Yearly Archives: 2022

Q.1. Fill in the blanks:
(a) Cleaning of water is process of removing __________
(b) Wastewater released by houses is called __________.
(c) Dried __________ is used as manure.
(d) Drains get blocked by __________ and __________.
Ans.(a) pollutants (b) sewage (c) sludge (d) (d) chemicals, kitchen waste

Q.2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Ans. Sewage is a liquid containing wastes which is disposed by households, industrial and agricultural activities in water. It is harmful to discharge untreated sewage into rivers or seas because it can pollute the whole sources of water. Sewage contains harmful substances and disease causing organisms. It is therefore dangerous to release untreated sewage in water.

Q.3. Why should oils and fats be not released in the drain? Explain.
Ans. Oils and fats should not be released in drains because they harden the soil in the pipes and block them. Fats get clogged in holes of the soil in the drain and block it. It does not allow the water to flow.

Q.4. Describe the steps involved in getting clarified water from wastewater.
Ans. Following steps are involved in the purification of water:

(i) Firstly all the physical impurities like stones, plastic bags, cans etc. are to be removed. It is done by passing the water through bar screens.
(ii) Then water is taken to grit and sand removal tank where impurities are removed by sedimentation.
(iii) Solid impurities and feaces etc. are collected from bottom of water. These impurities collected are called sludge.
(iv) Clarified water is cleaned of other impurities by aerator. All disease causing bacteria are removed by chlorination.

Q.5. What is sludge? Explain how it is treated.
Ans. Sludge is the collected solid waste from the wastewater during the treatment in water treatment plant. Sludge is decomposed in a separate tank by the anaerobic bacteria. Activated sludge is used as manure.

Q.6. Untreated human excreta is a health hazard. Explain.
Ans. Untreated human excreta can cause a lot of health related problems. It pollutes water, air and soil. The polluted water contain disease causing bacteria which can spread epidemics like cholera, meningitis etc.

Q.7. Name two chemicals used to disinfect water.
Ans. Chlorine and ozone

Q.8. Explain the Junction of bar screens in a wastewater treatment plant.
Ans. Bar screens clear the wastewater of all the physical impurities. Large size waste like napkins, plastics, cans etc. are removed from the wastewater through the bar screens.

Q.9. Explain the relationship between sanitation and disease.
Ans. Sanitation and disease are related to each other. Sanitation involves proper disposal of sewage and refuse from hou&e and public places. If sanitation is there, no disease will occur, but if sanitation is not there various types of disease will occur and spread. So sanitation should be kept to avoid disease.

Q.10. Outline your role as an active citizen in relation to sanitation.
Ans. As active citizen we should take care of our personal environmental sanitation. We should make people aware of the benefits of sanitation. We should help municipal corporations to cover all the open drains and remove disease causing substances thrown in open.

Q.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 cause cholera
7. A chemical to disinfect water

Ans

Q.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
Ans. (ii) (b) and (c)

Q.1. Explain how animals dwelling in the forest help it grow and regenerate.
Ans. Animals help in growing and regenerating forests in many ways. Animals work as the cleaning agents in the forest. Microorganisms work on dead bodies of plants and animals and degenerate them. An’imals also help in pollination which helps in growing a number of plants. Herbivores helps the carnivores to grow as they serve as food for them. Thus flora and fauna mutually grow in the forest.

Q.2. Explain how forests prevent floods.
Ans. Forests can absorb a lot of water. The roots of the trees absorb the water and prevent it from flowing away. Roots of trees also help in percolation of water into the soil. This helps in preventing floods.

Q.3. What are decomposers? Name any two of them. What do they do in the forest?
Ans. Decomposers are the organisms which feed on the dead bodies of plants and animals. They clean the forests decaying dead bodies and replenishing the nutrients back to the forest soil, e.g.„ beetles and grubs.

Q.4. Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Ans. Plants release oxygen in the atmosphere during the process of photosynthesis. This oxygen is inhaled by the animals for respiration. During respiration, they release carbon-dioxide which is absorbed by plants. In this way the oxygen and carbon dioxide cycle goes on. Since forests contain a large number of plants, they help much in this cycle and maintain balance in nature.

Q.5. Explain why there is no waste in a forest.
Ans. There is no waste in the forest because decomposers convert all the dead bodies of the plants and animals into the humus which gets added to the soil. Thus, no waste remains.

Q.6. List five products we get from forests.
Ans. (i) We get medicines from forests.
(ii) We get gum from forests.
(iii) We get wood which is used for many purposes like making furniture, paper etc.
(iv) We get food for animals from forests.
(v) We get sealing wax from forests.

Q.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 .
Ans. (a) pollination (b) water, air (c) lowest (d) soil as humus.

Q.8. Why should we worry about the conditions and issues related to forests far from us?
Ans. We should be worried about deforestation as it would lead to floods, increase in earth’s temperature, decreasing animals habitats and soil erosion. Damage to forests directly or indirectly affects human habitat and environment so it must be a matter of concern among us.

Q.9. Explain why there is a need of variety of animals and plants in a forest.
Ans. All plants and animals sustain the forest life and also C02 – 02 cycle goes on due to animals and plants. Animals convert the dead and decaying matters into humus and increase the fertility of soil, thus enhancing plant growth. All food chains and food webs need variety of plants and animals.

