3 SOIL I. Multiple choice questions: Tick ( ) the correct choice. 1. The process of soil formation is called (a) conservation (b) weathering (c) erosion (d) none Ans. (b) 2. Soil profile consists of (a) two layers (b) three layers (c) four layers (d) five layers Ans. (b) 3. Parent rock material is present in (a) A-horizon (b) B-horizon (c) C-horizon (d) bedrock 4. Humus is present in (a) A-horizon (b) B-horizon (c) C-horizon (d) bedrock 5. Soils best suited for plant growth are (a) loamy (b) clayey (c) sandy (d) none 6. A vertical section of the soil from the surface to the bedrock is called (a) soil erosion (b) soil profile (c) parent rock (d) A-horizon Ans. (b) 7. The soft, porous layer with a good water-retaining capacity forms the (a) A-horizon (b) B-horizon (c) C-horizon (d) bedrock 8. The layer with lumps of parent rock material is the (a) A-horizon (b) B-horizon (c) C-horizon (d) bedrock Biology Class VI 1 Question Bank
II. 9. The largest-sized particles in soil are of (a) clay (b) humus (c) sand (d) gravel Ans. (d) 10. The soil with the best water-retaining capacity is (a) clayey (b) sandy (c) loamy (d) none 11. Red colour of the soil is due to the presence of (a) iodine (b) oxygen (c) iron oxide (d) coal 12. Laterite soil is rich in (a) iron (b) oxygen (c) nutrients (d) magnesium 13. The study of soil is called (a) biology (b) geology (c) pedology (d) zoology 14. Humus and the smallest particles of rock form the (a) A-horizon (b) C-horizon (c) B-horizon (d) bedrock Fill in the blanks. 1. Clay particles range in size from... mm to... mm. 2. Humus is present in... horizon of the soil profife. 3. A-horizon is also known as.... 4. Bedrock is found below the... horizon. 5. Planting of trees is called.... 6. Red colour of soil is due to.... 7. Humus content is the highest in... soil. 8. The vertical section of the soil from the surface, down to the bedrock showing different horizons is called.... 9. The most fertile layer of the soil is.... 10.... soil has very good water-retaining capacity. 11.... soil is taken away from the parent rock by river water. 12. Desert soil lacks in... due to thin vegetation. Biology Class VI 2 Question Bank
13. Breaking down of huge pieces of rocks into fine particles by the action of water and changing temperature is called.... 14. Depletion of topsoil by rain or wind is called.... 15. The cutting down of trees on a large scale is known as.... Ans. 1. 0.005, 0.0005 2. A 3. Top soil 4. C 5. Afforestation 6. Iron oxide 7. Top 8. Soil profile 9. A-horizon 10. Clayey 11. Weathered 12. Humus 13. Weathering 14. Soil erosion 15. Deforestation III. Write true or false in front of the statements given below: 1. A fertile soil is rich in humus. 2. Sandy soils are best suited for plant growth. 3. A clayey soil has more proportion of fine particles. 4. Capillary water is the water available to the plants for absorption. 5. Dark-coloured soils are rich in organic matter. 6. Proper drainage in a field helps to prevent soil erosion. 7. Crop rotation enriches soil fertility. 8. Overgrazing is a means of soil conservation. 9. Soil is a non-renewable resource. 10. Soil has both living and non-living components. 11. Humus is formed by the decay of dead plants and animal matter. 12. The most fertile part of the soil is the C-horizon. 13. The water-retaining capacity of soil depends on the colour of the soil. 14. Pore spaces of clayey soil are large and hence the water movement is slow. 15. Soil is mainly formed from sedimentary rocks. 16. Mountain soil is rich in humus. 17. Soil formation takes place by weathering of rocks. 18. Roots of the plants help in controlling floods. Biology Class VI 3 Question Bank
