Class 7 Science Chapter 13 Question Answers - Wastewater Story

Very Short Q & A :

Q1: What is sewage?

Ans : Waste water released by houses is called sewage.

Q2: What per cent of earth’s water is fresh?

Ans : 3 per cent.

Q3: What constitutes waste water?

Ans : It can include human waste, food scraps and chemicals.

Q4: State one of the reasons for increasing scarcity of fresh water.

Ans : Population growth.

Q5: Which day is celebrated as World Water Day?

Ans : 22 March

Q6: What is cleaning of water?

Ans : Cleaning of water is the process of removing pollutants before it enters a water body or is reused.

Q7: In order to have safe drinking water, it should be ________.

Ans : Boiled

Q8: What are the adverse effects of drinking contaminated water?

Ans : Drinking contaminated water results in diseases such as cholera, typhoid and diarrhoea. Polluted water can also prove fatal.

Q9: Water gets contaminated and scarcity of clean water is due to :

• People take baths and wash clothes in rivers and lakes.
• Many people bathe their animals in rivers and lakes.
• Increase in the population, industries and improper disposal of waste
• All of the above.

Ans : All of the above.

Q10: What is sewage treatment?

Ans : Pollutants in waste water can be removed in several stages, and this process is called “sewage treatment.

Q11: Sewage contains organic and _______________ impurities.

Ans : Inorganic

Q12: Sewage contains disease-causing bacteria. True/False

Ans : True

Q13: Saprotrophic bacteria feed on dead organisms.True/False

Ans : True

Q14: Sewage contains some harmful nutrients, such as ______________and nitrogen.

Ans : Phosphorous

Q15: Wastewater has many impurities and these impurities should be removed by _______________.

Ans : Water treatment.

Q16: What is the purpose of filtering waste water?

Ans : To remove large impurities.

Q17: What is a clarifier?

Ans : A clarifier is a tank with its central part inclined downwards so as to allow faeces to settle down. The inclined waste is then removed using a scraper.

Q18: Name some biological contaminants in water.

Ans : bacteria and microbes

Q19: Name the chemical used in water plant to clean water

Ans : Chlorine tablets or ozone.

Q20: Dried _ is used as manure.

Ans : Sludge

Q21: List the substances responsible for blockage of drain.

Ans : Tealeaves, solid food remains, soft toys, cotton, and sanitary towels.

Q22: Why should used tea leaves, solid food remains, etc. not be released in 

the drains?

Ans : Used tea leaves, solid food remains etc. should not be thrown down the drain as they may choke the drain.

Q23: What is the function of bar screens in waste water treatment plant?

Ans : The bar screen remove the large objects like rags, sticks, cans, plastics packets etc. from the sewage.

Q24: Why waste water is passed through bar screen?

Ans : Waste water is passed through bar screens to remove big objects like cans, sticks, rags etc.

Q25: What is the function of a skimmer?

Ans : A skimmer removes the floatable solids like oil, grease etc.

Q26: Why air is pumped into clarified water?

Ans : Air is pumped into clarified water to help aerobic bacteria to grow.

Q27: The suspended microbes in water treatment plant settle at the __________& the water is removed from the_____

Ans : Bottom and top.

Q28: State various uses of water.

Ans : Water is used for:

• Drinking
• Cooking
• Washing clothes, utensils
• Generating electricity
• Bathing

Q29: What is the actual reason behind improper sanitation?

Ans : Lack of knowledge and of money, illiteracy, large population and lack of social awareness results in improper sanitation

Q30: Onsite sewage disposal systems collect human excreta and store it in a hole or a pipe, and later direct it to a sewage treatment plant. True/False.

Ans : True

Q31: Septic tanks are not suitable for places such as hospitals, isolated buildings and clusters of houses where there is no sewage.True/False

Ans : False

Q32: What kind of toilets are in aeroplanes and trains?

Ans : Chemical toilets

Q33: Public places such as railway stations, bus depots, airports and hospitals generate a lot of waste, which leads to diseases. True/False.

Ans : True

Q34: Solids like faeces settle at the bottom by _____________ and are removed with a scraper.

Ans : Sedimentation