The level of organization in onion bulb is

An onion bulb represents the organ level of biological organisation. An organ is a structure made up of two or more different types of tissues working together to perform a specific function. The onion bulb consists of several tissue types: the fleshy scale leaves (modified leaves that store food), a short compressed stem (the basal plate), adventitious roots, and a protective outer covering of dry, papery scales. These different tissues are integrated into a single functional unit, making the bulb an organ.

A cell is the basic structural and functional unit of life, representing the simplest level. A tissue is a group of similar cells performing a single function (e.g. parenchyma tissue). A system is a group of organs working together to carry out a broad body function (e.g. the digestive system). The onion bulb is more complex than a single tissue but is not a system of multiple organs, so it falls at the organ level.

The hierarchy of biological organisation is: cell, tissue, organ, organ system, organism. Identifying the correct level requires asking how many types of tissues are present and whether they function as a coordinated unit.