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Chapter 9 Human Body Orientation 455
Section 9.4 Body Organization
In anatomy and physiology, the body is organized into five different levels.
These levels differ in complexity, from the most basic cell level to the organism
level that considers cells, tissues, organs, and body systems. In this section,
you will learn about body organization and about the characteristics of each
organizational level.
The terms below are some of those that will be introduced in Section 9.4.
To become familiar with these terms, reproduce each word on the line beside
it. Pronounce each term as you write it. You will learn the definitions of these
words as you complete this section.
1. body system _______________________________________________________________________________________
2. organism ___________________________________________________________________________________________
Concept 1: Five Levels of Organization
The human body is organized into five levels that progress from simple to
more complex. The five levels of organization are
• cells
• tissues
• organs
• body systems
• organisms
For example, cells make up tissue. Different types of tissue compose the organs
involved in digestion, including the organs of the alimentary canal (mouth, phar-
ynx, esophagus, stomach, small intestine, colon, rectum, and anus). The organs
involved in digestion make up the body system known as the digestive system.
Together, all of the body systems make up the human organism (Figure 9.16).