Free Biodiversity and Variety of Life MCQs with Answers

2441. In the light of recent classification of living organisms into three domains of life (bacteria, archaea and eukarya), which one of the following statements in true about archaea?

• A. Archaea completely differ from both prokaryotes and eukaryotes.
• B. Archaea completely differ from prokaryotes.
• C. All of these statements are correct.
• D. Archaea have some novel features that are absent in other prokaryotes and eukaryotes.

Explanation: Archaea are a unique group of prokaryotes that share some similarities with eukaryotes, yet they also have distinct features that set them apart. Their cell walls lack peptidoglycan, and they contain unique lipids in their membranes, which allow them to thrive in extreme environments. The presence of introns in their genetic material is another characteristic that is uncommon among prokaryotes but more common in eukaryotes. Therefore, while archaea are a type of prokaryote, they exhibit novel features that are not shared with other prokaryotic organisms or eukaryotic cells.

2442. Select the correct combination of the statements (iiv) regarding the characteristics of certain organisms. (i) Methanogens are archaebacteria which produce methane in marshy areas. (ii) Nostoc is a filamentous bluegreen alga which fixes atmospheric nitrogen. (iii) Chemosynthetic autotrophic bacteria synthesize cellulose from glucose. (iv) Mycoplasma lack a cell wall and can survive without oxygen. The correct statements are

• A. (ii) and (iii)
• B. (i), (ii) and (iii)
• C. (ii), (iii) and (iv)
• D. (i), (ii) and (iv)

Explanation: The correct statements are (i), (ii), and (iv). Methanogens are indeed archaebacteria that produce methane, particularly in anaerobic environments like marshes. Nostoc is a filamentous cyanobacterium (often referred to as blue-green algae) that has the ability to fix atmospheric nitrogen. Mycoplasma are unique among bacteria in that they lack a cell wall, allowing them to survive in various environments, including oxygen-free conditions.On the other hand, statement (iii) is incorrect. Chemosynthetic autotrophic bacteria do not synthesize cellulose from glucose; rather, they utilize inorganic materials to produce energy and organic compounds. This fundamental misunderstanding disqualifies options A, B, and C from being correct.

2443. Which structures perform the function of mi tochondria in bacteria?

• A. Nucleoid
• B. Ribosomes
• C. Cell wall
• D. Mesosomes

Explanation: Mesosomes are specialized structures in bacteria that function similarly to mitochondria in eukaryotic cells. They are formed by invaginations of the plasma membrane and contain enzymes involved in cellular respiration, thus playing a crucial role in energy metabolism.In contrast, the other options do not serve this function: the nucleoid is simply the region of genetic material; ribosomes are involved in protein synthesis; and the cell wall provides protection and shape but does not participate in energy production. Therefore, mesosomes are the correct answer as they fulfill a role akin to that of mitochondria.

2444. The structures that help some bacteria to attach to rocks and/or host tissues are

• A. Mesosomes
• B. Holdfast
• C. Rhizoids
• D. Fimbriae

Explanation: Fimbriae are indeed small, bristle-like structures that extend from the surface of bacterial cells and are crucial for adhesion to various surfaces, including rocks and host tissues. They allow bacteria to establish themselves in suitable environments, such as the urinary tract in the case of Neisseria gonorrhoeae. In contrast, mesosomes are involved in other cellular processes but do not primarily function in attachment. Holdfasts are specialized attachment structures, but they are not as ubiquitous as fimbriae across different bacterial species. Rhizoids, while serving a similar anchoring function in other organisms, are not characteristic of bacteria.

2445. A parasite living inside body of the host is called:

• A. Ectoparasite
• B. Obligate parasite
• C. Facultative parasite
• D. Endoparasite

Explanation: [A] Ectoparasite;parasite that lives outside of its host[B] obligate parasite is the parasite that cannot complete its life cycle without exploiting a host[C] Facultative Parasite's life cycle does not completely depend on the host[D] Endoparasite e.g tapeworm that lives insides the host

2446. The maximum growth rate occurs in the:

• A. Stationary phase
• B. Senescent phase
• C. Lag phase
• D. Exponential phase

Explanation: Maximum growth rate occurs in the exponential or acceleration or log phase. The point at which the exponential growth begins to slow down is known as the inflexion point. The exponential phase, also known as the exponential growth phase, refers to a stage in the growth of a population or a culture of microorganisms when the population size or biomass increases rapidly and continuously at a constant relative rate. This phase is characterized by a J-shaped growth curve on a graph where the population size or biomass increases exponentially over time.

2447. The type of locomotion shown by bacteria towards carbon and energy sources is

• A. positive chemotaxis.
• B. negative chemotaxis
• C. positive magnetotaxis
• D. negative magnetotaxis

Explanation: Positive chemotaxis means moving towards a chemical stimulus i.e. O2 and energy source. So option A is correct. All other options does not match the given statement.

2448. Escherichia coli is a facultative anaerobic bacterium because it can

• A. not survive in the presence of oxygen.
• B. utilise low concentration of oxygen only.
• C. survive without oxygen, but uses oxygen if it is present.
• D. neither use oxygen for its growth nor can be harmed by it.

Explanation: A facultative anaerobe, such as Escherichia coli, can grow in both aerobic (with oxygen) and anaerobic (without oxygen) environments. However, it thrives better when oxygen is available because it can generate more energy through aerobic respiration than anaerobic processes. Therefore, it does not require oxygen but will use it if present, which makes Option C correct. Option A is incorrect because Escherichia coli can indeed survive in oxygen. Option B is incorrect as facultative anaerobes are not limited to low concentrations of oxygen. Option D describes aerotolerant organisms, which makes it incorrect for this question.

2449. Which of the following statements CORRECTLY describes the obligate anaerobic bacteria?

• A. They are killed by free oxygen
• B. They essentially need free oxygen
• C. They can live with or without free oxygen
• D. They obtain free oxygen from the host's body

Explanation: Obligate anaerobic bacteria are organisms that cannot survive in the presence of oxygen. Oxygen is toxic to them, and they only thrive in environments devoid of it. This distinguishes them from aerobic bacteria, which require oxygen, and facultative anaerobes, which can survive with or without oxygen. Understanding these distinctions helps clarify that the correct statement about obligate anaerobes is that they are killed by free oxygen, as described in Option A. Options B, C, and D incorrectly describe characteristics of other types of bacteria or misrepresent the nature of obligate anaerobes.

2450. 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 given results, gram positive bacteria are found in samples:

• A. I
• B. IV
• C. I and IV
• D. II and III

Explanation: Gram staining is a method used to differentiate bacterial species into two groups based on the chemical and physical properties of their cell walls. Gram-positive bacteria retain the crystal violet stain and appear purple under a microscope. In this question, to identify which samples contain gram-positive bacteria, you must refer to the staining results. Samples II and III exhibit the characteristics of gram-positive bacteria, while Samples I and IV do not, as they are gram-negative, which shows a red-pink colour. Therefore, the correct answer is Sample II and III.