1
Microbiology Lab Exam Questions with
Correct Answers | Updated (100% Correct
Answers)
True or false: The high-dry lens will be optimal for observing
multicellular fungi or algae. Answer: False
True or false: The oil immersion objective is necessary to determine
the morphology of prokaryotes. Answer: True
What was the largest organism you observed? The smallest?
Answer: Fungi/mold; bacteria
What three shapes of bacteria did you observe? Answer: cocci,
spiral, bacilli
How does increased magnification increase the field of vision?
Answer: When magnification increases, it decreases the field of
vision
Why is it desirable that microscope objectives be par-focal? Answer:
If the organism is visible in one objective, it will be visible in all
objectives
Which objective focuses the closet to the slide when it is in focus?
Answer: oil immersion lens
© 2025 All rights reserved
,2
Which controls on the microscope affect the amount of light
reaching the ocular lens? Answer: iris diaphram
Is your lens corrected for chromatic aberrations? Answer: yes
Assume the diameter of the field of vision in your microscope is
2mm under low power. If one Bacillus cell is 2um, how many
Bacillus cells could fit end to end across the field? How many 10um
yeast cells could fit across the field? Answer: 1000 bacillus cells; 200
yeast cells
Name two ways in which you can enhance the resolving power.
Answer: ...
What are the advantages of the low-power objective for viewing
fungi or algae? Answer: able to see the entire organism instead of
just a magnified portion of it
What would occur if water were accidentally used in place of
mineral oil? Answer: the image would not be as clear because light
ray and the water do not have the same refractive index.
Assume you are looking for microorganisms in a tissue sample from
a lung biopsy. The microbes become apparent when you switch to
100x. What type of microbe is most likely? Answer: bacteria
Do you expect turbidity in the unsterilized nutrient broth that was
incubated? Answer: yes
© 2025 All rights reserved
, 3
Will nutrient broth or agar provide more information on the variety
of bacteria in an environment? Answer: nutrient agar
How do you know if bacteria is present on your agar plate? Answer:
colonies of growth will appear
What is the value of Petri plates in microbiology? Answer: they
provide a solid medium to grow bacteria on
What are bacteria using for nutrients in the agar? Answer: protein
within the agar
What is the purpose of agar? Answer: support growth on the
surface of a Petri plate and it is also used as a solidifying agent
Why is agar preferable to gelatin as a solidifying agent in culture
media? Answer: few bacteria can degrade it
Did all of the organisms living in or on the environments sampled
grow on your nutrient agar? Answer: No, because not all organisms
are culturable at this point in time
How could you determine whether the turbidity in your nutrient
broth tube was from a mixture of different microbes or from the
growth of only one kind of microbe? Answer: You could transfer
the sample to a Petri dish with agar and see if different types of
colonies grow
© 2025 All rights reserved
Microbiology Lab Exam Questions with
Correct Answers | Updated (100% Correct
Answers)
True or false: The high-dry lens will be optimal for observing
multicellular fungi or algae. Answer: False
True or false: The oil immersion objective is necessary to determine
the morphology of prokaryotes. Answer: True
What was the largest organism you observed? The smallest?
Answer: Fungi/mold; bacteria
What three shapes of bacteria did you observe? Answer: cocci,
spiral, bacilli
How does increased magnification increase the field of vision?
Answer: When magnification increases, it decreases the field of
vision
Why is it desirable that microscope objectives be par-focal? Answer:
If the organism is visible in one objective, it will be visible in all
objectives
Which objective focuses the closet to the slide when it is in focus?
Answer: oil immersion lens
© 2025 All rights reserved
,2
Which controls on the microscope affect the amount of light
reaching the ocular lens? Answer: iris diaphram
Is your lens corrected for chromatic aberrations? Answer: yes
Assume the diameter of the field of vision in your microscope is
2mm under low power. If one Bacillus cell is 2um, how many
Bacillus cells could fit end to end across the field? How many 10um
yeast cells could fit across the field? Answer: 1000 bacillus cells; 200
yeast cells
Name two ways in which you can enhance the resolving power.
Answer: ...
What are the advantages of the low-power objective for viewing
fungi or algae? Answer: able to see the entire organism instead of
just a magnified portion of it
What would occur if water were accidentally used in place of
mineral oil? Answer: the image would not be as clear because light
ray and the water do not have the same refractive index.
Assume you are looking for microorganisms in a tissue sample from
a lung biopsy. The microbes become apparent when you switch to
100x. What type of microbe is most likely? Answer: bacteria
Do you expect turbidity in the unsterilized nutrient broth that was
incubated? Answer: yes
© 2025 All rights reserved
, 3
Will nutrient broth or agar provide more information on the variety
of bacteria in an environment? Answer: nutrient agar
How do you know if bacteria is present on your agar plate? Answer:
colonies of growth will appear
What is the value of Petri plates in microbiology? Answer: they
provide a solid medium to grow bacteria on
What are bacteria using for nutrients in the agar? Answer: protein
within the agar
What is the purpose of agar? Answer: support growth on the
surface of a Petri plate and it is also used as a solidifying agent
Why is agar preferable to gelatin as a solidifying agent in culture
media? Answer: few bacteria can degrade it
Did all of the organisms living in or on the environments sampled
grow on your nutrient agar? Answer: No, because not all organisms
are culturable at this point in time
How could you determine whether the turbidity in your nutrient
broth tube was from a mixture of different microbes or from the
growth of only one kind of microbe? Answer: You could transfer
the sample to a Petri dish with agar and see if different types of
colonies grow
© 2025 All rights reserved
