Potato Osmosis activity

We talked about semi-permeable membranes and how nutrients, oxygen, and other things pass from the capillaries to the cells, or the alveoli to the capillaries, by diffusion or osmosis. This simple activity demonstrates the effects of osmosis. You cut a potato in half and put half of it in plain water and the other half in salt water. Then wait a few hours. (Put the cut side facing down; this picture shows it after we'd already turned it back over.) 

(White dish) Because there is a lower concentration of water in the salt water (the salt is "taking up" some of the space), the water in the potato cells moves out via osmosis. That makes the cells "floppy" or flaccid, since they have lost some of their water. You can feel that the potato is squishy and limp.

(Clear dish) The potato in the plain water stays firm and crisp. Because the concentration of water on the outside of the potato (in the dish) is the same as the concentration on the inside (in the cells), no osmosis occurs, and the cells stay firm and maintain their shape.

For another explanation of this, see here.

Heart Cookies

Not sure there is much to say about this. We made heart cookies. The little kids just used regular-shaped hearts and frosted them in sections with purple (unoxygenated blood) and pink (oxygenated blood) to show how blood flows through the heart. They had to show me the four chambers and describe the path of the circulation. (These cookies aren't pictured—the hearts below were just our leftovers!) Abe actually tried to shape his cookie into a real heart shape, though, and show the valves and the septum and so forth. I loved the way his cookie turned out!

Here are some other edible heart models you could make with graham crackers.

Blood Cells Under Microscope

After we did the blood typing activity we quickly smeared some of that nice blood onto a microscope slide so we could look at it! We have looked at blood cells before and they're very interesting, but it is harder than you think to get liquid blood! I've tried poking myself with a pin lots of times and I just can't get any blood (my survival instincts won't let me draw blood, I guess!). When I went to donate blood, I actually asked the nurse if I could have one of those little finger-pokers to use later, so I've got that one in reserve! But anyway, we already had some blood after blood-typing, so we leapt at the opportunity. :)

We're no experts in microscopy, so I'm not sure I can describe all the things we're seeing here, but you can definitely see those little flat/round cells! I am not sure if you can tell the red blood cells from the white? The white are bigger, we know. We thought we were picking out some differences but just weren't sure. And of course, my little iPhone photos don't really do justice to what we were seeing. It's hard to get in position a good picture without some sort of attachment for the phone!

We thought maybe that green triangle thing in the bottom left corner was a platelet?

And here is the blood as it was drying and starting to clot.

Blood typing activity

You know what's really fun? Testing your blood to find out what type it is. I already knew my blood type, but I wanted to do this activity anyway because its so fun smearing your blood around on the little test circle and seeing it clot (or not)! I highly recommend it.

And since none of the kids knew their blood types, it was extra fun to find them out! I ordered these blood typing kits from Amazon (the five-pack) and we would have happily used a couple more. They are very simple to use; just make sure you read the instructions and have everything set out and ready before you start.

I told the kids the finger-prick wouldn't hurt. And it didn't. But some of them were a bit offended by it anyway. (Here is Daisy pretending to be offended.) It did help to soak the fingers in warm water first so the blood would flow. Although with Abe, our first subject, the blood flowed a little TOO well and got everywhere! So we soaked the later kids for a little less time. You really don't need much blood. You don't need to saturate the entire circle with blood like they do for an infant PKU test. You just need enough to react with the antigen.

And here are the finished samples! Kind of fun to have them all collected on little cards like that.