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A System of Transport

A System of Transport

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  • Grades:
  • 6-8
  • Length: 60 Minutes

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Students work in teams to simulate the movement of blood through the circulatory system by transferring liquid into—and through—a series of containers.

This activity is from The Science of the Heart and Circulation Teacher's Guide, and was designed for students in grades 6–8. Lessons from the guide may be used with other grade levels as deemed appropriate.

Teacher Background

Every living organism—even single-celled organisms—must interact with its environment to exchange gases (oxygen and carbon dioxide), obtain nutrients and eliminate wastes. In general, larger and more complicated organisms (such as humans) have more sophisticated, efficient systems to transport needed materials to and remove waste from cells where exchanges occur.

The circulatory system in most adult humans circulates approximately 5.0 liters (5,000 mL) of blood around the body every minute. In newborns, half this amount of blood is pumped. And approximately 4.1–4.3 liters of blood circulates each minute in children and adolescents. With each contraction, an adult heart pumps about 60–130 mL of blood out from the left chamber (also called left ventricle) into the artery that leads to the body. In children and adolescents, the amount pumped is about 40 mL per contraction.

Humans have a closed circulatory system. This means that whole blood, for the most part, stays inside the blood vessels and heart, and does not mix with other body fluids. A good example of a closed system is the water treatment facility in your town. The facility sends clean water to your home through pipes. If the pipes are working properly, the water does not leak out. After you use the water, you pour it down the drain. From there, it travels through a different set of pipes back to the water treatment plant, where it gets cleaned again for re-use.

In much the same way, the human circulatory system moves blood to all parts of the body through the blood vessels (pipes or tubes). The pump that drives the blood through these vessels is the heart. Like water in pipes, whole blood stays inside the blood vessels. And just as large water mains divide into smaller and smaller pipes (like those under your sink), the large blood vessels attached to the heart divide into smaller and smaller vessels, so that each cell in the body is near to or touching tiny blood vessels. On the way back to the heart, blood vessels merge together into larger veins. Like water in a treatment facility, blood gets cleaned during each round-trip, and is made ready to use again and again.

The circulatory system is the “transportation system” for the body, and blood serves as the transport vehicle. Just as trucks deliver food, clothes, and other goods to houses and stores, blood circulates around the body, carrying and delivering the oxygen and nutrients needed by each cell. And like trucks that carry garbage away from our homes, the blood in our bodies picks up waste products (carbon dioxide and cellular waste) from cells, and takes wastes to organs that eliminate them from the body. As blood travels through some organs, it also makes special drop-offs and pick-ups.

  • At the lungs, blood drops off carbon dioxide (waste), water and heat, and picks up oxygen.

  • At the kidneys, blood drops off waste products, excess water, salts and vitamins.

  • At the intestines, blood picks up nutrients, minerals, water and some vitamins.

  • At other organs and glands, blood picks up hormones that help regulate body functions.

Objectives and Standards

Life Science

  • Living systems at all levels of organization demonstrate the complementary nature of structure and function. Important levels of organization for structure and function include cells, organs, tissues, organ systems, whole organisms and ecosystems.

Physical Science

  • The motion of an object can be described by its position, direction of motion, and speed. Motion can be measured and represented on a graph.

Science, Health and Math Skills

  • Measuring

  • Creating a model

  • Comparing

  • Questioning

  • Calculating

  • Drawing conclusions

Materials and Setup

Teacher Materials

  • Marker or labels for tubs

  • Timer or clock

Materials per Group of Students (see Setup below)

  • 6 tubs or buckets labeled A–F (5-liter capacity each)

  • 4 flexible plastic cups (soft plastic that can be cut with scissors)

  • 2 15-mL tablespoons for measuring

  • Graduated cylinder (100-mL or higher)

  • Pad of sticky notes

  • Pair of scissors

  • Paper towels

  • Roll of masking tape

Materials per Student

  • Copy of student sheet (see Lesson pdf)


  1. Have students conduct the activity in teams of six. For easier management, have two teams carry out the activity simultaneously, possibly as a relay race.

  2. For each team, label each of six large (at least five-liter) containers with a letter, A through F. Place five liters of water in container “A.” Leave the remaining containers empty.

  3. Before students begin the activity, write “5,000 mL” on a large sticky note and place it on the board. This number represents the five liters of blood pumped through the average adult circulatory system in one minute. But do not mention its significance until students post their group numbers (see Procedure, Item 10).

