MCAT Biology : Bacteria and Types of Prokaryotes

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #11 : Bacteria And Types Of Prokaryotes

Which of the following is not a tenet of the Cell Theory?

Possible Answers:

Cells are the basic functional unit of life

Cells carry genetic information in the form of DNA

All living things are made of cells

Cells arise from pre-existing cells

All cells have membrane-bound organelles

Correct answer:

All cells have membrane-bound organelles

Explanation:

All of the answer choices are tenets of the Cell Theory, except for the one concerning organelles. Not every cells has membrane-bound organelles (e.g. prokaryotic cells). 

Example Question #12 : Bacteria And Types Of Prokaryotes

 

Which of the following would not be found an E. Coli sample?

Possible Answers:

Nuclei

Circular DNA

Cell walls

Plasma membranes

Ribosomes

Correct answer:

Nuclei

Explanation:

E. Coli is a type of bacteria. Because bacteria are prokaryotes, they do not contain membrane-bound organelles. A nucleus is a membrane-bound organelle and therefore would not be found in bacteria.

Example Question #11 : Bacteria And Types Of Prokaryotes

Eukaryotes can share which of the following structures with prokaryotes?

Possible Answers:

Cell wall

Nucleoid

Golgi body

Mitochondria

Correct answer:

Cell wall

Explanation:

The chief difference between prokaryotic and eukaryotic cells is the presence of membrane-bound organelles. Mitochondria and Golgi bodies are examples of such organelles, and are only found in eukaryotes. Nucleoids are only found in prokaryotes, while eukaryotes use membrane-bound nuclei.

Cell walls can be found in either prokaryotes or eukaryotes. Many prokaryotic bacteria use cell walls as protection from the external environment, while eukaryotic plants cells use cell walls to help maintain rigidity and prevent water loss.

Example Question #13 : Bacteria And Types Of Prokaryotes

Which of the following organelles is not bound by a membrane?

Possible Answers:

Endoplasmic reticulum

Golgi apparatus

Ribosomes

Nucleus

Mitochondria

Correct answer:

Ribosomes

Explanation:

Ribosomes are not membrane-bound organelles. All of the other organelles are membrane-bound, and are thus only found in eukaryotes. Ribosomes, which are the site of protein synthesis, are found in both prokaryotes and eukaryotes.

Example Question #15 : Bacteria And Types Of Prokaryotes

Unlike eukaryotes, prokaryotes have no membrane-bound organelles. How, then, are prokaryotes able to generate energy?

Possible Answers:

Prokaryotes produce energy via photosynthesis

Prokaryotes generate sodium gradients across their nuclear membranes

Prokaryotes generate proton gradients across their plasma membranes

Prokaryotes have specialized mitochondria

Prokaryotes do not generate energy

Correct answer:

Prokaryotes generate proton gradients across their plasma membranes

Explanation:

This question has several components for understanding what it is asking, and what the answer is. The first clue is the use of the word "energy," which is often code for ATP in biology. In eukaryotes, ATP is generated in the mitochondria through a long multi-step process, in which a proton gradient is established to produce ATP from glucose metabolism in the presence of oxygen. Note that even autotrophs require mitochondria in conjunction with chloroplasts; photosynthesis does not negate the necessity of an ion gradient for ATP synthesis.

Prokaryotes do not have mitochondria, but do generate ATP to carry out many biomolecular functions. Because there are no membrane-bound organelles, in order to complete bacterial metabolism prokaryotes must generate a proton gradient between the intra- and extra-cellular spaces, generally between the plasma membrane and the cell wall. This allows an electron transport chain to function along the cell membrane, using the proton gradient between the membrane and the bacterial cell wall to generate ATP.

Example Question #11 : Bacteria And Types Of Prokaryotes

Which of the following is false regarding the bacterial membrane?

I. Bacteria contain plasma membranes that are made up of triglycerides

II. Gram staining reveals that bacteria contain cell walls, but no cell membranes

III. Bacteria do not contain a membrane-bound nucleus, but they contain an analogous membrane-bound structure called the nucleoid

Possible Answers:

I and III

I and II

I, II, and III

I only

Correct answer:

I, II, and III

Explanation:

All three statements are false.

