I wanted to follow up with our exploration of the blood stream
by discussing how molecules move in and out of the blood stream. So I turned to the The Body Book
by Sara Stein and read some of it to my children. Included in it was instructions for exploring diffusion with marbles. We used a wooden tray, making our “semi-permeable membrane” out of card paper. Two different colors of marbles were placed in the tray and we shuffled it back and forth on the floor to give the marbles some motion and watch how they spread out. (Holding it the way my son is in the picture makes the marbles all move whichever way it was titled, which defeats the purpose, but I didn’t get a picture of him using it properly.) We talked about how within the body the molecules themselves are moving, rather than the medium they are in causing them to move as happens in our model.
After that we moved into the kitchen to use water and food coloring to watch diffusion in action. We filled two jars with water, measured the temperatures, and then watched as the coloring diffused throughout them. We talked about the effect of temperature on the way the molecules move.
Then because I wanted them to connect the idea of diffusion with the blood stream better, we turned to youtube videos, starting with this animation. I wanted the children to understand a bit about the lipid bilayer, so I reminded them of the times we’ve tried to mix oil and water and we talked about that. At some point in the future we may use little cardpaper models to represent the phospholipids that make up the bilayer.
Another experiment I’m hoping to do on this topic to use an egg as a model of a cell and watch it shrink and grow following the instructions found here
. It might be a while before we do that though, because we tend to skip around on topics.
The children need time to let ideas sink in and to practice applying the ideas in their every day conversation. As we eat our lunch we’ll talk about how the fat molecules can diffuse across the lipid bilayer. As we clean up the blocks and other toys we can pretend that one of us is a transport protein allowing molecules to move through a membrane. Then we could challenge ourselves to figure out how to alter our play to represent different methods of active transport. I’m thinking we could represent vesicles with towels filled with blocks, but I might also make play dough, so that we have a substance where we can explore how to let the vesicle actually join into the membrane layer.
It is important to me as we learn about different methods of transportation across cell membranes that the children get to see the drawings in university level science textbooks. As young as they are they are already developing the ability to look at and interpret the pictures.