1. THE NITROGEN CYCLE

2. THIS IS THE CYCLING OF NITROGEN BETWEEN LIVING ORGANISMS AND THEIR ENVIRONMENT BY THE PROCESSES OF NITRIFICATION, ABSORPTION, FEEDING, DEATH, EXCRETION AND DECAY. WHAT IS THE NITROGEN CYCLE

4. THE CIRCULATION OF THE ELEMENT NITROGEN IN THE NITROGEN CYCLE Nitrates absorb from soil form protein in green plants. Animals make animal protein from plant protein eaten. Animal protein is broken down to urea (release as urine). Bacteria convert urea, dead plants and animals to ammonium compounds then to nitrites, then to nitrates in soil. Soil also receive nitrates from atmospheric nitrogen by nitrogen- fixing bacteria.

5. Describe how nitrogen is cycled within an ecosystem Nitrogen is an atmosphere (N2) is very inert and it takes a lot of energy to split the bonds in the nitrogen molecule so that it can form other compounds, such as nitrates and nitrites. However, nitrogen is an essential component of biological molecules such as protein and DNA. The only organism capable of splitting the nitrogen molecules are a few bacteria. They use it to form nitrates or nitrites, a process known as nitrogen fixation. This is the major way in nitrogen entering the biotic component of the ecosystem.

6. called nitrification. Decay and Nitrification Most plants depend on a supply of nitrate from the soil for the nitrates source. Animals in turn depend directly or indirectly for their nitrogen supply. The sequence from protein to nitrate is a series of oxidation, requiring oxygen and involving aerobic bacteria. Proteins are decomposed via amino acids to ammonia when an organism dies. Animal wastes and excreta are similarly decomposed. Chemosynthetic bacteria then oxidize ammonia to nitrate, a process

7. Nitrogen Fixation Nitrogen fixation is an energy consuming process because the two nitrogen atoms of the nitrogen molecules must first be separated. Nitrogen fixers achieve this by using an enzyme nitrogenase and energy from ATP. Non enzymatic separation requires the much greater energy of industrial processes or of ionizing events in the atmosphere, such as lightening and cosmic radiation. Nitrogen is so important for soil fertility and the demand for food production so great, that colossal amounts for ammonia are produced industrially each year to be used mainly for nitrogenous fertilizer such as ammonium nitrate (NH4 No3) and urea (CO(NH2)2). The amount of nitrogen fixed commercially are now approximately equivalent to the amount fixed naturally.

8. Denitrification Nitrification can be reversed by denitrifying bacteria (Denitrification) whose activities can therefore reduce soil fertility. They only do this under aerobic conditions, when nitrates are used instead of oxygen as an oxidizing agent for the oxidation of organic compounds. Nitrates it self is reduced. The bacteria are therefore facultative aerobes.