DELHI PUBLIC SCHOOL TAPI CLASS VII SUBJECT: SCIENCE Ch 9- SOIL Subjective Type Exercises A. Very Short Answer Questions 1. What is weathering? Ans: The process of breaking down of rocks by the action of wind, water and climate is called weathering. 2. What type of soil can be used to make toys? Ans: Clayey soil can be used to make toys. 3. How can a farmer convert acidic soil to neutral soil?[ncert Exemplar Problems] Ans: He can add a small quantity of quick lime or slaked lime solution to the soil. This will make the acidic soil neutral. 4. Name two places where we can see the soil profile. Ans: At the sides of a recently dugged ditch or well and digging at the construction site for laying foundation of a building. 5. How does sand remain dry? Ans: Sand remains dry because water can drain quickly through the spaces between sand particles. 6. How do clay particles hold water? Ans: Clay particles are smaller and packed tightly together leaving little space between them. So water can be held in tiny gaps between clay particles. 7. Write the steps followed in making pots. Ans: (i) Dry soil will be placed in a large tank and would be cleaned of pebbles etc. (ii) After removing these things the soil will be soaked for around 8 hours. (iii) This soil would be kneaded after mixing horse dung. (iv) The kneaded soil would be placed on the wheel and given appropriate shape. (v) The final shape is given with hands. (vi) The items are coloured after three days of drying. (viii) All the items are baked at high temperature after drying in the air. 8. Why is horse dung mixed in soil for making pots? Ans: Burnt horse dung helps open up the pores in the soil. So that water could percolate out of the matkas and surahis, evaporate and cools the water inside. 9. What is Sohagpur in Madhya Pradesh famous for? 1
Ans: Sohagpur in Madhya Pradesh is famous for surahi, matki, kalla (earthen frying pan) etc. 10. If it rains for 8 10 days, water level in a pond rises. What type of soil will allow water to reach a well faster and why? Ans: Sandy soil will allow water to reach the well faster because it helps water drain through it faster. 11. Suggest a method so that more rainwater percolates and reaches the water underground. Ans: More rainwater would percolate by filling sand in open pits and. mixing sand with soil in grounds. B. Short Answer Questions 1. Define humus. How is it formed? Ans: The dead plant and animal parts keep decaying and turn into dark lumps. This dark decayed matter is called humus. It is formed by the action of microbes like bacteria and fungi on these dead organisms. 2. Explain the terms (a) topsoil (b) bedrock. Ans: (a) The uppermost horizon is generally dark in colour as it is rich in humus and minerals. The humus makes the soil fertile and provides nutrients to growing plants. This layer is generally soft, porous and can retain more water. It is called the topsoil or the A-horizon. This provides shelter for many living organisms such as worms, rodents, moles and beetles. The roots of small plants are embedded entirely in the topsoil. (b) Bed rock is the lowest layer of soil profile which is made of small lumps of rocks with cracks and crevices. It is hard and difficult to dig. 3. Why is soil considered one of the most important natural resources? Ans: Soil is considered as one of the most important natural resource because it supports plant in growth and agriculture which provide food, clothing and shelter for all. It is thus, an indispensable part of our life. 4. "Polythene bags and plastics should be banned to prevent soil pollution." How are these harmful for soil? Ans: Polythene bags and plastics pollute the soil. They also kill the organisms living in the soil. 5. State how can the effect of waste products, chemicals and pesticides on soil be minimised. Ans: Waste products and chemicals should be treated before they are released into the soil. The use of pesticides should be minimized. 6. Which of the following situations A or B is advantageous for absorption of water and minerals? Why? Situation A : Growth and branching of roots in the C-horizon. Situation B : Growth and branching of roots in A and B-horizons. 2
