Monday, September 14, 2015

Biology: Cells Part 2

 We also talked about one of my favorite scientific concepts: diffusion.  It's amazing how many biological (and physical) processes rely on diffusion.

We started by dropping dye into hot and cold water.  The dye diffused slowly in dream like clouds in the cold water, but rapidly in the hot.

One kid observed that the hot water stirred itself, which is very apt:  the molecules are moving quickly, so they are mixing themselves around.

I also tried the trick of spraying perfume in one corner of the room and having the kids (who were sitting in a line) raise their hands when they smelled it.    

Last time I did this, it worked perfectly, with each kid smelling it as the diffusion progressed.   
This time I had kids with allergies who couldn't smell much, and the air conditioning was on which changed the air flow. A partial success.

We also talked about osmosis: diffusion of water across a membrane.  This is one of my favorite experiments!

In my first class of the week, we put eggs in vinegar.

By the second class, their shells were dissolved, leaving only the membrane.

We were ready to observe osmosis!

We put two in water, two in brine, and two in corn syrup, and we will see what they look like on Tuesday.

Lastly, we took a look at some beans which we had wrapped in damp paper towels during the first class.

One group was moistened with water, another with salt water, and a third with vinegar.

The idea was to design an experiment with a hypothesis and controls.

The water sprouted the beans, no big  surprise there.

The salt and vinegar both prevented sprouting and caused the color of the beans to bleed on the paper towels, with the added bonus that the acid in the vinegar shifted the bean color redder!

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