fixation is the process that converts N2 in the atmosphere into NH3 (ammonia), which is assimilated into amino acids and proteins. And is the opposite by which ammonia is converted to nitrites (NO2-) and then nitrates (NO3-) and this is done by .

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]