What organism usually fixes nitrogen into usable chemical forms?

Bacteria found in the roots of legumes(beans) do nitrogen fixation.

Endemic: An episode of a disease that exists for all time, in coherence, in a specific district or populace not spreading to different networks.

Epidemic: An episode of a transmissible, irresistible disease that assaults a network and quickly spreads among an enormous number of individuals, through one or a few networks.

Pandemic: A pandemic is the overall spread of another irresistible disease. It extends over a bigger zone, contaminates a greater number of individuals and causes a larger number of passings than a scourge. A pandemic causes serious monetary and social disturbance because of high paces of ailment and specialist non-appearance, particularly when influencing key administrations, for example, transportation, correspondence, or force.

Explanation:

A disease outbreak can spread quickly murdering thousands. It is proclaimed when a bigger number of instances of a disease than anticipated are recorded in one zone, either inside a little network or a few nations.  

An outbreak could be a solitary instance of an infectious disease new to a network or not seen for quite a while, going on for a couple of days or quite a long while.  

There are three kinds of outbreak:

Endemic: An episode of a disease that exists for all time, in coherence, in a specific district or populace not spreading to different networks.  It happens at an anticipated rate in a specific zone or among a set populace. Chickenpox is endemic as it happens at a high however unsurprising rate, among adolescents.  Endemics stay in a consistent state yet don't vanish from a populace.

Epidemic: An episode of a transmissible, irresistible disease that assaults a network and quickly spreads among an enormous number of individuals, through one or a few networks.  Somewhere in the range of 2013 and 2016, the Ebola epidemic in West Africa murdered 11,300 individuals.  In 2003, SARS epidemic murdered about 800 individuals. In 1968, Hong Kong flu murdered one million individuals.  In 1957, Asian flu murdered 2,000,000 individuals.  In 1918, Spanish flu murdered 40-50 million individuals.

Pandemic: A pandemic is the overall spread of another irresistible disease. It extends over a bigger zone, contaminates a greater number of individuals and causes a larger number of passings than a scourge. A pandemic causes serious monetary and social disturbance because of high paces of ailment and specialist non-appearance, particularly when influencing key administrations, for example, transportation, correspondence, or force.  Ever, there have been various obliterating pandemics including the Dark Passing which slaughtered in excess of 75 million individuals in 1350.  In 2009, a pandemic of swine influenza executed 14,286 individuals around the world.  

A viral pandemic happens when:  

another sub-type of infection emerges. As people have practically zero resistance to it, everybody is in danger.  The infection spreads effectively from individual to individual  The infection starts to cause genuine ailment around the world. With the speed of air travel today, general well being specialists accept that pandemic outbreaks could spread considerably more rapidly. All pieces of the world may not be influenced simultaneously.