The major levels of organization in the body, from the simplest to the most complex are: atoms, molecules, organelles, cells, tissues, organs, organ systems, and the human organism.
The significant degrees of association in the body, from the least difficult to the most perplexing are: particles, atoms, organelles, cells, tissues, organs, organ frameworks, and the human living being.
During the process of exocytosis, the cell membrane extends to engulf substances that are too big to pass through the cell membrane. Receptor proteins bind to signal molecules outside the cell.
