Class 7 Science Chapter 9 MCQ

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

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

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

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.

Loamy soil is a mixture of sand, clay, silt and humus in the right proportion. Loamy soil is the most fertile soil. Clayey soil is compact and sticky due to which the ploughing of clayey soil is quite difficult. Clayey soil is, however, rich in minerals which is good for the growth of plants. Clayey soil is more fertile than sandy soil not more fertile than sandy soil.

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

The largest size rock particles present in the soil are called gravel. Gravel is a kind of tiny stones. The amount of gravel present in a good top-soil is very small. The soil is mainly made up of different sized rock particles and humus. On the basis of their sizes, the rock particles present in soil can be divided into four groups: Clay, Silt, Sand and Gravel.

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

The smallest rock particles present in the soil form clay. The largest size rock particles present in the soil are called gravel. Gravel is a kind of tiny stones. The amount of gravel present in a good top-soil is very small.

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 %

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

The soil carried away from land by the flowing rain water gradually deposits on river beds. So, when it rains heavily, the river cannot take away all the rain water quickly. Due to this, river water overflows from its banks and cause severe floods by submerging surrounding areas. These floods cause damage to life and property.

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].

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.

A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable. Such as card board, paper, leaves, wood, jute bag etc. A material which is not easily decomposed by natural processes is termed as non-biodegradable. Such as plastic, synthetic materials etc.

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.

Remember, it is not a good practice to remove grass and small plants growing in an open, unused field because the plants cover the soil surface. Their roots bind the soil particles, holding and adhering them in place.

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.