How Small is a Virus--Real-Life Examples

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Students will compare and contrast the size of multiple viruses.

Big Idea

What makes a virus airborne? It's all about the size, my friend.

What Students Will Learn in this Lesson

1 minutes

Now that students have a good understanding of the size of both micrometers and nanometers and what a virus is, it is time to explore the diversity and size of viruses.  In this lesson, students not only make their own predictions, but they will modify those predictions based on what they have learned. They then compare virus size with the model organism E. coli. Students also answer the ever present question---how does a virus become airborne by exploring the major methods of transmission. Here is an overview of what students will learn today and why I use the methods I do to teach this content.  

Check for Understanding

3 minutes

1. Explain to students that today they will be exploring the size of viruses when compared to each other and two types of bacteria (E. coli and the Chlamydia elementary body) . 


2. Show students a slide show of viruses. Have the rank the viruses in order of size.  Ask students to predict how many times smaller these viruses are when compared to an E. coli bacterium.  

(Note:  I think this method is a great way to see what students have previously learned in regards to microscale sizes.  It also is a proven method for me to determine where they still might have misconceptions regarding size and scale.  I feel that comparing viral size with the model organism E. coli helps students reaffirm the size differential between viruses and a bacterium to which we will refer back many times throughout the year. It reinforces the homework that students should have completed from yesterday's lesson.


3. Have students record their predictions in their lab notebooks under the heading What Do You Think: My Predictions on Virus Size.  

(Note:  One of the biggest misconceptions that my students and the general public have about viruses is that any virus is at risk of becoming airborne.  Typically, whether or not a virus could become airborne depends upon the location of the free viruses in the host and the size of the virus.  As the class completes the student handout in their groups, they explore several aerosol studies. Data from these studies along with the virus size handout will aid students in determining the criteria that viruses must meet in order to become airborne.)

Student Activity: Construction of the micrometer scale

5 minutes

Using masking tape, have students make a 2 m long strip and apply it to the wall. Label this strip three. Strip three will be a model that represents 2 micrometers. The scale for strip two is 1 m represents 1 µm.  

On strip 3, mark where 2 µm, 1 µm, 250 nm, 500 nm, 750 nm, 1,000 nm, 1,250 nm, 1,500 nm, 1,750 nm and 2,000 nm would be located.    

(Note:  After students look at the two scales that they created yesterday, they should determine that neither scale truly fit their needs.  If they try to use the meter scale, all of the viruses are located on top of each other on the left side of the scale.  If they try to use the millimeter scale, all of the viruses are also located on top of each other on the left side of the scale. This really surprises students. Despite the time it takes, it is a good exercise to have them do because many students do not understand powers of 10. A micrometer scale needs to be constructed so that the viruses will be spaced far enough a part for comparison.)  

Student Activity: Comparison of virus size

10 minutes

Provide students with cutouts of viruses from the virus comparison sheet or have students cut out the individual items on the sheet. Encourage them to keep the size of the item on the cutout. Otherwise, it will be difficult to do the activity.  (I laminate the virus comparison sheet and then cut out the individual viruses and bacteria on the page. I give my students a package of the items so I can use them from year to year).

Have students place the viruses and bacteria on the correct location on the micrometer. Next, have students determine how many times larger the E. coli bacterium is than the viruses. (Note: The Chlamydia elementary body is a bacterium. It is just placed in the comparison sheet for reference for a lesson later in the year.) Students can leave the scale up on the wall for the entire unit so they have a reference for size.  

Revisit the predictions that students made at the beginning of the lesson.  Have students complete the actual size column in their lab notebook or use the provided handout.  After they have finished, have them rank the viruses by size.  

Teacher mini-lecture: How small?

22 minutes

Have students look back at their answers from the beginning of the day. Have students to calculate how many times smaller these viruses are when compared to an E. coli bacterium by taking the size of the virus/the size of E. coli * 100%. Have them record their answers in a data table in their lab notebook.  

Next ask students to consider what makes a virus airborne.  Ask student where in the body are most viruses found?  (Possible answers include:  saliva, semen, blood, cells, sweat, interstitial fluid)

One of the biggest misconceptions about viruses that people have is how a virus can become airborne. Typically, whether or not a virus could become airborne depends on location of the free viruses in the host and size of the virus. As a class complete the student handout together to explore several aerosol studies to aid students in determining what criteria a virus must meet to become airborne.  

First, go to Mount Sinai Hospital Hospital’s Department of Microbiology Webpage to determine how are diseases transferred. Students should popcorn read through the webpage. Project a copy of the Studying virus transmission worksheet and write an explanation or summary of transmission.  

Next, students should read the Summary portion silently and highlight according to the instructions. After several minutes. bring the class back together and question the students about their highlighting.  (Note: I make the student handout a pdf and use the tools in Preview to highlight this section.) Focus on comparing the droplet size to the virus size. Ask students if the viruses could fit in the droplet? Refer them back to the virus scale, if necessary.

Finally, analyze how scientists determine how far droplets travel and how fast they travel by popcorn reading the abstract and discussing the images and graphs.  (Note: I take separate screenshots of each of the figures in the assignment and project them.)

Putting it All Together

5 minutes

 To determine if students understand the lesson, have them write a modified minute paper about the following questions 

Will I get Ebola from a ride on the plane?  

Will Ebola ever become airborne?

When responding to this question, consider the following in your argument.

a)size of Ebola
b)size of aerosols
c)how far will the virus and the aerosols travel when talking, coughing, and sneezing. 

Homework: Students will listen to the NPR All Things Considered podcast “Why Won’t the Fear of Airborne Ebola Go Away?”  and write a one sentence summary.