  4. Note: It may be advisable to review metric units for measuring volume.

Procedure and Extensions

  1. Divide students into teams of six. Then have team members count off from one through six. Each number designates a different role on the team.

  2. Ask the Materials Manager and a helper from each group to pick up student worksheets, container “A” with five liters of water, other containers marked as B–F, a beaker or graduated cylinder, four plastic cups, scissors, two tablespoons, masking tape and several paper towels.

  3. Have students calibrate four plastic cups as measuring tools, as follows.

    • Using the graduated cylinder, fill two cups with 60 mL of water and two cups with 30 mL of water.

    • Wrap a piece of tape around each cup, with the top edge of the tape lined up with the level of the water.

    • Empty all cups and cut off the top of each at the upper edge of the masking tape.

  4. Explain to students that they will be participating in a “water relay race” by following a specific set of procedures. Each six-member relay team will work together to move five liters of water from container “A” all the way to container “F.” Each team member may move water only by using the measuring cup or tablespoon assigned to him or her. Teams may not skip any steps. Review the assignment for each team using the “Move It” student page.

  5. Set a time limit (three minutes is suggested) and tell student groups that they will measure the amount of water they are able to move to container “F” before the set time expires. Set up a system of tubs (A–F) arranged in a line to demonstrate a few steps in the procedure and ask if there are any questions.

  6. Have students set up their relay systems, two groups at a time. Before they begin, check each team’s setup. Start the activity with both groups simultaneously. All team members should stop when time is called.

  7. Each team should record on a sticky note the number of mL of water in container “F” (total volume moved during the relay). Each team’s note should be placed on the board in numerical order, before or after the 5,000 mL note that you had earlier placed on the board.

  8. When all teams have posted their results, ask, What do you think was modeled by the water relay race? Take time to consider all responses. [The relay models the amount of blood pumped around the body (cardiac output) for an average adult, per minute.]

  9. Next, refer to the numbers posted by each group. Ask, Why is the number, 5,000, on the board? Discuss and explain that this number represents the 5,000 mL (or five liters) of blood that typically are pumped from the heart through the body of an adult each minute.

  10. Ask, Which part of your team’s system modeled the amount of blood that leaves the heart with each contraction? [transfer of 60 mL of liquid into Container A] Sixty mL represents a typical amount of blood exiting the heart into the body (varies between 60 and 130 mL in adults). In the model, what other parts of the circulatory system were represented? Use a simplified illustration of the circulatory system (photocopy and make a transparency of the diagram on p. 2, or download a PowerPoint® slide of the circulatory system from to explain how, after blood is pumped from the heart into the body, it travels through a series of vessels, called arteries.

    Arteries become progressively smaller further away from the heart. The smallest vessels, called capillaries, are thinner than a hair. They allow the transfer of nutrients, oxygen, waste and carbon dioxide between blood and individual cells. In most of the body, nutrients and oxygen are transferred from blood into cells, while waste and carbon dioxide move from cells into blood, which carries them away to be eliminated from the body.

    Vessels that convey blood back to the heart, called veins, become progressively larger in diameter until they reach the vena cavas, through which blood enters the heart. Ask, Is your team’s system a good model of the circulatory system? What are the shortcomings? How might we make it better?

  11. Have student groups create a literary representation of arteries, veins and capillaries to help them remember the function of each vessel. The representations can take the form of a poem, acronym, acrostic, rebus or other mnemonic. All representations should convey the following concepts: arteries carry blood away from the heart and have a larger diameter than capillaries; capillaries are very narrow and very numerous, which permits the transfer of materials—such as nutrients, oxygen, carbon dioxide and waste—to cells; veins are comparable in size to arteries and bring blood back to the heart.

  12. Have students display their representations around the classroom. Ask, Why do you need to know about your blood vessels? Have you ever heard or seen an advertisement about health problems related to blood vessels? [for example, high blood pressure or blood clots]

  13. Have student groups add information to their concept maps, including answers to any questions posed earlier.

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    Heart and Circulation Teacher Guide

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Funded by the following grant(s)

National Space Biomedical Research Institute

National Space Biomedical Research Institute

This work was supported by National Space Biomedical Research Institute through NASA cooperative agreement NCC 9-58.