Do you mean "why"?
They are the main source for all living organisms because they provide energy, relatively short term, for any creature that consumes them.
True
This is true because most of the nitrogen is found in the atmosphere
The light-dependent reactions
Correct answer is "Species" is the lowest taxonomic rank, rank is the level of an organism or groups of organisms in taxonomy hierarchy.
Species is basic unit of biological classification which contains the fewest number of organisms and this makes it most specific.
Species which have the same ancestors are placed in one rank called genus.
Taxonomic ranks in order (from the biggest to the smallest) :)
-Domain
-Kingdom
-Phylum
-Class
-Order
-Family
-Genus
-Species
