describe the steps involved in water, oxygen, nitrogen and carbon cycle
Answers
Water cycle
The water cycle involves various steps like evaporation, transpiration, condensation and precipitation.
• When the water bodies are heated during the day, water enters the atmosphere as water vapour by the process of evaporation.
• There is another way in which water evaporates into the atmosphere. This happens through transpiration.
• The water vapours in the atmosphere changes to water droplets and collects to form clouds. This process is called condensation.
• Air currents move the clouds formed by condensation and carry them over the land, where they break into rain, snow or fog. This is called precipitation.
Nitrogen cycle
The sequence in which nitrogen passes from the atmosphere to the soil and organisms, and then is eventually released back into the atmosphere, is called the nitrogen cycle.
• Nitrogen makes up 78 percent of the earth’s atmosphere. The percentage of nitrogen in the atmosphere is maintained by nitrogen cycle.
• Nitrogen is an essential constituent of proteins, nucleic acids like DNA and RNA, vitamins, and chlorophyll.
• Plants and animals cannot utilise atmospheric nitrogen readily. It has to be fixed by some organisms called as nitrogen fixers.
• Nitrogen-fixing bacteria like Rhizobium live in symbiotic association in the root nodules of certain leguminous plants.. These bacteria convert atmospheric nitrogen into ammonia, which is utilised readily by plants.
• Nitrogen-fixing bacteria along with free living bacteria in the soil achieve 90 percent of nitrogen fixation.
• Lightning plays an important role in nitrogen fixation. When lightning occurs, the high temperature and pressure convert nitrogen and water into nitrates and nitrites.
• Nitrates and nitrites dissolve in water and are readily used by aquatic plants and animals.
• Ammonification is the process by which soil bacteria decompose dead organic matter and release ammonia into the soil.
• Nitrification is the process by which ammonia is converted into nitrites and nitrates.
• Denitrification is the process by which nitrates are converted into atmospheric nitrogen.
Oxygen cycle
The sequence in which oxygen from the atmosphere is used by organisms and eventually released back into the atmosphere through photosynthesis is called as oxygen cycle.
• Oxygen makes up 21 percent of the air. It is an essential constituent of carbohydrates, proteins, fats and nucleic acids.
• Oxygen is found in air, in combined form as carbon dioxide, and in the earth’s crust as carbonates, sulphates and nitrates.
• Plants and animals use atmospheric oxygen during respiration and release the same during photosynthesis.
• Fossil fuels require oxygen for combustion.
• The ozone layer is present in stratosphere, one of the layers of the atmosphere. Each molecule of ozone is made up of three oxygen atoms. The ozone layer prevents harmful radiations from reaching the earth’s surface, where they might damage life forms.
Solar radiation reaching the earth is reflected back into the atmosphere. Much of the heat is lost to the environment. But some of the energy is trapped by the atmosphere thereby causing Greenhouse effect
