Archive for the 'Lesson ideas' Category

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 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!


Concept Attainment Genetics Lesson

I got this genetics activity from the 2009 NSTA conference, and it was presented by a representative from the Center for the Integration of Science Education and Research at Texas Tech University (CISER).  The activity employs the concept attainment model.  It leads students to a concept by having them compare and contrast examples that contain the attributes of the concept with examples that do not contain the attributes.  Eventually, students should be able to identify the critical attributes of a concept.  CISER developed a genetics lesson using this method, and it has proven to be an effective, fun way to introduce my general biology students to genotypes.  Here is a link to the lesson:

Concept attainment genetics lesson

I guide students to  categorize a list of potential genotypes into two groups. The items categorized in the “YES” group possess the attributes of a properly written genotype.  Those categorized as “NO” items lack the proper attributes of a genotype.  I give a few examples of both “YES” items, and “NO” items before having students start to guess.  I have adapted this lesson to my Smartboard, and at the beginning of the lesson, it looks like this:

Students then drag the items through the blue revealer cone to see if they are a “YES” or a “NO” item.  Towards the end of the activity, the board looks like this:

Notice the final genotype being pulled through the revealer box.  Once we are finished categorizing the items in “YES” and “NO” groups, the class discusses what makes something a “YES.”  They will suggest attributes of genotypes, like, “there must be two of the same letter written consecutively” or “if only one of the two letters in a pair is capitalized, it must be written first.”  Typically, my students haven’t even been introduced to genes, alleles, or inheritance patterns when we complete this activity.  Once we get to Mendelian genetics, however, they very rarely make errors when using letters to represent dominant and recessive alleles.