By building a prokaryotic cell model, students learn the differences between eukaryotes and prokaryotes. They also explore why bacteria are a good model organism. Here is an overview of what students will learn today.
Project the Launch Lab presentation. In their lab notebooks, students should create a data table or use this data table. At the end of four minutes, ask the students what similarities they saw among the different cells by using these questions.
Next, ask students what differences they saw among the different cells by using these questions.
Remind the students that they will be returning to the Launch Lab at the end of the hour.
(Note: I have students download a copy of this presentation onto their laptops and view the presentation individually. Students can then proceed through the slides at their own pace. The slides will also appear with better resolution making it possible to see more of the specific details in the cells. Students may not get completely through with this Launch Lab as shown with this sample student work. However, it will be revisited at the end of the lesson.)
Using the presentation, walk students through constructing a bacterial cell. As each structure is being made, discuss how it models the structure in the electromicrograph. Also, discuss the limitations of each structure in the cell model as compare to the electromicrograph.
(Note: There are days when lecture cannot be avoided. To keep my students actively involved, I have my students build model of the bacterial cell being described. Each student should build a bacterial cell model. For large class, precutting the plasmids, ribosomes and the polypeptides is recommended.)
Here are some basic instructions for the construction of the model.
Once the model is constructed have the students all place their models in one location. Label that location a bacterial colony. (Note: If you have more than one section of biology, students can continue to place their models in the same location to demonstrate growth of the bacterial colony.)
Once students return to their seats, they should summarize the function of each of the structure in their lab notebooks. Finally, explain the limitations of using electron microscopes to view bacterial structures.
Have students recall how multicellular organisms are organized.
(Answer: organelles-->cells-->tissues-->organs-->organ systems-->organism)
Return to the Launch Lab and ask students to compare the Animalia and Plantae slides with the Bacteria cell model that students created in the activity.
Have students identify as many structures as they can on the images.
(Note: the plant image was taken using a light microscope as magnification. Students should be able to see the cell membrane, cytoplasm, and DNA. They will not be able to see chloroplasts, mitochondria, and other organelles. The animal cell image was taken with an electron microscope. Students should be able to see many organelles in this image.)
Discuss with students how animals, plants, and fungi are able to specialize and have tissues because how because of organelles in the cells. Bacteria do not have organelles and therefore remain small.
Finally, in their lab notebooks, have students label these four images (electromicrograph of a bacterial cell, artist's depiction of a gram stained membrane, bacteria at high power magnification, and bacteria at low power magnification) to allow them to understand the differences between organisms seen under a light microscope as compared to an electron microscope. Encourage students to notice certain structure. Explain why the bacterial cell must be stained in order to view it under a light microscope. Then have students brainstorm why bacteria would make a good model organism to prepare for tomorrow's lesson. Have students turn in their lab notebooks at the end of the hour for evaluation.