Hot Potato Lab

This year, my school is teaching our high school Biology classes through College Board's Pre-AP program. Even my Honors Biology class is going through Pre-AP Biology. One of the concepts that I have to teach with this curriculum that I haven't before at this level is Surface Area to Volume ratio in the context of how it plays a role in the size of cells. 

I teach this in AP Biology and we do the Surface Area to Volume diffusion lab using agar with phenolphthalein and sodium hydroxide and soak different sized cubes in dilute hydrochloric acid. I love this lab, but don't want to do it with my honors bio students, since they would do it again in AP Bio. So of course, I did a google search and found this hot potato inquiry lab. 

From the lab linked above (which is the answer key to the lab), I put together a google doc for my students to work with. Here is the link to that lab document.

I loved this lab, and I'll be keeping it in my curriculum for sure. Like many of the labs I do with students, I was so busy helping them trouble shoot and prepare that I forgot to take pictures. 

My students liked this lab because they got to use our Vernier temperature probes, and they love to use the probes. Since they used probes, students could just poke the probe right into the potato. They could also see through graphing the data what was happening with the rate of temperature loss. (But maybe this made me more excited than them.)

Here are some tips for the lab. I forgot to bring a crockpot to keep the potatoes hot during the day and I didn't cook them ahead of time. I have an incubator in my room whose maximum temperature is 60°C. In the morning, I put them in the incubator. Right before this last block class I put the potatoes in my classroom microwave for 5 minutes to make sure they were cooked all the way (soft), then put them back into the incubator until students needed them. The key is that they start with the potatoes hot. Even just being in the 60°C incubator was enough to keep the potatoes warm enough for the lab. 

None of the potatoes started at the same temperature, but that didn't matter since we were looking at the rate of temperature change for each of the potatoes.  Students used Google Sheets to collect their data and then graphed a scatter plot, added trend lines and the equation of the trend line. We then discussed how the slope of the trend line is the rate of heat loss from each potato. 

In House Microscope Repair...Literally!

By the end of this past school year, we had collected 7 microscopes that were not working well, or not working at all. As the science department head, I needed to do something about it. I really didn't want to schedule someone to come in to do microscope repair/maintenance since we're a relatively small private school with a smallish science budget. I wanted to maximize how much money we had for supplies and equipment. 

Now, these microscopes are fairly old and don't owe us anything, so I decided to try my hand at microscope repair over this summer. I started a YouTube playlist of microscope cleaning and maintenance videos and started watching them to get an idea of how it may go.  

After doing all of the summer prep that I wanted to do for my classes, it was time to tackle the microscopes.  I had found a maintenance and repair video done by Wards, so I started with our Boreal microscope. This microscope's problem involved slipping out of focus. Once it was focused, the stage would start to slowly go down (and the image would go out of focus). This was remedied by a quick tightening of the focus knob with an allen wrench (AKA a hex key).  This was super exciting, since I had that one working in under 5 minutes.

For every microscope, I wiped it down and cleaned each of the lenses with a drop of lens cleaning solution on a cotton swab. Actually, for one of the microscopes, the issue was a grossly dirty 40x objective lens. Maybe it got immersion oil on it? After a wipe down, the visual field was clear as a bell! Happily, all of the objective lenses unscrewed easily, which just made cleaning them less awkward than trying to do it while still attached. I just cleaned the lenses that faced out, only a few were dirty enough to clean the inside lens as well, but I tried to avoid that as much as possible.

We had two Labomed scopes whose views just looked like gray fuzz. No matter how much I moved the coarse or fine adjustment knobs, all I could see was gray fuzz. I wasn't sure what to do and decided to look up Labomed microscope repair and found exactly the instructions I need to do a focus stop repair. This was a little more involved, but the second one went much faster than the first. It helped to have already collected the correct tools. 

Another problem was with a mechanical stage.  The knob to move the slide forward and backward worked just fine, but the knob that moved it to the left or right kept slipping.  A 7mm socket wrench worked great to tighten the nut under and inside the knob. 

I didn't spend any money on supplies, I just raided my husband's tool supply, my craft supplies and some other items we had in the house. Here's my list...

1. Hex Keys (allen wrench)...1.5 mm and 5/64 in
2. offset box wrench...1/2 inch (although I think I probably could have used the socket wrench, but this was the first thing I found in my rummaging).
3. socket wrench...7 mm
4. cotton swabs
5. (eyeglass) lens cleaner
6. tweezers
7. prepared microscope slides...had to go back to school for these since it's pretty hard to test a microscope with nothing to look at. :)