What About the Stages of Mitosis?
By Peter A’Hearn
The stages of mitosis are really important.
I’m not being sarcastic. Every cell in your body (save those used to make babies) went through the stages of mitosis. And if the stages of mitosis didn’t work with great precision at coordinating the dance of the chromosomes, you would not be a very well functioning human being. So the stages of mitosis are very important.
As a starting biology teacher, I spent much time and energy making sure my students knew the phases of mitosis. I brought in straw hats and flannel shirts and had my students do a “Mitosis Square Dance.” We tried to identify the phases in onion cells under the microscope. I came up with mnemonics so stupid I can’t remember them.
Turns out neither could the students. They would perform abysmally the first time they were tested on them, and by the time the final rolled around, only my two or three who remembered EVERYTHING knew them. This got me thinking about if they really were important. I had been taught them, and the book devoted considerable pages to them, so they must be something the students needed to know. I re-read the standards (the 98 standards at the time) and couldn’t find the stages of mitosis.
I did find meiosis (the baby making type of cell division) in the high school standards:
HS Biology 2a Students know meiosis is an early step in sexual reproduction in which the pairs of chromosomes separate and segregate randomly during cell division to produce gametes containing one chromosome of each type.
This got me reflecting on why I was teaching it. I couldn’t think of anything students could actually DO with their knowledge of the phases of mitosis. What real world problem could they understand or solve? It might come up on Jeopardy someday. It might come up on a college test-- if magically they could remember something three of four years out that they couldn’t remember for a week. And in that case, the stages of mitosis would have been re-taught anyway.
Maybe a former student when they get to grad school will become involved in medical research involving understanding of and manipulation of the stages of mitosis. It would be cool to think so! If they do, they will have plenty of time for detailed study and will learn them in the ways that expert knowledge is learned, through deep engagement and problem solving. It would pretty arrogant as a high school teacher to think my square dances and silly mnemonics had anything to do with it.
So… what does this have to do with the NGSS? One of the challenges of implementation is that teachers are having a hard time deciding what to cut out. There are things teachers have taught and have come to accept as important knowledge that are not in the NGSS. If a teacher is thinking about NGSS as something to pile on top of everything you already teach, then transitioning to NGSS might seem like an impossible goal. We need to make hard choices about what to cut out.
Many teachers want to transition to NGSS but, at the same time, have a hard time letting go of content they have been teaching. Examples are the periodic table in 5th grade, the gas laws in high school chemistry, and lots of content in biology-- the parts of the cell, the details of each body system, classification, and oh yeah, the stages of mitosis.
Does that mean that these details have no place in NGSS? Is NGSS just about vague generalities?
No! Our teaching under NGSS should be anchored in specific real world questions or problems so as not to be vague. A teacher could start with the problem of a genetic disease caused by mistakes in mitosis. This is true of many cancers. Using this context, students would learn as many details as needed to understand the problem and model their understanding. It’s not hard to see how several performance expectations could be bundled in a unit that is centered around genetic diseases. They might include:
HS-LS3-1: Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring.
HS-LS1-1: Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells.
HS-LS1-2: Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
And finally, the place where mitosis does occur in NGSS:
HS-LS1-4: Use a model to illustrate the role of cellular division (mitosis) and differentiation in producing and maintaining complex organisms.
The assessment boundary leaves the importance of the phases pretty clear:
Assessment Boundary: Assessment does not include specific gene control mechanisms or rote memorization of the steps of mitosis.
So in a unit like this, it would be clear that mitosis is very important. It helps understand where living things come from and how they develop. It can explain how genetic information is duplicated and how mistakes can be made that lead to both diversity and disorder. It also makes it clear that memorizing the details is not a productive use of time.
The transition to NGSS is an opportunity to reflect on what we teach: Is it deep? Does it help explain the real world? Will it result in lasting learning?