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Activity 6-1: Pressure, Resistance, and Flow

PLAN

Summary Students investigate the relationships among pressure, resistance, and flow using tubes, containers, and water. The water represents the blood, while the tubes represent the blood vessels. In Part A, students explore resistance by using tubes of differing diameters to demonstrate that the rate of flow in the narrow tube is less than the rate of flow in the wider tube. In Part B, students explore pressure and flow by using a large water reservoir with holes at three levels to demonstrate that the greater the pressure (hole closest to the bottom), the greater the flow of water.

Objectives

Students:

\checkmark demonstrate that narrower tubes have more resistance than wider tubes, thus decreasing rate of flow.

\checkmark describe how greater pressure means increased rate of flow.

\checkmark describe pressure, resistance, and flow of blood from the heart and through the blood vessels.

Student Materials

  • Activity Report
  • 2 large containers or beakers; 2 equal lengths of flexible tubing of different inside diameters; Clamp; Metric ruler; Plastic bottle; Tape; Large nail; Water; Sink or container to collect water

Teacher Materials

  • Activity Report Answer Key
  • Towels and sponges for cleanup

Advance Preparation

Part A: Find tubing with differing diameters. The diameters must be different enough to clearly demonstrate a difference in the rate of flow.

Part B: Collect plastic containers. Gallon milk bottles work well.

Estimated Time One 50-\mathrm{minute} class period

Interdisciplinary Connection

Math In the class, students can calculate the rate of flow for each of the containers. The volume and time must be measured, and the rate calculated by the following formula.

\text{Rate} = \frac{\text{Volume}}{\text{Time}}

Prerequisites and Background Information

Students need some experience with the development of line graphs. Students should have some knowledge of pressure heads and resistance, concepts studied earlier in this unit, and how they affect the flow of water from a container.

Like the inside wall of blood vessels, the walls of the tubes create friction that decreases the flow in the tubes. If resistance is lowered in a tube, the flow will increase unless the pressure is decreased. When the pressure is increased, as it is for the holes on the bottom of the large container of water, the rate of flow is increased. The heart must work harder to provide the pressure necessary to push the blood through the tubes in order to maintain the blood flow in diseased arteries that are narrower.

Helpful Hint

Monitor time to allow for adequate cleanup.

IMPLEMENT

Part A

Steps 1 - 8

Place the setups for Parts A and B so that the water can flow into the sink or into a large tray or container.

Make sure the same amount of water is in each beaker. Also make sure no water leaks out as students submerge their tubes.

Make sure students organize the tasks. Make sure someone is timing the flow and someone is recording the data. Monitor the location of the tubes. This activity can get messy if the tubes are not pointed into the container or the sink.

Part B

Steps 1-6

Review the safety rules. Remind students to be careful when making the holes with the nails. Make sure the holes are at different heights. It is helpful if the holes are slightly at a downward angle as well. Again, make sure the holes are facing the container or sink. Make sure someone is timing the flow and someone is recording the data.

Guide students in effective and timely cleanup.

Extend Activity 6-1 by suggesting possible variations that can demonstrate the relationships among pressure, resistance, and flow in the circulatory system.

ASSESS

Use the results of the experiment and written responses to the Activity Report to assess if students can:

\checkmark explain the effect of different diameters of tubes on the rate of flow.

\checkmark describe the relationship between resistance and rate of flow.

\checkmark describe the relationship between pressure and rate of flow.

\checkmark make connections between the experiment and the heart and blood vessels.

\checkmark explain how their predictions compared to the actual results.

Activity 6-1: Pressure, Resistance, and Flow - 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.

Part A

  1. How many seconds did it take to empty Beaker A?______ Beaker B?_____
  2. From which beaker does the water flow the fastest? _____ the slowest?
  3. a. From which beaker does the flow go the farthest out of the tube? b.The difference in the stream of water is due to resistance. Explain.
  4. What is one thing that this experiment tells you about how vessels in the circulatory system function?
  5. How do you think the heart compensates for arteries narrowed by fat and cholesterol deposits?
  6. What happens if the vessel (artery) becomes completely clogged with fat?

