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Related Concept Videos

The Nitrogen Cycle01:49

The Nitrogen Cycle

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Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of nitrogen on Earth is nitrogen gas, which cannot be used by most animals and plants. Thus, nitrogen gas must first be converted into a usable form by nitrogen-fixing bacteria before it can be cycled through other living organisms. The use of nitrogen-containing fertilizers and animal waste products in human agriculture has greatly influenced the...
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Overview of Nitrogen Metabolism01:20

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Nitrogen is a very important element for life because it is a major constituent of proteins and nucleic acids. It is a macronutrient, and in nature, it is recycled from organic compounds and stored in the form of  ammonia, ammonium ions, nitrate, nitrite, or  nitrogen gas by many metabolic processes. Many of these metabolic processes are carried out only by prokaryotes.
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this...
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Inorganic Nitrogen Assimilation01:22

Inorganic Nitrogen Assimilation

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Nitrogen is an essential element in biological systems, forming a crucial component of proteins, nucleic acids, and other cellular constituents. Many bacteria and archaea acquire nitrogen in the form of nitrate (NO₃⁻) or ammonia (NH₃), which are then assimilated into biomolecules through specific enzymatic pathways.Assimilatory Nitrate ReductionWhen nitrate enters the cell, it undergoes a two-step reduction process known as assimilatory nitrate reduction. Initially, the enzyme...
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Fixation and Sectioning01:03

Fixation and Sectioning

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Two basic types of preparation are used to visualize specimens with a light microscope: wet mounts and fixed specimens.
The simplest type of preparation is the wet mount, in which the specimen is placed in a drop of liquid on the slide. A liquid specimen can be directly deposited on the slide using a dropper. Solid specimens, such as skin scraping, can be placed on the slide before adding a drop of liquid to prepare the wet mount. Sometimes the liquid is simply water, but stains are often added...
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Chirality at Nitrogen, Phosphorus, and Sulfur02:30

Chirality at Nitrogen, Phosphorus, and Sulfur

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Chirality is most prevalent in carbon-based tetrahedral compounds, but this important facet of molecular symmetry extends to sp3-hybridized nitrogen, phosphorus and sulfur centers, including trivalent molecules with lone pairs. Here, the lone pair behaves as a functional group in addition to the other three substituents to form an analogous tetrahedral center that can be chiral.
A consequence of chirality is the need for enantiomeric resolution. While this is theoretically possible for all...
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Carbon-dioxide Fixation01:28

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Carbon dioxide fixation in prokaryotes enables the assimilation of inorganic carbon into organic molecules, supporting biosynthetic pathways, sustaining ecosystems, and contributing to the global carbon cycle. It also has industrial applications in carbon capture and bioproduct synthesis. Autotrophic organisms rely on this process to utilize CO₂ as a carbon source in diverse environments.The Calvin CycleThe Calvin cycle is the most widespread carbon fixation mechanism, primarily used by...
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Whole Animal Perfusion Fixation for Rodents
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STUDIES ON NITROGEN FIXATION BY ALNUS CRISPA.

David A Dalton1, Aubrey W Naylor1

  • 1Department of Botany, Duke University, Durham, North Carolina, 27706.

American Journal of Botany
|August 25, 2018
PubMed
Summary

Alnus crispa root nodules host a symbiotic nitrogen-fixing organism, confirmed by acetylene reduction assays. This nitrogen fixation does not increase surrounding soil nitrogen levels.

Area of Science:

  • Plant biology
  • Microbiology
  • Biochemistry

Background:

  • Alnus crispa (Ait.) Pursh, commonly known as green alder, forms root nodules.
  • These nodules are known to harbor symbiotic organisms.

Purpose of the Study:

  • To confirm the presence of a symbiotic nitrogen-fixing organism within Alnus crispa root nodules.
  • To quantify the nitrogen-fixing activity.
  • To investigate the impact of this activity on soil nitrogen levels.

Main Methods:

  • Acetylene reduction assay using gas chromatography to measure nitrogenase activity.
  • Microscopic examination of nodule structure and endophyte presence.
  • Soil nitrogen level analysis.

Main Results:

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  • Nitrogen-fixing activity was confirmed, with ethylene production measured at 5.1 μmoles/g excised nodule · hr.
  • Microscopic analysis revealed spherical endophyte cells packed within cortical cells, with uninfected outer cortex.
  • Winter examination showed shrunken nodules and random endophyte distribution.
  • Soil nitrogen levels near Alnus crispa did not exceed those in adjacent areas.

Conclusions:

  • Alnus crispa root nodules contain a functional symbiotic nitrogen-fixing system.
  • The endophyte resides within specific cortical cells.
  • Nitrogen fixation by Alnus crispa does not appear to enrich the surrounding soil nitrogen content.