Free Biodiversity and Variety of Life MCQs with Answers

2251. In which of the following growth phases does the number of bacteria increase most rapidly?

• A. Lag phase
• B. Log phase
• C. Stationary phase
• D. Death/Decline phase

Explanation: The exponential or the log phase is the phase during which the bacterium increases the most rapidly. In the figure below, the x-axis represents time and the y-axis represents log of the number of bacteria. Hence, the slope of the graph is directly proportional to the rate of multiplication of bacteria; the exponential phase has the greatest rate of multiplication of bacteria due to having the greatest slope.

2252. Treponema pallidum causes:

• A. AIDS
• B. Genital herpes
• C. Syphilis
• D. Gonorrhea

Explanation: Treponema pallidum is the bacterium responsible for causing syphilis, a sexually transmitted infection.

2253. The DNA of the bacterium is present in distinct region called:

• A. Nucleolus
• B. Centrosome
• C. Nucleoid
• D. Nucleus

Explanation: The correct answer is nucleoid. In bacteria, which are prokaryotic organisms, the genetic material is located in a region known as the nucleoid. This region is not enclosed by a membrane, distinguishing it from the nucleus found in eukaryotic cells. The other options, such as the nucleolus, centrosome, and nucleus, refer to structures found in eukaryotic cells and are not applicable to bacteria.

2254. Who discovered the bacteria causing tuberculosis and also developed various techniques of media preparation and maintenance of pure culture?

• A. Robert Koch
• B. Louis Pasteur
• C. Alexander Fleming
• D. Antonie van Leeuwenhoek

Explanation: Historical Perspectives Centennial: Koch's Discovery of the Tubercle Bacillus. On March 24, 1882, Robert Koch announced to the Berlin Physiological Society that he had discovered the cause of tuberculosis. Three weeks later, on April 10, he published an article entitled "The Etiology of Tuberculosis".

2255. Which of the following is true about both bacterial conjugation and meiosis?

• A. Both processes produce four haploid cells
• B. Both processes are a form of asexual reproduction
• C. Both processes involve genetic recombination
• D. None of these options are correct

Explanation: Both bacterial conjugation and meiosis involve genetic recombination, which is the process of exchanging genetic material to create diversity. In meiosis, genetic recombination occurs during crossing over in prophase I, resulting in four genetically unique haploid cells. In bacterial conjugation, DNA is transferred from a donor to a recipient cell, introducing new genetic material, but it does not result in the production of new cells. Thus, option C is correct. Option A is incorrect because only meiosis produces four haploid cells. Option B is incorrect because both processes are linked to sexual reproduction due to their involvement in genetic recombination. Option D is incorrect because option C is a true statement.

2256. What is the method of asexual reproduction?

• A. Sporulation
• B. Fission
• C. Apomixis
• D. All of these options are correct

Explanation: All of the above given options are different mode of sexual reproduction in living beings. Binary fission, multiple fission (animal like protoctists) budding (Hydra) parthenogenesis, tissue culturing, cloning and identical twins are the common asexual methods of reproduction.

2257. An example of a bacteria requiring low concentration of oxygen is?

• A. Spirochete
• B. Escherichia coli (E. coli)
• C. Pseudomonas
• D. Campylobacter

Explanation: Option D: Campylobacter is the correct answer as it is a microaerophilic bacterium, requiring low levels of oxygen to survive and grow. This characteristic distinguishes it from the other options. Option A: Spirochetes can survive in a range of oxygen levels and are not exclusively microaerophilic. Option B: E. coli is a facultative anaerobe, adaptable to both oxygen-rich and oxygen-poor environments. Option C: Pseudomonas are versatile in their oxygen requirements and are not limited to low-oxygen conditions.

2258. Which of the following is basic function of bacterial slime capsule?

• A. Protection from enviroment
• B. Protection from engulfment
• C. Protection from osmotic lysis
• D. All of the above

Explanation: Capsule is tightly bound to the bacterial cell. It is a part of the cell envelope. It protects cells from engulfment by Eukaryotic cells such as macrophages and it also protects the cells from pathogenicity. Hence option B is correct.Option A and C is incorrect because the cell wall of bacteria protects the cell against osmotic lysis and against environment.

2259. The Gram-positive bacteria appear in which color under gram staining?

• A. Purple
• B. Red
• C. Pink
• D. Blue

Explanation: Gram-positive bacteria appear purple under Gram staining because they retain the crystal violet stain due to their thick peptidoglycan layer, which forms a stable crystal violet-iodine complex. During the decolorization step, this complex is not washed out, allowing the bacteria to retain the purple color. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer and a higher lipid content in their cell walls, causing them to lose the crystal violet-iodine complex during the decolorization step and subsequently take up the red or pink safranin counterstain. Therefore, Gram-negative bacteria appear red or pink, not purple.

2260. Chemical substances used on living tissues that inhibit the growth of microorganism are called?

• A. Disinfectant
• B. Sanitizer
• C. Antibiotic
• D. Antiseptics

Explanation: Antiseptics are specifically designed for use on living tissues to inhibit or kill microorganisms, making them the correct answer. Disinfectants are meant for non-living surfaces, sanitizers are used to reduce microbes to safe levels on surfaces, and antibiotics are used internally to treat infections, not applied to tissue surfaces.