Part B

  1. How does the flow from each of the three holes differ? Why?
  2. In Part A you saw that increasing the resistance (the narrower tube) decreased the flow. In Part B the resistance provided by all three holes is the same since their diameters are the same. Why is there a difference in the flow from each of the three holes?
  3. What do you predict will happen if you replace one of the rubber tubes with a glass tube of the same length and inside diameter? Explain.

The You in You Students draw the circulatory system in an outline of their body.

  • A Suggested responses will be provided upon request. Please send an email to teachers-requests@ck12.org.

Remember that your heart is two pumps working together. Which pump is stronger? You know both pumps have to pump the same amount of blood. Why does one have to be stronger than the others?

Cold Toes Students do a library search to explore frostbite, gangrene, and circulation.

In which blood vessels is the rate of blood flow the slowest? In which blood vessels is blood pressure the lowest?

Activity 6-2: How a Controller Works

PLAN

Summary Students learn how controllers work in their bodies by regulating the temperature of a water bath. Students control the temperature of a water bath around a set point of 37^\circ Celsius (98.6^\circ F), which is also their body temperature. When disturbances occur, they add ice or heat. They graph the results and study the effects of the 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 the water bath.

\checkmark explain how the control system of the body regulates temperature and relate the system to the way the heart and blood vessels are controlled.

Student Materials

  • Activity Report
  • Resource Sheets 1, 2, and 3
  • Water bath 0,000\;\mathrm{ml} beaker); Thermometer; Crushed ice in container; Hot plate or other heat source; Paper towels

Teacher Materials

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

Advance Preparation

Be sure to have a custodian confirm that the electrical outlets will handle the necessary electrical load. Prepare containers of ice water in advance. Position hot plates so the cords are not a hazard. Prepare safety rules for using hot plates, electricity, and water.

Estimated Time One 50-\mathrm{minute} period

Prerequisites and Background Information

Students need some experience with reading a thermometer. They needs some skills in creating tables and graphs.

IMPLEMENT

Introduce Activity 6-2 by discussing with your students the following questions: What makes your heart beat faster? What makes it beat slower?

Steps 1-2

Make sure you model safe behavior in the lab by wearing goggles. Make sure the students wear goggles during this 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 the thermometer.
  • review safety procedures with students including turning off the hot plate when finished.
  • review with students the information in the text. You may want them to summarize the information in their own words either as an oral presentation with a partner or in writing. It is essential that they are familiar with the concept of a variable prior to completing the activity.

Divide the class into groups of four. Remind students of the following four jobs in each group.

Student 1 watches the thermometer and tells the others to add ice or heat in order to keep the temperature at 37^\circ Celsius.

Student 2 adds ice water to the bath if the thermometer reads greater than 37^\circ C.

Student 3 turns on the hot plate if the thermometer reads less than 37^\circ C.

Student 4 is the recorder and completes the temperature table.

Steps 3-7

At beginning of each class, be sure the water bath is less than one-fourth full of ice water. Remind students of the safety rules for using hot plates, heat, and electricity. Post the safety rules.

Make sure students are taking the temperature at 2-\mathrm{minute} intervals for 20\;\mathrm{minutes}. Model for students how to plot the data.

Allow enough time for cleanup.

Extend Activity 6-2 by asking students do one or more of the following.

  • Design and build a thermostat.
  • Role-play a control system.
  • Research other control systems of the body.
  • Create a drawing illustrating how a control system works.

Helpful Hints

  • This activity works well in groups of 2, 3, or 4 students. However, if students are in groups of fewer than four, one or two students will have to function in more than one role.
  • Monitor the use of ice.
  • For safety considerations, DON'T substitute alcohol or Bunsen burners for hot plates.
  • Identify students who can help set up for the next class.
  • 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) after the activity and compare the students' data for these.

