Statistics in AP Biology

We’re getting into the statistics potion of the class in AP Biology. Last week I taught the students how to do a chi square test on M&Ms, and this week we’re going to work more on using chi square tests to evaluate whether Punnett squares accurately predict the outcomes of genetic crosses. Many of my students don’t see the need for statistics. Either the data match what you expected or they don’t. They’ve never had to do any statistics before in other classes, and we don’t offer statistics as a math class.

In addition to more chi square practice, I also intend to have the students analyze their data from the onion root lab using by calculating means and standard errors. Last week we grew onions in various concentrations of caffeine and measured the length and number of roots each day. I had the students input their data to a Google spreadsheet so they can analyze the whole class’s data this week. I hope that they will see the need for statistics when they see the variation in data from one group to the next.

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Next Generation Science Standards

The latest draft of the Next Generation Science Standards (NGSS) was released on Tuesday. We looked at them in my department’s PLC meeting on Wednesday. I really like how the standards emphasize the doing of science and have eliminated some of the picky little details. (Why did students ever need to know the function of the Golgi apparatus?)

I do have two concerns about the new standards. First, for students to get to the level demanded by the high school standards, middle schools have to adequately teach the middle school standards. Some middle schools have great science programs, but many have dialed back on science education in favor of English and math, since those subjects are tested more. Which brings me to my second concern – there are no plans right now for any standardized tests for the NGSS. What gets tested is what gets taught, so if there are no tests, why would any middle school that has trouble making AYP bother to teach science? I know that high schools will continue to teach science because colleges demand it, but I bet that we will end up teaching the middle school standards, not the high school standards.

Finally, NGSS is not Common Core!!!!!!

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Teaching ecology with Planet Earth

Like last year, I will begin the second semester of biology with the ecology unit. Many teachers leave ecology until the end of the year or teach it at the very beginning of the year, but I’ve found that it’s a good unit to begin the second semester with. After a semester of cells and genetics, the students find ecology much easier to comprehend. Also, our next unit is evolution, and the examples that I use in ecology to explain how species function in their environment lead nicely into explanations of why species look the way they do.

Since we live in the Central Valley of California and have no money for field trips, I take the students around the world with Planet Earth. For example, for our first lesson we talk about how ecology is the study of interactions between biotic and abiotic factors in the environment. I show this clip and have the students jot down the characteristics of the environment.

After the video, they decide whether each characteristic is biotic or abiotic and state how it interacts with the other parts of the environment. (There are always a few students who debate whether snow is alive…)

This strategy of introducing an idea, showing a video clip, and then discussing it works for most topics in ecology (predator-prey relationships, food webs, competition, community vs. ecosystem), but I’m still looking for a good way to teach nutrient cycles. It’s difficult to find a video showing invisible interactions like bacteria fixing nitrogen. Last year I just lectured about the cycles, but the students couldn’t find a reason to care. Nitrogen isn’t cute and cuddly like a panda. I’ll see what I come up with for this year.

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Algebra in 90 minutes

In my school, most classes are 50 minutes long, but every class has one 90-minute period per week. I love teaching science in 90 minutes. I could do 90 minutes of AP Biology every day. I’m having trouble filling the algebra periods, though. There’s only so much I do-we do-you do possible during one class period! I can stretch the intro stuff and the I do-we do part to about 30 minutes. We’re a 1-to-1 school, so I have the students practice on Khan Academy and IXL, but they can only sustain that for about 30 minutes. What do I do with the last 30 minutes of these periods?? Last fall was my first semester teaching algebra, and I just kind of limped along. This spring, I think I’ll try some of Dan Meyer’s three-acts on the long days. We’re doing radicals this week, so maybe the taco cart problem? I definitely need to step up my game in the algebra classes this spring.

