A. Group of cells
Cells - Tissue - Organ ...
If you want to know more - look for "Biological Organisation"
Answer:
Explanation:
The nitrogen cycle is an important cycle to the atmosphere. Nitrogen is an essential part of biological molecules such as proteins and nucleic acid, which makes nitrogen essential for all living organisms. Nitrogen makes up 78 percent of the atmosphere.
The ability of an animal to maintain a stable internal environment is called homeostasis.