ASSESS

Use the results of the activity and written answers on the Activity Report to assess if students can:

\checkmark observe and read a thermometer.

\checkmark construct and read a table and graph.

\checkmark explain the importance of an efficient regulating system.

\checkmark describe how the water bath example relates to the negative feedback regulation of blood pressure to keep the cardiovascular system in homeostasis.

Activity 6-2: How a Controller Works 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\;\mathrm{minutes}? Explain.
  2. What adjustments did you make to keep the temperature constant?
  3. Describe your graph.
  4. Where in your brain is the controller for blood pressure?
  5. On the diagrams of control systems below, add the terms temperature, your role, water temperature, add ice, turn up heat, and thermometer where appropriate. Write a brief paragraph to explain how a control system works. Use Resource 1 to check your answers.
  • A Suggested responses will be provided upon request. Please send an email to teachers-requests@ck12.org.

Why might doctors watch diastolic pressure more carefully than systolic pressure?

Suppose you find a person who has cut himself and lost a lot of blood. He may be unconscious. He's pale. His heart beats fast but his pulse is weak and hard to find. Put all these observations together to explain what you have observed.

His skin is pale. Why? The body closes down nonessential capillary systems so those more important ones, such as those to the heart and brain, can be filled with what little blood is left. The heart beats faster and harder because the control system is trying to restore blood pressure in the aorta. The pulse is weak because there is too little blood in the arteries to give a fuller pulse. The blood that should have been in the arteries is now on the pavement. The person is in shock and needs help immediately.

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. Describe two factors that affect cardiac output.
  2. Why is the muscular wall on one side of the heart thicker than on the other side?
  3. What is the difference between systolic and diastolic pressure?
  4. How does a controller work?
  5. What does the term homeostasis mean? How does it relate to blood flow?

Activity 6-1 Report: Pressure, Resistance, and Flow

Part A

1. How many seconds did it take to empty

Beaker A?_______

Beaker B?_______

2. From which beaker does the water flow the fastest? _______ The slowest?_______

3. a. From which beaker does the flow go the farthest out of the tube?

b. The difference in the stream of water is due to resistance. Explain.

4. What is one thing that this experiment tells you about how vessels in the circulatory system function?

5. How do you think the heart compensates for arteries narrowed by fat and cholesterol deposits?

6. What happens if the vessel (artery) becomes completely clogged with fat?

Part B

7. How does the flow from each of the three holes differ? Why?

8. In Part A you saw that increasing the resistance (the narrower tube) decreased the flow. In Part B the resistance provided by all three holes is the same since their diameters are the same. Why is there a difference in the flow from each of the three holes?

9. What do you predict will happen if you replace one of the rubber tubes with a glass tube of the same length and inside diameter? Explain.

Activity 6-2 Resource 1: How a Controller Works

If blood pressure increases, sensors in arteries send nerve impulses to the medulla. The medulla sends fewer signals to the heart. This decreases the heart rate and force of contraction, lowering blood pressure.

If the blood pressure decreases, sensors in arteries send nerve impulses to the medulla. The medulla sends more signals to the heart. This increases the heart rate and force of contraction, raising blood pressure.

Activity 6-2 Resource 2: How a Controller Works

Use this table to record your observation data.

Time Water temperature ^\circ C
0
2
4
6
8
10
12
14
16
18
20

Activity 6-2 Resource 3: How a Controller Works

Graph your data.

Activity 6-2 Report: How a Controller Works

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

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

3. Describe your graph.

4. Where in your brain is the controller for blood pressure?

5. On the diagrams of control systems below, add the terms temperature, your role, water temperature, add ice, turn up heat, and thermometer where appropriate. Write a brief paragraph to explain how a control system works. Use Resource 1 to check your answers.

a.

b.

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