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sharks, whales, and dolphins share similar features such as body shape and the position of fins. however, sharks have gills for breathing, while
whales and dolphins have lungs. these differences indicate that the organisms share a common ancestor for
whales also possess a vestigial pelvic bone. the presence of the pelvis bone may indicate that whales

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.