage
5. Micro-organisms which causes cholera
7. A chemical to disinfect water
Solution:
Across
3. Sewage
4. Sludge
6. Sanitation
8. Excreta
Down
1. Wastewater
2. Sewer
5. Bacteria
7. Ozone
12. Study the following statements about ozone:
(a) It is essential for breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.
(d) Its proportion in air is about 3%. Which of these statements are correct?
(i) (a), (b) and (c)
(ii) (b) and (c)
(iii) (a) and (d)
(iv) All four
Solution:
The answer is (ii) (b) and (c)
This chapter specifically deals with the issue of contaminants in water. Water is an important resource not just for humans but for all the organisms on earth. Therefore, contaminating this natural resource has dire consequences. The main reasons for water pollution are our commercial and industrial activities. All the waste effluents that reach water bodies results in water pollution. In the long run, this can cause many diseases and health hazards for us.
For instance, in Minamata City, Japan, mercury runoff from a factory polluted the waters, and the poisoning went undetected for decades. It came to notice only when the people saw their newborns had birth defects. It was found that the mercury runoff had contaminated the marine ecosystem, resulting in fish species ingesting the mercury. Over a period of time, mercury accumulation in fish species got transferred into humans who consumed contaminated fish. This adversely affected bodily functions and caused a lot of problems for the people and their descendants. Hence, we need to take care of such issues by preventing industrial effluents which pollute our most precious resource – water.
Wastewater Story Chapter has 8 subtopics which are listed below.
Water is a resource that we use for almost all of our activities. Consequently, polluting this resource can adversely affect our health. It is mainly polluted by human activities as a result of commercial or industrial exploits. The waste by-products contain many poisonous chemicals that disrupt the marine ecosystem. Also, human excreta poses a major threat and could potentially be a bio-hazard due to many harmful microbes it carries. These microbes or chemicals could leech into the aquatic environment affecting every life form that comes in contact with it.
Wastewater Story guides the students to segregate waste in a way to reduce water pollution. This chapter demonstrates the importance of water in balancing the ecosystem. Students will get to study the meaning of sewage, its treatment and disposal methods. This chapter creates an awareness of sanitation in students, which helps them to become responsible citizens.