Why Circulate?

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In this activity related to the human circulatory system (on page 10 of the PDF), learners observe the dispersion of a drop of food coloring in water, draw conclusions about the movement of dissolved substances, and develop explanations about the importance of organisms' internal transport systems. This activity allows learners to investigate the process of diffusion and to consider why many organisms have internal transport systems. This lesson guide includes background information, setup and management tips, and a handout.

Quick Guide

Preparation Time:
5 to 10 minutes

Learning Time:
45 to 60 minutes

Estimated Materials Cost:
1 cent - $1 per group of students

Age Range:
Ages 8 - 14

Resource Types:
Activity, Experiment/Lab Activity, Lesson/Lesson Plan


Materials List (per group of students)

  • 2 sheets of graph paper (0.5-cm grid)
  • Graduated cylinder (100-mL or 250-mL)
  • Lid or bottom of a Petri dish
  • Pencil
  • Small dropper bottle of food coloring (red, blue or green; do not use yellow)
  • Tape
  • Timer, watch or clock
  • Digital camera for recording observations (optional)
  • Copies of student sheet (p.12)


  • Life Sciences
    • Cells
      • Cell Structure and Function
      • Cell Metabolism
    • Human Body
      • Circulation
  • Physical Sciences
    • Chemistry
      • Solutions
  • Mathematics
    • Data Analysis and Probability
      • Data Analysis
      • Data Collection
      • Data Representation
    • Measurement
      • Rate
    • Number and Operations
  • The Nature of Science
    • The Scientific Process
      • Conducting Investigations
      • Gathering Data
      • Formulating Explanations
      • Communicating Results


To use this activity, learners need to:

  • see
  • see color
  • read
  • touch

Learning styles supported:

  • Involves teamwork and communication skills
  • Involves hands-on or lab activities


Includes alignment to state and/or national standards:

Includes assesments for student learning:

This resource is part of:

Access Rights:

  • Free access


  • Tharp, Barbara Z. ; Erdmann, Deanne B. ; Matyas, Marsha L. ; McNeel, Ronald L. ; Moreno, Nancy P.


  • All rights reserved, Baylor College of Medicine, 2009

Funding Source:

  • NASA, NCC 9-58