Human Mitosis Model Activity

A quick activity that I did when I had a little time left over at the end of a class. Could be developed into a more formal activity if you have the time or inclination to plan it. I did a skeletal version, but I'm thinking next year I will make it a central activity and get more elaborate with it.

Students act the parts of the major players in mitosis. In this model, I used the classroom walls as the cell membrane - not enough students to have a human cell membrane, but that would be a nice addition.

Two girls represent sister chromatids of a maternal chromosome.

Two boys represent the sister chromatids of the paternal homolog (yes, they were upset at playing the role of sisters, and refused to touch each other (lock arms) to represent the centromere connection - boys!).

A group of students form a nuclear membrane around the chromosomes.

Two students stand outside the nucleus to represent the centrioles that will migrate to the poles. I used twine to represent the spindle fibers.

Teacher calls out the phases of mitosis, students enact the events.

Prophase - nuclear membrane "breaks down" (students disperse into the "cytoplasm" of the cell). In a real cell, the chromosomes would become visible, but in the model the students can't exactly be invisible and then appear - Oh the limitations of models!

Metaphase - chromosomes line up along the equator (middle of classroom), centrioles migrate to poles (front & back of the room).

Anaphase - spindle fibers attach to centromeres (students have to use hands for this part), begin to pull chromatids toward poles.

Telophase - nuclear membranes re-form around the chromosomes at each pole, forming two new nuclei. Each nucleus now contains an unduplicated paternal chromosome and an unduplicated maternal chromosome.

Repeat. Try to make it a smooth uninterrupted process, fluid. It's a nice reinforcement of the concepts. Have students as much as possible plan the activity. Plan ahead and have students wear color-coded clothing for an even more dramatic effect. A nice open space obviously helps.

Mitosis Models With Pipe Cleaners

Ok. My prepared slides of mitosis are missing, so I had to scramble to find an activity to do on the subject with my classes. I remembered seeing some students from years past doing models of mitosis with pipe cleaners to represent (obviously) the chromosomes.

Now, I had thought this was a pretty lame activity - look at the pictures in the book, reproduce the stages of mitosis (P-M-A-T) with pieces of pipe cleaner and move on. Nonetheless, I needed some kind of activity and I didn't have much time to look for something else. So I threw together the materials and headed to class. Explained the procedure. Showed students the pictures in the book (we had already discussed the cell cycle & stages of mitosis, read the chapter & answered questions, etc), made a few suggestions like only using one or at most a pair of chromosomes, identical colors for sister chromatids, different color for the homologs, etc.

I was wrong about the lame thing. They really struggled. Because they weren't just copying the pictures in the books, they had to think about the process and sort out how the chromosomes separated and figure out how to model that with real materials. Early on, some students were using different colors for the "sisters" (I don't care if they know the term chromatids at this point. So I let them just shorten it to sisters. Having told them this, they proceeded to use the term sister chromatids anyway!). Others were using the same colors for both chromosomes in a homologous pair. Some of their models ended up with daughter cells having pairs of sister chromatids rather than a homologous pair. I got questions like, "How long should the spindles be?" All these issues had to be sorted out. The funny thing is, they had no trouble answering questions from our discussion & the textbook that could be answered by simply memorizing information about the process - "What happens in metaphase?" e.g.) But those were just words. They didn't actually have a mental model yet of the process.

A more disturbing problem (for me looking at it from a pedagogical standpoint) was a sort of intellectual laziness, for lack of a better term. I had given them the option of using one chromosome or a pair of chromosomes in their models, and emphasized repeatedly that we were making a very simplified model, and that different organisms have any number of possible chromosome numbers, and whatever happened in our model to a single chromosome, happens in the real world to all the chromosomes in a cell. We have mostly talked about humans and our 46, but some organisms have only 2 chromosomes, others over a hundred. (Bacteria have a single chromosome, but they don't divide by mitosis). The problem came when I illustrated metaphase on the whiteboard using 3 chromosomes - just to use a different number from theirs. Afterward I walked around, and several students had placed - you guessed it - three chromosomes in their metaphase, even though they only had one or 2 chromosomes in their prophase! They were looking for someone to just tell them what to do without investing any more thought than absolutely necessary. I might not be so critical if they had at least asked questions about it before making the mistake, but they didn't.

I can see two important things happening in this process. First, they are clarifying their thinking about a fundamental process - and it's good that I see the difficulty now rather than later when we move on to meiosis. Secondly, they are learning how to make models - a skill in itself. The whole concept that in a model we often need some way of indicating that two things are either the same (sister chromatids) or different (homologous pairs) was apparently a new idea for some students.

I highly recommend this or a similar activity for students learning mitosis & meiosis. If I have time, I will do a more formal write-up with lab sheets and post it all later.

