The Carbon Cycle: The carbon cycle shows how carbon atoms are passed from one organism to another and to their environment as they live, breathe, eat, die and decay. 1 The atmosphere contains about 0.03% carbon dioxide. During photosynthesis, plants use carbon dioxide from the atmosphere to make carbohydrates, proteins and lipids. This is the first source of carbon in living organisms - as a part of the plantS body. 2 Animals then obtain their supply of carbon by eating plants or other animals that have eaten plants. 3 As plants and animals respire, molecules of carbon dioxide are released back into the atmosphere. 4 Waste materials from living organisms (like urine and faeces) and their dead bodies (all organisms die), are used as food sources by decomposers. Decomposers, like bacteria and fungi, feed on dead organic matter. Carbon atoms then become incorporated into the bodies of the decomposers. 5_ Respiration of the decomposers releases carbon dioxide into the atmosphere. 6 In waterlogged soils where oxygen was in short supply, decomposers were not able to break down tissues completely in dead bodies and the remains accumulated. For example, in the Carboniferous period (about 290 million years ago) huge areas of waterlogged swamps covered many parts of the world. When the swamp plants died, partially decomposed plant material accumulated and eventually turned to coal, a solid fossil fuel Oil and natural gas are liquid fossil fuels that formed in a similar way from the remains of plants and animals that died in oceans. Fossil fuels contain a large proportion of carbon. 7 The burning of fossil fuels (combustion) releases carbon dioxide into the atmosphere. And so the cycle continues, carbon in the atmosphere is taken up by plants, which are eaten by animals, and returned to the atmosphere through respiration, decomposition or combustion of fossil fuels. . Note the importance of plants in this cycle. Without plants, the carbon stays in the atmosphere and cannot be reused and incorporated into the bodies of animals. If there were no plants, there would be no animals. NOT SURE IF YALL GAH GE DE HUMAN EFFECT AND D GREENHOUSE EFFECT BUT LUK IT ANYWAY: THe human effect on the carbon cycle: The rise in human population has been supported by an increase in manufacturing and other types of industries. Since the Industrial Revolution humans have been burning fossil fuels to release energy for machines. This has added carbon dioxide to the air at an alarmingly fast rate. The carbon was locked away in the solid or liquid forms of fossil fuel for millions of years. Increased combustion of these fossil fuels increases the carbon dioxide concentration in the air. Increased concentration of carbon dioxide in the atmosphere is associated with an environmental problem known as global warming. THe Greenhouse effect and global warming: When heat from the Sun reaches the Earth much of it bounces straight back into space. Within the Earths atmosphere there are gases like carbon dioxide and methane that absorb some of the escaping heat and send it back to the Earths surface, keeping it trapped around the Earth. They act like a greenhouse around the Earth and thus are called greenhouse gases. This is a natural process which helps keep the- surface of the Earth warm. Without this natural greenhouse effect, the Earth would be too cold for most of the organisms living on it. A problem arises when the proportions of these gases in the atmosphere increase. They bounce more of the heat back to the Earths surface. This is called the enhanced greenhouse effect. As a result the temperature of the Earth global warming il- increases, which is known as global warming. Carbon dioxide concentration in the Earths atmosphere has increased by about 20% over the last 100 years. This effect has also been worsened by deforestation. Trees (forests) remove carbon dioxide from the atmosphere during photosynthesis. Large areas of forests are being removed by cutting or burning, and so there are fewer trees to remove carbon dioxide by photosynthesis from the atmosphere. It is not proven that higher carbon dioxide levels cause temperature rises, but scientific research suggests that the two may be associated. Some people think that global warming might cause the Earths temperature to rise between 1.5 DCand 4.5 DCby the end of the 21st century. Possible Effects of global warming: ••The polar ice caps may melt which could cause sea levels allover the world to rise Significantly. Many millions of people now live in lowland areas and these may be flooded, driving people from their homes. . •• Fertile, crop-producing land could be lost by flooding. The distribution of organisms over the face of the Earth may change as land floods and temperature and rainfall patterns change . •• Changes in the amount of land and sea could change weather patterns. This could increase rainfall in some places and increase periods of drought in others. Natural storms like hurricanes, tornadoes and typhoons may also be more severe . •• Cold countries may become more temperate and fertile. We must be very careful not to say that every example of extreme weather is due to global warming. There have always been variations in climate over the years, and over centuries. Also, we must be careful not to make unjustified assumptions about future changes. For example, on the island of Svalbard in the Arctic Ocean, one of the glaciers is retreating, but a neighbouring glacier has advanced by more than a mile in seven years. Some sea levels are said to be lower now than in the eighteenth century - for example mean sea level in the Cook Islands has apparently dropped by about 20 em in 200 years. Globally, mean