Q: Which of the following is a correct formula for calculating the value of one ocular division in micrometers?

$$\text{Ocular value} = \frac{(\text{Number of stage divisions}) \times 10\ \mu m}{\text{Number of ocular divisions}}$$

Question 1

Which of the following best describes the purpose of calibrating an ocular micrometer in microbiology?

Accepted Answer

To determine the exact size of microorganisms by relating ocular divisions to known stage micrometer measurements

Question 2

If 25 ocular divisions align with 10 stage micrometer divisions, and each stage division is $$10\ \mu m$$, what is the value of one ocular division in micrometers?

Accepted Answer

$$2.5\ \mu m$$

Question 3

A student observes a bacterium that spans 8 ocular divisions under oil immersion (calibration factor $$= 1.0\ \mu m/$$division). What is the actual length of the bacterium?

Accepted Answer

$$8.0\ \mu m$$

Question 4

Which of the following statements about Bacillus species is CORRECT?

Accepted Answer

They are Gram-positive rods, often found in chains, and can form endospores.

Question 5

A field diameter under high power (400X) is measured as $$0.52\ mm. If a $$microorganism spans 1/10 of the field, what is its approximate length in micrometers?

Accepted Answer

$$52\ \mu m$$

Question 6

Which feature distinguishes Staphylococcus aureus from Escherichia coli under the microscope?

Accepted Answer

S. aureus forms clusters of cocci, while E. coli appears as single rods.

Question 7

If 50 ocular divisions cover 1 mm on the stage micrometer, what is the calibration factor in micrometers per division?

Accepted Answer

$$20\ \mu m/$$division

Question 8

Which of the following is a correct step in calibrating an ocular micrometer?

Accepted Answer

Superimpose the ocular micrometer scale over the stage micrometer scale and count how many ocular divisions match a known number of stage divisions.

Question 9

Escherichia coli is best described as:

Accepted Answer

A Gram-negative rod, motile with peritrichous flagella, commonly found in the intestines of warm-blooded animals

Question 10

A student measures a Staphylococcus aureus cell as 1.2 ocular divisions under oil immersion (calibration factor $$= 1.0\ \mu m/$$division). What is the cell's diameter?

Accepted Answer

$$1.2\ \mu m$$

Question 11

Which of the following is a reason why accurate measurement of microorganisms is important in microbiology?

Accepted Answer

It helps distinguish and identify microorganisms based on their size and morphology.

Question 12

A Bacillus species is observed to be 6 ocular divisions long under high power (calibration factor $$= 2.5\ \mu m/$$division). What is its length?

Accepted Answer

$$15.0\ \mu m$$

Question 13

Which of the following best describes the arrangement and motility of Bacillus species?

Accepted Answer

Rods in chains, motile with peritrichous flagella

Question 14

A student calibrates the ocular micrometer and finds that 40 ocular divisions align with 20 stage micrometer divisions. Each stage division is $$10\ \mu m. $$What is the calibration factor?

Accepted Answer

$$5.0\ \mu m/$$division

Question 15

Which of the following is NOT a characteristic of Staphylococcus aureus?

Accepted Answer

Motile with peritrichous flagella

Question 16

If a field diameter is $$0.52\ mm at 400X$$, what would be the field diameter at 1000X, assuming the field number remains constant?

Accepted Answer

$$0.208\ mm$$

Question 17

Which of the following best explains why the calibration factor changes with different objectives?

Accepted Answer

The magnification changes, altering the apparent size of the ocular divisions relative to the stage micrometer.

Question 18

A student observes E. coli under oil immersion and measures a cell as 2.5 ocular divisions. If the calibration factor is $$1.0\ \mu m/$$division, what is the cell's length?

Accepted Answer

$$2.5\ \mu m$$

Question 19

Which of the following is a correct formula for calculating the value of one ocular division in micrometers?

Accepted Answer

$$	ext{Ocular value} = \frac{(	ext{Number of stage divisions}) 	imes 10\ \mu m}{	ext{Number of ocular divisions}}$$

Calibrating the Ocular Micrometer and Measuring Microorganisms

Study Guide - Practice Questions

Study Guide - Flashcards