MIMG 101: Midterm 1 Final Exam
Questions and All Correct Answers
2025-2026 Updated.
What is the ratio of human to bacteria cells in the body? - Answer It is about 1:1; About 38
trillion bacterial cells and 30 trillion body cells (25 trillion of which are BRC's)
What falls under the umbrella of "microorganism?" What are the different categories that they
fall under? - Answer Bacteria and archaea (which are prokaryotes)
Algae, fungi, and Protozoa (Which are eukaryotes)
Viruses and prions (which are not cellular to begin with)
How did Pasteur disprove spontaneous generation? - Answer 1. Disproved that heating
destroys life-generating substances; he heated a substance, showed nothing grew with a cork
stuck in, but when cork was removed, microorganisms grew
2. Showed that spontaneous generation doesn't occur even with oxygen; in 2 flasks with
oxygens that were identical, the one in which microbes go in had microbes; the other one with
a swan neck, so that dust settled at the bottom of the curve, didn't have microbes growing
inside the flask
3. He proved that spontaneous generation doesn't occur, but organisms were found in air
What was the goal of Koch's postulates? What are the specific postulates? - Answer Koch's
postulates are meant to be a procedure for defining the agent of any disease.
1. The microbe is present in diseased animals and absent from healthy ones. Check the blood or
tissue within the organisms, health and diseased. Compare the two and see if there's a
pathogen in the diseased one but not in the other.
2. The next step is isolate the microbe in pure culture (agar). Two important things: THIS IS THE
HARDEST TO ACHIEVE OUT OF KOCH'S POSTULATES. And, it introduces the idea that SINGLE
COLONIES ARE CLONAL
3. When cells from a pure culture are inoculated into a susceptible healthy animal, disease
results. Take microbes that you isolated and grew in a culture, and inject/give it to a susceptible
animal. Wait to see if disease results in the animal.
,4. Being able to re-isolate the organism from the animal to which you have given the disease
and show it is the same as the original. You check the tissues of the diseased animal (that you
inoculated with the suspected microbe). If you can find the microbe again and isolate again, it's
likely that it is the disease being sought.
What features can you expect in all cells? - Answer 1. Nucleic acids (DNA, RNA)
2. Plasma membrane
3. Cytoplasm
4. Ribosomes
What are distinguishing features of prokaryotes? - Answer Has DNA nucleoid, not a nucleus
Generally lack membrane bound organelles
Often have flagella, pili, vesicles, spores, PEPIDOGLYCAN, and/or 1 chromosome
What are distinguishing features of eukaryotes? - Answer Have a nucleus
have membrane-bound organelles
Have CYTOSKELETON
Often have flagella, cilia, peroxisome, lysosomes (vacuole)
List the following items from smallest to biggest: prokaryotic cell, virus, eukaryotic cell, nucleus.
Some might fall into a similar range. - Answer Virus, prokaryotic cell/nucleus, eukaryotic cell
What is the distinction between magnification and resolution? What is the limiting factor in
microscopy? - Answer Magnification -- enlargement -- size of image/size of object
Resolution -- ability to distinguish 2 adjacent points
Resolution is the limiting factor
Why is the compound light microscope, on its own, limited in its ability to view things such as E.
Coli - Answer For a light microscope, the magnification is about 1000x and resolution is 0.2
micrometers
Due to the wavelength of light, it is not very good at detecting E. Coli at a good resolution
, How does bright field microscopy work? What do you do about samples that have low contrast?
- Answer The microscope detects light scattered by cells and compares it to light scattered by
surrounding media.
Bacterial cells are particularly difficult to see due to low differences in contrast.
Samples with low contrast need to be stained in order to scatter light better
What are details of the staining samples for bright-field microscopy? What is a drawback to this
method? - Answer Use positively charged dyes to stain negatively charged cellular
components such as DNA and lipids
Used to fix dyes with heat, use chemical means now for fixation to get the proteins and stuff to
stick together
Drawback to this method: it kills cells
What are 2 major categories of bacteriology? How can you distinguish between the two of
them? - Answer Gram-positive and gram-negative
Gram-positive have a THICK layer of PEPTIDOGLYCAN on the outside and thin membrane inside
Gram-negative have a THIN layer of PEPTIDOGLYCAN, over the membrane. Over the
peptidoglycan are lipopolysaccharide and protein layers
Gram-positive is usually found in places like skin; gram-negative is usually located in places like
the gut
Differential Staining Using the Gram Stain
(IMPORTANT TO KNOW STEPS AND WHY THEY ARE IMPORTANT) - Answer 1. Flood the heat-
fixed smear with crystal violet for 1 minute; all cells are purple. Alcohol facilitates movement of
dye into cell.
2. Add iodine solution for 3 minutes. All cells remain purple. The iodine and dye form an
iodine:dye complex -- creates big globules inside the cell so when they get in, they can't get out
due to the peptidoglycan in gram-positive cells (BECAUSE IT'S THICKER THERE)
3. Decolorize with alcohol briefly (for about 20 seconds)' this leaves gram-positive cells purple
and the gram-negative cells colorless (this is called an EtOH destain?)
