Free Biodiversity and Variety of Life MCQs with Answers

311. Reverse transcriptase is:

• A. RNA-dependent RNA polymerase
• B. DNA-dependent RNA polymerase
• C. DNA-dependent DNA polymerase
• D. RNA-dependent DNA polymerase

Explanation: The term "reverse transcriptase" refers to an enzyme found in retroviruses (a type of RNA virus) that can synthesize a complementary DNA strand (cDNA) from an RNA template. This is a unique process because it involves the synthesis of DNA from an RNA template, which is the reverse of the typical flow of genetic information.

312. Which one of the following statements about viruses is correct?

• A. Viruses possess their own metabolic system
• B. Viruses are obligate parasite
• C. All viruses contain both RNA and DNA
• D. The nucleic acid of viruses is known as capsid

Explanation: Viruses are obligate parasites, meaning they require a host cell to replicate and complete their life cycle.

313. Bacteria that convert nitrates into free nitrogen are:

• A. Ammonifying
• B. Denitrifying
• C. Nitrifying
• D. Nitrogen-fixing bacteria

Explanation: Denitrifying bacteria are responsible for converting nitrates (NO3-) into free nitrogen gas (N2) through a process known as denitrification. This process helps to return nitrogen in the environment back to its atmospheric form, completing the nitrogen cycle. Denitrification occurs in anaerobic conditions (environments with little to no oxygen), where these bacteria use nitrates as an alternative source of oxygen, leading to the production of nitrogen gas.

314. All are the characteristics of Gram-positive bacteria except:

• A. High content of peptidoglycan
• B. High permeability
• C. Teichoic acid is present
• D. Stain pink with primary dye

Explanation: Gram-positive bacteria stain purple with the primary dye in the Gram staining procedure. This is due to their thick peptidoglycan layer that retains the crystal violet dye during the staining process. Gram-negative bacteria, on the other hand, stain pink due to the thinner peptidoglycan layer and the presence of an outer membrane that can be penetrated by the counterstain safranin.

315. Bacteria differ from viruses in:

• A. Pathogenic nature
• B. Having well-defined cytoplasm
• C. Genetic material
• D. Lacking proper nucleus

Explanation: Bacteria are unicellular organisms that have well-defined cellular structures, including a well-defined cytoplasm. They have cell membranes, cytoplasm, ribosomes, and other cellular components that are essential for carrying out various life processes. In contrast, viruses are not cells and lack cellular structures like cytoplasm. Instead, viruses consist of genetic material (DNA or RNA) surrounded by a protein coat.

316. A bacterium divides every 36 minutes. If a culture containing 105 cells/ml is grown for 180 minutes, what will be the cell concentration after that period?

• A. 175 x 10^5
• B. 5 x 10^5
• C. 35 x 10^5
• D. 32 x 10^5

Explanation: To calculate the cell concentration after a certain period of growth, you can use the formula: Final cell concentration = Initial cell concentration × 2(number of divisions) In this case, the bacterium divides every 36 minutes, so it doubles its population every 36 minutes. The initial cell concentration is 105 cells/ml, and the growth period is 180 minutes. Number of divisions = Growth period / Division time = 180 minutes / 36 minutes/division = 5 divisions. Now, plug the values into the formula: Final cell concentration = 105 cells/ml × 25 = 105 cells/ml × 32 = 32 x 105 cells/ml. So, the correct answer is 32 x 105 cells/ml.

317. Which vitamin is synthesized by bacteria in the human gut?

• A. A
• B. D
• C. C
• D. K

Explanation: Vitamin K is synthesized by bacteria in the human gut. Specifically, the bacteria found in the colon are responsible for producing vitamin K. This vitamin plays a crucial role in blood clotting and bone health.

318. In case of HIV, only_ can infect host cells.

• A. Single stranded RNA
• B. Double stranded DNA
• C. Double stranded RNA
• D. Single stranded DNA

Explanation: While the original genetic material of HIV is single-stranded RNA, the virus undergoes a process called reverse transcription. During this process, the single-stranded RNA is converted into a complementary single-stranded DNA (cDNA) molecule. This cDNA is then integrated into the host cell's genome, forming a double-stranded DNA structure that can infect host cells.

319. Reverse transcriptase can convert:

• A. Single-stranded RNA genome into single-stranded DNA
• B. Single-stranded RNA genome into double-stranded DNA
• C. Double-stranded DNA genome into single-stranded RNA
• D. Double-stranded DNA genome into double-stranded RNA

Explanation: Reverse transcriptase is a key enzyme in certain viruses, such as retroviruses, which include HIV. It allows these viruses to replicate their RNA genome into DNA and integrate it into the host cell's genome. This conversion is crucial for the virus's life cycle and is an essential step in retroviral replication.

320. The double-stranded viral DNA can be incorporated into the host T4 genome as a:

• A. Prophage
• B. Provirus
• C. Bacteriophage
• D. Phage virus

Explanation: A prophage is a phage DNA that has been integrated into the DNA of a bacterial host cell. This is a common phenomenon in bacterial viruses like the T4 bacteriophage. The viral DNA becomes a part of the host cell's genome and remains dormant within the host until certain conditions trigger its activation and subsequent replication, leading to the lytic cycle where new phage particles are produced and released.