Classifying Microorganisms
A certain microorganism is unicellular, has distinct nucleus, contains chitin cell walls, and obtains energy by absorbing organic chemicals.
a) Which group of microorganisms does it belong to?
b) Is it a prokaryote or a eukaryote?
c) Give one example of an organism that belongs to this group
a) Fungi
b) Eukaryote
c) Yeast
In Pasteur’s swan-neck flask experiment, air could enter the flask, but airborne dust became trapped in the neck. Why was allowing air into the flask important to the experimental design?
The air itself did not cause the spontaneous generation of microorganisms
True or False: To achieve the highest possible resolution in a compound light microscope, you should use a longer wavelength of light and omit immersion oil when using the 100× objective lens
False. (Explanation: Resolution increases with shorter wavelengths. Immersion oil is necessary at 100× to prevent light refraction and loss, improving resolution.)
Which of the following statements about Gram staining are correct?
A. Gram-positive bacteria have thick peptidoglycan cell walls
B. Gram-negative bacteria appear purple
C. Gram-negative bacteria have a lipopolysaccharide layer
D. Gram-positive bacteria are resistant to antibiotics
E. Gram-negative bacteria appear pink
A,C,E
A. Gram-positive bacteria have thick peptidoglycan cell walls
C. Gram-negative bacteria have a lipopolysaccharide layer
E. Gram-negative bacteria appear pink
Which of the following statements correctly describes the cell wall composition of the three domains and fungi?
A) Bacteria have peptidoglycan; Archaea have chitin; Fungi have cellulose.
B) Bacteria have peptidoglycan; Archaea lack peptidoglycan; Fungi have chitin.
C) Bacteria have cellulose; Archaea have peptidoglycan; Fungi lack a cell wall.
D) Bacteria have chitin; Archaea have peptidoglycan; Fungi have cellulose.
B) Bacteria have peptidoglycan; Archaea lack peptidoglycan; Fungi have chitin
Arrange the following events in chronological order, following the progression of microbiology
A. John Needham conducted experiments with heated broth in flask
B. Robert Hooke marked beginning of cell theory: all living things are composed of cells
C. Ferdinand Cohn discovered endospores, the heat-resistant forms of bacteria
D. Louis Pasteur proved biogenesis with experiment using swan-necked flask
E. Anton van Leeuwenhoek observed “animalcules” through single-lense microscopes
F. Francesco Redi conducted decaying meat in a jar experiment
B->E-> F-> A-> D-> C
A scientist wants to observe the internal structures of living, unstained cells. The microscope converts phase differences in transmitted light into differences in brightness, and halos may appear around the cells. Which technique is being used?
A) Phase-contrast microscopy
B) Fluorescence microscopy
C) Super-resolution microscopy
D) Darkfield microscopy
A) Phase-contrast microscopy
Match each observation with the most appropriate staining technique. Use each answer once.
A) Gram stain
B) Acid-fast stain
C) Capsule stain
D) Endospore stain
E) Flagella stain
Green oval structures are visible inside some pink bacterial cells and free outside others.
Clear halos surround cells against a stained background.
Some cells remain red after acid-alcohol treatment, while other cells appear blue after counterstaining.
Thin, hairlike appendages become visible after a coating procedure increases their thickness.
A bacterial mixture contains purple cocci and pink rods after differential staining.
1. D — Endospore stain
2. C — Capsule stain
3. B — Acid-fast stain
4. E — Flagella stain
5. A — Gram stain
Three infectious agents have the following characteristics:
1. Contains either DNA or RNA surrounded by a protein coat.
2. Consists only of a short RNA molecule without a protein coat.
3. Consists entirely of misfolded proteins without DNA or RNA.
Which option correctly identifies agents 1, 2, and 3, respectively?
A. Virus – Prion – Viroid
B. Viroid – Virus – Prion
C. Prion – Viroid – Virus
D. Virus – Viroid – Prion
E. Viroid – Prion – Virus
D. Virus – Viroid – Prion
In 1928, which scientist discovered penicillin after observing that a mold inhibited the growth of nearby bacteria?
Alexander Fleming.
A researcher wants to observe living, unstained microorganisms suspended in liquid. The organisms appear bright against a dark background.
a) Which type of microscope should be used?
b) What type of light enters the objective lens?
a) Darkfield microscope.
b) Only light reflected or scattered by the specimen enters the objective lens, making the microorganisms appear bright against a dark background.
A sputum sample from a patient with pneumonia is stained using the Gram stain procedure. Under the microscope, the bacteria appear pink/red. Based on this result, classify the bacteria (Gram-positive or Gram-negative) and explain what structural feature of the cell wall causes it to appear this color. Finally, explain why these bacteria are generally more resistant to penicillin compared to purple-stained bacteria.
Classification: Gram-negative.
Why it appears pink/red: They have a thin peptidoglycan cell wall and an outer protective layer. During the alcohol decolorization step, the outer layer is disrupted, and the purple crystal violet-iodine complex is easily washed out of the thin peptidoglycan. They appear colorless until counterstained pink by safranin.
Why more resistant to penicillin: Their outer protective layer acts as a barrier, preventing the antibiotic from penetrating the cell wall and reaching its target.