19. Desert soil cann t hold much water. 20. Loss of fertile soil is called deforestation. Ans. 1. True 2. False 3. True 4. True 5. True 6. True 7. True 8. False 9. False 10. True 11. True 12. False 13. False 14. False 15. True 16. True 17. True 18. True 19. True 20. False IV. Choose the odd one out: 1. Top soil, Subsoil, Parent rock, Bedrock. 2. Erosion, Deforestation, Overgrazing, Afforestation. 3. Gravel, Sand, Silt, Laterite. 4. Alluvial soil, Black soil, Mountain soil, Top soil. 5. A-horizon, B-horizon, C-horizon, X-horizon. Ans. 1. Top soil 2. Afforestation 3. Laterite 4. Black soil 5. X-horizon V. Define the following: 1. Soil Ans. Soil. Soil is one of the main components of this life sustaining environment. Where living organisms live. It has been formed from rock material over millions of years. It is the uppermost layer of earth s crust, in which plants grow. 2. Weathering Ans. Weathering. The process by which soil formation takes place is called weathering. It is a very slow process and takes millions of years. 3. Soil erosion Ans. Soil erosion. It is the removal of top fertile layer of the soil. It occurs by some physical agents like running water, wind etc. Now-a-days the main cause of soil erosion is deforestation because to meet the demand of population, we are cutting forests are cut down to increase the land available for cultivation and other uses. 4. Loam Ans. Loam. Loamy soil is the best soil for plant growth as it contains a lot of humus. It is the soil with an almost equal proportion of sand and clay. Biology Class VI 4 Question Bank
5. Humus Ans. Humus. Humus is the non-living organic matter. It is formed from the dead plants and animals by the activity of microorganisms. Fertility of soil is depend upon the amount of humus. More the humus, more the fertility of soil. VI. Answer the following questions: 1. Which soil horizon is rich in humus? Ans. The uppermost layer is called the A-Horizon. It is rich in humus. 2. Which type of soil is best suited for growth of plants? Give reasons in support of your answer. Ans. Loamy soils are the best for plant growth due to following regions: (i) It has good quantity of humus that provide fertility to the soil. (ii) Due to presence of smaller particles, it holds good amount of water. (iii) It has proper aeration due to presence of some large particles. These are the factors that make it best for proper growth of plants. 3. How is soil formed? Describe in brief. Ans. Soil is formed by rocks. Rocks breakdown by a process called weathering. These weathered particles are the source of inorganic material that mixed up with humus. Soil formation is very slow process. 4. Name the different types of particles present in soil. Ans. There are four types of particles present in the soil: Types of particle Diameter Gravel Above 2.0 mm Sand 0.05 to 2 mm Silt 0.005 to 0.05 mm Clay Below 0.005 mm Biology Class VI 5 Question Bank
5. Describe the composition of soil. Ans. Formation of soil is a very slow process. It takes thousands of years. During this period several physical and chemical agents play an important role. Soil is composed of living and nonliving components. These components are: (i) Different soil particles (ii) Humus (iii) Soil water with some inorganic salts (iv) Soil air (v) Soil organisms (Bacteria, fungi). 6. Mention the characteristics of mountainous soil and black soil. Ans. Mountainous soil. (i) It is found in depressions and valley basins. (ii) It contains maximum amount of humus. Thus, it is very fertile. (iii) It consists of sand stones, clay, shales and limestones. Black soil. (i) Black soil is rich in iron, magnesium and calcium derived from basaltic rocks. (ii) Soil is clayey that has good water-retention capacity. (iii) It contains dead organic matter and good for cotton and sugarcane production. 7. Distinguish between sandy, clayey and loamy soils. Ans. Sandy soil Clayey soil Loamy soil (1) It contains particles (1) It contain particles (1) It contains particles 0.05 to 2.0 mm below 0.005 mm of various diameter. diameter diameter (2) It is highly porous. (2) It has little air in (2) It contains some air in between the between the particles particles. due to presence of some large particles. Biology Class VI 6 Question Bank
