Modeling the Prokaryotic Cell (Part 2/2)
Lesson 2 of 4
Objective: The students will use several protocols to identify and classify unknown prokaryotic cells. Students will compare and contrast how a bacterial cell differs structurally from an eukaryotic cell.
Students will look at several ways scientists use to identify bacteria. They will also compare prokaryotic and eukaryotic cell models to understand the importance of cell specialization in multicellular organisms. Here is an overview of what students will learn today.
Introduce the terms prokaryote and eukaryote as essential vocabulary. Using the Frayer method, have students define those terms in their lab notebook section.
Stations 1-3 will be set up at separate lab stations. Typically, all students start with Station 1. Then student groups either go to Station 2 or 3. Lab station 4 is at the students' desks. During Station 4, students will use the POGIL, Prokaryotic and Eukaryotic Cells, by Flinn Scientific. (Note: This is a free resource to teachers and it can be found on the Biology POGIL page on the Flinn Scientific Website. Look in the lower left hand corner of the page under the heading Additional Resources.)
Students should complete the sections on the POGIL regarding Model 1 and 2 during the Exploratorium. (Note: For those who are not familiar with POGIL (Process Oriented Guided Inquiry Learning), it is a teaching method that presents content using an inquiry-based learning approach. In this particular POGIL, by analyzing certain cell models, students learn how scientists classify cells as prokaryotic or eukaryotic. This pedagogical method was first used in teaching chemistry, but it now has been applied to both biology and physics as well.)
By the end of the exploratorium, students should have a good understanding concerning the different methods scientists use to compare bacterial species with each other. They should also understand how bacteria compare with eukaryotic cells and how the cells of multicellular organisms adapt to perform specific functions.
Station 1: Gram Staining
Students will follow the gram staining protocol and make a slide of their own. Once students are finished, they should take their slides with them to the next lab station. Use this rubric to evaluate student work. Once they have completed this portion of the exploratorium, they can move to the next station if it is free. Otherwise, they can take their seats and work on the next portion of the POGIL.
Station 2: Cell Shape
Use the cell shape cards (links shown below) at the station.
- Bacteria Types
- Cell arrangement for bacilli
- Cell arrangement of cocci bacteria
Students are to familiarize themselves with cell morphology (cell shape and cell arrangement). There are artist depictions of the types of cells--coccus, bacillus, spirullum, spirochete, and vibrio. There are also images of these types of cells taken under a light microscope. I give students a magnifying glass so they can examine the images in more detail. Students are also given a Vis-a-Vis pen to draw on the cards to help them distinguish structures and cell arrangement. Students should make sketches of these cell shapes and arrangements in their lab notebooks along with a short description of the distinguishing characteristics of each.
After they finish making their sketches, students should use a light microscope to look at the bacteria found on their gram stain slide. They should make a sketch of the bacteria on the slide paying close attention to the cell shape and grouping of the cell. They should also identify if the cell is gram (-) or gram (+).
Finally, they should test their understanding by determining the cell shape and arrangement of this unknown bacteria.
Once they have completed this portion of the exploratorium, they can move to station 3 if it is free. Otherwise, they can take their seats and work on the next portion of the POGIL.
Station 3: Flagella
Use the cards (links shown below) at the station.
Students are to familiarize themselves with the bacterial flagellum arrangement and the number of flagella that bacteria can have. They should make a sketch of each specimen in their lab notebook and write a brief description of the specimen.
Then students are to look at unknown bacteria on the image at the station. They should make a sketch of the bacteria in their lab notebook (or student handout) paying close attention to the number of flagella the bacteria has. They should also identify if the cell is gram (-) or gram (+).
Students can test their understanding by determining the classification of this bacterium.
Once they have completed this portion of the exploratorium, they can move to station 2 if it is free. Otherwise, they can take their seats and work on the next portion of the POGIL.
Use the Prokaryotic and Eukaryotic Cells POGIL for this station. This exercise is designed so students can work independently. During the exploratorium, students should complete the Model 1 Section (from the POGIL) where they analyze several prokaryotic cells. They may also complete the Model 2 Section (from the POGIL) where they analyze animal and plant cells.
(Note: This is a free resource to teachers and it can be found on the Biology POGIL page on the Flinn Scientific Website. Look in the lower left hand corner of the page under the heading Additional Resources.)
Before students move onto Model 3 (in the POGIL), poll the students as to which model (1 or 2) they think is more complex. Randomly call on several students to give supporting reasons for their choice. After a brief discourse, instruct the students to move onto Model 3.
Putting It All Together
Using the POGIL activity, discuss the Extension Questions as a class. Have students consider how multi-celled organisms specialize in order to perform specific functions. Point out the adaptations that these specialized cells must undergo in order to help all of the cells of a multicellular organism function as an unit.
Ask the students to compare these specialized cells with the bacteria they viewed today. Remind the class that the bacteria they viewed today are a specific form of a prokaryotic cell (Model 1 in the POGIL). Then poll the class again to see if anyone has changed their thinking about which model, 1 or 2, is more complex.
Have students write an one sentence summary in their lab notebooks to explain why they conclude that Model 2 is more complex and how that complexity is important to the ways that systems in multicellular organisms interact to ensure certain tasks get done.