NCERT Solutions for Class 9 Science Chapter 14

Atmosphere maintains temperature of the earth suitable for the living organisms during day time and whole life. It prevents sudden increase in temperature during day time as well as night. Life does not exist on other planets due to absence of the atmosphere.

Role of Sun: Sun heats up rocks during the day time by which they expands. During night, rocks cool down and contract. Since all the parts of rocks do not expand and contract at the same rate, this results in the formation of cracks and ultimately the huge rock breaks up into smaller pieces.
Dust as a pollutant:
(i) It suspends in air which can cause allergy and respiratory problems.
(ii) It covers stomata of plants and affects exchange of gases and retards plant growth.
(iii) It can causes irritation in eyes.
(iv) It can act as a carrier of vapours of lead and other heavier metals which are toxic.

Uneven heating of air over land and water bodies causes wind.

(a) When water bodies are heated during day time, a large amount of water evaporates and goes into air.
(b) The hot air rises up carrying water vapours with it.
(c) As air rises, it expands and cools.
(d) This cooling causes the water vapour in the air to condense in the form of tiny droplets and form clouds.

(i) Water in needed for all cellular activities.
(ii) Transportation of nutrients takes place with the help of water.
(iii) Plants require water for photosynthesis.
(iv) Our body contains 70% of water which maintains body temperature.

Rivers passes through land and rocks which contains minerals. The minerals get dissolved in water. Minerals are carried by the river to sea water.

Lichens and moss grow on rocks. They release substances (chemical) which breakdown the stones into fine particles resulting in the formation of soil. The mode of action is chemical.

The atmosphere is essential for life because it maintains an appropriate climate for the sustenance of life by carrying out the following activities: (i) Atmosphere keeps the average temperature of the Earth fairly constant during day time. (ii) It prevents a sudden increase in temperature during day time. (iii) It also slows down the escape of heat from the surface of the Earth into outer space during nighttime.

Water is essential for life because of the following reasons: (i) Most biological reactions occur when substances are dissolved in water. Thus, all cellular processes need water as a medium to take place. (ii) Transportation of biological substances needs water as a medium.

Almost all living organisms are dependent on soil. Some depend directly, while some depend indirectly. Plants need soil for getting support as well as nutrients to prepare their food. On the other hand, organisms depend on plants for food and other substances that are essential for life. Herbivores depend directly upon plants, and carnivores depend upon animals, which in turn depend upon plants for food. This makes them depend on soil indirectly. Organisms that live in water are not totally independent of soil as a resource. These organisms depend on aquatic plants for food and other substances. These aquatic plants in turn require minerals for their sustenance. These minerals are carried to water bodies from soil by rivers, rain water, etc. Without the supply of minerals from the soil to the water bodies, it is impossible to imagine aquatic life.

The meteorological department of the government collects data on the elements of weather such as maximum and minimum temperatures, maximum and minimum humidity, rainfall, wind speed, etc. They are able to study these elements using various instruments. The maximum and minimum temperature of a day is measured by a thermometer known as the maximum−minimum thermometer. Rain fall is measured by an instrument known as the rain gauge. Wind speed is measured by anemometers. There are various instruments used to measure humidity.