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Activity 4-1: How Does a Controller Work?

PLAN

Summary Students relate how controllers work in their bodies to the control of temperature in a water bath. They control the temperature of a water bath around a set point of 37^\circ C (degrees Celsius), which is also their body temperature. Changes in temperature occur when they add ice or heat. Students graph the results and study the effects of overshoot and delay of a variable on a control system.

Objectives

Students:

\checkmark identify the effects of a specific change (adding ice or heat) on the regulating system of a water bath.

\checkmark relate the regulating system of a water bath to regulating systems of the body.

Student Materials

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

Teacher Materials

  • 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)

Helpful Hints

This activity works well in groups of 2, 3, or 4 students.

Monitor use of ice.

It is recommended for safety considerations, not to substitute alcohol or Bunsen burners for hot plates.

Identify students who can help in the setup for the next class.

Advance Preparation

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.

Estimated Time One 50-minute period

Interdisciplinary Connections

Performing Arts Students write and perform a role-play demonstrating how a control system works using temperature or breathing as examples.

Visual Arts Students create a cartoon illustrating how a control system works.

Prerequisite and Background Information

Students need to know how to read a thermometer. They also should have basic knowledge of how to work with tables and graphs.

Control loops utilize negative feedback in which the system counteracts a change with a response in the opposite direction that brings the output back to a set point. A sensor recognizes a rise or fall from the set value of the variable being measured (temperature in this instance), and the controller (the student) compensates for the change in the opposite direction by adding ice or heat.

IMPLEMENT

Introduce Activity 4-1 by reviewing with students the related text information. You may want them to summarize the information in their own words verbally with a partner or in writing.

It is essential that students can identify a variable and have experience working with variables prior to completing the activity.

As a part of your introduction to the activity you may want to demonstrate how to position the thermometer so that it doesn't rest on the bottom of the water bath. A ring stand works well to secure thermometer.

Review safety procedures with students including wearing safety goggles and turning off the hot plate when finished.

Helpful Hints

Coordinate with math teachers regarding table and graph skills. Students may make their table and graph in math class prior to doing the activity.

As an option, you may want to provide the table (Resource 2) and graph (Resource 3).

Since controllers are common in physiological systems and central to maintaining homeostasis, this activity occurs in 3 places in the curriculum: (1) Circulation, (2) Breathing, and (3) Nervous System.

Steps 1-2 You might want to list the roles on the chalkboard or on poster board and post it in the front of the room.

Step 3-5 Remind students of safety rules for using hot plates or any heating device. Act as a model by wearing safety goggles when using a hot plate.

At the beginning of each class, be sure the water bath is less than onefourth full of ice water.

ASSESS

Use observations during the activity and the written answers on the Activity Report to assess if students can

\checkmark construct and read a table and graph.

\checkmark summarize the importance of an efficient regulating system.

\checkmark explain how the water bath example relates to the regulation of the exchange of gases in their body.

Activity 4-1: How Does a Controller Work? – Activity Report Answer Key

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. Was your group able to keep the temperature constant (close to 37^\circ C) over the 20 minutes? Explain.
  2. What adjustments did you make to keep the temperature constant?
  3. Describe your graph. Explain.
  4. Where in your brain is the controller for body temperature?
  5. On the diagram of a control system below, add the terms temperature, your role, water bath, and thermometer. Write a brief paragraph to explain how a control system works. Use Resource 1 to check your answers.
    1. If the temperature of the water increases (Figure 4.1a) the sensor signals the controller to add ice to the water, causing the temperature of the water to decrease to 37^\circ C
    2. If the temperature of the water decreases (Figure 4.1b) the sensor signals the controller to turn up the heat, causing the temperature of the water to increase to 37^\circ C.

    What Do You Think?

    What is your opinion about the procedure that some athletes use called “blood doping”? Some athletes have some of their blood withdrawn and put in cold storage. Their bodies make new red blood cells to replace the ones that were withdrawn. The athletes have their stored blood transfused back into their bodies just before the event. This increases the number of red blood cells in their blood and the amount of oxygen they are able to take up from each breath. Why do you think an athlete might do this? Do you think blood doping should be an illegal procedure? Why or why not?

Review Questions/Answers

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. How does the need for oxygen change as you exercise? How does the amount of oxygen in your blood change as you go to a higher altitude?
  2. Describe how your body's controllers work like thermostats by using negative feedback.
  3. How does your breathing controller work?
  4. Describe how red blood cells and diffusion relate to breathing.

Activity 4-1 Resource 1: How Does a Controller Work? (Student Reproducible)

At the start of the experiment, the temperature was adjusted to 37^\circ C. The temperature was monitored by the thermometer (sensor) for 20 minutes. If the temperature (variable) of the water in the water bath (controlled system) went up, you (controller) added ice to the water bath. If the temperature of the water in the water bath went down, you turned on the heater under the water bath.

Activity 4-1 Resource 2: How Does a Controller Work? (Student Reproducible)

Time Water Temp. in degrees C
0
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4
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20

Activity 4-1 Resource 3: How Does a Controller Work? (Student Reproducible)

Activity 4-1 Report: How Does a Controller Work? (Student Reproducible)

1. Was your group able to keep the temperature constant (close to 37^\circ C) over the 20 minutes? Explain.

2. What adjustments did you make to keep the temperature constant?

3. Describe your graph. Explain.

4. Where in your brain is the controller for body temperature?

5. On the diagram of a control system below, add the terms temperature, your role, water bath, and thermometer. Write a brief paragraph to explain how a control system works. Use Resource 1 to check your answers.

a.

b.

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