Membrane Models

Today in my Living Environment class, we started talking about cell membranes and the idea of them being selectively permeable.  Since we can't actually see the structure of the lipid bilayer, we built it.  We talked about the hydrophilic heads and the two hydrophobic tails of each phospholipid. We also talked about the proteins embedded in the bilayer that allow molecules through that couldn't otherwise pass through the bilayer.

Each student had a slightly different vision of their membrane. We had some very spread out phospholipids and some very tightly packed ones. Some were more fluid than others. The idea came from a pin on Pinterest.  It was just a pin of a picture, so I'm not sure who to attribute it to.  I typed up a version of the activity for my students based on the picture.  I just made it on a half page, so it would fit easily in their notebooks.  

This bilayer got squeezed into one layer. Oops!

We capped the class off with our diffusion and osmosis lab, so they could see the actual movement of molecules across a membrane. 

Unit 5 Reading Guides--Mendelian Genetics

The Mitosis and Meiosis unit will actually get us to Christmas break. I've made some revisions to the guided reading questions for this two-chapter unit. Here are the Holzclaw guided reading questions pared down to fit within the new AP Biology framework.

Chapter 14 Mendel and the Gene Idea

Chapter 15 The Chromosomal Basis of Inheritance

Introducing the Cell Cycle

Last year I found a lab that worked perfectly for introducing the cell cycle unit.  It was on Darci Harland's blog STEM Mom, titled Engineering Cell Division-a NGSS Lesson. I didn't even reformat it--just printed it as is.

I laid out a box of random supplies such as yarn, string, beads, pipe cleaners, play dough, modeling clay, and gummy worms.  The gummy worms just add an element of fun.  I think they look like chromosomes, but my students usually use them for something else in the cell. They happily eat the worms when they finish the project.

We do this before they even start taking notes on the mitosis and meiosis chapters.  As they work through the design and questions, we can talk about what they are realizing has to happen in a cell before it can divide.  It's so much more than just making a copy of the DNA.  This activity also gives me something concrete to refer back to as we delve into the details of the cell cycle.

Modifying the AP Biology Respiration Lab

Last year when it came time for the respiration lab, we dutifully put together the microrespirometers to complete the lab.  It was fairly labor-intensive, with gluing in the capillary tubes, and gluing on nuts and bolts to make sure the respirometer would sink in the water bath. We had a few leaks, and not all of the respirometers gave us reliable data.

At some point, I read the tips on the College Board website for this lab.  One teacher mentioned that her class made respirometers with test tubes, one-hole stoppers, and a 2 mL pipet.  I spoke with another teacher at an AP Biology workshop I attended last year, and she did the respiration lab with crickets. I decided to give both ideas a try this year.

Before the lab, I made a trip to Lowe's to figure out how to keep the respirometers from floating. Steel pipe couplers provided the solution, The test tubes slid right into them. I also did some searching to find a respiration lab that used crickets.  I found one I liked on Mr. Yeung's website. Here's the link to the lab. The key change we made was using germinating peas instead of meal worms to go along with the crickets. Fortunately I found these white plant trays in the science closet at school, which worked great for the water baths. We also took readings every 2 minutes for 20 minutes.

What a difference a few changes make!  The test tube respirometers worked fabulously.  We had no leaks, and had good readings for most of the respirometers.  A storm was moving through the day we did the lab, and we saw some movement of water into and out of our control respirometers with the plastic beads. We were able to use those readings to make some corrections to the corresponding respirometers. Our biggest challenge was getting the crickets into the test tubes! I am happy to report that all of the crickets survived the experiment.

Next year, I'd like to try KOH pellets or soda lime pellets instead of the liquid KOH we use.  I've seen several teachers mention they like using the pellets better.