JK Academy Std 7 Science Chapter 3 Properties of Natural Resources Solution
EXERCISE
1. Fill in the blanks with the appropriate term.
(a) The capacity of air to hold moisture depends upon the temperature of the air.
b) Water does not have a shape but has definite mass and volume.
(c) While freezing the tempertaure of water is lowered.
(d) Neutral soil has pH 7.
2. Why is it said that –
(a) Air is a homogeneous mixture of various gases.
ANS: 1. Air is a homogenous mixture of the gaseous substances nitrogen, oxygen and smaller amounts of other substances.
2. Salt, sugar and many other substances dissolve in water to form the homogeneous mixture.
(b) Water is a universal solvent.
ANS: 1. Water is a universal solvent because it is capable of dissolving more substances than any other liquid.
(c) There is no alternative to water for cleaning purposes.
ANS: 1. Because it dissolves everything that is added in it.
2. Water is useful for cleaning purposes such as for bathing, washing clothes.
3. What will happen if…..
(a) The amount of water vapor in the air increases.
ANS: 1. As the amount of water vapor increases the level of humidity also increases.
2. Higher the level of humidity results in excessive sweating and this sweat does not dry quickly and leaves the body sticky and feeling hot.
(b) Only one crop is grown repeatedly in the soil.
ANS: 1. If only one crop is grown repeatedly in the soil, it looses its fertility and gets devoid of nutrients.
4. With whom should I pair up?
| Group ‘A’ | Group ‘B |
| (1) Air | (a) Excretion |
| (2) Water | b) Scattering of light |
| (3) Soil | (c) Plasticity |
ANS: 1- B 2-A 3-C
5. State whether the following statements are true or false.
(a) Sandy soil has low capacity for holding water.
ANS: True
(b) The substance in which a solute dissolves is called a solvent.
ANS: True
(c) The pressure exerted by air is called atmospheric pressure.
ANS: True
6. Explain the picture in your own words.
ANS: In Picture (a) water is filled in the crack of a rock.
In Picture (b) water has frozen and expanded which has resulted in the width of the crack also increasing. This is because water expands when it is frozen.
7. Write answers to the following questions in your own words.
(a) How is light scattered by the air?
ANS: Air is a mixture of very fine particles of some gases, dust, smoke and moisture. When rays of light fall on these minute particles, the particles spread the light in all the directions. This natural phenomenon is called scattering of light.
(b) Explain the various properties of water.
ANS: 1. Water is useful for water transport due to its fluidity.
2. Water is a good coolant and is used in motor vehicles to control the temperature of the engine.
3. Water is useful for cleaning purposes such as for bathing, washing clothes.
c) Why is the density of seawater more than that of rainwater ?
ANS: Sea water has more density than rain water because it contains salt ions. These salt ions make the seawater heavier, which means the mass of the water increases due to the presence of salt ions.
d) What is the importance of good soil structure?
ANS: The fertility of soil depends upon soil structure. The advantages of good soil structure are as follows:
1. Roots get a sufficient supply of oxygen.
2. Water drainage is good. Therefore, the roots of plants grow well.
(e) What are the various uses of soil?
ANS: 1. Plant conservation: To help plants grow.
2. Water conservation: Soil holds water. As a result, by means of bunds and lakes, we can get water for use throughout the year.
3. Plasticity: Soil can be given any required shape. This property of soil is called plasticity. Because of its plasticity, we can use it to make articles of a variety of shapes. These articles can be baked to make them hard. Water storage earthen pots, earthen lamps, idols, bricks, etc. are articles made from soil.
(f) What is the need and importance of soil testing from the point of view of farmers?
ANS: The proportions of the various ingredients of soil can be determined by ‘soil testing’. During soil testing, the soil is examined for colour, texture and the proportion of organic matter in it. Soil is tested to find out if there is a deficiency of any ingredients.
(h) Why should a glass bottle completely filled with water never be kept in a freezer?
ANS: Remember that when glass bottle with water is kept in a freezer, the water inside the bottle expands due to lowering of the temperature.
Let’s recall.
