1 / 17

THE NITROGEN CYCLE @ Described i n 1889 by the Polish scientist Sergei Winogradsky @ It consists of three phases:

THE NITROGEN CYCLE @ Described i n 1889 by the Polish scientist Sergei Winogradsky @ It consists of three phases: # Nitrogen fixation # Nitrogen assimilation # Nitrogen recovery. Nitrogen Fixation: @ This is reduction (adding H) of atmospheric

dale
Télécharger la présentation

THE NITROGEN CYCLE @ Described i n 1889 by the Polish scientist Sergei Winogradsky @ It consists of three phases:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. THE NITROGEN CYCLE @ Described in 1889 by the Polish scientist Sergei Winogradsky @ It consists of three phases: # Nitrogen fixation # Nitrogen assimilation # Nitrogen recovery

  2. Nitrogen Fixation: @ This is reduction (adding H) of atmospheric nitrogen to ammonia, nitrites and nitrates. @ Nitrogen fixation can occur in two ways: # By electrical (lightening) reactions in the atmosphere. # By microorganisms, e.g. fungi, cyanobacteria, and free-living bacteria.

  3. @ These organisms fix nitrogen symbiotically or non-symbiotically & form ammonia inside their cells.(تعايش) @ They are grouped into three categories: # Free-living nitrogen-fixing bacteria: * Obligate aerobes: Azotobacter * Facultative anaerobes: Klebsiella * Obligate anaerobes: Clostridium # Cyanobacteria(Blue-green bacteria) # Symbiotic bacteria of legume plants (البقوليات)

  4. Non-symbiotic nitrogen fixation: @ Free-living bacteria existing in soil make non-symbiotic nitrogen fixation by secreting nitrogenase enzyme. @ Nitrogenase enzyme binds with atmospheric nitrogen and an electron carrier, in presence of ATP. Then picks up hydrogen to form ammonia, ADP, & inorganic phosphate. Nitrogenase N2 + 6H+ + 6e- + 2ATP-------→2NH3 + 12ADP + 12Pi

  5. Symbiotic Nitrogen Fixation: @ This is done by soil bacteria called Rhizobium that infect roots of the legume plants @ The two partners (bacteria & plant) come in contact by their cell surfaces. @ The bacteria establish themselves in roots of plants & formroot nodules @ Nitrogen in soil is picked up by these nodules & converted into ammonia by a process called ammonification.

  6. Nitrogen Assimilation: @ The ammonia is used by the plant nitrogen- fixing organisms to form plant protein @ Animals eat plants, and plant proteins are converted to animal proteins. @ Nitrogen is used by organisms in two ways: # Deamination to ammonia, and then used for making proteins. # Transamination to ammonium, which is converted to nitrites, and later to nitrates.

  7. @Most organisms use ammonia as nitrogen source @ Others use nitrate as a nitrogen source, and reduces it to ammonia inside cell. @ Ammonia is converted to nitrates in two steps: # Soil nitrite bacteria) Nitrosomonas)oxidize ammonia to nitrites. # Then soil nitrate bacteria) Nitrobacter ) oxidize these nitrites to nitrates.

  8. Nitrogen Recovery: @ The proteins produced by plants are consumed by them & then pass to the soil as decaying products. @ Animal carcasses also pass to the soil as waste products @ Soil bacteria decompose these decaying & waste products into ammonium, nitrites, and finally into nitrates. @ Soil denitrifying bacteria complete the nitrogen cycle by converting nitrates into nitrogen gas which passes to the atmosphere.

More Related