Lab 4: Structure and Microscopy (100 points)

• Each question on the lab worksheet must be answered completely, thoroughly, in complete sentences and correctly in order to be considered for full credit
• If the question asks you to do research or find a source, a reputable, credible and/or scholarly source citation must be included in order to be considered for full credit
• If a math formula is required to arrive to an answer, work must be shown otherwise, no credit will be awarded

*Note-This lab is designed to be completed without the use of a microscope.

Pre-Lab Questions

1. Most bacteria have a cell wall made of peptidoglycan, the structure of which makes the cell wall very strong. Explain the specific components that make up the bacterial cell wall which give it strength and protection (10 points)
2. What are the three key objectives for heat fixing a sample before beginning a staining procedure? (5 points)
3. Bacteria have many different shapes that often determine their class. Research and form a hypothesis on the evolutionary reasons for so many different bacterial morphologies. (5 points)
4. Do a search online or look in your textbook for 2 antibiotics that affect Gram-positive bacteria and list them. On what part of the cell do the antibiotics inhibit?
5. Explain the reasons why is it important to identify the bacterial disease in a patient before prescribing any antibiotic treatments? (Be specific.) (5 points)

Experiment 1 Results Tables

• Table 1: Experiment 1 Staining Observations (5 points)

Experiment 1 Post-Lab Questions

1. Explain how negative staining works to enhance the visualization of bacterial cells? (5 points)
2. What was the stain used as the simple stain in this lab? What are the limitations of using a simple stain? (10 points)

Experiment 2 Results Tables

• Table 2: Experiment 2 Staining Observations (5 points)

Experiment 2 Post-Lab Questions

1. After visualizing the stained samples (your samples or by looking at the sample images provided in the eScience manual), describe what physical/visual characteristics you were able to observe after performing the negative staining vs. after performing the simple stain. (5 points)
2. In this lab, you have used one type of simple stain and one type of negative stain, yet there are many other simple and negative dyes available.

Pick one simple dye and one negative dye and discuss how those dyes differ from the ones you used in this lab. Give a scenario in which their use would be appropriate. (5 points)

Experiment 3 Results Tables

• Table 3: Experiment 3 Staining Observations (5 points)

Experiment 3 Post-Lab Questions

1. Explain what are the different characteristic(s) that exist between the two groups of Gram-positive and Gram-negative bacteria that account for the different staining conditions? (5 points)
2. What is the purpose of the Gram iodine addition in the Gram staining procedure? (5 points)
3. What is the purpose of adding counterstain (safranin) to the Gram staining procedure? (5 points)
4. What are the advantages of performing a Gram stain vs. a simple stain for visualizing bacteria? (5 points)
5. Using either a textbook or a reputable online resource, research some of the typical characteristics of bacteria, and discuss why it might be important for a researcher or a hospital technician to be able to differentiate between Gram-positive and Gram-negative bacteria. (5 points)