Ecology is best defined as…
a) the scientific study of the distribution and abundance of organisms and their interactions with the environment.
b) the scientific study of the interactions between plants and animals
c) the scientific study of life.
d) the scientific study of biotic distributions and interactions.

A) The scientific study of the distribution and abundance of organisms and their interactions with the environment.

Explanation:

Ecology is the part of biology that is concerned with the study of the relationships established between living beings and theirs with the environment in which they live.  It is a term derived from the Greek that was formed from the junctions of the words "oikos" and "logos", which mean, respectively, home and study. Thus, the term Ecology refers to the study of the “home” of every organism on the planet.

The term Ecology was first used in 1866 by a German zoologist named Ernst Haeckel, in a work called "Generelle Morphologie der Organismen". In this work, the author defined Ecology as "the scientific study of the interactions between organisms and their environment."

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

b. read the phase at the intersection of any given temperature and pressure.