BEFORE YOU MOVE ON
LOOKING BACK: Human anatomy is the study of the structure of the human body and the relative relationships among body parts. Human physiology is the study of normal function in the human body. To gain a complete understanding of human biology, knowledge of both structure (anatomy) and function (physiology) is essential.
Levels of organization: In the exercise just completed, you examined the internal organs by observing their relative positions to other organs and organ systems. Your observations were focused on the three highest levels of organization: organ systems, organs, and tissues. The next investigation of organs in an organ system will be the integumentary system (Exercise 6). However, to fully appreciate the unique structure of organs, you will first study two lower levels of organization: the cellular level in Exercises 3 and 4, and the tissue level in Exercise 5. Explain why a solid understanding of the cellular and tissue levels of organization is critical to understanding the structure and function of organs, organ systems, and the complete organism.
At the organ level, two or more tissues work together to form a well-defined, three-dimensional shape and a specific bodily function. At the tissue level, collections of cells perform a specific function. At the cellular level, organelles, which are composed of molecules, are organized in a unique way to form cells. The cell represents the fundamental unit of life. At the chemical level, the chemical bonds between atoms give rise to molecules.
LOOKING FORWARD: The study of cells and tissues is facilitated by the use of several types of microscopes. Scientists use microscopes to view images of objects too small for the naked eye to discern. In the following exercise, you will learn how to correctly use a compound light microscope, which employs a series of lenses to bend or refract light waves that pass through an object, like a section of tissue. As a result, the image is magnified typically 40 to 1000 times.
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