Lock and Key Analogy with Enzymes

Written by Michelle Zurawski, Moraine Valley Community College

This is an analogy that is used during the enzyme discussion. I compare the enzyme substrate complex with a lock and key. My car is a cheap fuel efficient little car so I tell the students that I would like upgrade to a nicer Prius. I ask them if I could go to the parking lot and open a nice new Prius with my key. I then tell them that this is one of the ways that enzymes work to save energy. You only need a small amount of enzyme (1 key) to work with a specific substrate (1 car). Just think if you had to make a new key every time you opened up your car door. That saves energy by using that same enzyme (car key) over and over for the same reaction (car). Enzymes are specific to one substrate just like the key to my car is specific to my car. You can also use the two puzzle pieces fitting together like an enzyme and a substrate only fitting together in one way.

The Energy Barrier for a Chocolate-Craving Pregnant Woman

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

When discussing the energy of activation (EA) related to enzymes, I tell students about when I was pregnant and ate ice cream every night. I explain that after dinner I would sink into my deep, fluffy sofa. When I deemed it ice cream time, it was challenging to get up to get from the sofa with a big belly. I would complain and huff and puff,  etc. But sometimes, my lovely husband would hold his arm out and help to pull me off the sofa. In this analogy, my husband is the enzyme (catalyst) because he lowered the energy barrier for me. However, he didn’t make the impossible happen—I would have gotten that ice cream on my own—he just made it easier and faster for me to be a happy pregnant woman full of ice cream (the product of the reaction).

Using Food and Drink to Describe Osmosis

Written by Jennifer Wiatrowski, Pasco-Hernando Community College

I use two different analogies to relate osmosis to the real world:

a. I use two large beakers (beakers A and B), a jug of water and lemonade mix or fruit punch mix (these are dry powders). I then tell the class I am going to mix two classes of a refreshing beverage (nice in a hot climate like Florida). I tell them that I will make the first beverage very sweet, and pour in a large amount of lemonade or punch mix. The second beverage will not be nearly as sweet and I pour in a small amount of the powder. I then fill each of the beakers to equal volumes. I then ask the class if the two beakers have equivalent solutions. (They say no!). So, although the two beakers appear to have equal volumes, the amount of water is varies between the beakers. This shows students that the amount of water in a given space is influenced by the amount of solute. I then ask the students to imagine connecting the beakers together with a selectively permeable membrane and then ask them which way the water would flow  (from beaker A to B or B to A?)

b. I then talk about Martha Stewart. Martha always says that you should never toss your salad until your guests arrive or you are ready to serve it (I was recently informed by my students that “toss the salad” has taken on additional meaning……so this gets a good laugh out of the class). So, at the beginning of class, I take a bag of salad and some dressing and mix them. I then put it aside for awhile. In the meantime we talk about hypertonic and hypotonic. I then ask to think about the scenario with the salad and the dressing. They eventually reason that the salad is hypotonic to the dressing (or the dressing is hypertonic to the salad) and the consequence of this is a watery salad as the dressing pulls water out of the greens. This would make Martha HORRIFIED.  To finish, we take look at the salad we mixed earlier.

The Earthquake Richter Scale and the pH Scale

Written by SuEarl McReynolds, Palo Alto College, San Antonio, TX

When discussing how the pH scale is logarithmic and a one number change is equivalent to 10 times as acidic or basic, I ask if they know what the Richter Scale is. Usually several people know that it has to do with measuring earthquake strength. So I ask how much difference they think there would be between earthquakes with a magnitude of 8 and a magnitude of 9. It’s “only one number.” In reality a magnitude 8 can cause serious damage over several hundred miles, but a magnitude 9 can cause devastating damage over several thousand miles. So one number change is a big difference in these kinds of scales.

When I get to buffers, I have a picture in my PowerPoint of a man working on a floor with a big buffering machine. He’s smoothing out the drastic high spots and low spots on the floor, making it more even. Or a person may act as a buffer between two friends with opposite personalities—again making things more smooth, the differences less pronounced—maybe helping the shy one feel freer to express opinions and the loud one less likely to interrupt and dominate the conversation.

Relating Chemical Bonds to Everyday Ideas

Written by SuEarl McReynolds, Palo Alto College, San Antonio, TX

I use several analogies when talking about chemical bonds. I compare them to different kinds of glue. I ask the students if they have a “junk drawer” at home. They smile, and I ask if it’s got some different kinds of glue in it—maybe paper glue, Elmer’s glue, wood glue, Super Glue.  Just like you need different kinds of glue to stick different materials together, you need different kinds of bonds to hold different kinds of atoms together. Probably a lot of people compare the attraction of the oppositely charged ions in an ionic bond to the attraction of the opposite ends of a magnet. Another common analogy probably is to compare the sharing of electrons in covalent bonds to holding hands (as in carbon is an atom that has four hands sticking out to hold with other atoms). Covalent bonds could also be compared to kids who want to play with the same toy. So they set a timer and switch off who gets to play with the toy.

