STD 7 Basic Science: Chapter 06 For a Pollution-Free Nature - Questions and Answers | Teaching Manual


Textbooks Solution for Class 7 Basic Science (English Medium) നിർമലമായ പ്രകൃതിക്കായി | Text Books Solution Basic Science Chapter 06 For a Pollution Free Nature - Teaching Manual & Teachers Handbook


ഈ അധ്യായത്തിന്റെ Teachers Handbook, Teaching Manual എന്നിവ ഡൗൺലോഡ് ചെയ്യാനുള്ള ലിങ്ക് ചോദ്യോത്തരങ്ങളുടെ അവസാനം നൽകിയിട്ടുണ്ട്.

Chapter 06: For a Pollution Free Nature - Textual Questions and Answers & Model Questions
1. All living beings depend on factors such as
a) soil
b) air
c) water
d) All the above.
Answer: All the above.

2. organic matter gets decomposed in the soil by the action of microorganisms such as
a) bacteria
b) fungi
c) both
d) none
Answer: bacteria

3. Components of soil suitable for agriculture are
a) Minerals 45%
b) Water 25%
c) Air 25%
d) Organic matter 5%
e) All the above.
Answer: All the above.

4. Soil erosion occurs mostly during in
a) summer season
b) monsoon season
c) winter season.
d) none
Answer: monsoon season

5. What is the content of soil?
Answer: Soil contains air, water, minerals and organic matter.

6. Soil, water and air are essential for the existence of a tree. How do other living beings make use of them? Complete the table.
7. Is the soil around us the same everywhere? Collect samples of soil from different places and examine them. Which are these places?
• Paddy field
• Garden
• Places from where the soil  has been removed for construction purposes
What should be observed?
• Colour
• Size of grains of soil
• Other particles
Tabulate the results of the observation in the science diary.
Answer:
• Paddy fields
* Light grey colour
* Grains are very small
*  Silt, clay and organic matters are present.
• Garden:
* Brown in colour
*  Grains are bigger
*  Sand, granules and organic matters are present.
• Places from where soil has been removed for construction purposes
* Red in colour
* Grains are bigger
* granules are present.

8. Take a jar half-filled with garden soil.  Fill the jar fully with water and stir well using a stick. Keep the jar aside for a while.  Observe the jar after the topwater layer becomes clear.
Don't you see large granules, organic matter and mud getting
separated? 
Answer: 
Observation: Granules are settled at the bottom of the jar. Mud is settled above the layer of granules. Above the mud, we can see organic matters.
Findings:
Soil is composed of different particles like granules, clay, organic matters etc...

9. Moisture in soil
i. Does soil contain water? Collect soil up to a quarter of a boiling tube from the school premises. Close the boiling tube with a piece of cotton. Heat it for some time using a spirit lamp. After cooling, observe the inner wall of the boiling tube. What do you observe?
Answer: We can see tiny water droplets in the inner wall of the boiling tube.
ii. Repeat the experiment using soil collected from different places.
Consider the following factors when you observe:
• Do you see any trace of water on the inner wall of the boiling tube?
• Does the water content differ in different types of soil?
Write down the experiment note in the science diary.
Answer
Aim:-
To find out whether the soil contains water content.
Required Materials:-
A boiling tube, a piece of cotton, soil from the school garden, ground, and a paddy field; spirit lamp, and a stand
Procedure:-
Collect the soil up to a quarter of a boiling tube from the school garden. Close the boiling tube with a piece of cotton. Heat it for some time using a spirit lamp. Repeat the experiment with soil from the school ground and veranda
Observation:- 
We can see trace of water on the inner wall of the boiling tube. But, the water content differs in different types of soil. When the soil collected from the paddy field and garden was heated, more water content could be seen in the inner wall of the boiling tube. When the soil collected from school ground was heated, less water content could be seen in the inner wall of the boiling tube.
Conclusion:-
We can see a trace of water in soils. But, the water content differ in different types of soil

