Fun, early biology activity with observations and patterns...

Students go from cup to cup observing the size of water absorbing spheres.  Each cup has a slightly different concentration of salt.  I use little cups numbered 1-10, where one is pure water and 10 is pure salt, while 2-9 represents the continuum of saltiness.

Cups 1 (pure water-left) through 10 (pure salt-right) placed in order.  These cups are placed around the room, so students can observe them in order through stations around the room. 

There are two of each cup, so that there is a back up when students spill one of the cups.  Students easily notice the pattern that the "cells" gain progressively less water as the salt concentration increases.

Here are three of the stations...

Station 2 low salt

Station 8 salty water

Station 10 pure salt

Observing patterns and generating explanations to describe those patterns are at the heart of the Crosscutting Concepts of the NGSS.  This activity has students observe patterns about cell transport by using anything after a google search of "balls that absorb water".  Here is a link to one one source of these beads.

What I like about this...
1.) Students quickly construct an understanding of membranes that includes selective permeability where water goes through a membrane easily while salt may limit the flow of water into a cell.
2.) Students get a concrete experience with cell membranes.
3.) Students move, observe, and find patterns with materials that they associate with cool and fun.
4.) This transitions nicely into potato mass change labs and/or egg diffusion/osmosis experiments.
5.) This provides an example of something that is not living and the opportunity to clarify what it means to be alive.
6.) They start to describe movement of particles into and out of cells using evidence.
7.) This lays the foundation for the cell membrane as homeostasis helper as the "cells" don't explode.

What I don't like about this...
1.) I am not sure that these things are really made of.
2.) Some students have a conception that the salt blocks the pores of the "cells", which I don't think transfers nicely into formal osmosis principles.

Students using their lab notebook to gather data to find patterns.

The next step after this is for students to observe the mass of potatoes in different conditions. After the potatoes change mass one day, they will place the potato into another solution to try to bring that potatoe mass back up (reinforcing homeostasis).  This will come in a future post.