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,” 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:

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

The Carbon Footprint

Written by Michelle Zurawski, Moraine Valley Community College

Learning Outcomes:

– Students will be able to define carbon footprint and other associated ecological terms.

– Students will understand the factors that affect their carbon footprint and determine how to change them.

– Students will understand the impact of diet on the carbon footprint.

– Students will think about the socioeconomics of the carbon footprint.

Activity Description: Students use a website that helps them to calculate their carbon footprint and answer worksheet questions. This activity can be assigned as homework or can be done during class time with computers. Some discussion questions could be made into clicker questions if you had a large classroom of students.

Time Needed: It takes about 5 minutes to do the carbon footprint and 30 minutes or more for a discussion of the material.

Materials Needed: Student computersWatch Cyberbully (2015) Full Movie Online Streaming Online and Download

Activity Instructions: With a smaller class, use a carousel to promote student discussion. How to set up a carousel: choose some of the discussion questions and post them on the dry erase board or on large pieces of paper taped to the walls. Group 3-4 students together and give each group 1 minute to write answers to the questions. Each group has a different color marker.  Groups rotate to each station for 1 minute and provide their answers. The groups may add to what has been written, or they may subtract by crossing off. This ensures during discussion you can ask, for example, why the green group crossed off what the purple group wrote. After all groups have finished, each group will give a summary of what was written on their original question.

If the carousel approach won’t work with a large class, create clicker questions around the assignment questions or simply hold a discussion in class.

In an online class, you may choose some of the questions to be used as discussion questions on the discussion board. I generally require students to post one original posting of 150 words or more and respond to two or more students with 50 words or more.

Worksheet: The Carbon Footprint Worksheet

Calculations to Show How Deer Growth Is Unchecked in the Suburbs

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

Learning Outcomes:

– To practice using the equation for exponential population growth

– To relate population growth to a species students are familiar with

Activity Description: Students are given a worksheet with background reading describing how deer are thriving in the suburbs of theU.S. After students finish, the class will discuss ways deer populations can be controlled.

Time Needed: 20 minutes

Materials Needed: Worksheet for students

Activity Instructions: Have students complete the attached worksheet once they have been introduced to the topic of population growth.

Worksheet: Deer Population Growth WorksheetDeer Population Growth Worksheet KEY

Community Interactions and Fun Analogies

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

Learning Outcomes:

– To take definitions of community interactions and apply the concepts through analogy

– To have a better understanding of interference competition, exploitative competition, resource portioning, mutualism, and commensalism

Activity Description: Students work in pairs to come up with three analogies for community interactions that they write on separate index cards. For example, the analogies might describe how siblings compete for limited resources like cookies. Students then randomly pass cards to neighbors again and again until each pair of partners has new, unknown cards. They read the cards and determine what the phrase describes. The students then share the fun, interesting analogies their classmates made, giving the class more practice with these terms.

Time Needed: 10 minutes for card writing and 10-15 minutes for discussion

Materials Needed: 3 x 5 index cards (3 per student pair)

Activity Instructions: After discussing interference competition, exploitative competition, resource portioning, mutualism, and commensalism, put these instructions on PowerPoint for the students:

  • The front of a flashcard should have an analogy for any of these phrases:

–        Interference competition

–        Commensalism

–        Resource partitioning

–        Exploitative competition

–        Mutualism

  • The back of the card in small print should tell which of these phrases your analogy describes
  • Think about roommates, teammates, parents, classmates, siblings etc.. Get creative. (If humorous, even better but keep it CLEAN!)
  • We’ll then pass these around to see if others can guess your analogy and I’ll collect and read some. Synthesizing your own analogies = excellent studying!

After the students complete their three cards, they pass them to neighbors who pass them to neighbors until the cards get shuffled well in the classroom. The partners spend time reading their new cards and seeing if they can guess what the analogy is for. (They can flip the card over to see if they guessed correctly.)

Next, ask students if they have a really creative card. If so, ask them to read it to the class. Let the class guess what the analogy describes. Read several others.  Ask if anyone has a card in which they did not agree with the authors’ description of a phrase. Have them read this to the class and discuss why it might be a good or not so good analogy.

