Unit D


Biology 20 and Biology 30 include the study of the complex systems of the human body. Although these systems will be introduced individually, they work together to maintain life.

The human body is remarkable because it can withstand an enormous range of internal and external conditions while maintaining a consistent internal environment. The process by which the human body maintains a stable internal environment is called homeostasis. When a system is out of balance, this is detected by a sensor, which triggers an effector to change the internal conditions so that they are brought back into the normal range. This system is known as a negative feedback loop.


Watch the videos below for an introduction to homeostasis in the body.


Read "Human Systems" and "Homeostasis and Negative Feedback" on pages 202 to 203 of your textbook. As you move through Unit D, you will have to identify positive and negative feedback loops, so pay special attention to Figure P4.2.