MCAT Biology : Prokaryotic Reproduction and Physiology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Prokaryotic Reproduction And Physiology

A researcher isolates a strain of bacteria. When he adds an antibiotic, he notices that the bacterial cell division stops and the sample of bacteria dies out over time. What can the researcher conclude about the antibiotic and its effects on mitosis?

Possible Answers:

Mitosis is irrelevant to this question because bacterial cells do not undergo mitosis

It stops mitosis, but the researcher needs more information to determine the prevention mechanism

It stops mitosis by preventing the formation of the mitotic spindle apparatus

It stops mitosis by improperly aligning DNA at the metaphase plate

Correct answer:

Mitosis is irrelevant to this question because bacterial cells do not undergo mitosis

Explanation:

The question states that the antibiotic halts the bacterial cell division. Recall that mitosis is a form of asexual reproduction that produces two diploid daughter cells with identical DNA. Mitosis, however, is only found in eukaryotic cells. The analogous asexual reproduction in prokaryotic cells is called binary fission. In binary fission, bacterial cells replicate their circular DNA in such a way that the end products are two double-stranded, circular DNA molecules. Each DNA molecule migrates to opposite ends of the cell and the cell splits into two new daughter cells with identical DNA. The question asks about the effect of the antibiotic on mitosis; since the process doesn’t occur in prokaryotic cells, mitosis is irrelevant to this question.

Example Question #2 : Prokaryotic Reproduction And Physiology

Which of the following is a form of asexual reproduction in prokaryotic cells?

Possible Answers:

Binary fission

Binary fission and meiosis

Binary fission and mitosis

Binary fission and transformation

Correct answer:

Binary fission

Explanation:

Prokaryotic cells can reproduce either sexually and asexually. In a bacterial cell, sexual reproduction occurs via three different methods: conjugation, transformation, and transduction. Conjugation involves the exchange of genetic material (plasmids) between bacterial cells through a bridge called the sex pilus. Transformation involves the incorporation of extracellular DNA from the environment. Transduction involves the transmission of genetic material from one bacterial cell to another by a viral vector. These three processes are considered forms of sexual reproduction because all of them involve genetic recombination.

Prokaryotic cells can reproduce asexually only through binary fission. Binary fission is the process by which a bacterial cell splits into two identical daughter cells. This is a very fast process and contributes to the rapid growth and replication of bacteria.

Mitosis and meiosis are only found in eukaryotic cells. Mitosis is a form of asexual reproduction and meiosis is a form of sexual reproduction, since it involves genetically unique daughter cells. Binary fission is the prokaryotic analog of mitosis, but is a distinctly different process.

Example Question #3 : Prokaryotic Reproduction And Physiology

What is the significance of endospores?

Possible Answers:

They allow gram-negative bacteria to reproduce

They allow fungi to survive in extreme climates

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

They allow fungi to store nutrients that 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 #4 : Prokaryotic Reproduction And Physiology

Which of the following types of bacterial reproduction is most similar to mitosis?

Possible Answers:

Conjugation

Binary fission

Transduction

Transformation

Correct answer:

Binary fission

Explanation:

Mitosis is a form of asexual reproduction in which genetic recombination does not take place; the daughter cells are identical to the parent cell. Prokaryotes are able to divide asexually using binary fission, producing two exact copies of the parent cell. The mechanisms governing binary fission are quite different from those governing mitosis, but the end result is the same.

The other three options are examples in which prokaryotic genetic recombination takes place. Conjugation involves the transfer of genetic material between two bacteria via a sex pilus. Transduction is the transfer of genetic material to a bacterium via a vector, such as a bacteriophage. Transformation occurs when the bacterium uptakes exogenous DNA from the environment.

Example Question #5 : Prokaryotic Reproduction And Physiology

A microbiologist sees that a certain strain of E. coli grew in population size from 20,000 cells to 160,000 cells in two hours. How long would it take this strain to undergo 15 doubling cycles?

Possible Answers:

5h

600hr

10hr

20hr

30h

Correct answer:

10hr

Explanation:

We must first find out how long a doubling cycle is for this strain.  We can determine the following relationships from the information in the question.

So, in two hours, the bacteria has undergone three doubling cycles from 20000 to 160000. That means the doubling time is one-third of two hours, or one-third of 120 minutes.

 

The doubling time is 40 minutes.

The bacteria will undergo 15 doubling cycles in 600 minutes, or ten hours.

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