The nitrogen cycle. The nitrogen cycle moves nitrogen from the atmosphere and into soils through several fixation pathways, including the production of fertilizers by humans. In the soil, nitrogen can exist in several forms. Denitrifying bacteria releases nitrogen back into the atmosphere.
REPLICATION CYCLE Influenza A virus shown in diagram. The virus is taken up by the cell as a result of receptor-mediated endocytosis. Once in the endosome, the envelop of the virus degrades ("uncoating") and the remaining proteins are released into the host cell. These proteins are viral DNA or RNA, which then undergo replication. Replication is often assisted by viral enzymes released from the endosome. Sneaky buggers, viruses.