Answer: Cell
Step-by-step explanation:
The cell is the structural and functional unit of life. It is the the most basic level. A life starts from a single cell.
When a male and female gamete(germ cell) fuse together they form zygote. Firstly it is a single cell surviving inside the mother's womb.
Then differentiation takes place and the cell keeps on dividing to form different tissue layers and then organs form which makes a complete baby. Hence, zygote and germ cell are cellular level of organization.