The instructor might want to demonstrate analogies within the lecture before the activity. Here are some ideas:

Interference competition: Jake and Lexi are siblings. There is only one bag of goldfish crackers. Lexi grabs the bag and won’t let Jake have any. She pushes him when he tries to reach for some crackers.

Exploitative competition: Jake and Lexi are siblings. There is only one bag of goldfish crackers and not too many left. Lexi grabs a small handful. Jake, realizing there are not too many crackers left, grabs a larger handful than Lexi on his first serving.

Resource partitioning: Jake and Lexi are siblings. There is only one bag of goldfish crackers. Being aware that they must share or lose the crackers altogether, Lexi decides she will take just the pink crackers and Jake will have the other colors.

Jake and Lexi eating their colored goldfish crackers. Photo by Kelly Hogan.

Mutualism: It is 7:00 PM, and it is Jake’s bedtime. He wants to stay up past his bedtime and pleads with his mother to stay up late. His mother agrees on the condition that he first go to the kitchen and do her a “favor” by grabbing her some chocolate to snack on.

Commensalism: In passing, Kelly mentions to her neighbor, Evette, that she is going to their health club later that day. Evette says, “Since you are going, can I hitch a ride with you?” Kelly says, “Sure, no problem.”

Examples that my students came up. You can also read them to students and let them decide what they are analogies for.

1. Professors get paid to teach, students get an education in return.

2. My brother tackles me to get the one Wii remote.

3. My roommate drinks all the water from my Brita filter and never refills it, so I hardly ever have good water to drink.

4. I use my friend’s notes from last semester.

5. When two siblings both want to ride in the front seat, one rushes out of the house first and waits in the front seat.

6. Studying with a friend.

7. I drive to class every day. Yesterday a friend of mine asked if she could ride with me after she missed the bus.

8. My sister and I buy a bag of candy. She eats her favorite colors (orange and green) and I eat my favorite colors (red and purple)

9. Tarheel’s basketball player Harrison Barnes gives teammate Tyler Zeller an assist. They both get stat increases, and the team benefits.

10. We only have one shower in my suite. My suitemates and I take showers at different times.

11. Eating earlier at the dining hall to ensure you get chocolate cake before others.

  1. Mutualism
  2. Interference competition
  3. Exploitative competition
  4. Commensalism
  5. Interference competition
  6. Mutualism
  7. Commensalism
  8. Resource portioning
  9. Mutualism
  10. Resource partitioning
  11. Exploitative competition

Leaf, Stem, Root, or Flower? A Game

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

Learning Outcomes:

– To examine the basic structures of plants and the variations on the body plan

– To encourage a little fun and competition in the class related to plants

Activity Description: A few students are chosen to play a game in front of the class, but the rest of the class must also play the game on a piece of paper like a quiz. Students are shown various food plant parts they are familiar with and must then determine if what they eat is the leaf, stem, root, or flower of the plant. Students have a lot of fun, as some of the foods are intentionally tricky!

Time Needed: 15 minutes

Materials Needed: A PowerPoint presentation showing the images of the foods described

Activity Instructions: Before the game, students need to know about some basic plant structures. Randomly choose two teams of students to compete for a prize. (You may choose to give a plant food as a prize!) A website such as has a unique way of choosing students if you enter the roster into the fruit machine. As you move through the PowerPoint slides, keep track of the score between the two teams. Have the students at their seats also write down their answers in order to self-grade.

I have given a list of foods you may want to use. At the top of each slide, make the title, “Leaf, Stem, Root, or Flower?”

  1. Potato – This is a stem, an underground storage stem called a tuber.
  2. Carrot – This is a modified tap root, for storage.
  3. Celery – Leaf; the part we eat is an enlarged petiole (the stem of the leaf).
  4. Broccoli tops — These are sometimes called florets, meaning flowers. They are immature flowers.
  5. Sweet potato – Root; despite being called a potato, this kind of potato is a modified root for storage. (Unlike a regular potato which grows “eyes” as leaves bud from it when left on the counter too long, this does not happen from sweet potatoes.)
  6. Onion layers – The bulb of the onion contains both a modified stem, in the center, but most of what we eat are layers that are modified underground leaves.
  7. Artichokes – All the green “layers” are part of a flower bud that is picked before the large purple flower blooms.
  8. Ginger – Often called ginger root, it is not a root. It is a modified storage stem called a rhizome.