Archive for January, 2012

Lesson Ideas: Genetic Engineering Coupled with an In-Depth Look at a Fascinating Mutualism

Recently, my general Biology students engineered glowing bacteria, photographed by my colleague, Ms. Amy Bonner.  I appreciate her recent post, commenting on the often overlooked connection between art and science.  The glowing phenotype was achieved by transferring genes from a bioluminescent marine bacterium, Vibrio fischeri, into E. coli, which is easy to grow in the lab.  While the experiment is designed to teach students about bacterial transformation, the laboratory also provides a perfect opportunity to take an in-depth look at an awe-inspiring mutualism between Vibrio fischeri and the bobtail squid.  Here, I will detail a few practical aspects regarding the experiment and how I have used this laboratory as a starting point to explore this fascinating symbiosis.

If you haven’t undertaken a molecular biology experiment with your students, don’t be intimidated.  Although the set up is more time intensive than the average high school lab, this kit from Carolina Biological Supply has detailed instructions and provides ready-made LB agar nutrient media to simplify preparations.  I have tried similar kits from Ward’s Natural Science, but I like that Carolina provides enough extra materials to account for occasional student errors.  While transformations can be tricky, I have always gotten good results with this kit.  It is helpful to have a water bath, although I have managed with a good old-fashioned hot plate, beaker, and thermometer.  Notably, Carolina’s student worksheet accompanying this lab is extremely well-written.  It emphasizes important concepts about positive and negative controls and walks students through a calculation of transformation efficiency.

Before beginning the transformation experiment, students watch this clip introducing them to the bobtail squid:

The clip (and the images below) are taken from Dr. Bonnie Bassler’s 2009 HHMI Holiday Lecture, “Shedding Light on an Invisible World.”  After watching the clip, we discuss the fact that, while the bobtail squid hides during the day, it must come out at night to hunt.  It inhabits shallow water.  Thus, moonlight can reveal the outline of the squid to predators lurking below.  A predator’s view would look like this:

As a way of camouflaging itself in its environment, the bobtail squid has evolved a unique symbiosis with Vibrio fischeri.  The squid assumes the expense of feeding the bacteria, housing them in a specialized light organ.

With the bioluminescent bacteria in tow, the outline of the squid from a predator’s perspective is more difficult to make out:

The squid does not have the genes necessary to produce this adaptive glow.  Thus, it provides nutrients and a protected environment for the resident bioluminescent bacterium, whose lux genes generate this glowing phenotype.  These bacterial genes have been engineered into a plasmid, included in the kit from Carolina that I discussed above.  Once my students understand where these genes come from, we move on to replicating the beautiful glow in the lab by moving the plasmid  into easy-to-grow E. coli.

With more advanced classes, I discuss the daily cycle of bacterial growth within the light organ.  As it turns out, the bacterium’s stay within the squid is temporary.  The bacteria are sent packing as day breaks since it is too energetically expensive for the squid to house large amounts of bacteria for a full twenty-four hour period.  As nightfall approaches, bacteria reproduce, increasing in number within the light organ.  What’s more, the bacteria are polite guests and wait to produce the expensive glowing phenotype until it is dark and the squid needs the camouflage.  How do bacteria sense when it is time to produce this glow?

It is all about population density, and bacteria can gage their numbers within their environment.  This is a phenomenon known as quorum sensing, which is a ubiquitous form of communication among bacteria.  The phenomenon can be studied easily in Vibrio fischeri because of the visible phenotype produced when quorum sensing is at work.  I hope to post more about Bonnie Bassler’s fascinating studies on quorum sensing in the future, which have piqued my interest in recent weeks.

The intricate symbiotic relationship between the bobtail squid and Vibrio fischeri is but one example of the remarkable ways in which organisms have evolved to work together.  Do you have a favorite mutualism?


Upgrades – Part II

In my last post, I introduced my plans to revamp my assignment on a series of articles from the NYTs, The DNA Age.  I hoped to upgrade this assignment by hosting the discussion on Edmodo, rather than having a traditional classroom discussion.  Here, I detail how I set up the assignment and some interesting things that I learned while exploring with my students.

I first made the decision to use Edmodo, in part because it is easy to set up a protected online environment for students.  While I think I would eventually like to have students making blog posts publicly, I wanted something private since it was the first time my students and I tried this type of thing in the classroom.  Once I settled on Edmodo, I set up a group and had students register for the site.  Students are not required to provide an email address to sign up for Edmodo, and many of them already had accounts from other classes.

Before the students wrote their posts, we discussed the advantage of writing online as opposed to writing on paper.  The students generated ideas, suggesting things like:

  • It is easier to share work.
  • It feels more natural than traditional writing since we communicate online a lot already.
  • Writing online enables the author to link to other sites and to incorporate pictures and videos into his or her writing.

