More Biology

One of my goals with this class is to make it a transition class towards college.  I've been teaching the kids to take notes, study, keep a lab notebook, and (hopefully) learn at a college rate. 

I'm not sure why high school science is usually presented so slowly, but I've always thought the slow bit rate was an interest killer. Not a problem in this class!

Last week we learned (in one two hour class) all the parts of the cell.  I wrote out and explained the parts using candy as models for all the organelles.  If you've ever seen a ribosome, I think you'll agree, they look exactly like nerd candies!

When I had finished my explanation, I had them build cells, using the candy and jello.  The animal cell was a wiggly orange heap, but the plant cell had a firm (tupperware) cell wall!

They then identified and explained and ate their models...

Next, I assigned two organelles to each kid and had them put on a skit in which they portrayed their cell parts.   I used a sheet as the cell membrane.  Mxyl did an excellent nucleus: "Hey!  I tell everyone around here what to do!  Get back to work!!!"

Then we went on to talk about diffusion and osmosis.  I used perfume to show diffusion in air (spray at one end of the room and have kids tell you as they smell it).  And I used food coloring in three jars of water (cold, medium and hot) to show diffusion in liquid. 

Osmosis was the most fun!  Osmosis is the movement of water from an area of greater concentration to less concentration across a membrane.  Really, it's a specialized form of diffusion and very handy to know about whether you are making pickles or washing your contacts or dealing with a sick child!

First, I skinned some eggs.  Unfertilized chicken eggs are a single large cell, but they are hard to look at as a cell unless you take the shell off or "skin" them.  You can do this easily by soaking them in vinegar for two days. As an extra bonus, the vinegar not only dissolves the shell (very fizzy and cool by itself!), it also toughens the membrane so you can pick the skinned egg up and carry it around!  It should be noted that the egg is still completely raw...

We put one egg into water (hypotonic), one into corn syrup (hypertonic), and one into salt water (isotonic?  the Zoomlians made this part up!).

Here's what they look like:

The top one is the corn syrup and you can see how the membrane shriveled as it the water was drawn out of the egg and it shrank.

The next one down is the salt water egg.  It wasn't completely isotonic, probably because the concentration of water is determined by more than salt; the egg contains a lot of protein, so the water was drawn in and it swelled.

The bottom jar is our egg in water, and it is swollen nearly to bursting!  It has a weird taut feel... 

In all of these, the same thing is happening: water is moving from an area of greater concentration (outside the membrane in the water jar, inside the membrane in the corn syrup jar) to an area of lesser concentration (inside the membrane in the water jar, outside the membrane in the corn syrup jar).

I had done 8 eggs total, so we had one left over (each family had their own experiment).  Zorg decided to try his own experiment, throwing the last egg (I think to see if it was really raw).

It was quite spectacular!   He threw it hard enough that he ruptured the membrane!  The white flew about 10 feet and the (denser) yolk flew about 20 feet!  Both were, in fact, quite raw.  An excellent demonstration of physics!  A great idea to do that outside!