Unit 5 and the benefits of "lab first"

I'll admit, I may have strayed from the central theme of modeling instruction-- "the model."  I'm still struggling with the concept of the "model" for biology.  Our models just end up being, well, notes.  I realize I haven't even been using the word "model" this semester as I did in the earlier units.  I should try to improve upon that and re-incorporate the concept of the model.

But I have become an ardent fan of the "lab first" style of teaching science.  I don't think I'll ever go back to a traditional lecture/lab structure.  One of many teachers' criticisms of labs is that the students often miss the point.  I frequently saw this myself:  you'd cover a topic like osmosis and diffusion, then go into the lab supposedly to reinforce the concepts.  The problem was the students often couldn't put two and two together and just ended up going through the motions.  I'd frequently skip discussing the lab in lieu of just having them answer questions about the lab, which they often answered poorly.

The benefits of switching to lab first are innumerable.  Two of the biggest are that it forces you to actually discuss the lab results and it gives the students something tangible to make connections with.  The only downside is that I occasionally get a snarky comment from a student who thinks he/she knows it all ("I don't get how this is supposed to show us ______.").  But even those are rare and have greatly decreased.

For example, this week I have been covering cell membranes and transport.  Hypertonic, Hypotonic, and Isotonic are terms students traditionally struggle with.  So earlier this week, we made rubber eggs (instead of the potato lab) that were ready for today:

From left to right, eggs soaked in distilled water, a mixture of corn syrup and water, and corn syrup alone

The students were able to talk out what happened to the eggs and form a conclusion based on what they already learned about osmosis.  All I had to do was introduce the new terms.  The concept of "hypertonic" is a million types easier for a student to grasp when they are quite literally grasping a deflated egg in their hand.  And when they got confused, I just reminded them to think about the eggs.

I gave my classes Unit 5 Exercise 2 today (I replaced "potato" with "egg").  Several of my students told me it was "easy."  That's nice to hear for a change!