Remind students that the purpose of the 2-bottle systems is to gather data about what happens to water after it disappears. Today they will carefully study changes in their "home" system and record their observations using annotated drawings.

Today's investigation question is:

What is happening in the 2-bottle systems?

What is a system?

Introduce the term system.

• school system
• respiratory system
• transportation system
• solar system

Highlight these three essential ideas:

1. Systems have components.

   For a school system, some components include: students, teachers, classrooms, a curriculum, administrators, etc.

   For the 2-bottle systems, the components are: water; blue food coloring, or salt, or earth materials, depending on the system; the air inside the bottles; and the inside surface of the plastic bottles. Heat from the lamp is energy that comes from outside of the system and has an influence on the interactions of the components.

2. Systems have boundaries (edges or limits).

   Determining the boundary means choosing what's inside and what's outside the system.

   For the 2-bottle systems, the boundary is the plastic material that makes up the bottles. The lamp is outside the system, but the energy from the lamp is an input to the 2-bottle system.

3. The components of a system interact within the boundaries.

   In a school system, the teachers, students, the curriculum, administrators, etc. all interact.

   The interactions of the components of the 2-bottle system (such as water, air, and earth materials) are the focus of our next set of investigations.

The 2-bottle system is a closed system. Elements inside the system will remain there, and nothing new will be added to the system. The mini-lakes with the covers off are open systems.