Class 7 Science Chapter 9 MCQ

Weathering is the breaking down of huge pieces of rocks into smaller pieces by the action of natural forces such as water, glaciers, wind and roots of plants.

Soil is one of the most important natural resources. Soil supports for growth of plants and trees by holding their roots firmly and by supplying them with water and nutrients. Hence, soil is used to grow all types of plants not only for cotton plants.

The microorganisms present in the soil having plenty of water and nutrients are present in the habitat of forest.

Availability of water and minerals in the soil for maximum absorption by roots is in A- horizon. A- horizon is called the topsoil and this layer is generally soft, porous and can retain more water.

Here, all the statements are correct. Hence, your answer will be option [D].

The sub-soil contains very little living organisms. The roots of some of the trees are, however, able to reach to the sub-soil. The sub-soil has very little humus or decayed organic matter. Due to this, sub-soil is much less fertile as compared to the top-soil. Sub-soil is however, rich in soluble minerals.

Here, Volume of water percolated = 200 mL And, Time taken for percolation = 40 min Now, we know the formula = Percolation rate = Volume of water percolated/ time taken for percolation Percolation rate = 200 ml / 40 min = 5 ml / min

Soil conservation measures mainly aim at protecting top soil, which is rich in humus and nutrients making it fertile to grow plants.

Here, all the situations are correct told by Boojho where Paheli can see the soil profile. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Sandy soil has large particles with large spaces between them a disadvantage of sandy soil is that it cannot hold much water in it because the water gets the drained out quickly through large spaces between its particles so sandy soil dries out quickly which is not good for plants

In this case, Original mass of soil = 200 g Mass of dried soil = 170 g Mass of water in soil = 200 – 170 = 30 g As, we know that = Percentage of water in soil = Mass of water in soil / Original mass of soil x 100 = 30 g / 200 g x 100 = 30 / 2 = 15 %

The soil with a low percolation rate of water would be the most suitable for growing paddy or rice crop.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Soil erosion can be prevented by afforestation, large scale growing of forest trees in place of cut down trees.

The process by which huge rocks are broken down into small particles by the action of sun’s heat, wind, rain and flowing water, etc., is called Weathering. It is called weathering because the rocks are worn away to form small particles by long exposure to these elements of weather. Although weathering of rocks is a very slow process. It takes thousands of years to weather huge rocks or break down huge rocks into fine particles to make soil.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Deserts are made up of sand, thus when the rain water falls on land, it percolates immediately downwards in the spaces between sand particles. So, the streams of water in desert region are not visible even during rainy season.

Soil erosion is caused mainly by the large scale of cutting down of forest trees and other plants which is called deforestation. Tree plantation means planting trees and plants at a large scale. The purpose of planting trees is to save the endangered environment. Silviculture is the branch of forestry concerned with the theory and practice of controlling forest establishment, composition, and growth.

Clay soil and loamy soil are both suitable for growing cereals like wheat and gram. Soil rich in clay and organic matter and having good capacity to retain water is ideal for growing paddy or rice crop.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Option A is correct with reference to soil while weathering is a slow process of soil formation and loamy soil consists of sand, clay and silt along with humus.