CBSE Class 9 Science, Natural Resources -2, Biogeochemical Cycles

what comes first the nut or the tree that may be a tough call to take whether it's the seasons or life on Earth nature works in cycles in this lesson you will learn about biogeochemical cycles the greenhouse effect and the ozone layer by the end of this lesson you will be able to define biogeochemical cycle describe the water cycle describe the carbon cycle describe the nitrogen cycle describe the oxygen cycle explain the greenhouse effect describe the ozone layer and explain the consequences of the depletion of the ozone layer the cycling of chemicals between the biological and the geological world is called biogeochemical cycle the biotic and abiotic components of the biosphere constantly interact through these cycles during these interactions there is a transfer of nutrients between living organisms or bio and nonliving environment or Geo hi there I'm oxy I shall join you on this journey to explore the different biogeochemical cycles do you know the four most important biogeochemical cycles they are the water nitrogen carbon and oxygen cycles we know that water evaporates from water bodies but have you ever seen seas and oceans drying up well they never do thanks to the water cycle let's see how water evaporates from the water bodies and returns as green which in turn flows back into the Seas via rivers this cycle of water between the land the ocean and the atmosphere is called the water cycle let's take a closer look at the cycle when the oceans are heated during the day water enters the atmosphere as water vapor by the process of evaporation there is another way in which water evaporates into the atmosphere this happens through transpiration water from plants evaporates as vapor into the atmosphere through stoma in the leaves and stems this water vapor in the atmosphere changes to water droplets and collects to form clouds this process is called condensation Seabreeze moves these clouds and carries them over the land where they break into rain snow or fog this is called precipitation Wow it's raining here do you know what happens to the green water now where does it go much of the rainwater flows into the water bodies and eventually runs off into the ocean some of it penetrates the Earth's surface and is logged as groundwater now I get it this is how water is maintained in the biosphere by the water cycle hey do you know what this is it's a diamond do you know what it's made of a diamond is made of an element called carbon carbon is found in various forms on the earth it is present in the atmosphere as carbon dioxide and is an essential part of carbohydrates fats proteins nucleic acids and vitamins as you can guess it's important to maintain the correct amount of carbon in the biosphere this happens through the carbon cycle let us now look at the carbon cycle in detail the cycle starts in plants plants in the presence of sunlight use carbon dioxide in the atmosphere and convert it to carbohydrates through photosynthesis wondering what happens to the carbohydrates when all plants and animals break down carbohydrates for energy and release carbon dioxide through respiration dead plants and animals are decomposed by fungi and bacteria this decomposition releases the carbon in the remains as carbon dioxide dead plant and animal remains in the soil are converted into coal petroleum and natural gas better known as fossil fuels these fuels are used for cooking transportation and industrial processes on burning these fuels carbon dioxide is released into the atmosphere that is how the biological and the geological words come together to maintain the carbon balance in the biosphere let's now look at an element that makes up 78% of the atmospheric air nitrogen is an essential constituent of proteins nucleic acids like DNA and RNA vitamins and chlorophyll this makes nitrogen an essential nutrient for all life-forms interestingly most living organisms cannot use nitrogen directly so it needs to be converted into usable forms by fixation either biologically or physically you're awesome legumes do you know what these are these are nothing but pulses that you should regularly have they have an important part of the nitrogen cycle let's see how legumes have nitrogen-fixing bacteria in their root nodules these bacteria convert atmospheric nitrogen into ammonia which is readily utilized by the plants nitrogen-fixing bacteria along with free-living bacteria in the soil achieved 90% of nitrogen fixation that was the biological process of nitrogen fixation did you know that lightning plays an important role in nitrogen fixation surprised let's see how when lightning occurs the high temperature and pressure combine nitrogen and water to form nitrates and nitrites these compounds dissolve in water and are readily used by plants now that nitrogen is taken up by the plants it is used to make proteins once the plants and animals die the bacteria in the soil decompose the organic matter and release ammonia into the soil this process is called a modification thereafter through biological oxidation ammonia is converted to nitrate and nitrite to nitrate by bacteria in the soil this process is called nitrification the nitrite and nitrate are finally converted to gaseous nitrogen by denitrifying bacteria here's the cycle once again for you the nitrogen cycle is the sequence in which nitrogen passes from the atmosphere to the soil and organisms and then is eventually released back into the atmosphere now let's take a look at the cycle I like most the oxygen cycle oxygen makes up 21% of the air and is an essential constituent of carbohydrates proteins fats and nucleic acids oxygen is found in air in the combined form as carbon dioxide and in the Earth's crust as carbonates sulfates and nitrates here's a detailed look at how the cycle works plants and animals use atmospheric oxygen during respiration fossil fuels like coal and wood need atmospheric oxygen for combustion we have seen how oxygen is used from the atmosphere can you think of a way in which oxygen is returned to the atmosphere take a look as you know oxygen is returned to the atmosphere by photosynthesis in plants here's another look at the oxygen cycle the sequence in which oxygen from the atmosphere is used by the organisms and eventually released into the atmosphere is called the oxygen cycle we have already seen how biogeochemical cycles maintain balance in the biosphere there are other processes that stabilize temperature on the earth let's explore this a little can you guess where I am it's a greenhouse how it works he distract by glass hence the temperature inside a glass house is much higher than the surroundings such enclosures are called greenhouses you must be wondering what greenhouses have to do with the bias here take a look solar radiation reaching the earth is reflected back into the atmosphere although much of this radiant heat is lost to space atmospheric gases like carbon dioxide trapped the heat this is called the greenhouse effect it dips the earth warm to sustain life hi buddy meet my good friend ozone he lives in the upper layer of the atmosphere known as the stratosphere atmospheric oxygen contains two oxygen atoms while ozone has three the ozone absorbs harmful ultraviolet radiations from the Sun this prevents the radiations from reaching the Earth's surface where they might damage life-forms here's a disturbing fact for all of us recent discoveries have revealed that the ozone layer is depleting due to an increase in man-made compounds like chlorofluorocarbons these are carbon compounds having both chlorine and fluorine the consequences of the vanishing ozone layer could be dangerous in the future you [Applause] [Applause] you


  1. Thirupathi chinthala

    Really very gud explanation tq so much for dis video nd if u have soil pollution class 9 biology videos plzz can u send me a link????

  2. Meena Mahajan

    This is honestly the only reasonable and relevant explanation on YouTube. Thank you so much. I have revisions tomorrow and am trying to cut it short instead of reading the book completely as i have a science project too to focus on.
    You have really helped a lot to sum it all up.πŸ‘


    ihad download this video and show in my school as powerpoint. thanks for posting such a wonderful video.i ask y friends to subscribe shiksha house.


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