Biology Lab Flashcards: UV, Osmolarity, Catalase & Negative Stain
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70 Terms
What UV wavelength was used in the lab?
260 nm (short-wave UV).
What does UV radiation damage?
DNA.
What does UV radiation form in DNA?
Pyrimidine dimers.
What specific pyrimidine dimers are named in the lab?
Thymine dimers.
What happens to DNA when pyrimidine dimers form?
The DNA double helix becomes distorted.
How does UV damage affect DNA replication?
DNA replication cannot proceed successfully.
What can severe UV DNA damage result in?
Death of the organism.
What was the goal of the UV experiment?
To determine the minimum UV exposure needed to kill 100% of the organisms.
Which organisms were used in the UV lab?
Bacillus megaterium and Staphylococcus epidermidis.
What UV exposure times were tested?
1, 5, 10, and 30 minutes.
What was covered during the UV experiment?
Half of the plate was covered with an index card.
Why was half of the plate covered?
To provide a comparison between the UV-exposed and protected areas.
What type of UV lamp was used?
Short-wave UV at 260 nm.
What should be protected from UV exposure during the lab?
Skin should be covered and gloves should be worn.
What does osmolarity study?
The effect of water activity (solutes) on the life of microorganisms.
What is osmosis?
The diffusion of water across a selectively permeable membrane.
In osmosis, water moves from what to what?
From a lower solute concentration toward a higher solute concentration.
What is an isotonic solution?
A solution with equal concentrations of impermeable solutes on both sides of the membrane.
What happens to a cell in an isotonic solution?
The cell neither swells nor shrinks.
What is a hypotonic solution?
A solution with a lower solute concentration compared with another solution.
What can happen to a cell in a hypotonic solution?
The cell can burst.
What is a hypertonic solution?
A solution with a higher solute concentration compared with another solution.
What happens to a microorganism in a hypertonic solution?
The organism loses water.
What process is associated with hypertonic conditions?
Plasmolysis.
Why can hypertonic solutions preserve food?
Microorganisms lose water in the high-salt environment.
What is a halotolerant/facultative halophile?
An organism that can grow in saline conditions up to a certain limit.
What is an obligate halophile?
An organism that needs salt to grow.
Which organism in the osmolarity lab needs salt to grow?
Halobacterium salinarum.
Which organisms were tested in the osmolarity lab?
E. coli, Staphylococcus saprophyticus, Staphylococcus epidermidis, and Halobacterium salinarum.
What organisms were inoculated for the osmolarity lab?
E. coli, S. saprophyticus, S. epidermidis, and H. salinarum.
What enzyme does the catalase test detect?
Catalase.
What reagent is used in the catalase test?
Hydrogen peroxide (H₂O₂).
What is the catalase reaction?
2 H₂O₂ → 2 H₂O + O₂.
What causes bubbles in a catalase test?
Oxygen (O₂) production.
What does bubbling indicate?
A catalase-positive reaction.
What is the catalase test useful for differentiating?
Streptococcus and Staphylococcus.
What is the procedure for the catalase test?
Place a drop of H₂O₂ on a Petri plate, add a colony to the H₂O₂ using a flat toothpick, and mix.
What enzyme breaks down hydrogen peroxide?
Catalase.
What are the products of catalase breaking down hydrogen peroxide?
Water and oxygen.
What gas is responsible for the visible bubbles in the catalase test?
Oxygen.
What is the purpose of a negative stain?
To observe cell morphology and capsules.
Why is negative staining useful for observing capsules?
Capsules can be difficult to stain using simple staining.
What is a bacterial capsule?
A mucoid layer made of polysaccharides or polypeptides.
What stain is used for negative staining in this lab?
Nigrosin.
What type of stain is nigrosin?
An acidic stain.
Why does nigrosin not enter the bacterial cell?
Both the stain and the cell membrane are negatively charged.
What does the background look like in a negative stain?
The background is dark.
What do the bacterial cells look like in a negative stain?
The cells appear clear against the dark background.
What medium is used for the negative stain?
Burk's media.
Which organisms were used for the negative stain?
Paenibacillus velaei and Bacillus megaterium.
How is the organism mixed with the nigrosin?
A sterile loop is used to obtain the sample and place the organism into the nigrosin.
What angle is the second clean slide held at?
About 45°.
What is done with the second slide?
It is used to pull the stain across the first slide to create a thin film.
How should the negative stain be dried?
It should be allowed to air-dry completely.
Should the negative stain be heat-fixed?
No.
Why should you NOT heat-fix a negative stain?
Heat can dislodge the capsule and change cell size.
What objective is used to observe the negative stain?
Oil immersion.
What should the cells look like under the microscope?
Clear cells against a dark background.
What causes the damage in the UV lab?
UV radiation at 260 nm.
What does UV damage in the UV lab?
DNA.
What moves across the membrane in osmolarity?
Water.
Which direction does water move in osmosis?
From lower solute concentration toward higher solute concentration.
What happens in a hypertonic solution?
Water leaves the cell and plasmolysis can occur.
What happens in a hypotonic solution?
Water enters the cell and the cell can burst.
What reagent is added in the catalase test?
Hydrogen peroxide.
What indicates a positive result in the catalase test?
Bubbles.
What gas makes the bubbles in the catalase test?
Oxygen.
What gets stained in a negative stain?
The background, not the cells.
What color/appearance are the cells in a negative stain?
Clear against a dark background.
Is heat-fixing allowed in a negative stain?
No.