lab pt 4

How do an anaerobic jar and chamber differ in effectiveness?

A jar provides anaerobic incubation; a chamber also allows cultures to be handled in an oxygen-free workspace.

What is a bacteriophage?

A virus that infects bacteria.

What is a plaque?

A clear zone on a bacterial lawn where phages have infected and destroyed bacterial cells.

How does a plaque form?

Phages infect bacteria, replicate, and release new phages that infect surrounding cells.

What is a phage titer and what units express it?

The concentration of infectious bacteriophages, expressed as PFU/mL (plaque-forming units per milliliter).

What is serial dilution?

A series of stepwise dilutions that progressively decrease a sample's concentration.

What is a tenfold dilution?

A dilution that reduces the sample concentration to one-tenth of its previous concentration.

What do 10⁻¹ and 10⁻² dilutions mean?

10⁻¹: one-tenth concentration; 10⁻²: one-hundredth concentration.

Why is serial dilution used in phage titration?

To obtain a countable number of plaques instead of too many overlapping plaques.

How is a phage titer determined?

Serially dilute phages, mix with susceptible bacteria, plate with soft agar, incubate, and count plaques.

What is a bacterial lawn?

A continuous layer of bacterial growth covering an agar surface.

What is the phage titer formula?

PFU/mL = number of plaques ÷ (dilution × volume plated in mL).

What is the titer if 50 plaques form from a 10⁻⁶ dilution and 0.1 mL is plated?

50 ÷ (10⁻⁶ × 0.1) = 5 × 10⁸ PFU/mL.

What is osmosis?

Movement of water across a selectively permeable membrane toward the side with higher solute concentration.

What is osmotic pressure?

Pressure associated with water movement across a selectively permeable membrane due to solute concentration differences.

What is a hypotonic environment?

An environment with a lower solute concentration than the cell's interior.

What happens to bacteria in a hypotonic environment?

Water enters the cell, increasing internal pressure; the cell wall generally prevents bursting.

What is a hypertonic environment?

An environment with a higher solute concentration than the cell's interior.

What happens to bacteria in a hypertonic environment?

Water leaves the cell, causing plasmolysis and potentially inhibiting growth.

What is an isotonic environment?

An environment with approximately equal solute concentrations inside and outside the cell.

What happens to bacteria in an isotonic environment?

There is no net movement of water.

What is plasmolysis?

Shrinking of the cytoplasm away from the cell wall due to water loss.

Why can high salt or sugar concentrations inhibit bacteria?

They create hypertonic conditions that draw water out of bacterial cells.

What are halophiles and halotolerant organisms?

Halophiles require high salt; halotolerant organisms tolerate high salt but do not require it.

What are osmophiles?

Organisms that grow best in high-solute environments, particularly high-sugar environments.

What is pH?

A measurement related to hydrogen ion concentration in a solution.

What are acidic, neutral, and alkaline pH values?

Acidic: below 7; neutral: 7; alkaline/basic: above 7.

How does pH affect bacterial growth?

Extreme pH interferes with enzymes, proteins, membranes, and metabolic processes.

What are neutrophiles, acidophiles, and alkaliphiles?

Neutrophiles grow best near neutral pH; acidophiles in acidic conditions; alkaliphiles in alkaline conditions.

How can pH be measured?

Using pH paper, indicator solutions, or an electronic pH meter.