Midterm

Question 1

What is the field diameter at 1000x?

Answer 1

0.2mm

Question 2

What characterizes a gram - cell wall?

Answer 2

Thin layer of peptidoglycan with outer lipid membrane; stains pink

Question 3

What characterizes a gram + cell wall

Answer 3

Very thick peptidoglycan layer; stains purple

Question 4

What are the gram stain steps?

Answer 4

1. Crystal violet, 30 sec
2. Rinse with DI water
3. Gram’s Iodine (mordant): 30 sec
4. Rinse with DI water
5. Acetone alcohol (decolorizer): rinse off ASAP
6. Secondary stain: Safranin, 1 min
7. Rinse with DI water
8. Blot dry with kimwipe

Question 5

How do you determine cell size?

Answer 5

Field diameter/#of cells that fit across the field of view

Question 6

What is the function of a mordant?

Answer 6

Prevents the crystal violet from leaving the gram + cell wall

Question 7

What step in the gram stain is differential & why?

Answer 7

The decolorizer is the differential step, because gram negative bacteria will lose the purple color.

Question 8

What are the 3 basic cell shapes?

Answer 8

Bacilli, cocci, spirilla

Question 9

What are the 4 cell arrangements

Answer 9

Single (any shape)
Diplo (bacilli or cocci)
Staphylo (cocci only)
Strepto (cocci or bacilli)

Question 10

What is meant by supportive media?

Answer 10

It grows only certain kinds of bacteria.

Question 11

What is the formula for a positive catalase test

Answer 11

2H2O2 → 2H2O + O2

Question 12

What is the equation for the oxidase test?

Answer 12

Indophenol
Oxidase
O2 + 4H+ + 4e- ——>2H2O