GRE Subject Test: Biology : Bacteria

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Bacteria

Which bacterial reproductive process does not involve any genetic recombination?

Possible Answers:

Transformation

Binary fission

Conjugation

Transduction

Correct answer:

Binary fission

Explanation:

Bacteria are capable of reproducing in a variety of ways. Binary fission is most similar to mitosis in animals, and does not involve any genetic recombination. DNA is replicated and passed to identical daughter cells.

In contrast, the other listed methods involve the incorporation of foreign DNA into the bacteria genome. In conjugation, plasmids are exchanged between bacteria via a sex pilus. In transformation the bacterium is capable of incorporating DNA directly from its surrounding environment. In transduction, a bacteriophage vector is used to introduce foreign DNA into the bacterial cell.

Example Question #1 : Understanding Bacteria

Penicillin is a drug that inhibits the formation of peptidoglycan. Based on this mechanism, which infection could be treated using penicillin?

Possible Answers:

Bacterial infection

Allergic reactions

Viral infection

Fungal infection

Correct answer:

Bacterial infection

Explanation:

Peptidoglycan is most well-known for its role in the formation of bacterial cell walls. By inhibiting the production of peptidoglycan, penicillin prevents bacteria from fully developing and is very effective at treating bacterial infections.

Anti-histamines an anti-inflammatory medications can be used to help prevent the autoimmune response that triggers allergic reactions. Fungicides are used to kill fungal infections. Viruses are harder to treat, as they are not technically alive and cannot be "killed."

Example Question #2 : Understanding Bacteria

Which of the following microorganisms are single-celled and reproduce by binary fission?

Possible Answers:

Bacteria

Protozoa

Viruses

Helminths

Fungi

Correct answer:

Bacteria

Explanation:

Bacteria are single-celled organisms that reproduce by binary fission, in which identical copies of the original cell are produced.

Viruses require living cells in order to multiply. The viruses invade cells and redirect the host organelles from their normal functions to instead replicate the virus. Fungi are very different from bactria in that their structure is more complex (eukaryotic) and they reproduce by budding (among other mechanisms). Protozoa include unicellular animal-like microorganisms. Common protozoan infections include malaria and sleeping sickness. Helminths are worm-like animals, including pinworms and tapeworms. 

Example Question #1 : Prokaryotic Reproduction And Physiology

What is the significance of endospores?

Possible Answers:

They allow fungi to survive in extreme climates

They allow gram-negative bacteria to reproduce

They allow fungi to store nutrients that can survive extreme conditions

They are produced by gram-positive bacteria which can survive extreme conditions

Correct answer:

They are produced by gram-positive bacteria which can survive extreme conditions

Explanation:

Endospores are produced by gram-positive bacteria and can lie dormant for years. Endospores are crucial to growth of gram-positive bacteria because they resist harsh conditions such as extreme temperatures, ultraviolet radiation, and many chemicals. Endospores are not used by fungi by any means. They are also uninvolved in the reproductive processes of bacteria. 

Example Question #1 : Identifying Bacteria

What is the difference between gram-negative and gram-positive bacteria?

Possible Answers:

Gram-positive bacteria contain large amounts of peptidoglycan, while gram-negative bacteria contain only trace amounts

Gram-negative bacteria belong exclusively to the domain archaea

Gram-positive bacteria belong exclusively to the domain archaea

Gram-negative bacteria contain large amounts of peptidoglycan, while gram-positive bacteria contain only trace amounts

Correct answer:

Gram-positive bacteria contain large amounts of peptidoglycan, while gram-negative bacteria contain only trace amounts

Explanation:

The main reaction that happens during a gram stain is the detection of the presence of peptidoglycan. Most bacterial cell walls contain peptidoglycan, but in varying amounts. If the cell contains large amounts of peptidoglycan, it will retain the crystal violet dye and display a purple coloration (this is gram-positive). If the cell does not contain a large quantity of peptidoglycan, it will display the counterstain and appear pink (this is gram-negative).

The gram-stain does not dictate whether or not a species belongs to the domain archaea. Archaea cell walls do not contain peptidoglycan and will not react to the stain. Note that archaea and bacteria are different domains altogether, though they share some similar characteristics.

Example Question #21 : Divisions Of Life And Viruses

Which type of bacteria is referred to as "rod-shaped?"

Possible Answers:

Vibrios

Bacilli

Spirochetes

Spirilla

Cocci

Correct answer:

Bacilli

Explanation:

There are three principal forms of bacteria. Spherical bacteria are termed cocci. Rod-shaped bacteria are called bacilli. Spiral bacteria are rigid (spirilla), flexible (spirochetes), or curved (vibrios). 

Example Question #1 : Identifying Bacteria

When seen under the microscope using a gram stain, the bacteria that causes strept throat whould have which of the following appearances?

Possible Answers:

Purple rod-shaped organisms

Clusters of pink spheres

Chains of purple spheres

Pink comma-shaped organisms

Purple spiral-shaped organisms

Correct answer:

Chains of purple spheres

Explanation:

Streptococcus, the causative agent of strep throat, is a genus of gram-postitive (purple staining) cocci (spheres), in which the cells tend to form chains. Bacteria are described by a combination of their response to gram stain and their appearance. For example, "gram-positive streptococcus" indicate chains of spheres that stain purple. 

Example Question #332 : Gre Subject Test: Biology

The Gram stain distinguishes between Gram-positive and Gram-negative bacteria. Which of the following is true about the Gram stain?

Possible Answers:

Lipopolysaccharides are stained through a Gram stain, and Gram-positive bacteria are more virulent than Gram-negative bacteria

Peptidoglycan is stained through a Gram stains, and Gram-positive bacteria are more virulent than Gram-negative bacteria

Lipopolysaccharides are stained through a Gram stain, and Gram-negative bacteria are more virulent than Gram-positive bacteria

Peptidoglycan is stained through a Gram stain, and Gram-positive and Gram-negative bacteria have comparable virulence

Peptidoglycan is stained through a Gram stain, and Gram-negative bacteria are more virulent than Gram-positive bacteria

Correct answer:

Peptidoglycan is stained through a Gram stain, and Gram-negative bacteria are more virulent than Gram-positive bacteria

Explanation:

The peptidoglycan layer of bacteria retains the Gram stain. In general, Gram-negative bacteria are more virulent than Gram-positive bacteria. This is due in part to an outer layer of lipopolysaccharides present on Gram-negative bacteria that invokes immune responses (particularly via a component called lipid-A), and are somewhat more difficult to target with antibiotics.

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