Population Growth Curves with Bubbles

This was another mini lab from the collection of labs from Dr. Close that I blogged about here. In this lab students were recreating the 3 different population growth curves by caring or not caring for a population of bubbles.

For the growth curve of k selected species who care for their young to maturity, students blow a bubble and do everything in their power to not let the bubble pop. This included blowing on the bubble and fanning it away from obstacles. This section certainly takes the longest because the bubbles last the longest. I started getting nervous that we wouldn't finish within out 80 minute time frame while students worked on this population, but fortunately, the other two population types go more quickly. Personally, I found this the most hysterical section of the lab, and I think students would agree. (Although none of my pictures quite captured how funny they looked chasing their bubbles around.)

In the next population, students blew a bubble, but could not help it along. This was a hard transition after protecting the first 50 bubbles so carefully.

In the final population, not only could students not help the bubbles, but for them to survive past birth, the bubble had to cross over a meter stick that was one meter in front of the bubble blower. These results mimic the r selected species, often where parents lay many eggs with no parental involvement past that.

After data was collected, students graphed their data on semi-log paper to see how well it matched to the graphs in their textbook.  I reformatted the lab into this document. For the semi log paper, I like the paper from here and choose the 2 decades paper.

This was a great lab to get students outside and moving around a lot. The lab also gave them a real experience to relate back to the graph they needed to understand.

Hardy-Weinberg Population Modeling Lab for AP Bio

I decided that this year, we would bite the bullet and do the AP Biology mathematical modeling lab for populations.  Last year I found a YouTube video of a teacher explaining how to set up the spreadsheet to start the lab.  He did a nice job of explaining what the formulas that students would need to use meant.  For his class, they used Excel, but we generally use Sheets in our class.

I was stoked to see a new resource this December in the College Board AP Biology Community. This resource, done by Brittany Franckowiak was step by step instructions for students to set up a population in Sheets that was in Hardy-Weinberg equilibrium.  Then students are set free to figure out formulas to represent populations that are exhibiting heterozygote advantage, fatal recessive, or small population size (genetic drift).

When I'm doing a lab for the first time, I like to do it myself before I ask my students to. It was easy to follow the step by step directions to create the 5 generations of populations in Hardy-Weinberg Equilibrium.

Then I started thinking about how to represent heterozygote advantage.  In the card based Hardy-Weinberg lab we did last year, for heterozygote advantage we tossed a coin when a homozygous individual was born.  If the coin was heads, they lived, tails, they died.  In the first part of the mathematical model we create, we used an "if" function with the "random" function. I decided that I could add an extra "if" and "random" function to the existing "if" statement that counted homozygous genotypes of zygotes. It would act like a coin toss to decide if the individual would survive or not.

I excitedly shared my newly created formula with my computer programmer husband who regularly manages spreadsheets with a million rows or more.  He gave me a further suggestion.  My formula is done with the assumption that homozygous individuals have a 50% chance of survival, but I can change rand()>=0.5 to rand()>=0.3 if they have a 70% chance of survival (or a 30% chance of dying). I could adjust that number to match whatever a known survival rate is.  I loved this suggestion, although I'm not sure if my students will get that far.  I don't plan to share my formula with them, since I want them to figure out a way to model heterozygote advantage themselves.

Fatal recessive and small population size should be a little easier for them to figure out how to model. I may offer some incentives to encourage them to stick with determining how to model the heterozygote advantage.

I only made a few changes to the document by Brittany Franckowiak and it's here. Also, here is the sample Google Sheet I was working on.  In my sample, I added an additional tab to show heterozygote advantage, but I will have my students make a copy of their original sheet and then modify it for different scenarios.  Keeping it all in one sheet makes A LOT of rows to update every time someone makes a change and can be slow going.