Curriculum & Text

After careful consideration and review, I believe that the rest of my course sequence pretty much follows textbook units, though not necessarily in the order presented in the textbook. I will therefore only need to make minor modifications. For example, I'm deciding whether to follow mitosis/meiosis with all the DNA material -structure, replication, etc., or with basic cell biology - structure, movement of materials, biochemistry. It makes sense to cover this material before DNA, but it also make sense to teach DNA after mitosis/meiosis. What a dilemma. I've posted the current version here.

I've also reached the conclusion that the Holt textbook is useful almost exclusively as a source of great photos. It's nearly impossible to read the text and come away with any understanding of what's going on. If you read a single section or paragraph, it might make sense. But the sections are not constructed well, each one seems to read like a stand-alone encyclopedia or dictionary entry. The big picture is hard to see, the connections between ideas are not well developed. The chapters are also jam packed with topics. I find it just too complicated to tell student not to worry about Topic X, ignore questions 3, 7, 15, etc. I nowrealize how difficult it is (for me at least) to evaluate a text without actually using it in a classroom setting. When looking at the textbooks last year, I simply opened to a few isolated sections and read them, trying to imagine how difficult it would be for students to understand the section. My evaluation strategy seems to have meshed well with the textbook style, and I wonder how many textbook evaluators fall into the same trap.

I am also using as a review book the Amsco publication: "The Living Environment: Biology" by Rick Hallman. This is almost the polar opposite of the Holt text - not many pretty pictures, not many diagrams or sidebars, but a lot of text reasonably well written. Hallman does a nice job of writing a cohesive narrative for each chapter and each major topic. By limiting pictures and making the ones that are present black & white, the eye/brain can really focus on the reading and following the narrative. The Holt text is a visual nightmare, from the pictures to the sidebars - tips, reviews, objectives, real-world applications - to the overly visually stylized text itself, full of colorful numbered lists, colorful bulleted lists, colorfully highlighted vocabulary words, - it's a disaster!

And I don't buy the notion that the "MTV generation" needs this kind of stimulation. That kind of visual bombardment may be great for entertaining or holding attention, but I simply do not believe that it allows for, much less promotes, critical thinking.

Rethinking Curriculum Sequence

There is of course a downside to any attempt at circumventing the tedious and traditional approach to teaching biology "from the ground up." There simply aren't any biology textbooks that are at the same time constructivist and content rich, at least not any that I have seen. There was a big discussion within the biology teacher's listserv from NSTA (members only, manage listserv subscriptions from your member page) that I subscribe to regarding textbooks vs. inquiry. Here's an excerpt from one that got me thinking about the ridiculous amount of work I do this year:

I teach high school now, but in my student teaching year I taught a 6th grade science/math core using FOSS kits. We didn't have a textbook at all. I loved the FOSS kits and all of the cool equipment, but the content support was lacking. Without a textbook, I found myself writing little articles for my students to take home and read. That was a LOT of work, I tell you!

Sounds like me now trying to teach "outside the textbook" and searching desperately for materials or in many cases writing my own materials to support the concepts I teach in the classroom. It's not that the textbook I have doesn't cover the concepts I teach, it's just put together the wrong way. There's a separate chapter, for example, for cellular reproduction and heredity. The chapter on meiosis & mitosis precedes the chapter on heredity, and of course the chapter on heredity assumes knowledge of those concepts and incorporates modern understanding into Mendel's model. I chose to teach heredity as much as possible from Mendel's perspective, from a time when chromosomes and DNA were unknown. Thus I can't assign students to read the chapter in the textbook on Mendel, because they will be totally confused by all the meiosis/mitosis vocabulary. In hindsight, without the aid of a textbook to guide me and the students through such a process, I would not do it this way again. It's just too much information for me to try to pull together from too many sources, not to mention trying to structure a sequence of lessons and activities that would allow students to reach some of the conclusions Mendel reached. Finally, I believe the "right way" to do this would involve students actually growing some plants (like Wisconsin Fast Plants, e.g.) and recording some actual data. Of course even "fast plants" are too slow for a regents level biology class, where Mendelian heredity should be prior knowledge already (from middle school).

What this example illustrates is the power of textbooks to dictate curriculum. Developing our own curriculum is overwhelming. Students need more than good classroom instruction - they need enrichment materials, study guides, reinforcement activities. These materials should be aligned with classroom instruction for maximum benefit. Given these needs, teachers make the logical choice to align their instruction to the materials available to them, even if those materials are poorly suited to state standards and good pedagogy. The alternative is to spend 12 hours per day including weekends developing materials and still feeling like you are coming up short.

I will be revising the sequence and structure of my instructional plans in the coming weeks, which I will post & comment on when the changes have been made.