Free Biodiversity and Variety of Life MCQs with Answers

2451. A microbiologist used Gram staining method in a laboratory to identify different types of infectious bacteria in four different samples (I, II, III and IV). The given table shows the results.Based on the results of sample I and IV, he infers that the cell walls of Escherichia coli and Salmonella typhi have

• A. Thin peptidoglycan layer
• B. Thick peptidoglycan layer
• C. Outer membrane of lipoprotein
• D. Outer membrane of lipopolysaccharide

Explanation: Gram staining is a method used to classify bacteria into two major groups: Gram-positive and Gram-negative, based on the structure of their cell walls. Gram-negative bacteria, such as Escherichia coli and Salmonella typhi, have a thin peptidoglycan layer located between the cell membrane and an outer membrane composed of lipopolysaccharides, lipoproteins, and phospholipids. This structure is significant in determining the bacteria's response to Gram staining, where Gram-negative bacteria do not retain the crystal violet stain and instead take up the counterstain (safranin), appearing pink. Thus, the inference that the cell walls of E. coli and S. typhi have a thin peptidoglycan layer is correct. Other options either incorrectly describe the cell wall structure of Gram-negative bacteria or are partially correct.

2452. The given diagram shows a phenomenon in bacteria.

• A. Conjugation
• B. Transduction
• C. Transformation
• D. Endospore formation

Explanation: Bacterial transformation is the process where bacteria take up foreign DNA from their environment and incorporate it into their own genome, leading to new genetic traits. So option C is correct. Other processes like conjugation, transduction and endospore formation do not relate to the figure.

2453. Different methods of sterilisation are used to kill microorganisms.The method which kills the microorganisms by disrupting their DNA is

• A. Dry heat
• B. Radiation
• C. Fltration
• D. Moist heat

Explanation: The correct answer is radiation. Ionizing radiation, such as gamma rays or X-rays, is used in sterilization because it can penetrate cells and disrupt their DNA, leading to the death of the microorganisms. This method is particularly useful for sterilizing medical equipment and other materials that cannot withstand heat.Dry heat and moist heat sterilization methods kill microorganisms through thermal denaturation of proteins and other cell components, rather than by disrupting DNA.Filtration removes microorganisms from solutions by physically trapping them in a filter but does not affect the DNA or kill the microorganisms, which makes it unsuitable when complete destruction is necessary.

2454. The given diagram shows the process of conjugation in bacteria.The option that correctly identifies the labelled structure X, cells Y and Z is

• A. A
• B. B
• C. C
• D. D

Explanation: Structure X is pilus. Bacteria possessing the F plasmid are designated as F+. So Y is F+.Bacteria lacking the F plasmid are designated as F-. So Z is F-.. This makes option B correct. All other options are incorrect.

2455. Which of the following features is related to thermophilic bacteria?

• A. Bacteria that thrive in high-temperature environments like hot springs
• B. Cyanobacteria play an important role in nitrogen fixation
• C. The bacterial species Salmonella typhi causes typhoid in humans
• D. Bacteria in the large intestine of humans synthesize vitamins

Explanation: The correct answer is Option A:Bacteria that thrive in high-temperature environments like hot springsThermophilic bacteria are known for their ability to survive and function at high temperatures, often found in environments such as hot springs and hydrothermal vents. The other options describe features of different types of bacteria or their roles in ecosystems, but do not specifically relate to thermophilic bacteria.

2456. Based on the modes of nutrition, bacteria that serve the role of decomposers in the environment are categorised as

• A. Photoautotrophs
• B. Chemoautotrophs
• C. Photoheterotrophs
• D. Chemoheterotrophs

Explanation: Decomposers play a crucial role in ecosystems by breaking down dead organic material and recycling nutrients. These organisms are classified as chemoheterotrophs because they obtain their energy and carbon from organic compounds, which they decompose. In contrast, photoautotrophs and chemoautotrophs derive their carbon from carbon dioxide and not from decomposing organic matter. Photoheterotrophs use light for energy but, like chemoautotrophs, are not primarily decomposers.

2457. One of the hypotheses about origin of life is that life began deep in the oceans, in underwaterhot springs. The occurrence of which of the following organisms supports the givenhypothesis?

• A. Sycon
• B. Green algae
• C. Zooflagellates
• D. Archaebacteria

Explanation: Archaebacteria are a group of microorganisms that are well-known for their ability to thrive in extreme environments, such as those found in deep ocean hydrothermal vents. This supports the hypothesis that life could have originated in such harsh conditions. In contrast, the other organisms listed-Sycon, green algae, and zooflagellates-do not specifically exhibit adaptations for surviving in these extreme environments. Green algae, for instance, require sunlight for photosynthesis and are not typically found in the dark depths of the ocean. Sycon and zooflagellates also lack the specialized adaptations necessary for life in hydrothermal vent conditions.

2458. The arrangement of flagella in bacterial cells shown in the diagram is:

• A. Monotrichous
• B. lopotrichous
• C. peritrichous
• D. monopolar bitrichous

Explanation: The lophotrichous bacteria have several flagella located at the same place on their surface. When a tuft of flagella arises from one side of bacteria it is lophotrichous arrangement.

2459. In bacterial cells the absorption of DNA from medium to cell results in

• A. Transformation
• B. Transduction
• C. Conjugation
• D. Translation

Explanation: The process of absorption of DNA into the cell from its immediate environment is called transformation.As a result cell is transformed into new type of cell.

2460. The bacterium, with a tuft of flagella present at each of the two poles, is called:

• A. Amphitrichous
• B. Lophotrichous
• C. Peritrichous
• D. Monotrichous

Explanation: Amphitrichous refers to a type of bacterial flagellation where a single flagellum is present at both ends of the cell. This arrangement allows for movement in both directions, giving the bacteria greater mobility and versatility in navigating their environment.