Which term can be defined as "a level of ecological study that includes all biotic and abiotic factors in an area"?
a. community
b. population dynamics
c. climatology
d. ecosystem

in a word, a scientific question is testable. a testable question is one that asks about objects, organisms or events found in the world around it

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.