Notes of chapter: Natural Resources are presented below. Indepth notes along with worksheets and NCERT Solutions for Class 9.
(1)Natural resources –
Natural resources are resources which are available without human action.
Eg:- Land, Water and air.
(2)Parts of the Earth-
The earth has three parts. Name of these are –
The outer crust of the earth is known as lithosphere. It covers 21% of the Earth.
The water on the earth covers 75% of the Erath’s surface. It also found underground and is known as hydrosphere.
The air that covers the earth like a blanket is known as atmosphere.
The all three sphere makes life possible on Earth and called as biosphere.
(i) Air is breath of life.
(ii) It is mixture of many gasses such as oxygen, nitrogen carbon – di – oxide etc.
(iii) There are many activities on the Earth which needs oxygen and produces carbon – di – oxide.
(iv) Planets Venus and Mars have carbon – di oxide as a main constituent up to 95 – 97% of the atmosphere. Therefore, planets Venus and Mars have no life.
Reasons we released carbon – dioxide in atmosphere-
(i) We take oxygen and release carbon – di – oxide at the time of breathing.
(ii) Eukaryotic cells and prokaryotic cells need oxygen to break down glucose molecules and get energy for their activities. They released carbon – di – oxide.
(iii) In process of combustion, oxygen is needed in burning and carbon – di – oxide is produced.
But, carbon – di – oxide is found in atmosphere in very low percentage up to .04%. The reason for it are discussed below-
(i) Green plants convert carbon – dioxide into glucose in the presence of Sunlight,ie, the processes of photosynthesis.
(ii) Many marine animals use carbonates dissolved in sea – water to make their shells.
The role of the atmosphere in climate control-
Air is a bad conductor of the heat. Therefore, atmosphere prevents sudden increase in the temperature in day and escape of heat at nights.
There is no atmosphere on the moon. Therefore, the temperature ranges from -1900C to 1100C.
The movement of the air from high pressure to low pressure is called wind.
The wind can be gentle breeze, strong wind and terrible storm. These phenomena depend on the heating of air and formation of water vapours.
Water bodies and land heated up during the day by sun. Therefore, air above water bodies and land also heated up by radiation and rises up. The air above land gets heated faster and start rising and creates a low pressure area over land. The air above the sea which is cooler in comparison of air above lands moves into the area of low pressure. During the day movement of the wind is sea to land.
But in night, air above land and water bodies begins to cool. But water cools down slower than the land. Therefore, air above water bodies is warmer than the air above the land. So, air above land moves into the area of low pressure above water bodies. This time direction of the air if land to sea.
When water bodies are heated during the day, water evaporates. The air above water bodies also gets warm, which rises up with water vapours. Air rises up, it expands and cools there. This cooling causes the water vapours to condense in the form of tiny droplets. These droplets grow bigger because of condensation and fall down in the form of rain. When temperature of air is very low precipitation may occur in the form of snow or hail.
Pollution of air-
When oxides of nitrogen and sulphur increases in the air, the air is called polluted.
For detailed study go to link – Pollution of air
(i) Water covers 75% of earth’s surface.
(ii) Some water exists in the form of water vapours in the atmosphere.
(iii) Most of the water found in the sea and ocean and is saline.
Fresh water sources –
(i) frozen in the ice – caps at the two poles
(ii) snow covered mountain
(iii) underground water
(iv) water of lakes, rivers and ponds
Necessity of water-
(i) All the reactions that take place within our body and within the cells occur between substances that are dissolved in water.
(ii) Substances are transported in body in a dissolved form.
(iii) Organisms need water to stay alive.
When harmful substances like sewage , waste of factories etc mixed with water is called, water pollution.
For detailed study link- water pollution
Soil is an important resource that decides the diversity of life in an area.
Over long period of time, thousands and millions of years, the rocks at or near the surface broken down by various physical, chemical and some biological processes.
Factors those are responsible to make soil –
(i) The sun heats up the rock and expands. Its cools down at night and contract. But, all parts of the rock do not expand and contracts at the same rate, therefore, cracks forms. Ultimately the huge rocks break up into smaller pieces.
(a) Water could get into the cracks of the rocks and freezes there. It would cause the cracks to widen.
(b) The fast flow of water brings big pieces of rocks down which rub against other rocks and causes the rocks to wear down in to small pieces.
(iii)The strong winds also erode rocks down. The wind also carries sand from one place to another.
(iv) Living organisms like lichen, moss etc. grow on the surface of rock and releases certain substances which powder down the rock surface.
The roots of big trees also cause cracks to widen.
