STRAIGHTERLINE BIO250L
MICROBIOLOGY LABS 1 THROUGH 8
EXAM SCRIPT 2026 COMPLETE
QUESTIONS AND CORRET
EXAM
1.Q: What is the term for the movement of molecules from an area of higher
concentration to an area of lower concentration?
A: Diffusion.
Ration: This is the fundamental definition of passive diffusion, a core concept in Lab
1. Q: What is the diffusion of water across a selectively permeable membrane
called?
A: Osmosis.
Ration: Osmosis is a specific type of diffusion, focusing solely on the solvent
(water).
2. Q: If a cell is placed in a hypertonic solution, which way will the water move?
A: Water will move out of the cell.
Ration: "Hyper" means above; the solution has a higher solute concentration
than the cell, so water moves from low solute (inside) to high solute (outside) to
equalize.
3. Q: What is the total magnification when using a 10x ocular lens and a 100x oil
immersion objective?
A: 1000x.
Ration: Total magnification is calculated by multiplying the ocular lens power by
the objective lens power (10 * 100 = 1000).
4. Q: Why is oil immersion necessary for the 100x objective lens?
A: To prevent light from bending (refracting) and increase the resolution.
, Ration: Immersion oil has the same refractive index as glass, creating a
continuous path for light to travel directly into the lens, preventing light loss and
blurring.
5. Q: What is the primary purpose of the Gram stain?
A: To classify bacteria into two major groups based on their cell wall structure.
Ration: It differentiates Gram-positive (thick peptidoglycan) from Gram-negative
(thin peptidoglycan with an outer membrane).
6. Q: In a Gram stain, what is the purpose of the iodine (mordant)?
A: It forms a crystal violet-iodine complex that gets trapped in the thick
peptidoglycan of Gram-positive cells.
Ration: Iodine acts as a mordant to "set" or trap the primary stain.
7. Q: What is the color of a Gram-negative bacterium at the end of a properly
performed Gram stain?
A: Pink/Red.
Ration: Gram-negative cells, with their thin peptidoglycan, are decolorized by
alcohol/acetone and then take up the counterstain, safranin.
8. Q: What is the color of a Gram-positive bacterium at the end of a Gram stain?
A: Purple/Violet.
Ration: The crystal violet-iodine complex is retained within the thick cell wall and
is not removed by the decolorizer.
9. Q: Why is it important to use a fresh (young) culture for a Gram stain?
A: Older cells can have damaged cell walls and may not stain correctly, often
appearing Gram-negative when they are truly Gram-positive.
Ration: The integrity of the cell wall is crucial for the stain to work as intended.
10. Q: What is aseptic technique?
A: A set of practices used to prevent contamination by unwanted microbes.
Ration: This is the most important rule in the microbiology lab (Lab 2), ensuring
pure cultures and researcher safety.
MICROBIOLOGY LABS 1 THROUGH 8
EXAM SCRIPT 2026 COMPLETE
QUESTIONS AND CORRET
EXAM
1.Q: What is the term for the movement of molecules from an area of higher
concentration to an area of lower concentration?
A: Diffusion.
Ration: This is the fundamental definition of passive diffusion, a core concept in Lab
1. Q: What is the diffusion of water across a selectively permeable membrane
called?
A: Osmosis.
Ration: Osmosis is a specific type of diffusion, focusing solely on the solvent
(water).
2. Q: If a cell is placed in a hypertonic solution, which way will the water move?
A: Water will move out of the cell.
Ration: "Hyper" means above; the solution has a higher solute concentration
than the cell, so water moves from low solute (inside) to high solute (outside) to
equalize.
3. Q: What is the total magnification when using a 10x ocular lens and a 100x oil
immersion objective?
A: 1000x.
Ration: Total magnification is calculated by multiplying the ocular lens power by
the objective lens power (10 * 100 = 1000).
4. Q: Why is oil immersion necessary for the 100x objective lens?
A: To prevent light from bending (refracting) and increase the resolution.
, Ration: Immersion oil has the same refractive index as glass, creating a
continuous path for light to travel directly into the lens, preventing light loss and
blurring.
5. Q: What is the primary purpose of the Gram stain?
A: To classify bacteria into two major groups based on their cell wall structure.
Ration: It differentiates Gram-positive (thick peptidoglycan) from Gram-negative
(thin peptidoglycan with an outer membrane).
6. Q: In a Gram stain, what is the purpose of the iodine (mordant)?
A: It forms a crystal violet-iodine complex that gets trapped in the thick
peptidoglycan of Gram-positive cells.
Ration: Iodine acts as a mordant to "set" or trap the primary stain.
7. Q: What is the color of a Gram-negative bacterium at the end of a properly
performed Gram stain?
A: Pink/Red.
Ration: Gram-negative cells, with their thin peptidoglycan, are decolorized by
alcohol/acetone and then take up the counterstain, safranin.
8. Q: What is the color of a Gram-positive bacterium at the end of a Gram stain?
A: Purple/Violet.
Ration: The crystal violet-iodine complex is retained within the thick cell wall and
is not removed by the decolorizer.
9. Q: Why is it important to use a fresh (young) culture for a Gram stain?
A: Older cells can have damaged cell walls and may not stain correctly, often
appearing Gram-negative when they are truly Gram-positive.
Ration: The integrity of the cell wall is crucial for the stain to work as intended.
10. Q: What is aseptic technique?
A: A set of practices used to prevent contamination by unwanted microbes.
Ration: This is the most important rule in the microbiology lab (Lab 2), ensuring
pure cultures and researcher safety.
