Why are trophic levels often displayed as a pyramid?
it is just an attractive way to show them.
it shows how there are many more of the lower levels than the higher ones.
it shows how large the animals are in the levels.
both b & c are correct.

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.