What is the smallest level on the hierarchy of organization that is considered living?

Movement toward a stimulus is considered a positive response, while ... Describe the biological levels of organization from the smallest to highest level ... to the entire biosphere, living organisms are part of a highly structured hierarchy.

The biological levels of organization of living things are arranged from the simplest to most complex. Here is a list.

organelle, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystem, and biosphere.

So organelle would be the smallest.