What is the fundamental unit of biology?

The cell is considered the fundamental unit of biology because it is the smallest structural and functional unit of living organisms. Cells carry out all essential life processes, including metabolism, energy conversion, growth, and reproduction. Every living organism, whether unicellular or multicellular, is made up of cells.

In unicellular organisms such as bacteria and protozoa, one cell performs all necessary functions for survival. In multicellular organisms, cells specialize and work together to form tissues, organs, and systems, but they all share the basic characteristics of life. This cellular organization is crucial in understanding how living organisms function, interact, and develop.

The other options, while important in biological organization, do not represent the fundamental unit. The atom refers to the basic unit of matter, which, while essential for forming biological molecules, does not perform life functions independently. Tissue and organ levels of organization are formed from groups of cells and involve complex functions that rely on the integrity and activities of cells themselves. Thus, it is the cell that stands out as the foundational building block of life in biology.