[NCERT Exemplar Problems] Ans: Situation B is advantageous to plants because A- and B- horizons are rich in water, minerals and humus. 7. Explain how soil is formed.[ncert] Ans: Soil is formed through the process of weathering. Weathering is a process of physical breakdown and chemical decomposition of rocks and minerals near or at the surface of the earth. This physical and chemical decomposition is primarily done by wind, water, and climate. As a result of these processes, large rock pieces are converted into smaller pieces and eventually to soil. 8. Is it a good practice to remove grass and small plants that are growing in an open, unused field? Give reason to support your answer. [NCERT Exemplar Problems] Ans: No, it is not a good practice. Plants cover the soil surface and their roots bind the soil particles and hold them in place. During strong winds and rains they prevent soil erosion and thereby protect the top soil. 9. Compare sandy soil, loamy soil and clayey soil on the basis of their particle size. Ans: Sandy Soil Clayey Soil Loamy Soil Sand particle size are big. Clay particle size are very small. Particle size are intermediate between the two. They are coarse in touch. They are smooth and sticky. They are partially gritty and smooth. 10. How is clayey soil useful for crops?[ncert] Ans: Clayey soil is rich in humus and are very fertile, so it is suitable for growing cereals like wheat and gram. Such soil is good at retaining water. For paddy, soils rich in clay and organic matter and 3
having a good capacity to retain water are ideal. For lentils (masoor) and other pulses, loamy soils, which drain water easily, are required. 11. List the differences between clayey soil and sandy soil.[ncert] Ans: Clayey Soil Sandy Soil Ratio of fine particles is higher. Ratio of large particles is higher. Soil retains water and becomes Loose particles, air permeate through the sticky and wet. soil. Difficult to plough when wet. Dries up easily. Cannot retain water. It is heavy and has little space for air. It is light and well aerated. Suitable for crops like paddy, Suitable for vegetables, peanuts and wheat and gram. cotton cultivation. 12. What is alluvial soil? Where does it come from? Ans: Alluvial soil is the black soil which is brought down from mountains by HimaIayan was to the Northern Plains and is rich in sand, silt, clay and gravel. It is very fertile. 13. List the features of loamy soil that make it the best topsoil for plant growth. Ans: Loamy soil is a mixture of sand, clay and silt. It has the right water holding capacity for growth of plants. It is rich in humus and hence fertile. 14. A man digging a pit found that he could dig with ease initially but digging became difficult as he went deeper. He could not dig beyond a depth of 5 feet. Provide a suitable scientific explanation.[ncert Exemplar Problems] Ans: The soil surface has loose top soil which is easier to dig. At deeper layers, partially weathered rocks or bedrocks are present, which are hard making digging difficult. 15. Gardeners gently dig up the soil around the roots of garden herbs (plants) frequently. Give reasons.[ncert Exemplar Problems] Ans: (a) For enabling easy root growth; (b) For easier percolation of water; (c) For aerating the soil/enabling air to get into deeper layers of soil; (d) For removing the weeds. 16. How does water get disappeared on a kutcha road but not on a pucca road? Ans: Kutcha road has a soil cover through which water percolates into the ground. Pucca road is covered with cement through which water cannot percolate into the earth. 17. How is raw soil different from baked soil? How is the soil from which 'matkas' are made different from the soil used to make statues?[hots] Ans: The raw soil can be moulded into different shapes and is soft in texture. Baked soil is very hard 4
and cannot be moulded into any further form. Soil used to make matkas and surahis is clayey loam which has open pores through which some water percolates for cooling. Soil used to make statues has closely packed particles which give strength to the structure. 18. Distinguish between water percolation and water retention in soil. Is percolation the same as water absorption? Ans: The drainage of water through the soil into deeper layer is percolation. The retention of water above its surface is retention. In absorption of water, the water occupies space between soil particles. But in percolation, water passes down through different layers of soil. 19. What is soil erosion? List its causes. Ans: The removal of land surface by water, wind or ice is known as erosion. Plant roots firmly bind the soil. It is caused due to deforestation or overgrazing by animals. It is severe in areas of little or no vegetation, such as deserts or bare lands. 20. Explain how soil pollution and soil erosion could be prevented.[ncert] Ans: Prevention of Soil Pollution: Use manures instead of chemical fertilizers. Industrial waste should be treated before release. Avoid use of polythene and plastic or they should not get mixed in soil. Prevention of Soil Erosion: Afforestation: large scale planting in place of cut down forests. Avoiding over-grazing of grass lands. Use of step-farming in hill regions. 5