Sandy soil Clayey soil Loamy soil (3) It does not hold (3) It holds enough (3) It also contains much water. water. sufficient water due to presence of smaller particles. (4) It is not suitable (4) It has some ability (4) It has good power for for plant growth. for plant growth. plant growth. 8. Distinguish between residual and transported soils. Ans. Residual soil Transported soil (1) In residual soil, whole (1) In transporated soil process of soil formation weathering occurs at one takes place at the same place and development place. occurs at another place. (2) Residual soil is the product (2) The characteristics of of chemical weathering. transported soil are Thus, their characteristics dependent also on another are dependent upon environ- factors like humus. mental factors of climate. 9. How is soil important to us? Explain. Ans. Soil is important to us because a number of living things depend on it for their survival. Life on land depends on soil because terrestrial plants need it for minerals, water and support for their survival. On the other hand, land animals need it because they eat plants and other animals which eat plants. 10. Describe the factors which cause soil erosion. Ans. Soil erosion is the removal of top fertile soil. This is brought about by wind, water or rain. Thus, the fertility of soil is lost. Soil erosion is caused by: (i) Rain (ii) Wind (iii) Deforestation (iv) Overgrazing (v) Unscientific agricultural practices. Biology Class VI 7 Question Bank
11. How can soil erosion be prevented? Ans. Preventions of soil erosion: There are some factors by which we can control soil erosion. (i) Afforestation. We should maintain plantation in barren areas and the areas in which we have already cut plants. These plant s roots hold the soil in place. (ii) Crop rotation. To maintain the fertility of soil it is advisable to grow different crops. By this method, soil can also maintain water-holding capacity. (iii) Terrace forming. It should be practised in sloping areas to check soil erosion and to reduce the steepness of the slopes. (iv) There should be the boundries of the fields with trees, to reduce the effect of strong winds. (v) We should maintain proper drainage and irrigation arrangements. 12. Why is A-horizon considered to be the most fertile layer? Ans. A-horizon is considered to be the most fertile layer of soil profile, because it contains lots of humus which makes the soil fertile. It also contain some living organisms that also play an important role in soil fertility. 13. What is bedrock? Ans. It is the part below horizon-c. It contains unweathered parent rock and provide base to other three horizons. 14. Why is desert soil not good for the growth of plants? Ans. Desert soil is not good for the growth of plants because top fertile layer of soil is blown away by wind. The soil is dry, sandy, porous and contains minerals. It also lacks in humus due to thin vegetation. 15. Why do rocks crack when the water inside rock crevices freezes? Ans. When the water enters inside the crevices of rocks and freezes. As a resulty of freezing the volume of water increases which leads to cracking of rocks into smaller pieces. Biology Class VI 8 Question Bank
16. How is soil classified on the basis of the size of particles present in it? Ans. On the basis of the size of particles present in the soil, soil may be of following type: (i) Clayey soil: It has a large portion of clay particles and a little sand. It has good water-retaining capacity due to small pore spaces in between the particles. (ii) Sandy soil. It has a large portion of sand particles. It has low water-retaining capacity due to large pore spaces. (iii) Loamy soil. It is the soil with an almost equal proportion of sand and clay. It has good water-retaining capacity. 17. Give two uses of the soil. Ans. Uses of soil: (i) It provides minerals and water to the plants. (ii) It is the raw material for making bricks, pottery and porcelain. 18. Give two difference between heavy and light soil. Ans. Heavy Soil Light Soil (1) Soil in which clay particles (1) Soil in which large predominate and has crumb inorganic particles give its structure. sandy texture. (2) The crumb structure of a (2) Its water-holding properties clay soil can be improved and nitrogen content can by growing grass in it be improved by adding for a year. farmyard manure. 19. Name four minerals that are used for agricultural purposes. Ans. (i) Calcium, (ii) Potash, (iii) Phosphorus (iv) Sulphur 20. Name the soil rich in iron. Ans. Red soil 21. How does the planting of trees prevent soil erosion? Ans. We should be planted more and more plants because the roots of plants bind the soil. They also prevent flood. Hence planting more trees and not cutting them down helps to conserve soil. **** Biology Class VI 9 Question Bank