Students will be able to analyze and evaluate a gram stain in order to determine if a cultured yogurt sample has been contaminated by potential pathogens and identify the type of bacteria in a sample using a microscope.
National Biotechnology Standard(s):
BT.5.1 Distinguish between prokaryotic cells, eukaryotic cells, and non-living entities such as viruses.
BT.2.3 Identify impact of past and current discoveries and developments in fields such as, diagnostics (i.e. Gram-Staining), medical devices (i.e. microscopes), pharmaceuticals, and research and development.
Engage (Activate Student Thinking)
1. The discovery of the light microscope has been viewed as one of the most important biotechnology innovations in the history of this exciting field. Based on what you already know about microscopes or what you may have experienced DEFEND this viewpoint.
2. Access the following URL and address the prompt below:
Explain how the history of what we call “cell theory” has been shaped by advancements in the biotechnology called the microscope.
Explore (Guided/Student-Centered Activity)
Virtual Tour of the Microscope
Objective – Students will gain familiarity with the compound microscope by exploring an online virtual microscope.
1. Use the following URL to access this microscope simulation:
2. Make sure your volume is on then click “Start Tour” at the bottom right of the “Getting Started” box.
3. When it asks you to select a slide begin with the green specimen- Onion Root Tip, this is the easiest to see (2nd from top).
4. Click the “Switch Objectives” tutorial under the Getting Started box and LISTEN carefully to the instructions!
CHECKPOINT: Which lens does the tutorial tell you to start with? __________x
5. Follow the tutorial prompts to learn how to center the slide and focus your specimen. HINT!!! Use the checklist box on the left side of the screen to monitor your progress!
CHECKPOINT: In your own words, describe how the coarse and fine focus knobs differ. When is it most appropriate to utilize your coarse focus knob?
6. Once your specimen is in focus using the 4X lens, use the revolving nosepiece at the bottom left of your screen to move the 10X lens into place. Use the fine focus to adjust.
CHECKPOINT: What happens if you try to use the coarse adjustment when the 10X lens is in place? What happens to your image if you try to magnify it using 40x or 100x?
7. Draw the Onion Root Tip using 10x magnification in the appropriate circle in the student lesson/lab guide.
8. Follow the same procedure for the bacterial capsules and cheek cells slides. Draw the images using the total magnification shown under each circle.
Explain (Formulate Ideas)
1. What objective lens should be in place as you begin to look at your specimen?
2. True or False: You only use the course focus knob when you have the 4X-scanning objective in place. (Explain your reasoning.)
3. Assuming the light is on and the oculars are in place what are the next 2 steps to properly view a specimen placed on the microscope stage?
4. Complete the following: If you need more light to view your specimen, it is best to adjust the...
Elaborate (Apply and Extend Understanding)
Digital Training Course
Objective – Students will conduct a virtual microscope lab that builds on the Gram Staining Virtual Lab completed previously. This real-world application will enable students to discover the overall purpose, structure and function of parts of the microscope and how the microscope will be used in a future lab.
1. Access the following URL: http://virtuallab.nmsu.edu/micro.php
2. What do the numbers on the side of each objective lens indicate? Predict which lens would be referred to as “low power” and “high power”.
3. What is the total magnification of the 40x objective lens? (EXPLAIN how you arrived at your answer!)
4. Explain the following statement: The 100x lens has “superpowers”!
5. The presence of which type of bacteria (Gram-positive or Gram-negative) would indicate that the yogurt sample was indeed contaminated? EXPLAIN!
6. Based on what you observed using the virtual light microscope, does the sample of cultured yogurt from the dairy plant contain Gram-positive or Gram-negative bacteria? (Elaborate about how you were able to draw your conclusion.)
Evaluate (Monitor Understanding)
Microscope Technique Practice
Objective – Students will conduct a hands-on microscope lab demonstrating mastery of both the theoretical and practical aspects of microscopy.
1. Using a letter from a word in a newspaper, make a wet mount of it by placing the letter on the slide, adding a tiny drop of water to the paper, and then placing a cover slip on the paper. Use “low power” to focus on the letter. What do you notice about the orientation of the letter? Draw what you see in your lab notebook and record your observations.
2. Find a color picture from the newspaper and make a wet mount of it on a slide. Use low power to focus on the picture. What do you notice about the color of the picture under “low power”. Resolution is the ability to distinguish two separate objects as being separate. How does magnification affect resolution? Draw what you see in your notebook and record your observations.
3. Use good microscope techniques to observe the slide your group prepared during the Gram Staining Lab. Draw what you see using low and high power. Describe the sample of bacteria on the slide. Does the sample contain gram (+) or gram (-) bacteria or perhaps BOTH? Record your conclusion in your lab notebook.
1. Describe what you learned about microscopes. Discuss at least ONE challenge you faced when working with the microscope.
2. Discuss the need for staining cells to study them under the microscope.