Bacteria are prokaryotic organisms that do not contain any membrane-bound organelles; however, they do contain a cell wall and a plasma membrane as outer coverings for containment. The bacterial plasma membrane is analogous to the plasma membrane found in eukaryotes because both are made up of a phospholipid bilayer. Bacterial plasma membranes are mostly made up of phospholipids, not triglycerides. Recall that triglycerides are also a type of lipid, but their primary function is to store energy.

Gram staining is a lab procedure that is widely used to classify bacteria. A bacterium can be either gram positive or gram negative. The difference between the two classifications lies in the thickness of the cell wall. A thicker cell wall, found in gram positive cells, retains the gram stain whereas a thinner cell wall, found in gram negative cells, allows the gram stain to leave the cell. This leads to a discrepancy in the stained cell’s color (purple for gram positive and pink for gram negative), which can be used to classify the bacterium. Gram staining is irrelevant for cell membranes. Remember that all bacterial cells (whether gram positive or gram negative) have cell membranes. 

It is true that bacterial cells do not contain membrane-bound organelles, such as the nucleus. Instead of a nucleus, bacterial cells contain a region called the nucleoid that houses the genetic material of the bacterial cell; however, the nucleoid is not a membrane-bound structure.

Example Question #14 : Bacteria And Types Of Prokaryotes

Compared to gram negative bacteria, how many more membrane-bound organelles do gram positive bacteria contain?

Possible Answers:

Zero

One

Three

Two

Correct answer:

Zero

Explanation:

The main difference between a gram positive and a gram negative bacterial species is the thickness of their cell walls: gram positive bacteria have thicker cell walls than gram negative bacteria. The interior of each bacterium, however, contains the same types of structures. Recall that bacteria, in general, have no membrane-bound organelles; therefore, both gram positive and gram negative bacteria will have zero membrane-bound organelles. The internal structures of each bacterial class are essentially indistinguishable.

Example Question #991 : Biology

Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.

The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.

Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.

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A scientist views his Gram stained Neisseria under a microscope, and finds that they are present in groups of two, each of which is a round cell. In what category of bacteria does Neisseria most likely fall?

Possible Answers:

Eukaryotic

Spirochete

Protozoan

Cocci

Bacilli

Correct answer:

Cocci

Explanation:

Round bacterial cells are considered cocci. In this case, with two cells, it would be classified specifically as a diploccocus.

Example Question #1021 : Mcat Biological Sciences

Which of the following bacteria possesses a spherical shape?

Possible Answers:

Staphylococcus aureus

Bacillus anthracis

Escherichia coli

Spirilum minus

Correct answer:

Staphylococcus aureus

Explanation:

The term "coccus" refers to a spherical shape and the term "staphyl" refers to a tendency to group together in clusters. Staphylococcus bacterial species will appear round in shape and tend to cluster together, creating a grape-like appearance.

The term "bacillus" refers to a rod-shaped bacterial species, while the term "spirilli" refers to spiral or helical bacteria. Bacillus anthracis is rod-like in shape. Escherichia coli is also rod-like in shape. Spirillum minus is spiral in shape. 

Example Question #62 : Microbiology

A researcher observes an unknown bacterium under the microscope. His results reveal that the bacterium is gram positive and has a spherical shape. Which of the following is a possible identity of this bacterium?

Possible Answers:

None of these

Staphylococcus aureus

Bacillus anthracis

Spirillum minus

Correct answer:

Staphylococcus aureus

Explanation:

Recall that the shape of a bacteria classifies the bacteria as either a bacillus, coccus, or spirilla. Bacillus bacteria are rod-shaped, coccus bacteria are spherically shaped, and spirilla bacteria twist into a spiral. Since the researcher observes a spherical shape, the bacteria must be a coccus.

Bacteria classified as coccus often contain the word ‘coccus’ in their names. Of the three bacteria listed, only the Staphylococcus aureus contains the word ‘coccus’ in its name. This means that it is a coccus and, therefore, is a possible identity of this bacteria.

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