Today we are conducting a lab on the things that can be found in yogurt – namely bacteria!  Each group will be given the opportunity to observe a solution of yogurt and water through their microscope and report to the rest of the class what they find living in their yogurt.  As a follow-up to the lab you will be required to write a laboratory report in your lab notebook.  One member of your group will come up to the front and prepare your slide, during this time the rest of your group should be starting to write your lab report to reduce your homework.  The written work will be set up according to the guidelines for lab report sheet located in your science binder.


Remember to act safely and conduct your work in an appropriate manner or you will receive a zero for today’s assignment.  Now lets get started and see what you really eat!


Laboratory Procedure

1. Place a very small dot of the yogurt and water mixture on a microscope slide using a flat toothpick.

2. Add a small drop of methylene blue dye to your slide to stain the bacterial cells

3. Gently drop the cover slip over the mixture and make sure to wipe away any excess liquid.

4. Carefully carry your slide back to your group and allow them to observe your yogurt slide before you place it on the microscope.

5. Observe the slide using your 10X and 40X objectives. If you wish, you can try your 100X but be careful to not crack the slide or lens.

6. You should be able to see colored bodies on the slide; these will be groups or individual rod-shaped bacterial cells. You are now looking at the Lactobacillus acidophilus we mentioned earlier.  If you cannot see the bacteria clearly try adjusting the focus on the microscope or change the amount of light. 

7. Allow each member of the group to view and draw a few of the bacterial cells in the space below as they appear under your 40X or 100X objective.

8. Carefully clean up your workstation, and place the slide in the area provided.
















Bacteria seen at 40X                                                    Bacteria seen at 100X

Lab Report

Remember to include in your lab report the following:




Procedure (an abbreviated version will do)

Results (a written description of what you saw in your yogurt and the diagrams from page One)


Include in the discussion a summary of what you did and what you found out.  Also include answers to the following points in paragraph form:


1.         Give a basic description of a bacterial cell and describe the two kingdoms that bacteria can belong to. 

2.         Define the differences between the two kingdoms and explain why scientists have classified the bacteria into these two groups. 

3.         Explain the shape and type of bacteria you saw through the microscope and place it into one of the two kingdoms.