I tried to emphasize this third point, which I view as one of the greatest advantages of writing online.  It can be really interactive, prompting readers to explore topics in depth beyond what is actually written in a post. Once we discussed the assignment, students were given the rest of the class period to write their posts.  The assignment on Edmodo looked like this:

The following day, students were assigned to read and comment on other groups’ posts.  We began by discussing how to compose a good comment.  I showed students a post and comment written on Extreme Biology, which is the best biology classroom blog I have seen so far.  We then compared the comment to these guidelines first published by Mrs. Yolis and reposted by Silvia Tolisano on her amazing Langwitches Blog:

I should note that the Langwitches Blog is a fantastic resource for teachers interested in blogging with students. Her series on blogging gave me the confidence to get started and some valuable resources as I walked my students through their first blogging assignment.

In addition to discussing the guidelines pictured above, I also gave my students the following comment starters, which I again first came across on the Langwitches Blog.  They were originally published on Youth Radio Blog Netiquette.

My students did an excellent job with this assignment.  Their posts reflected my students’ strong writing abilities, their willingness to explore different points of view, and an enthusiasm for discussing ethical issues pertaining to DNA technology.  Thus, it was important to give them constructive feedback.  Yet again, the Langwitches Blog was a valuable resource, and I was able to adapt the rubrics that Silvia Tolisano published on her site to fit my own needs.

I think that the assignment was a really positive experience for my students.  As I look back on the posts and comments my students created, I wanted to detail both what I thought of Edmodo and a couple of things that surprised me.

As far as Edmodo is concerned, I’m not sure it was apt for a blogging assignment.  My colleague, Amy Bonner, highlights many of Edmodo’s strengths in a recent post.  While I appreciated how easy it is to use, it didn’t allow my students to format or categorize their posts.  Furthermore, it is really designed for short posts and conversations.  Thus, it didn’t prompt students to add a title, and several groups consequently forgot to title their post.  I will probably search for a different site when I do similar assignments in the future.

I found two things that I didn’t anticipate about the assignment:

  • While my students’ posts were fantastic, integrating links, videos, and pictures did not come naturally to many of them.  These items were often inserted at the end of their posts or clumsily inserted within the post.  They will need to work on incorporating these items more fluidly into their writing.
  • Blogging proved to be a wonderful outlet for my international students to express themselves.  I currently have two in my Biology class, and both of them were able to contribute meaningfully to the class discussion in a way I hadn’t seen them partake before.  I think this is because they had more time to compose their thoughts.

Several of my students noted that the thing they liked best about the assignment was that everyone got to participate in the class discussion, rather than simply the most vocal students.  I agree with them, and the most important thing I learned is that blogging is an incredibly valuable classroom tool that gives every student a voice.  For this reason, I will strive to make blogging a regular part of my classroom activities.

Upgrades – Part I

I recently attended a conference that was so inspiring, it would leave just about any educator with a pulse on fire to try new things in the classroom: Preparing 21st Century Minds: Using Brain Research to Enhance Cognitive Skills for the Future.  The conference introduced me to a rich, large community of educators who are incredibly deliberate about employing teaching methods that take into account how students learn best and what skills they will need in the future.  The presenters are so mindful about how to really serve our students, tapping into what is important to them while providing them with an engaging environment to learn and explore.  The experience was invigorating, renewing my passion to keep my teaching relevant, fresh, and meaningful.

I am a relatively new teacher, reaching the midpoint of my fourth year in the classroom.  While I don’t feel like being the new teacher on the block confers many advantages in a field where experience counts, I used to think I had a tiny edge when it came to technology.   I was proficient in managing a course web page, had students completing virtual labs, and became reasonably skilled with my SmartBoard.  However, this conference left me with the unshakable feeling that some of my most thoughtful, timely (so I thought!), original lessons were already collecting dust.

While no teacher can be expected to reinvent the wheel every single year, education leader, Heidi Hayes Jacobs, implores educators to be mindful about consistent “strategic improvements” or “upgrades”  in the classroom.  She was one of the best presenters at the “Preparing 21st Century Minds” conference.  She is a dynamic speaker who advocates for thoughtful use of technology in the classroom.  I think she has tremendous insights and is worth listening to:

After hearing her speak, I began contemplating how I could perk up some tired lessons. Hayes Jacobs notes that making the type of improvement she suggests really “is something that anyone can do Monday.” Anyone, including me.

Thus, I took an older assignment and worked with our school’s Director of Curricular Technology to make such an “upgrade.”  For several years, I have been using a Pulitzer Prize-winning series of articles, “The DNA Age,” from the NYTs as a springboard for discussing ethical issues associated with DNA technology.  It has always seemed like a nice way to cap off my biotechnology unit.  I like it because I see students realize that their technical knowledge can not only inform their own opinions on issues that matter, but it also helps them to better understand those of others.

In the past, students have worked in groups to orally present the articles and the ethical dilemmas they raise to their classmates.  In a world that practically revolves around the internet, the place to publish, process, and discuss information, a simple oral classroom discussion didn’t seem like the most engaging format.   Thus, this year, I decided to host the class discussion on Edmodo, a free Web 2.0 site that enables students to interact in a safe online environment.  In my next post, I hope to update you on how I set up the assignment, what I liked and didn’t like about Edmodo, and what type of online discussion the assignment generated among my students. (Upgrades Part II)

Have you made any interesting upgrades this year?  Please share!