sea level is .rising at about 3 mID per year. So although global warming is a reality, and many experts attribute this to the enhanced greenhouse effect, we should not be too quick: to predict catastrophe! THe NITROGEN CYCLE: About 79% of the air around us is nitrogen gas. This gas is very unreactive - it passes in and out of animals bodies unchanged when they breathe. However, nitrogen is an essential component of biological molecules such as proteins and DNA. Muscle is composed of long strands of protein and DNA is the molecule in each nucleus of a cell which contains the information about how to build that cell and make it work. .Plants manufacture protein by absorbing nitrogen from the soil mostly as nitrate ions. These are combined with carbon, hydrogen and oxygen taken from glucose that was made during photosynthesis. The elements are then arranged in another way as they combine with the nitrogen, to make the building blocks for proteins and DNA .Animals obtain their nitrogen from the protein in their diet, through eating plants or other animals. The protein they eat is digested, absorbed and used as needed in the feeding animal. That is, the nitrogen obtained from the protein of a piece of plant material or meat can be used to build growing muscles, make DNA, enzymes and other proteins, and everything else requiring nitrogen. The nitrogen cycle consists of four main processes: .• nitrogen fixation; .• decay; .• nitrification; .• denitrification. FOR THESE NUMBERS THINGYS BELOW LOOK AT U DIAGRAM______ Nitrogen fixation (1)· This occurs in nitrogen-fixing bacteria which convert nitrogen gas in the air, to nitrate. Some of these bacteria, like Azotobacter and Clostridium, live in the soil and convert the nitrogen gas found in the air in the soil to nitrate. Plants cannot absorb nitrogen gas, only substances that contain it, like nitrates. So nitrogen-fixing bacteria thus make nitrogen available to plants in a form they can absorb. Plants use the nitrogen from nitrates in the soil to make proteiris and DNA. Other kinds of nitrogen-fixing bacteria, called Rhizobium, live in the roots of legumes (plants of the pea family). There, nitrogen gas is converted to nitrates and used directly inside the plant to make protein. The relationship between the plants and the nitrogen-fixing bacteria is an example of mutualism as discussed on page 19. Decay (2) When plants and animals die, their bodies are decomposed by decomposers to make ammonium compounds in the soil. Animal wastes, like faeces and urine, are also decomposed by bacteria living freely in the soil. nitrification ~ Nitrification (3) The ammonium compounds formed during decay are converted to nitrites and then nitrates. The processes that lead to the formation of nitrates in the soil are called nitrification and are carried out by nitrifying bacteria like Nitrosomonas and Nitrobacter. Plants take up nitrate ions from the soil and make proteins. Denitrification (4) The nitrogen cycle is completed by denitrifying bacteria. They convert nitrates in the soil back to nitrogen gas. The activities of these bacteria reduce soil fertility, since they take nitrates out of the soil which the plants need to grow well. In nature, a little nitrogen fixation occurs during thunderstorms (5). Lightning provides the energy to convert nitrogen to nitrogen oxides. These gases dissolve in rain droplets to form nitrates that plants can use. To make crops grow better, we add artificial and natural fertilisers to the soil to increase the levels of nitrates (6). As rain water passes through the soil on its way to the rivers, lakes or seas, it carries with it dissolved nitrates and other soil nutrients. So the nitrates can be washed out of the soil. This is called leaching. The nitrogen cycle is thus essential to life as nitrogen is a vital component of every living organism. This biogeochemical cycle allows nitrogen to be reused over and over by living organisms. Nitrogen atoms cannot be created and there is only a certain amount on Earth. The importance of bacteria should be noted, since they are an integral part of this cycle. Nitrifying bacteria can be considered good bacteria, without which living organisms would slowly become extinct. ACID RAIN.... Combustion of fossil fuels in industry and from motor vehicles releases addic gases such as sulphur dioxide and nitrogen dioxide. These gases dissolve in atmospheric water vapour in clouds and later fall as add rain. Sulphur dioxide dissolves in atmospheric water to give, eventually, dilute sulphuric add. Oxides of nitrogen dissolve to form dilute nitric add. The add clouds may be carried hundreds of miles away from the source of the pollution by air currents. It has been recorded that rain With a pH as low as 4 has fallen over Scandinavia, Germany and Canada. • Add rain may kill plants and trees. Some forests, like the Black Forest in Germany, have been severely damaged (see figure 4.9). Recently, though, it has been found that acid rain enhances the growth of pine forests in Scandinavia. • Add rain also dissolves some poisonous metals thus introducing them into lakes and rivers. This poisons organisms living in the water. About 400 lakes in Norway have been rendered fishless because of add rain. o In cities, stone (statues and carvings) and metal structures have been damaged because of erosion due to add rain. Governments are trying to reduce add rain by introducing regulations that demand that industries do not release atmospheric pollutants. The design of engines for motor vehicles is also important to reduce the amount of pollutant gases that they make.
Posted on: Fri, 29 Nov 2013 23:57:41 +0000
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