EARTH SCIENCE FOR GRADE 11, Summaries of Earth science

Download EARTH SCIENCE FOR GRADE 11 and more Summaries Earth science in PDF only on Docsity! NITROGEN CYCLE - is a type of nutrient cycle. - Atoms of nitrogen don't just stay in one place. They move slowly between living things, dead things, the air, soil and water - crucial for all life on Earth because N2 is used for DNA, RNA, amino acids (protein), ATP, nucleic acids. - N2 (nitrogen gas) makes up about 78% of the atmosphere - NOT USABLE BECAUSE OF TRIPLE BOND making it unreactive. - In plants, much of the nitrogen is used in chlorophyll molecules which are essential for photosynthesis and further growth. - All organisms are autotrophs, which means that they take carbon dioxide as their carbon source for growth. (carbcy) - Nitric Oxide (NO) is released into the atmosphere when any type of fuel is burned. This includes byproducts of internal combustion engines. Nitrous Oxide (N2O) is released into the atmosphere through bacteria in livestock waste and commercial fertilizers applied to the soil. USABLE NITROGEN: - high energy processes like lightning bolt or volcanic activity can break the bonds of atmospheric nitrogen molecules. Free nitrogen atoms in the air bond with oxygen in the air to create nitrogen oxides, which dissolve in moisture to form nitrates that are carried to Earth's surface by PRECIPITATION. 1. NITROGEN FIXATION - Bacteria that contain enzymes called nitrogenase can break the triple bond of N2 in the air (found in soil or root nodules of certain plants like LEGUMES - pea plants, lentils, beans, alfalfa, peanuts, clover). They break nitrogen apart and add hydrogen to make it AMMONIA (NH3) or AMMONIUM (NH4+) - same but ionized. - Ammonia can be taken up by plants and used to make important biological molecules like DNA and protein. (This process of uptake into plants is called ASSIMILATION). - Assimilatory bacteria - azotobacter and clostridium. - But not all is assimilated because too much ammonia is toxic and some plants prefer other nitrogen compounds such as nitrate. - rhizobium live in the roots, azotobacter in the soil CYANOBACTERIA - convert N2 into organic form such as nitrate or ammonia. (Aquatic ecosystems: blue- green algae) 2. NITRIFICATION OR MINERALIZATION - conversion of ammonia into nitrates. - done by NITRIFYING BACTERIA - they oxidize ammonia - first convert the ammonia to NITRITE (NO2-) and then to NITRATE (NO3-). - nitrification happens best in soils that are well-aired. - nitrate and ammonia are both plant fertilizers that undergo assimilation to make key bio molecules. - nitrogen from plants can pass to other living things through FOOD WEBS. - nitrosomonas or nitrosococcus (nitrite - ammonium producing), nitrobacter (nitrate) 3. AMMONIFICATION - Mineralization is the process by which organic matter is broken down into inorganic matter. - when living things die and decompose to the soil, it returns the nitrogen to the soil as ammonia which can be used again by plants in assimilation or converted to nitrates through nitrification. - sapriobionts - are decomposers that digest dead organisms externally by secreting enzymes and then absorb the useful products. - saprobiotic nutrition - digestion or decay of dead organic matter by extracellular enzymes - in oxygen-rich water, ammonium is easily transformed to nitrate and in oxygen-poor water to molecular nitrogen. Ammonium and nitrate comprise most of the inorganic nitrogen in precipitation. - clostridium and bacillus. 4. DENITRIFICATION - nitrogen goes back up to the air because nitrates are converted back into N2, - happens best in low oxygen environments (anaerobic conditions) like waterlogged soils and it reduces the fertility of soil. - done by heterotrophic bacteria such as pseudomonas and paracoccus. - Nitrogen Fertilizer - can actually increase the nitrogen so much that soil fertility actually decreases. Four forms of nitrogen are used as fertilizer: Nitrate, Ammonia, Ammonium, Urea.