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Learners observe and compare the sizes of three toy “growing” crocodiles made from water-absorbent polymers. One is it its original state, dry, hard, and about 10cm long. One is immersed in salt water in a 2-liter bottle, a bit softer, and about 20cm long. The third is in pure water in a 2-liter bottle and completely fills the bottle. This is a long-term activity. Learners can observe and record the growth of the crocodile over a period of days; it can last in this state indefinitely.

Quick Guide

Preparation Time:
5 to 10 minutes

Learning Time:
1 to 7 days

Estimated Materials Cost:
$5 - $10 per group of students

Age Range:
Ages 6 - adult

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per group of students)

  • Two clear 2-liter soft drink bottles with caps
  • Three crocodile grow creatures (available at many toy stores, the OMSI Science Store, or Flinn Scientific, 1-800-452-1261)
  • water
  • salt


  • Physical Sciences
    • Chemistry
      • Solutions

Informal Categories

  • Toys


To use this activity, learners need to:

  • see

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access



Funding Source:

  • National Science Foundation