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Key Ideas

  • The body has control systems that regulate essential body functions mostly through negative feedback.
  • Controllers allow the respiratory system to adapt to changing conditions, such as exercise or changing levels of oxygen in air.
  • Red blood cells pick up and deliver oxygen to cells as needed and help get rid of excess carbon dioxide. Your body can adapt to changing conditions by making existing cells work harder, or by making more red blood cells to increase capacity.


Students extend their knowledge of the human respiratory system from the previous sections by investigating the control systems of the body and how they affect short- and long-term changes in breathing. In the controller activity, students use a model of negative feedback and relate it to the body's control system for regulating temperatures and the exchange of oxygen and carbon dioxide gases.



\checkmark describe how a negative feedback system works.

\checkmark explain how homeostasis relates to feedback.

\checkmark manipulate a model to learn about how a negative feedback system works.

\checkmark relate a water bath control system to the body's temperature control system.

\checkmark discuss the role of the nervous system in the regulation of the breathing system.


blood gas level, control systems, feedback information, homeostasis, thermostat

Student Materials

Activity 4-1: How Does a Controller Work?

  • Resource 1
  • Resource 2
  • Resource 3
  • Activity Report
  • Water bath (e.g., 1,000-ml beaker); Thermometer; Crushed ice in container; Heater (hot plate)

Teacher Materials

Activity 4-1: How Does a Controller Work?

  • Activity Report Answer Key
  • Additional supply of ice and towels
  • Cold water; Examples of other controllers such as a thermostat (demonstration)
  • Extension cords; Hot pads; Diagram of brain showing hypothalamus, pons, and medulla; Multiple plug electrical strip (surge protector)

Advance Preparation

See Activity 4-1 in the Student Edition

Activity 4-1: How Does a Controller Work?

  • Confirm that the electrical outlets will handle the electrical load.
  • Prepare containers of ice water in advance.
  • Position hot plates so the cords are not a hazard.

Enrichment Activity

Enrichment 4-1: Using a Bicycle to Demonstrate How Controllers Work

Background Information

The terms regulation and control might seem to be interchangeable, but they are different. Regulation refers to maintaining a desired value within specific limits, while control implies the ability to change a process or the rate of a reaction. Feedback information in physiological systems is used to regulate many body functions. The information provided by feedback is compared to the desired value (set point), and any differences result in corrective action to return to the desired value. Negative feedback is the most widely used feedback in physiological systems and maintains the desired value. The information results in a change of direction back toward the desired value. For example, when body temperature is falling, negative feedback reverses it, resulting in an increase in body temperature back to normal. Positive feedback would amplify the initial response of the falling temperature. You can see why negative feedback makes good sense for physiological regulatory systems. We use the term controller in the student edition when discussing the regulation of physiological systems because it is more appropriate for students in middle grades.

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