Quiz 2: Bacterial Structures and Light Microscopy

Label the parts of the microscope and describe the function of each one

1. Arm of microscope: where the microscope is held when relocating it

2. Coarse focus knob: moves the lens for coarse focus

3. Fine focus knob: moves the lens for fine focus

4. Stage knobs: moves the stage 

5. Base of microscope

6. Light knob: adjusts light intensity

7. Light switch: turns on the lamp

8. Light source (lamp): provides light for specimen analysis

9. Iris diaphragm: adjusts light intensity 

10.  Condenser Lens: a focused light beam passes through the specimen

11.  Specimen: item being analyzed

12.  Objective lenses: 4x, 10x, 40x, and 100x

13. Ocular lens: where the eyes are placed on to see the specimen

    1. Provides an additional 10x magnification

Purpose of Gram staining:

differentiates bacteria based on the properties of their cell wall

Steps for Gram Staining:

1. Heat: application of heat to fixate the sample (specimen smear)

2. Crystal violet: application of primary stains to specimen smear to form a colorful complex (CVI) which is trapped inside the cell wall

   1. Followed by a water rinse

3. Gram iodine: application of primary stains to specimen smear to form a colorful complex (CVI) which is trapped inside the cell wall

   1. Followed by water rinse

4. Alcohol: decolonization of the same with alcohol (decolorizer)

   1. Gram-negative cells lose the CVI complex, while Gram-positive cells retain it

   2. Followed by water rinse

5. Safranin: application of counterstain to the sample

   1. Followed by water rinse

   2. Reveals color to determine whether specimen is gram positive or negative

What color would indicate Gram-positive and Gram-negative?

1. Gram-positive bacteria: purple or dark blue

   1. have a thick cell wall outside their plasma (cell) membrane composed of many layers of peptidoglycan

2. Gram-negative bacteria: pink or reddish

   1. have a very different composition outside of the plasma membrane.

Identify accurately the shape and cell arrangement of cells on a microscope slide.

1. Two main categories of bacterial shape:

   1. Cocci: sphere-shaped

   2. Bacilli: rod-shaped

2. Other shapes:

   1. Curved rods: comma-shaped

   2. Spirochete-shaped bacteria: spiral-shaped

Arrangement of bacterial cells can indicate their speicies:

• coccus: single bacterial cell

• diplococci: double

• staphylococci: a bunch of grapes

• Streptococci: long chain

• Sarcina: eight cells clumped together

• tetrad: four cells arranged together in the same plane

Purpose of immersion oil

1. has the same refractive index as glass and will minimize the loss of light and light refraction creating a crystal-clear image of the cells.

   1. a drop of immersion oil is added on top of the slide to replace the air in the working distance.

List of PPE

personal protective equipment:

• Blue lab coat since it is fire resistant

• Gloves

• Goggles

describe the proper handling of food, drinks and cosmetics in the lab

1. No food, drinks, or gum are allowed in lab

2. No putting on any sort of cosmetics during lab, not even chapstick

describe the proper clothing to wear in the lab as well as the safe ways to wear your hair and jewelry 

1. Long pants

2. Closed-toe shoes

3. Tie back hair and tuck under lab coat if necessary

4. Take off any loose jewelry that might possible get in the way of the lab procedure

describe when you need to disinfect the benches

1. Disinfect lab benches before and after use

which structure does the gram-stain stain and how do we get two different results based on the cell structure?

the cell wall is stained with a gram-stain

• we get two different results depending on the thickness of the peptidoglycan layer in the cell wall and its capability to trap the CVI complex