Lab 9 – Observing Bacterial Cultures

These question-and-answer flashcards review key concepts from Lab 9, including prokaryotic structure, reproduction, horizontal gene transfer, bacterial shapes, colony morphology, staining techniques, and laboratory safety.

Which two Domains and two Kingdoms contain prokaryotes?

Domains Bacteria and Archaea; Kingdoms Eubacteria and Archaebacteria.

What is the typical size range of bacterial cells?

Approximately 1–10 micrometers (µm).

Where is the bacterial chromosome located?

In the nucleoid region of the cytosol (not enclosed by a nucleus).

What are plasmids?

Small, circular pieces of DNA that carry a few genes and can be transferred between bacteria.

How do prokaryotic ribosomes differ from eukaryotic ribosomes?

They are smaller and less dense but perform the same function—protein synthesis.

Of what material is the bacterial cell wall composed?

Peptidoglycan.

Which structure lies between the cell wall and cytoplasm and controls substance passage?

The plasma membrane.

What are fimbriae and their function?

Surface projections used for attachment to teeth, rocks, roots, or other cells.

What is the primary role of bacterial flagella?

Locomotion (movement).

Why might a bacterium produce a capsule?

To protect itself from destruction (e.g., by host defenses).

By what asexual process do bacteria reproduce?

Binary fission.

What is vertical gene transfer?

Passing genetic material from parent to offspring during binary fission.

Why does binary fission alone limit genetic diversity?

Because it produces genetic clones of the parent cell.

Name two mechanisms of horizontal gene transfer (HGT).

Transformation and conjugation.

Describe transformation in bacteria.

A cell takes up free DNA fragments from its environment and incorporates them into its genome.

Describe conjugation in bacteria.

A donor cell transfers DNA or a plasmid to a recipient through a conjugation bridge, altering the recipient’s genome.

How can HGT contribute to antibiotic resistance?

A resistant bacterium can transfer its resistance gene to neighboring cells, spreading the trait through the population.

List the three main shapes of bacterial cells.

Cocci (spherical), bacilli (rod-like), and spirilla (spiral).

What term describes spherical bacteria arranged in chains?

Streptococci.

What term describes rod-shaped bacteria occurring in pairs?

Diplobacilli.

What name is given to spiral-shaped bacterial cells?

Spirilla (singular: spirillum).

What is a vibrio?

A curved, comma-shaped rod bacterium.

Give four common colony shapes seen on agar plates.

Circular, filamentous, irregular, and rhizoid (spindle is another possible form).

What is heat-fixing and why is it performed?

Passing a dried smear through heat to make cells adhere to the slide so they are not washed off during staining.

What could happen if too much heat is applied during heat-fixing?

Cells can be distorted, damaged, or completely destroyed.

Why must bacterial cells be stained before observation under high magnification?

They are naturally colorless; staining provides contrast so their shapes and arrangements are visible.

Why might fungal colonies appear on a bacterial agar plate?

Airborne fungal spores land on the nutrient agar and grow alongside the bacteria.

Why are moist sites like toilets or drinking fountains not ideal for swabbing bacteria in this lab?

Such areas are often cleaned or may contain chemicals that inhibit bacterial growth, yielding few culturable bacteria.

Where should used bacterial Petri plates and gloves be discarded?

In the red biohazard bin.

Why is an inoculating loop sterilized before and after touching a bacterial sample?

To kill any existing microbes and prevent cross-contamination of samples.

What medium is most commonly used to culture bacterial colonies in the lab?

Nutrient agar in a Petri plate.

What microscope objective and accessory are required to view stained bacteria clearly?

The 100× oil-immersion lens used with immersion oil.