The Cell Membrane: A Thought Experiment

A number of years ago, I developed a method for teaching students about the basic structure of the cell membrane that has proven to be both enjoyable and memorable, and after receiving positive feedback upon sharing this activity with my friends at the Center for BioMolecular Modeling at the Milwaukee School of Engineering, I figured that it is time that a share it with a larger community of individuals.

Simply, the method is a “thought experiment” in which students graphically hypothesize the arrangement of a collection of molecules unknown to them (phospholipids) in three sequential situations, in order to personally discover the self-assembly of phospholipids in generating a simplified cell membrane.


Once students have discovered this basic image of a cell for themselves it becomes easier for them to supplement it generating a more complex conception of the cell.

In fact, I usually draw an analogy between the cellular container and the test tubes and beakers used in chemistry.  Student readily understand that cells, “as places where chemical reactions occur” require:

  • a container (the goal of this series of thought experiments),
  • reactants,
  • points of entry and exit (the membrane and supplemental proteins),
  • a solvent (the water inside this simple cell),
  • catalysts as biological enzymes,
  • energy,
  • and a controlling region or some means of regulation.

A summary of the “thought experiment” follows but for those that want more details, including images, or would rather read offline, I have created a document explaining this Cell Membrane Thought Experiment.

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Why Surface for Air?

Observations of tadpoles in a local pond

Two days ago, while driving my eldest daughter and a friend to morning swim practice, we ran across, but not over, a rather large snapping turtle crossing the road.  This happened just east of Mission Road on 71st Street in Shawnee Misson, Kansas (it appears that he may have grown up in Indian Hills County Club).  Although the turtle appears to have lived quite a productive live to that moment, we figured that we might increase its life span by moving him somewhere a little bit less populated.

Yesterday, my two younger children and I, released our find in a wetland area adjacent to the Blue River in southern Johnson County.  While there, I treated my kids to one of the ponds I frequent with students when I am teaching about amphibians.  Here is an interesting observation that we made…

A quick google search this morning suggests that field biologist may not fully understand this behavior, and not for lack of thoughtful consideration and experimentation.  I know that school is out and that critical observations and experimentation are dependent on the life cycle of an organism who doesn’t realize that, but I share this observation none-the-less, for its potential…

…and if you want to ID the tadpoles you can do that too…

Home, Home on the Range

Where the Mule Deer and the Pronghorn Antelope Play…

Reflections on the KABT Field Trip in Logan County, June 4-6, 2010

I am not sure what KABT’s goal for the field trip were but for me they were two-fold.  I wanted to provide an inspirational outdoor experience for four of my senior students, and two of my children, who eagerly participated in the trip, while learning myself about the wonderful short-grass prairie from our very own sage, the Yoda-like natural history master, Stan Roth. 

In both regards the trip was a resounding success, even though I failed to continue to follow Noah’s driving lead into better pastures where he was finally able to witness the character of our pursuit, the endangered a recently re-established Black-Footed Ferret (see Noah’s posts). 

If you are sad that you missed the trip, continue on since I did my best to record it all for you…

More specifically, follow along to see what I saw, learn what I learned, listen while I contemplate what KABT may have learned, and educate yourself on the prairie dog wars of Logan County, Kansas in hopes of a return trip to this wonderful county… 

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2010 KABT Spring Field Trip

OK. I have a lot of thoughts that I need to put down about the field trip to Logan Co., KS this last weekend. I will need some time to organize those. But for now, I will post this pic with words describing this amazing experience to soon follow.

More thoughts on Milkweeds and Aphids

What are those dark ones?

In last week’s  “Biology Challenge”, I challenged biology teachers to contribute identifications and descriptions of the relationships illustrated in a photo of aphids, ants and milkweeds.  Sure enough, within an hour the milkweed was successfully identified as Asclepias syrica and the aphids as Aphis nerii.  A number of various Formica species were sent in as tentative identification for the ants in the image.   Though, I would not begin to suggest I know much about ants I am pretty sure you’ll find that these ants belong to the genus Crematogaster–the acrobat ants.   Mark DuBois produced a Checklist of Kansas Ants in the Kansas School Naturalist that includes possible candidates.  There are any number of resources on the web that might lead us to an identification if I collected some of the ants.

But what I really want to get to is the nature of the interactions taking place on the tip of the milkweed leaf.  Several people noted that the ants were tending the aphids in a classic ant/aphid mutualistic relationship.  There’s several items that complicate this however and I think this image can serve as an open door to an incredible landscape of accessible student study.  For starters, while ants do tend aphids on milkweed–the aphids tend to be Aphis asclepias and not A. nerii–that’s what caught my eye.  Hmmmm…A. nerii presumably sports the bright yellows and oranges as warning coloration.  If ants don’t typically tend A. nerii then perhaps the aphid’s  “honeydew” is somehow not as toxic as normal in this instance.   Milkweed plants vary in their toxicity–perhaps parts of the individual milkweed vary in toxicity as well.

Check out, Anurag Agrawal’s web site for a truly in depth introduction to the milkweed ecological community.  In particular check out his powerpoints and videos under the Multimedia tab.  These will introduce you to the incredible complexity of community level interactions that he and his colleagues are uncovering.  Specifically link to his Publications tab–there, you’ll find a very rich resource of pdf’s that will help you to see the milkweed communities in a different light and help you to guide your students inquiry.   I have spent hours reading these papers.  I think you’ll find that many of them are very accessible.  Here’s a Discover blog post that introduces one of the studies:  Mooney, K. A. and A. A. Agrawal. Plant genotype shapes ant-aphid interactions: implications for community structure and indirect plant defense. American Naturalist 171: E195–E205. Here’s another relevant paper and a link to it:    Smith, R.A., K.A. Mooney and A. A. Agrawal. Coexistence of three specialist aphids on the common milkweed Asclepias syriaca. Ecology 89: 2187–2196.

Once a person starts to focus observations on a relationship like that illustrated in the photo from my original post, then all sorts of questions come to mind.  I propose that this is one of our jobs as biology teachers–put students into a situation/an environment that promotes original and accessible student questions.  Help them to focus their observations and reconcile them with what they know and don’t know.  Questions will follow.   What does this take in the classroom?  Not much really,  start a butterfly garden,  participate in the Monarch Watch’s Waystation Program.  Participate in Monarch Larval Monitoring project.  Here’s a resource on aphid from the MLMP:  Monitoring Aphids.  Participate in the earthworm project that Eric shared.  Participation in projects like these almost invariably leads to students asking all kinds of questions.  At first they are very general and non-focused but with only a little help with some guiding questions from their instructor the students natural curiosity can be turned to powerful questions for study.

Years ago, in the process of helping to establish the Monarch Watch with Chip Taylor, I would promote Monarchs in the classroom by reminding folks of Karl Von Frisch’s description of his honeybees:

“The bee’s life is like a magic well: the more you draw from it, the more it fills with water”.

Really, any natural system is like that once you start to pay attention to detail. Natural systems exude wonder and complexity that begs study. Exploit this with your students—introduce them to doing science by “drawing from the well”….