7 Sci Chp 18 Solsn

 

Solutions for Class 7th: Ch 18 Wastewater Story

Exercises

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 ____________.

Answer

(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.

Answer

Sewage is a liquid waste released by homes, industries, hospitals, offices and other users which also includes rainwater that has run down the street during a storm or heavy rain.

when sewage discharge untreated into rivers or seas, it will be dangerous for aquatic plants and animals.

3. Why should oils and fats be not released in the drain? Explain.

Answer

Oil and fats should not be released in the drain because they can harden and block the pipes. In an open drain the fats block the soil pores reducing its effectiveness in filtering water.

4. Describe the steps involved in getting clarified water from wastewater.

Answer

Steps involved in getting clarified water from wastewater:

(i) Wastewater is shaken well and left to stand in the sun for some days.

(ii) After that, it is stir several times using an aerator or mechanical stirrer or a mixer which remove bad odour from water.

(iii) The stirred product is then filtered and sediment to remove insoluble waste.

(iv) Chlorination is used to kill the germs in filtered water. Now, the wastewater is fit for drinking purpose.

5. What is sludge? Explain how it is treated.

Answer

Solids waste like faeces settle at the bottom of tank during sedimentation is called sludge.

Sludge is removed with a scraper and then transferred to a separate tank where it is decomposed by the anaerobic bacteria to produce biogas.

6. Untreated human excreta is a health hazard. Explain.

Answer

Untreated human excreta is a health hazard as it can cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Thus, it becomes the most common route for water borne diseases which include cholera, typhoid, polio, meningitis, hepatitis and dysentery. It is also a big threat to sanitation.

7. Name two chemicals used to disinfect water.

Answer

Two chemicals used to disinfect water are chlorine and ozone.

8. Explain the function of bar screens in a wastewater treatment plant.

Answer

Bar screen in a wastewater treatment plant is used to remove the large objects like rags, sticks, cans, plastic packets and napkins.

9. Explain the relationship between sanitation and disease.

Answer

Sanitation and disease are closely related as lack of sanitation leads to unhygienic condition and ultimately disease. Proper sanitation is necessary to avoid certain kinds of disease. Where there is sanitation, there is no disease and vice versa.

10. Outline your role as an active citizen in relation to sanitation.

Answer

Role as an active citizen in relation to sanitation:

(i) Contribute in maintaining sanitation at public places and should not scatter litter anywhere.

(ii) Throwing garbage or waste at its desired place.

(iii) Ensure that my surrounding and neighbourhood is clean and help the municipality in maintaining proper sanity.

(iv) Preventing clogging of drains by not releasing oil and fat and solid waste into the drain.

(v) Immediately inform the municipality about any sewage leakage and for the maintenance of dustbins.

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

Answer

Across

3. Liquid waste products → Sewage

4. Solid waste extracted in sewage treatment → Sludge

6. A word related to hygiene → Sanitation

8. Waste matter discharged from human body → Excreta

Down

1. Used water → Wastewater

2. A pipe carrying sewage → Sewer

5. Micro-organisms which causes cholera → Bacteria

7. A chemical to disinfect water → Ozone

Page No: 229

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

► (ii) (b) and (c)

7 Sci Chp 17 solusn

Solutions for Class 7th: Ch 17 Forests: Our Lifeline Science

 Exercises

1. Explain how animals dwelling in the forest help it grow and regenerate.

Answer

Animals dwelling in the forest help in various way for growth and regenerate. Some of them are:

(i) Herbivores animals clear the land by eating grass for the new growth of vegetation.

(ii) Animals also help in the seed dispersal and pollination.

(iii) Dead and decaying bodies of animals convert to humus after decomposition which increase the fertility of the soil of the forest.

(iv) Dungs of animals provide nutrient to various types of seedling to grow.

2. Explain how forests prevent floods.

Answer

Forest  acts as a natural absorber of rainwater and allows it to seep. It helps in controlling the flow of water and slows it down which helps in preventing flood. Also, the trees present in the forest prevents the rain from directly hitting the ground and bind the soil together which helps in absorption of the rain water and thus prevent flood.

3. What are decomposers? Name any two of them. What do they do in the forest?

Answer

The micro-organisms which convert the dead plants and animals to humus are known as decomposers.

Bacteria and fungi are the two examples of decomposers.

They play an important role in the decomposition of dead remains of the plants and animals

 and converting them to humus which add nutrient to the soil.

4. Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.

Answer

Forest play an important role in maintaining the balance between oxygen and carbon dioxide in the atmosphere. The green plants and trees present in the forest take in carbon dioxide which is released by the animals and release oxygen through the process of photosynthesis which are breathe in by the animals and thus maintains the balance between oxygen and carbon dioxide in the atmosphere.

5. Explain why there is no waste in a forest.

Answer

There is no waste in a forest because whatever produced here are utilized by the other organisms or plants for sustainability. Even the waste materials and dead remains which are produced are bodegradable and converted into humus which returns back the nutrient back to the soil.