10. Try doing the following activities.
Collect separately some sand, soil from a paddy field and soil from your yard and dry them.
Fold a filter paper into a cone and place it in the funnel in a beaker. Measure out half a cup of sand into the funnel. Arrange separate beakers and funnels in a similar manner with soil from the paddy field and yard. Using a dropper add water drop by drop into the three funnels. Make sure that the soil gets wet thoroughly. Do not forget to record the number of water drops added to each funnel. Continue adding water till the first drop of water drips from the funnel into the beaker.
i) Complete the table. (Textbook Page:82)
Answer:
ii) From which type of soil did water drip out first?
Answer: Sand

iii) Which one absorbed the maximum amount of water?
Answer: Soil from a yard

iv) Write down the experiment note in your science diary.
Answer:
Aim:-
To find the absorption capacity of different types of soil
Materials required:-
Three filter papers, three funnels, beakers, sand, soil from the paddy field and yard, dropper
Procedure:-
Fold a filter paper into a cone and place it in the funnel in a beaker. Measure out half a cup of sand into the funnel. Arrange separate beakers and funnels in a similar manner with soil from the paddy field and yard. Using a dropper add water drop by drop into the three funnels. Make sure that the soil gets wet thoroughly. count the number of water drops added to each funnel. Continue adding water till the first drop of water drips from the funnel into the beaker.
Observation:-
From sand, water drip out first. Soil from the yard absorbed the maximum amount of water.
Conclusion:-
The capacity to retain water in different soils is different. Soil with high organic content has a high water absorption capacity.

11. Take equal quantities of sand, red soil and the soil from an area full of trees in three different test tubes. Pour a little hydrogen peroxide into each test tube.
i) Which test tube produced the highest effervescence?
Answer: The soil from an area full of trees

ii) Which soil has the highest organic content? Why?
Answer: The soil from an area full of trees has the highest organic content.
Because it produced more effervescence. Hydrogen peroxide dissociates faster in soil with high organic content.

12. What are the reasons for the variation in the water content in different types of soil?
Answer: Availability of water, differences in the rate of evaporation, the capacity to retain water and differences in organic content are the reasons for the variation in the water content in different types of soil.

13. What will be the colour of the soil with high organic content?
Answer: Dark brown

14. Examine the topsoil and the deep soil collected from the same area. Is there any difference in colour?
Answer: The deep soil is light in colour than the topsoil.

15. What are the situations leading to the loss of topsoil?
Answer: Flooding, Logging and Mining, Construction, Heavy Winds etc...

16. Haven't you seen topsoil rich in organic content being washed away by rainwater? From which type of land does the soil get washed away?
Answer: Places with no trees and plants, Slope land etc.

17. What are the components of soil Suitable for agriculture?
Answer: Air, water, minerals and organic matter.

18. Which soil is suitable for agriculture?
Answer: Soil with high organic content is Suitable for agriculture and has a high water absorption capacity.

19. The water absorption capacity is less for sand. Why?
Answer: The water absorption capacity is less for sand due to its lower organic content.

20. How the microorganisms such as fungi and bacteria increase soil fertility?
Answer: Soil contains microorganisms such as fungi and bacteria. They decompose Organic matter and thus improve the fertility of the soil.

21. What are the different methods to be adopted to prevent soil erosion?
Answer:
• Preventing excessive grazing.
• Prevention of deforestation.
• Plantation of trees and plants.
• Mulch matting can be used to reduce erosion on the slopes.
• Put a series of fibre logs to prevent any water or soil from washing away.

22. How does plastic prevents the growth of roots?
Answer: Plastic is non-degradable. It remains in the soil for long without degrading. It prevents the seeping of water into the soil and thus prevents the growth of roots.

23. What do chemical pesticides do?
Answer: Chemical pesticides destroy harmful insects which destroy crops, harmless Microorganisms.

24. "Chemical pesticides and chemical fertilizers are harmful to our nature and its living beings. Why?
Answer: Chemical pesticides destroy not only harmful insects which destroy crops but also harmless microorganisms. Chemical fertilizers increase the number of certain components in the soil. Chemicals cause the destruction of earthworms and other microorganisms found in the soil.

25. What can be done for proper garbage disposal?
Answer:
• Sorting garbage by type and disposing of them.
• Making biofertilizers using organic waste.
• Controlling the use of plastics, reusing them.

