Nitrogen Fixation F215

Plants need nitrogen for proteins and nucleic acid. The most abundant form of nitrogen is in the air which is 78% nitrogen.

In this form nitrogen exists as molecular nitrogen where two nitrogen molecules are linked with a triple covalent bond. In this form nitrogen is very unreactive.

The molecular nitrogen must be converted to a different form such as

• Ammonia (NH3)
• Nitrate (NO3-)

This is called: Nitrogen Fixation

There are three different types of fixation's:

• Atmospheric Fixation (lightning)
• Industrial Fixation (Haber Process)
• Fixation by living organisms

Nitrogen Fixation By Living Organisms

One of the best known nitrogen fixing bacteria is Rhizobium. This is present freely in the soil and in the roots of species of plants, especially leguminous plants like peas and beans.

When the leguminous plant germinates its roots produce proteins called lectins. These bind to the polysacchrides on on the cell surface of the bacteria.

The bacteria invade the roots and spread along the root hairs.…