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Student resistance to thinking

I found an article yesterday that explains some of the resistance to thinking that I’ve been seeing in my AP Biology students. This is my first year teaching AP Biology, and it’s also the first year of the redesigned AP Biology course. The AP Bio test was traditionally all about brute force memorization for the multiple choice questions, with some application and synthesis tacked on for the free response questions. Starting this year, the multiple choice questions will require much more thought. Here is an example of a traditional multiple choice question:

If plant cells are immersed in distilled water, the resulting movement of water into the cells is called
A) conduction
B) active transport
C) transpiration
D) osmosis
E) facilitated diffusion

Here is an example of the new type of question:


Paramecia are unicellular protists that have contractile vacuoles to remove excess intracellular water. In an experimental investigation, paramecia were placed in salt solutions of increasing osmolarity. The rate at which the contractile vacuole contracted to pump out excess water was determined and plotted against osmolarity of the solutions, as shown in the graph. Which of the following is the correct explanation for the data?
A) At higher osmolarity, lower rates of contraction are required because more salt diffuses into the paramecia.
B) The contraction rate increases as the osmolarity decreases because the amount of water entering the paramecia by osmosis increases.
C) The contractile vacuole is less efficient in solutions of high osmolarity because of the reduced amount of ATP produced from cellular respiration.
D) In an isosmotic salt solution, there is no diffusion of water into or out of the paramecia, so the contraction rate is zero.

These two questions test the same concept, but at different levels in Bloom’s taxonomy. The traditional question asks the student to recall the definition of osmosis. The new question requires the student to interpret the graph, read ALL of that information, and figure out that the contraction rate increases as the osmolarity decreases to get rid of the excess water that’s entering the cell.

My students DO NOT like the new questions. For the semester final in December, I used 28 of the new multiple choice questions and 1 free response question. The students’ scores were similar to the other tests during the semester, which did not include as many critical thinking questions, but the students were frustrated just the same. A common refrain: “The study guide questions didn’t have anything to do with the exam!” Well, no, I did not ask you anything about contractile rates of paramecia on the study guide, but I did ask you about osmosis and had you draw pictures of situations when water would move into and out of cells. You then had to APPLY that information to answer the question. My students would rather just RECALL exactly what they wrote down on the study guide.

The article I mentioned above highlighted these attitudes from students in a first-year college biology course. The author noted that “students in this class usually struggle with the higher-level MC questions on the exams, and tend to perceive them as “tricky” (on the part of the instructor), rather than challenging (i.e., requiring higher-level thinking skills).” (p. 295) The author was testing to see whether students would learn more critical thinking on tests that only include multiple choice questions, or on tests that include multiple choice and free response questions. The students ended up doing better on critical thinking multiple choice questions when also given free response questions, and the author concluded that students study differently for the two types of tests. However, although they performed better, the students did not like the experience. They thought that “the instructor should ‘just teach biology’ rather than emphasize higher-level thinking skills.” (p. 302)

My overall reaction is that I’m glad I’m not the only instructor seeing these attitudes from students. I hate all the jargon that goes along with Bloom’s taxonomy (my school’s administrators love to go on about “higher-level Bloom’s”), but we do need to encourage students to think more. My AP Bio tests always include free response questions, but this is the first class my high school students have taken that includes higher-level thinking multiple choice questions. My challenge for the spring is to convince the students that science is not about memorizing facts and regurgitating them back on the tests; science is about memorizing those facts and doing something useful and interesting with them.

Posted in AP Biology, Critical thinking | 1 Comment

I guess I’ll try this blogging thing

I’ve been getting caught up on my reading during winter break, and I finally decided to take the blog plunge for myself. I’ve been reading blogs for several years now (although I just started putting them in Google Reader today). I’ve been participating in the forums at A to Z Teacher Stuff for a few years, but that site is more geared to a general discussion about education, and it’s difficult to sustain a conversation about teaching high school biology in particular. I finished BTSA a few years ago, and while it wasn’t great professional development, it did force me to reflect on what I do, and I need to do more of that. So those are all of my various reasons for beginning to blog!

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