Q.10. In fig. 1 7.15 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, cabon dioxide, oxygen, plants, animals, soil, roots, water table.

Q.11.Which of the following is not a forest product?
(i) Gum (ii) Plywood (iii) Sealing wax (iv) Kerosene
Ans.(iv) Kerosene

Q.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.
(iu) Soil helps forests to grow and regenerate.
Ans.(ii) Plants and animals in a forest are not dependent on one another.

Q.13.Micro-organisms act upon the dead plants to produce
(i) sand (ii) mushrooms (iii) humus (iu) wood
Ans. (i) Humus

Q.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)

Ans. (a) T (b) F (c) F (d) T

Q.2. Explain how groundwater is recharged.
Ans. The groundwater gets recharged through the process of infiltration. Infiltration means seeping of water from rivers and lakes into the empty spaces and cracks deep below the ground.

Q.3.There are ten tubewells in a lane of fifty houses. What could be the long-term impact on the water table?
Ans.The effect on the water table depends on the replenishment of underground water. Only five families will share a tubewell, the water used for daily domestic purposes will not effect the water table. But if there is shortage of rains, the water used by the family will not replenished and water table will fall down.

Q.4.You have been asked to maintain a garden. How will you minimise the use of water? „
Ans.To minimise the wastage of water we will use the drip irrigation which throws the water at the base of plants. We will check the leakages in the water pipes and arrange small pits for rainwater harvesting. The collected rainwater will be used later.

Q.5.Explain the factors responsible for the depletion of water table.
Ans.Various factors responsible for the depletion of water table are:
(i) Increased population: Demand of water has been increased by the increased population. As the number of humans increase, the consumption of water also increases.
(ii) Increasing industries: All industries need water. As the number of human population increase, the number of industries are also increased which definitely increases the consumption of water.

(iii) Lack of water conservation techniques: Main source of water on earth and for the underground water is rain. The water of the rain, if conserved can increase the ground water level. But this is not done due to lack of water conservative techniques.
(iv) Agricultural activities: India is a country which depends on agriculture. The land used for cultivation has increased. So, the consumption of water for agriculture has increased. Irregular rainfall has increased the consumption of groundwater. This has increased the depletion of groundwater.

Q.6.Fill in the blanks with the appropriate answers: .
(a) People obtain groundwater through and .
(b) Three forms of water are solid, and .
(c) The water bearing layer of the earth is .
(d) The process of water seepage into the ground is called .
Ans.(a) wells, hand pumps
(b) liquid, gas
(c) aquifer
(d) infiltration

Q.7.Which one of the following is not responsible for water shortage?
(i) Rapid growth of industries
(ii) Increasing population
(iii) Heavy rainfall
(iv) Mismanagement of water resources
Ans.(iii) heavy rainfall

Q.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.
Ans.(iv) of the world remains constant.

Q.9.Make a sketch shoyving groundwater and water table. Label it.
Ans

Q.1.Fill in the blanks:
(a) An image that cannot be obtained on a screen is called ___________ .
(b) Image formed by a convex is __________ always virtual and smaller in size.

(c) An image formed by a __________ mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called a __________ image.
(e) An image formed by a concave __________ cannot be obtained on a screen.
Ans.(a) virtual image (b) mirror (c) plane (d) real (e) lens

Q.2.Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)
(b) A concave lens always form a virtual image. (T/F)
(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)
(d) A real image cannot be obtained on a screen. (T/F)
(e) A concave mirror always form a real image. (T/F)
Ans. a) F (b) T (c) T (d) F (e) F

Q.3. Match the items given in Column I with one or more items of Column II

Ans.

Q.4.State the characteristics of the image formed by a plane mirror.
Ans.(i) Plane mirror forms an erect image.
(ii) It forms a virtual image.
(iii) Size of the image is same as that of the object.
(iv)Image is formed at the same distance behind the mirror as the object stands in front of it.
(v) Image formed is a laterally inverted image i.e., right hand side of the object seems to be the left hand side and vice-versa.

Q.5.Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.
Ans.Letters like A, H, I, M, O, T, U ,V, W etc. appear same when seen through a plane mirror

Q.6.What is a virtual image? Give one situation where a virtual image is formed.
Ans.The image which cannot be taken on a screen is called virtual image. When some object is placed very close to the concave mirror we don’t get any image on the white screen placed behind the mirror. Such image is called virtual image.

Q.7. State two differences between a convex and a concave lens.

Q.8. Give one use each of a concave and a convex mirror.
Ans. Use of concave mirror:
Concave mirror is used by dentists to examine the teeth.
Use of convex mirror:
Convex mirror is used as side view mirror in vehicles

Q.9. Which type of mirror can form a real image?
Ans. Concave mirror can form a real image.

Q.10. Which type of lens forms always a virtual image?
Ans. Concave lens always forms a virtual image.

Choose the correct option in Questions 11-13:

Q.11. A virtual image larger than the object can be produced by a
(i) concave lens (ii) concave mirror (iii) convex mirror (iv) plane mirror

Ans. (ii) concave mirror

Q.12. David is observing his image in a plane mirror. Die distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be
(i) 3 m (ii) 5 m (iii) 6 m (iv) 8 m

Ans. (iii) 6 m

Q.13. The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear mew mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be
(i) 1 m/s (ii) 2 m/s (iii) 4 m/s {iv) 8 m/s

Ans. (ii) 4 m/s