26. Do you think waste reaches only the soil?
Answer: No, water sources, atmosphere are also get polluted.
i) Are the water sources such as ponds, rivers and streams in your locality polluted?
Answer: Yes, the water sources such as ponds, rivers and streams in our locality are polluted.
ii) What are the types of pollutants that reach these sources?
Answer: Sewage wastes, chemical fertilizers, chemical pesticides, factory wastes, wastes from nearby houses reach these sources.

27. Diseases that spread through drinking water are
a) Typhoid
b) cholera
c) dysentery
d) jaundice.
e) All the above.
Answer: All the above.

28. which elements are present in water?
Answer: Water contains various minerals, oxygen, microorganisms and insoluble impurities.

29. Prepare an action plan to keep the water sources in your locality pollution-free.
Answer:
• Ensure minimal use of bleach or detergents. ...
• Reduce the use of herbicides, pesticides, and fertilizers. ...
• Proper sewage treatment and management.
• Dispose of trash properly
• Prevent the disposal of wastes into water bodies

30. What is the pH value of water?
Answer: Pure water is neutral. That is, Its pH is 7.

31. What is the pH value of drinking water?
Answer: Water with a pH value between 6.5 and 7.5 is used as drinking water.

32. The highest quality of water is required for which purpose?
Answer: The highest quality is required for drinking water.

33. What are the methods by which we can purify polluted drinking water?
Answer:
• Boiling.
• Chlorination.
• Reverse Osmosis (RO)
• Distillation.
• Filtration.

34. What are the water resources in our surroundings?
Answer: The resources are given below:
• Well
• pond
• river
• lake

35. How diseases are spread through water?
Answer: Diseases spread through the water when the disease Causes microorganisms to grow in water used for drinking. Mixing up excreta and other pollutants with drinking water is one reason for the pollution of drinking water. The presence of the bacteria E Coli, which reach water through excreta causes the disease diarrhoea. Typhoid, cholera, dysentery and jaundice are some of the other diseases that spread through drinking water.

36. You have been familiarized with the conventional methods of purification of water in your locality. Which are they?
Answer: Filtration, chlorine disinfection, sedimentation are the conventional methods of purification of water.

37. What are the important steps in the process of water purification in a water treatment plant?
Answer:
Step 1:
Aeration - The process of mixing water with air. Thus the amount of oxygen in the water increases.
Step 2
Coagulation – This is an important step in the process of water purification in a water treatment plant. This enables the sedimentation of solid matter present in water. Alum is added for this. When alum is added the pH value of water decreases. Lime is added to regulate the pH value.
Step 3
Clariflocculation – After the solid waste settles, the clear water is fed into filters
Step 4
Filtration – Impurities which do not get settled are removed by the filter. Fine sand and gravel are used respectively in the upper and lower portions of the filter unit.
Step 5
Chlorination – Chlorine gas or bleaching powder is mixed with it to sterilize the filtered water
Step 6
Storage – After purification, water is stored in a water reservoir.

38. How the water purifiers used at houses purifies water?
Answer: Water purifiers used to purify water at home have a filter unit and facilities to let ultraviolet rays pass through. Ultraviolet rays are used instead of chlorine treatment

39. Make a notice or poster to spread the message that drinking water should be used with care.
Answer: "Water is Life Don't Wase it"

40. Haven't you seen health workers sprinkling bleaching powder into wells to prevent contagious diseases. Why?
Answer: Yes, I saw health workers sprinkling bleaching powder into wells to prevent contagious diseases. It is widely used for water treatment. It is used for the disinfection of water in the treatment process. The chlorine released by the Bleaching powder kills Pathogens (Disease-causing Bacteria). The residual effect of this chlorine protects water from getting infected / contaminated with pathogens.

