The human body is composed of cells that typically live in groups of the same or similar cell types called tissue. Tissue forms organs, which are self-contained groups of tissue that perform a specific function. Organs work together to carry out a specific function as an organ system. Together, all of the organ systems make up the organism.

Atoms form structures such as DNA. DNA and other substances form cells. Cells can group together to form tissue. Groups of tissue form an organ. Organs form organ systems, and these systems together create an organism.

Figure 1: The structure of the human body when viewed from different levels. The chemical level (1) - atoms make up chemicals that form DNA. The cellular level (2) - DNA forms cells. The tissue level (3) - cells form tissue. The organ level (4) - tissue forms organs. The system level (5) - organs form organ systems. The organismal level (6) - organ systems form organisms.