Natural Resources Question Answers: NCERT Class 9 Science

Earth’s atmosphere is different from those of Venus and Mars. The atmosphere of Earth contains a mixture of nitrogen (78.08%), oxygen (20.95%), and a small fraction of carbon dioxide (0.03%), water vapours and other gases. This makes the existence of life possible on Earth. On the other hand, the atmosphere on Venus and Mars mainly contains carbon dioxide, i.e, about 95-97%. It may be the reason that due to this, no life is known to exist in both Venus and Mars.

The atmosphere acts as a blanket by performing the following functions:

(a) Ozone absorbs harmful UV radiations coming from the Sun.

(b) Carbon-dioxide and water vapours trap the heat and regulate the temperature of the Earth by keeping it ambient by absorbing heat rays during the day and by reflecting the heat trapped during the daytime at night.

(c) It slows down the escape of heat from the surface of the Earth into outer space during night time.

Therefore, the atmosphere covers and protects the Earth like a blanket.

Wind is caused by a difference in atmospheric pressure. Around areas of low pressure, air rises upwards in the atmosphere as air rises upwards, more air moves in (sideways) to replace it. As a result, a region of low pressure is created. Then, air from a high pressure region moves to a low pressure region, causing wind.

Clouds are formed when air contains as much water vapour as it can hold. This is called the saturation point and it can be reached in two ways. First, moisture accumulates until it reaches the maximum amount the volume of air can hold. The other method reduces the temperature of the moisture filled air, which in turn lowers the amount of moisture it can contain. Saturation, therefore, is reached through evaporation and condensation, respectively. When the saturation occurs, moisture becomes visible water droplets in the form of fog and clouds.

The following three human activities would lead to air pollution:

(i) Burning of fossil fuels like coal and petroleum.

(ii) Emission of harmful gases and dust particles from vehicles .

(iii) Smoke released from industries containing harmful gases like sulphur dioxide, oxides of nitrogen.

Organisms need water for the following reasons:

(i) All cellular processes need water for their functioning.

(ii) Substances dissolve in water for reactions to take place within the place.

(ii) Since most of the substances are transported in a dissolved form, water is necessary.

(iv) It helps to maintain body temperature.

River is a major source of freshwater.

The discharge of wastewater from homes, dumping of industrial waste, global warming, acid rain and oil pollution in the water body, etc. into the river pollutes this fresh water source.

Soil is the uppermost layer of earth crust formed by weathering of rocks. It is the mixture of living or non-living material. Soil formation is a bidirectional process, i.e from the upper side by decomposition (depends on sunlight, temperature, moisture, water) of detritus and from the lower side by breakdown of large rocks.

The blowing away or washing away of land surface by wind or water is known as soil erosion.

The methods of preventing or reducing soil erosion are:

(i) Afforestation or planting of trees.

(ii) Growth of vegetation.

During the water cycle, water is found in three different states such as solid state (snow, ice), liquid state (rain, ground water), and gaseous state (water vapour).

Two biologically important compounds that contain both oxygen and nitrogen are:

(i) Proteins.

(ii) Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).

The following three human activities would lead to air pollution:

(i) Burning of fossil fuels like coal and petroleum.

(ii) Emission of harmful gases and dust particles from vehicles.

(iii) Smoke released from industries containing harmful gases like sulphur dioxide, oxides of nitrogen.

The greenhouse effect is the way in which heat is trapped close to the surface of the Earth by “greenhouse gases”. These heat - trapping gases can be thought of as a blanket wrapped around the Earth, which keeps it tastier than it without them. Greenhouse gases include carbon dioxide, methane and nitrous oxides. An increase in the content of such gases would lead to a situation of global warming.

The two forms of oxygen found in the atmosphere are:

(i) Diatomic molecular form with chemical formula O₂.

(ii) Triatomic molecular form with chemical formula O₃ known as ozone.

The atmosphere is essential for life because it is the mixture of gases forming a blanket surrounding the Earth. It maintains an appropriate climate for the sustenance of life by carrying out the following activities :

(i) Atmosphere consists of oxygen. Oxygen is required by living organisms for its survival.

(ii) Atmosphere filters out the harmful ultraviolet rays of the Sun.

(iii) Atmosphere also slows down the escape of heat from the surface of the Earth into outer space during night time.

No living being on Earth can survive without water. Water is essential for life because of the following reasons:

(i) Water is a prerequisite for human health and well being as well as for the preservation of the environment.

(ii) Water is also necessary for agriculture and for many industrial processes.

Almost all living organisms are directly or indirectly dependent on soil. Plants obtain water, minerals from the soil and prepare food for animals.

On the other hand, other organisms that live in water are not totally independent of soil because the microbes growing on the soil in water are the primary producers which start the food chain and even microbes that live in the soil help in the decomposition of dead plants and animals in water to return the nutrients back to the water.

A daily weather forecast is the work of people working for the weather department to collect data on the elements of weather such as maximum and minimum temperatures, maximum and minimum humidity, rainfall, wind speed, etc. Weather satellites are present to take photographs of clouds from space. The maximum and minimum temperature of a day is measured by a thermometer known as the maximum−minimum thermometer. Rainfall is measured by an instrument known as the rain gauge. Wind speed is measured by anemometers. There are various instruments used to measure humidity.

Yes. Isolating human activities to specific areas would help in reducing levels of pollution.

For example ;

(i) Having heavy industries outside the main city will control pollution to some extent.

(ii) The pollution caused by these industries will not contaminate water resources, agriculture land, fertile land, etc.

Forests influence the quality of our air, soil, and water resources in various ways.

Some of them are:

(i) Adds nutrients to the soil due to the lot of vegetation present in the forest getting decomposed . Water : Forest helps in bringing rain and increasing the level of water in the underground and water bodies.

(ii) Forests prevent soil erosion. Roots of plants bind the soil tightly in a way that the surface of the soil cannot be eroded away by wind, water, etc.

(iii) Forests maintain the oxygen level in the atmosphere and also reduce the carbon dioxide level. Forests maintain the temperature of the environment.