For detail study go to link – Soil
(6) Biogeochemical Cycles-
The interaction between biotic and abiotic components consists of a transfer of matter and energy between the different components of the biosphere is known as biogeochemical cycle.
(i) Water cycle-
The whole process in which water evaporates and falls on the land as rain and later flows back into the sea via rivers is known as water cycle.
Process of water cycle-
The water that fall on the land does not go back into water bodies. Some of it seeps into soil and increase level of underground water. Some of the underground water comes out through springs and some we bring out on the surface through well or tube wells.
The rivers carry many nutrients because when water flows from the mountain some minerals soluble in water and mix up with river.
Water cycle is represented below –
(ii)Nitrogen Cycle –
The Nitrogen Cycle is a biogeochemical cycle by which nitrogen is converted into multiple chemical forms of nitrogen which is circulated in atmosphere, marine and terrestrial ecosystem.
(a) It covers 78% of our atmosphere.
(b)It is a part of many proteins, nucleic acid (DNA and RNA) and some vitamins.
(c) It is found in alkaloids and urea.
(d) It is very essential for life but we cannot take it directly from atmosphere.
Process of nitrogen cycle-
(a)The ‘nitrogen fixing” bacteria converts nitrogen into nitrates and nitrites which can be taken up by many life – forms. These bacteria are found in roots of legumes.
(b) During lightning, the high temperature and pressures created in the air converts nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain.
Nitrates and nitrites taken up by the plants and convert them into amino acids which are used to make proteins. These proteins are taken up by the animals. When plants or animals dies, other bacteria of soil convert the various compounds of nitrogen back into nitrates and nitrites. These nitrates and nitrites are converted into elemental nitrogen by a different type of bacteria.
Nitrogen cycle is represented below –
(iii) Carbon cycle-
The carbon cycle is a process in which carbon atoms travels from atmosphere to earth and then to atmosphere again.
(a) It occurs in the elemental form as diamond and graphite.
(b) In combined form as carbon – dioxide in atmosphere.
(c) It is found as carbonate and hydrogen carbonate salts in various mineral.
Necessity of carbon –
(a) All life forms are based on carbon containg molecules like proteins, carbohydrates, fats, nucleic acid and vitamins.
(b) The endoskeletons and exoskeletons of various animals are also formed from carbonate salts.
Process of carbon cycle-
(a) The carbon is taken from atmosphere in the process of photosynthesis by plants as carbon di oxide. The carbon – dioxide converts into glucose which is taken by animals and due to respiration process carbon – dioxide released by converting glucose in carbon- dioxide.
(b) In the combustion process fuels are used to provide energy for heating, cooking, transportation etc.and carbon – dioxide released in the atmosphere.
Carbon cycle is represented below –
Greenhouse effect is a natural process in which radiation from the sun rays fall on the atmosphere of the Earth and a part of it is radiated back to space as heat by atmosphere. But, other part is absorbed by the earth’s surface. Now, earth heats up and released back radiation into atmosphere and space. The greenhouse gases which are present in the atmosphere absorbed reflected back radiation (heat). Less part of it emitted back to space and large part is absorbed by the greenhouse gases. These gases do not allow the absorbed heat to go back in space. The trapped radiation or absorbed radiation is good for human life because it keeps earth warm and makes life possible on the earth. Hence, the trapping of radiations by the Earth’s atmosphere is known as greenhouse effect. It is very necessary for life on the Earth.
The oxygen cycle refers to maintain the levels of oxygen in the atmosphere.
(a) It founds in the elemental form in the atmosphere up to 21%.
(b) It found as the oxides of most metals and silicon, carbonate, sulphate , nitrates and other minerals in the Earth’s crust.
(c) It found in the form of carbon- dioxide in the air.
Necessity of oxygen-
It is an essential component of most biological molecules like carbohydrates, proteins, nucleic acid and fats.
Process of oxygen cycle-
Oxygen from atmosphere used in combustion, respiration and in the formation of oxides of nitrogen.
Oxygen is returned to atmosphere only by photosynthesis.
Elemental oxygen works as poisonous for bacteria.
Oxygen cycle is represented below –
Ozone layer is a shield near to our atmosphere which absorbs ultraviolet rays of Sun.
Many man made compounds like CFCs (carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process) were found to persist in the atmosphere. When they reached to the ozone layer they reacted with ozone molecules. This resulted in a reduction of the ozone layer. Scientists discover a hole in the ozone layer above the Antartica.
Ozone layer is very useful for us. It absorbs ultraviolet rays that are very harmful. In absence of ozone layer, ultraviolet rays directly reach to us which will cause –
(i) Sun burn
(ii) Skin cancer
(iv) Weak immune system
(v) Plants can not survive in direct sun rays.