1. Which are the gases present in air? Why is air called a homogeneous mixture?
Ans: 1. Air is a homogenous mixture of the gaseous substances nitrogen, oxygen and smaller amounts of other substances.
2. Salt, sugar and many other substances dissolve in water to form the homogeneous mixture.
2. What are the uses of the various gases in air?
ANS: 1. Heating and cooling. In the commercial and residential sectors, gas is mainly used for space heating and cooling, water heating, and cooking.
2. Power generation. Power plants can use gas to generate electricity.
Find out.
1. Is there any atmospheric pressure on the moon?
Ans: No, there is no atmosphere on the moon. As thers is a very thin layer of gases on the lunar surface that can be called atmosphere.
Use your brain power!
1. What is the effect of increased temperature on the pressure of air?
ANS: When the temperature increases, the molecules present in the air becomes more active and collides with each other.
So, with the increase in temperature air pressure also increases.
2. What would happen if all the air surrounding us is removed?
ANS: If air surrounding will be removed, we will be no longer be able to survive. Organisms that need air would be die, plants and animals would be die.
2. Will sound be heard in space?
ANS: As there is no air in the space no sound can be heard in the space. Sound travels through the vibration of atoms and molecules in a medium.
3. In cold countries, how do aquatic animals remain alive even after the rivers or lakes freeze in winter?
ANS: In winter, a layer of ice is formed on the surface of lakes when the atmospheric temperature falls below 0o C.
Hence, In cold countries aquatic animals remain alive even after the rivers or lakes freeze in winter.
4. Why is it difficult to plough clay soil?
ANS: As calcium is not leached and the soil becomes acidic.
Heavy rains can saturate this soil so much that the crop may die from lack of oxygen.
Hence, it is difficult to plough clay soil.
5. Why is it easy to plough sandy soil?
ANS: Sand soil has larger particles with lot of gap in between the blades of plough easily pass.
Hence, it is easy to plough sandy soil.
6. What is the water holding capacity of silt soil?
ANS: The particles of silt soil are of medium size. Silt soil is not as ploughable as sandy soil. This soil contains a large proportion of organic materials. Its capacity to supply nutrients is much greater. Silt soil is also called sedimentary soil.
7. Which soil is suitable for cultivation? Why?
Ans: Alluvial soil is most preferable for cultivation. Because it was so fertile.
EXTRA QUESTION
- Air is a mixture of gases.
- Air like all other matter, it has mass and weight.
- The molecules of the gases in the air are in constant motion. When these molecules strike a body, they create pressure on that body. This is the pressure of air that we call ‘atmospheric pressure’.
- Atmospheric pressure is the same in all the directions.
- Under ordinary conditions, atmospheric pressure at sea level is about 1,01,400 Newtons per square metre.
- Atmospheric pressure can be measured with the help of a barometer.
- When rays of light fall on these minute particles, the particles spread the light in all the directions. This natural phenomenon is called scattering of light.
- Air is useful as a medium for the transmission of sound.
- In winter, the density of the air increases.
- Mass is measured in grams and volume in cubic centimetres.
- Water expands when the temperature falls below 40 C. This is called the anomalous behaviour of water.
- Water is a universal solvent.
- The substance in which the solute dissolves is called Solvent.
- Colour is an important property of soil.
- The colours of soil are useful for its classification.
- Soil contains particles of different sizes
- Silt soil is also called sedimentary soil.
- Silt soil is not as ploughable as sandy soil.
- Clay soil has a high water holding capacity.
- In soil, the proportion of small particles is maximum.
- The structure of soil depends upon the different shapes of the particles in it.
- The fertility of soil depends upon soil structure.
- Plant conservation to help plants grow.
- The proportions of the various ingredients of soil can be determined by ‘soil testing’.
- Roots get a sufficient supply of oxygen.
- Shadu soil it is whitish in colour.
- Multani soil this soil is used in cosmetics.
- Terracotta soil is red in colour.
- China clay is an industrial mineral of the type ‘Kaolinite’.
- Soil pH less than 6 or higher than 8.