When I talk about polar covalent bonds, which result from an unequal sharing of electrons, such as in the water molecule, I tell this story: “Suppose I come to class with a big chocolate chip cookie. I tell you that I’m feeling generous and am going to share my cookie with you. You anticipate that I’m going to break the cookie in half and keep half and give you half. But that’s not what I do! I really, really like chocolate chip cookies—so I break off a little piece for you and keep most of it for myself! Well, I did share.  I just didn’t share equally!”

When I get to the much weaker hydrogen bonds, I compare them to Post-It notes. I ask the students to visualize some inventor trying to formulate a new kind of Super Glue. He tries a lot of different variations and comes up with something that will hold things together when you want them held together but will release them without tearing them up or using a lot of energy when you want them separated. That’s the kind of adhesive that’s found in Post-It notes. It’s just a good thing he didn’t throw it in the trash because he had started out looking for a new kind of Super Glue! What would we do without Post-It notes? (I usually have one or two on my folders right there.) That’s what hydrogen bonds are like. An example would be the hydrogen bonds holding the two strands of DNA together. The strands need to be reliably held together most of the time, but sometimes they need to separate (of course I haven’t talked about replication or protein synthesis yet). It must happen without tearing the strands up or using an atom bomb’s worth of energy to make it happen. Then sometimes the strands will need to go back together (protein synthesis). That’s why the weak hydrogen bonds are important.

The Function of Antibodies and Complement Compared to Chocolate Chips

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

When explaining how complement or antibodies enhance the innate system’s phagocytes to engulf these coated pathogens, I explain my behavior at a buffet. I may see vanilla cake, plain ice cream, short bread cookies etc. and all of these might taste good if I chose them. However, if my eye catches something with chocolate chips on it, I am immediately drawn to it and choose this to eat.Movie Get Out (2017)

The Immune System as the Body’s Militia

Written by Gidi Shemer, University of North Carolina at Chapel Hill

When discussing the immune system in human physiology, the military is the star of the show. The first line defense (e.g. our skin) can be represented by the physical barriers we have in our borders, defending us from the enemy (e.g. bacteria). The second line of defense (e.g. the phagocytes of the innate immune system) is represented by the soldiers who are found at the front lines. The third defense, the adaptive immune system, our B and T cells, is represented by the elite forces. These elite forces are more expensive, hard to come by, and called to action by the plain soldiers, but they provide modern, selective, and sophisticated tactics to fight the enemy.

The Smell of Fresh Pizza and Cell Movement

Written by Sheri Kuslak, University of North Carolina at Chapel Hill

When discussing chemokines and chemotaxis of immune cells to an injury site I describe college students’ response to the smell of pizza. For example imagine a classroom containing a dozen freshly baked pizzas being similar to an injury site in the human body. As the smell of pizza (chemokines) wafts through the air into the hallways the students (immune cells) follow the smell to the source (chemotaxis). Once the students (immune cells) find the source they begin eating the pizza (healing the injury through specialized processes). Once the pizza is gone (injury is healed), the pizza smell (chemokines) subsides therefore not drawing in any more students to the classroom (the former injury site).

Article Alert: Can We “Level the Playing Field” with Active Learning?

Written by Kelly A. Hogan, University of North Carolina

We all intuitively know as instructors that the success of a student is tied to their high school preparation. Students coming from disadvantaged high schools will often struggle with the transition to college biology more so than other students. You know the type; they work hard and spin their wheels, only to feel frustrated with their ability to keep up and pass the tests. How do we reach these students and “level the playing field”?

David Glenn writes a summary of two studies examining the effect on the achievement gap when a large introductory biology class is redesigned into an active learning environment. The article, “Low-Cost Instructional Changes Can Cut Achievement Gap in Intro Biology,” http://chronicle.com/article/Low-Cost-Instructional-Changes/127747/ is a quick summary with links to the Science and Life Sciences CBE Education journal articles. The study was led by Scott Freeman at the University of Washington and concludes that active learning in this study cut the achievement gap by almost half. The study discusses some simple ideas like randomly calling on students in the large lecture class, having students write minute papers in class, and being quizzed on the reading.

What kinds of simple things have you done to improve the active learning environment of your class?

How Does a Tree Grow? Which Four Year Old Do You Agree With?

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

Learning Outcomes:

– To correct a misconception about how trees grow

– To describe primary growth in plants

Activity Description: A video is shown of two four-year-old boys who are asked what would happen to a basketball hoop nailed into a tree after many years of tree growth. Students must decide which boy they agree with. After answering on their own, they must then discuss and answer again.

Time Needed: 10 minutes

Materials Needed: Link to this video: http://www.flickr.com/photos/kelly_hogan_13/3369618928/in/photostream

Activity Instructions: Show the video above. Using the PowerPoint linked, poll the students, preferably through clickers, to find out what students think. My class was close to a 50/50 split without much introduction to the topic. This is a great question to have them find someone with a different answer and try to convince the other that they are correct. This generates a lot of discussion. In their discussion, I will often show them the two models of growth we are comparing with the question (see PowerPoint.)

In the end, I explain how Jake was correct (my son!). I use this as a launch into a discussion about primary growth from apical meristems.

PowerPoint Presentation: How Does a Tree Grow PowerPoint