Questions and All Correct Answers
2025-2026 Updated.
What is the ratio of human to bacteria cells in the body? - Answer It is about 1:1; About 38
trillion bacterial cells and 30 trillion body cells (25 trillion of which are BRC's)
What falls under the umbrella of "microorganism?" What are the different categories that they
fall under? - Answer Bacteria and archaea (which are prokaryotes)
Algae, fungi, and Protozoa (Which are eukaryotes)
Viruses and prions (which are not cellular to begin with)
How did Pasteur disprove spontaneous generation? - Answer 1. Disproved that heating
destroys life-generating substances; he heated a substance, showed nothing grew with a cork
stuck in, but when cork was removed, microorganisms grew
2. Showed that spontaneous generation doesn't occur even with oxygen; in 2 flasks with
oxygens that were identical, the one in which microbes go in had microbes; the other one with
a swan neck, so that dust settled at the bottom of the curve, didn't have microbes growing
inside the flask
3. He proved that spontaneous generation doesn't occur, but organisms were found in air
What was the goal of Koch's postulates? What are the specific postulates? - Answer Koch's
postulates are meant to be a procedure for defining the agent of any disease.
1. The microbe is present in diseased animals and absent from healthy ones. Check the blood or
tissue within the organisms, health and diseased. Compare the two and see if there's a
pathogen in the diseased one but not in the other.
2. The next step is isolate the microbe in pure culture (agar). Two important things: THIS IS THE
HARDEST TO ACHIEVE OUT OF KOCH'S POSTULATES. And, it introduces the idea that SINGLE
COLONIES ARE CLONAL
3. When cells from a pure culture are inoculated into a susceptible healthy animal, disease
results. Take microbes that you isolated and grew in a culture, and inject/give it to a susceptible
animal. Wait to see if disease results in the animal.
,4. Being able to re-isolate the organism from the animal to which you have given the disease
and show it is the same as the original. You check the tissues of the diseased animal (that you
inoculated with the suspected microbe). If you can find the microbe again and isolate again, it's
likely that it is the disease being sought.
What features can you expect in all cells? - Answer 1. Nucleic acids (DNA, RNA)
2. Plasma membrane
3. Cytoplasm
4. Ribosomes
What are distinguishing features of prokaryotes? - Answer Has DNA nucleoid, not a nucleus
Generally lack membrane bound organelles
Often have flagella, pili, vesicles, spores, PEPIDOGLYCAN, and/or 1 chromosome
What are distinguishing features of eukaryotes? - Answer Have a nucleus
have membrane-bound organelles
Have CYTOSKELETON
Often have flagella, cilia, peroxisome, lysosomes (vacuole)
List the following items from smallest to biggest: prokaryotic cell, virus, eukaryotic cell, nucleus.
Some might fall into a similar range. - Answer Virus, prokaryotic cell/nucleus, eukaryotic cell
What is the distinction between magnification and resolution? What is the limiting factor in
microscopy? - Answer Magnification -- enlargement -- size of image/size of object
Resolution -- ability to distinguish 2 adjacent points
Resolution is the limiting factor
Why is the compound light microscope, on its own, limited in its ability to view things such as E.
Coli - Answer For a light microscope, the magnification is about 1000x and resolution is 0.2
micrometers
Due to the wavelength of light, it is not very good at detecting E. Coli at a good resolution
, How does bright field microscopy work? What do you do about samples that have low contrast?
- Answer The microscope detects light scattered by cells and compares it to light scattered by
surrounding media.
Bacterial cells are particularly difficult to see due to low differences in contrast.
Samples with low contrast need to be stained in order to scatter light better
What are details of the staining samples for bright-field microscopy? What is a drawback to this
method? - Answer Use positively charged dyes to stain negatively charged cellular
components such as DNA and lipids
Used to fix dyes with heat, use chemical means now for fixation to get the proteins and stuff to
stick together
Drawback to this method: it kills cells
What are 2 major categories of bacteriology? How can you distinguish between the two of
them? - Answer Gram-positive and gram-negative
Gram-positive have a THICK layer of PEPTIDOGLYCAN on the outside and thin membrane inside
Gram-negative have a THIN layer of PEPTIDOGLYCAN, over the membrane. Over the
peptidoglycan are lipopolysaccharide and protein layers
Gram-positive is usually found in places like skin; gram-negative is usually located in places like
the gut
Differential Staining Using the Gram Stain
(IMPORTANT TO KNOW STEPS AND WHY THEY ARE IMPORTANT) - Answer 1. Flood the heat-
fixed smear with crystal violet for 1 minute; all cells are purple. Alcohol facilitates movement of
dye into cell.
2. Add iodine solution for 3 minutes. All cells remain purple. The iodine and dye form an
iodine:dye complex -- creates big globules inside the cell so when they get in, they can't get out
due to the peptidoglycan in gram-positive cells (BECAUSE IT'S THICKER THERE)
3. Decolorize with alcohol briefly (for about 20 seconds)' this leaves gram-positive cells purple
and the gram-negative cells colorless (this is called an EtOH destain?)