6. List five products we get from forests?

Answer

Five products we get from forests are:

(i) Wood

(ii) Resins

(iii) Gum

(iv) Honey

(v) Medicines

7. Fill in the blank:

(a) The insects, butterflies, honeybees and birds help flowering plants in ___________ .

(b) A forest is a purifier of _____________ and _______________ .

(c) Herbs form the ______________ layer in the forest.

(d) The decaying leaves and animal droppings in a forest enrich the ______________ .

Answer

(a) The insects, butterflies, honeybees and birds help flowering plants in pollination .

(b) A forest is a purifier of water and air .

(c) Herbs form the lowest layer in the forest.

(d) The decaying leaves and animal droppings in a forest enrich the soil .

8. Why should we worry about the conditions and issues related to forests far from us?

Answer

We should worry about the conditions and issues related to forests far from us because more or less we are dependent on it because:

(i) The amount of carbon dioxide in air will increase if forest will disappear and thus less oxygen in atmosphere o breathe in.

(ii) There will be more soil erosion and thus increase in floods as soil will not able to hold water.

(iii) Increase in the percentage of carbon dioxide will also leads to global warming.

(iv) Deforestation will endanger our life and environment and also there will be no shelter for animals.

(v) There is also imbalance in nature and thus causing climate changes and less rainfall.

9. Explain why there is a need of variety of animals and plants in a forest.

Answer

There is a need of variety of animals and plants in a forest as each of them contribute their for maintaining the ecosystem of the forest. It also helps forest in regeneration and growth. Herbivores are needed to eat green plants and to provide food for the carnivores and Carnivores are needed to eat herbivores and check their population. Also, decomposers are needed to maintain the supply of nutrients to the soil and to the growing plants.

10. In Fig. 17.15, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels:

clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil, roots, water table.

Answer

11. Which of the following is not a forest product?

(i) Gum

(ii) Plywood

(iii) Sealing wax

(iv) Kerosene

► (iv) Kerosene

12. Which of the following statements is not correct?

(i) Forests protect the soil from erosion.

(ii) Plants and animals in a forest are not dependent on one another.

(iii) Forests influence the climate and water cycle.

(iv) Soil helps forests to grow and regenerate.

► (ii) Plants and animals in a forest are not dependent on one another.

13. Micro-organisms act upon the dead plants to produce

(i) sand 

(ii) mushrooms

(iii) humus

(iv) wood

► (iii) humus

7 sci Chp 16 solusn

 

Solutions for Class 7th: Ch 16 Water: A Precious Resource Science

Exercises

1. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)

(b) Water shortage is a problem faced only by people living in rural areas. (T/F)

(c) Water from rivers is the only source for irrigation in the fields. (T/F)

(d) Rain is the ultimate source of water. (T/F)

Answer

(a) T

(b) F

(c) F

(d) T

2. Explain how groundwater is recharged?

Answer

The rainwater and water from other sources such as rivers and ponds seeps through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called infiltration. The groundwater thus gets recharged by this process.

3. There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?

Answer

This will lead to exploitation of water resource present underground if people of all the fifty houses in the lane use the ten tubewells regularly. In long term, the water level will go below and thus the depletion of tubewells.

4. You have been asked to maintain a garden. How will you minimise the use of water?

Answer

For minimising the use of water in maintenance of garden, i will use the technique of drip irrigation. In this method, required amount water is supplied directly to the roots of the plants using narrow pipes thus preventing the loss of water.

5. Explain the factors responsible for the depletion of water table.

Answer

Factors responsible for the depletion of water level:

(i) Increase in the demand of water due to overpopulation.

(ii) Deforestation leads to less rainfall which affect the recharge of river and pounds.

(iii) Increase the number of industries as they use a lot of water for their purpose.

(iv) Insignificant uses in agriculture activities as in many parts of the world people uses old techniques which waste a lot of water.

(v) Lack awareness in people is also a main reason behind the depletion of water level as they waste water without any uses.

6. Fill in the blanks with the appropriate answers:

(a) People obtain groundwater through________ and ________ .

(b) Three forms of water are ________, ________ and ________.

(c) The water bearing layer of the earth is ________.

(d) The process of water seepage into the ground is called ________.

Answer

(a) People obtain groundwater through tube wells and hand pumps.

(b) Three forms of water are ice, water and vapour.

(c) The water bearing layer of the earth is aquifer.

(d) The process of water seepage into the ground is called infiltration.

Page No: 204

7. Which one of the following is not responsbile for water shortage?

(i) Rapid growth of industries

(ii) Increasing population

(iii) Heavy rainfall

(iv) Mismanagement of water resources

Answer

(iii) Heavy rainfall

8. Choose the correct option. The total water

(i) in the lakes and rivers of the world remains constant.

(ii) under the ground remains constant.

(iii) in the seas and oceans of the world remains constant.

(iv) of the world remains constant.

Answer

(iv) of the world remains constant.

9. Make a sketch showing groundwater and water table. Label it.

Answer