GSEB Solutions for Class 9 Science and Technology – Our Natural Resources (English Medium)
GSEB SolutionsMathsScience
Exercise 72:
Solution 1.1:
B. O3
Ozone is a molecule that contains three atoms of oxygen. A layer of ozone present in the atmosphere protects the Earth from harmful effects of UV radiations.
Solution 1.2:
C. Denitrification
Denitrification is the reverse of nitrification and brought about by some microorganisms. It helps in circulation of nitrogen in the nitrogen cycle.
Solution 1.3:
A. Land faster than the water resources
Land always gets heated faster than water. As a result, air over land also heats up faster as compared to air over water resources. This creates a pressure difference and thus, winds are produced.
Solution 1.4:
B. Global warming
Due to green house effect, the heat is prevented from escaping out of the atmosphere. This results in overall heating of the earth and thus, global warming.
Solution 1.5:
C. Carbon dioxide
Carbon dioxide absorbs infrared radiations and prevents them from reflecting back. This results in keeping the earth warm and thus, results into global warming.
Solution 1.6:
B. Stratosphere
Ozone layer is located in the lower regions of the stratosphere about 23-35 kms above the surface of the earth.
Solution 1.7:
A. Temperature
The difference in temperature and pressure between the two places causes movement of air thus producing winds.
Solution 2.1:
Carbon dioxide and other gases in atmosphere absorb the infrared rays and reflect them back to the earth. This keeps earth and its surrounding atmosphere warm. This effect that occurs when escape of the heat from the atmosphere is prevented is called greenhouse effect.
Solution 2.2:
Atmospheric gas is the source of oxygen.
Solution 2.3:
Essential mineral elements are
- Carbon
- Hydrogen
- Nitrogen
- Oxygen
- Phosphorous
- Calcium
- Sulphur
- Magnesium
- Iron
- Manganese
- Zinc
- Boron
- Copper
- Molybdenum
- Aluminium
- Sodium
- Silicon
- Chlorine and
- Cobalt
Solution 2.4:
Chemical substances responsible for depletion of ozone layer are
- Chlorofluoro carbon
- Carbon Tetrachloride
- Methyl Chloroform
- Methyl bromide
Solution 2.5:
The greenhouse gases are:
- Carbon dioxide
- Methane
- Nitrous oxide
- Hydrofluorocarbon
- Chlorofluorocarbon
Solution 2.6:
The process of fixing atmospheric nitrogen to ammonium, nitrates and nitrites by soil microorganisms is called as nitrification.
Solution 2.7:
The process of fixing atmospheric nitrogen to ammonia by soil microorganisms is called ammonification.
Solution 2.8:
The four spheres of environment are
- Atmosphere
- Hydrosphere
- Lithosphere
- Biosphere
Solution 2.9:
Air is a layer of gases that surrounds the earth. It comprises of 78% nitrogen, 21% oxygen, 0.03% carbon and small amounts of helium, argon, hydrogen and other gases.
Oxygen present in the air is a vital requirement for most of the living organisms. It is required for respiration and combustion.
Carbon dioxide is essential for photosynthesis.
Nitrogen present in the air is fixed by many organisms and is used for making amino acids and proteins.
Air is also important for flying animals and dispersal of pollen, spores, seeds and fruits.
Solution 2.10:
Rhizobium is present in root nodules of legumes.
Exercise 72:
Solution 3.1:
Water is essential for life because
- Water plays an important role in controlling climatic conditions by keeping the atmosphere cool or warm.
- It is an important medium for chemical reactions in a cell.
- It is a universal solvent, and hence, an important medium for transport of nutrients and waste materials from one part of the body to another.
Solution 3.2:
The cycling of nutrients from the environment to organisms and from the organisms back to the environment is called biogeochemical cycle.
Three biogeochemical cycles that occur in nature are
- Oxygen cycle
- Nitrogen cycle
- Carbon cycle
Solution 3.3:
Natural resources are classified as follows:
Solution 3.4:
Wind is formed by movement of air caused by temperature or pressure differences. A pressure gradient exists when there are differences in pressure between two places. As a result of pressure gradient, air moves form high-pressure region to low pressure region.
example –
In coastal regions, during the day, the air above the land gets heated up and starts rising. As the air rises, a region of low pressure is created above the land and the air from above the sea moves into this area of low pressure above the land.
This movement of air from one region to another creates wind. The direction of wind during the day is from sea to land.
During night, both land and sea cool down. However, land cools faster than water. So, the air above the land also cools faster than the air above the sea and the air above the sea will be warmer as compared to the air above the land. Thus, the air above the sea rises and the cooler air from above the land moves above the sea. Thus, during night, the direction of the wind is from land to sea.
Solution 3.5:
Oxygen supports life of most of the life forms on the Earth. It is present on the Earth in the form of atmospheric gases and in the Earth’s crust, in combined form as oxides.
Oxygen cycle is a complex cycle.
Oxygen from the atmosphere is used up for combustion, respiration and in formation of oxides.
The oxygen is then returned back to the atmosphere by photosynthesis.
Oxygen also circulates in the atmosphere freely in the form of carbon dioxide. It also exists in combined forms with nitrogen and with metals.
Solution 3.6:
Earth is enveloped by a layer of atmosphere. Sunlight passes this atmosphere and reaches the Earth. As a result of this, earth gets heated up. Also, the sun rays reflect back from the surface of the earth and pass through the atmosphere to get dissipated into space.
However, due to the presence of carbon dioxide and other gases in the atmosphere, the infrared rays get absorbed in the atmosphere and get reflected back to the earth. This keeps earth and its surrounding atmosphere warm. This effect that occurs when heat is prevented to escape from the atmosphere is called greenhouse effect.
Solution 3.7:
Atmosphere plays an important role in controlling the climate of its surrounding environment.
Air is a bad conductor of heat. It thus helps to maintain an average temperature during the day and prevents a sudden rise in the temperature.
Also, during the night hours, it prevents the escape of all the heat from the atmosphere into outer space.
It thus helps to maintain steady temperature during the day as well as at night.
Solution 3.8:
Rain is a form of water that helps the circulation of water in the form of hydrological cycle.
Heat from the sun evaporates water from the ocean and other water bodies and forms water vapour.
Due to solar heat, air also gets heated up. The hot air along with water vapour rises up in the atmosphere.
As the air rises, it expands and cools. The water vapour present in the air also condenses forming tiny water droplets.
These droplets grow in size due to more and more condensation of water.
As these water droplets become heavy, they fall down in the form of rain.
This circulation of water from land to air and back to land is called as hydrological cycle or water cycle.
Solution 3.9:
Rain is a form of water that helps the circulation of water in the form of hydrological cycle.
Heat from the sun evaporates water from the ocean and other water bodies and forms water vapour.
Due to solar heat, air also gets heated up. The hot air along with water vapour rises up in the atmosphere.
As the air rises, it expands and cools. The water vapour present in the air also condenses forming tiny water droplets.
These droplets grow in size due to more and more condensation of water.
As these water droplets become heavy, they fall down in the form of rain.
This circulation of water from land to air and back to land is called as hydrological cycle or water cycle.