41. Which gas reduces the oxygen absorption capacity of blood?
a) Carbon monoxide
b) Carbon dioxide
c) Sulphur dioxide
d) Oxides of nitrogen.
Answer: Carbon monoxide

42. Which gas Causes global warming?
a) Carbon monoxide
b) Carbon dioxide
c) Sulphur dioxide
d) Oxides of nitrogen
Answer: Carbon dioxide

43. Which gas Causes irritation to the eyes, lung cancer and asthma?
a) Carbon monoxide
b) Carbon dioxide
c) Sulphur dioxide
d) Oxides of nitrogen
Answer: Sulphur dioxide

44. Which gas Causes acid rain?
a) Carbon monoxide
b) Carbon dioxide
c) Sulphur dioxide
d) Oxides of nitrogen
Answer: Oxides of nitrogen

45. What are the components of atmospheric air?
Answer:
• Nitrogen - 78 %
• Oxygen - 20.9%
• Carbon dioxide - 0.03%
• Others - 1.07%

46. What is the source of Carbon monoxide?
Answer: The source of Carbon monoxide is Smoke from automobiles.

47. Observe the pictures. 
Gases like carbon dioxide and carbon monoxide and smoke containing other chemicals reach the air. How does it affect the atmosphere?
Answer: Burning fossil fuels releases gases and chemicals into the air.’ It usually leads to climate change. “Air pollution in the form of carbon dioxide and methane raises the earth's temperature.

48. When the air is said to be polluted?
Answer: Air is said to be polluted when there is any change in the normal amount of any of the components of air or when foreign substances mix with air.

49. What is the source of Oxides of nitrogen?
Answer: The source of oxides of nitrogen is automobiles and factories.

50. What is the source of Sulphur dioxide?
Answer: the source of Sulphur dioxide is in factories.

51. Write some situations in which air gets polluted and also write its adverse effects?
Answer:
52. What steps can be taken to reduce air pollution? Discuss and record them in your science diary.
Answer:
• Use public vehicles than private vehicles.
• Buying vehicles that have a greater fuel efficiency
• Reduce the use of plastics.
• Reduction of forest fires and smoking
• Use of fans instead of Air Conditioner
• Avoid Over usage of crackers.

53. Didn’t you notice the opinions of different people living in the same locality?
Everyone needs facilities. Every new facility brings forth its own problems. The amount of waste also increases with the increase in population.
Shouldn't physical facilities increase?
Answer: The physical facilities should increase for the easiness of our different activities. But, it should not disturb the environment.

54. Does the increase in the number of vehicles increase the rate of air pollution? Do they pollute soil and water in any way?
Answer: The increase in the number of vehicles will increase the rate of air pollution. It emits large amounts of toxic substances like- carbon monoxide into the atmosphere, which will cause air pollution. Air pollution can significantly hurt the quality of soil and water resources. 

55. Aren't unpolluted air, water and soil the right of all living beings?
Answer: Yes, unpolluted air, water and soil are the rights of all living beings. We, humans, destroy all the resources for our greediness. It adversely affects all the living beings on the earth. 

56. Don't we need a mode of development that protects air, water and soil?
Answer: Yes, we need a mode of development that protects air, water and soil. Our earth is in a dangerous situation, because of our resource exploitation. In order to have healthy communities, we need clean air, natural resources, and a nontoxic environment.

Let us assess

1. In which of the following water samples should lime be added?
          a.       pH 7                              b.    pH 5
          c.       pH 9                              d.    pH 8
Answer:  b.    pH 5

2. When water is poured into a perforated coconut shell filled with gravel, water drops come out through the hole of the coconut shell quickly. What inference can be arrived at from this?
a. Organic content in soil is high.
b. Water absorbing capacity of soil is low.
c. Water absorbing capacity of soil is high.
d. The soil is suitable for cultivation.
Answer: 
b. Water absorbing capacity of soil is low.

3. What are the circumstances that cause an increase in the amount of carbon dioxide in the air?
Answer: Human activities such as the burning of fossil fuel, as well as deforestation are the primary cause of the increased carbon dioxide concentrations in the atmosphere

4. What are the precautions to be taken to prevent the spread of diseases through water?
Answer:
• Ensure water is not accumulated in around houses.
• Use clean water to brush your teeth, wash and prepare food.
• Wash your hands with soap and clean water before eating, cooking, feeding children, and after using the toilet.
• Store water in a clean container.  





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