Free Biodiversity and Variety of Life MCQs with Answers

2851. Which part of bacteria is most delicate and can damage bacterial cell immediately?

• A. Cell wall
• B. Cell membrane
• C. Slime layer
• D. Capsule

Explanation: The cell membrane is the most delicate part of the bacterial cell because it is thin and flexible. It plays a crucial role in protecting the cytoplasm and regulating the transport of substances into and out of the cell. Damage to the cell membrane can lead to the immediate death of the bacteria. In contrast, the cell wall, slime layer, and capsule are more robust structures that provide protection and support, but they are not as critical to the cell's immediate survival as the cell membrane.

2852. Cyanobacteria are related to eukaryotes in having:

• A. PS-I
• B. PS-II
• C. Both A and B
• D. None

Explanation: The correct answer is Option C: Both A and B. Cyanobacteria and eukaryotes share Photosystem I (PSI) and Photosystem II (PSII) as part of their photosynthetic machinery. These photosystems are essential for converting light energy into chemical energy during photosynthesis. PSI captures light energy to facilitate the transfer of electrons, while PSII uses light energy to extract electrons from water, releasing oxygen. Options A and B are incorrect because they only mention one of the photosystems, whereas both are necessary for the full range of photosynthetic functions shared between cyanobacteria and eukaryotes. Option D is incorrect because cyanobacteria do possess these photosystems.

2853. The size of Spirochete is approximately?

• A. 0.75-1.25 μm
• B. 100-200 nm
• C. 0.1-600 μm
• D. 500 μm

Explanation: The correct answer is Option D: 500 μm. Spirochetes are known for their unique spiral shape and can vary significantly in size. While most bacteria are much smaller, some spirochetes can indeed reach lengths of up to 500 micrometers, making them among the largest known bacteria. Option A (0.75-1.25 μm) is more typical of many smaller bacterial species. Option B (100-200 nm) is incorrect as it falls within the size range of viruses, not bacteria. Option C (0.1-600 μm) is overly broad and not specific to spirochetes.

2854. Which of the following bacteria is equal to the size of hyphen?

• A. Epulopiscium fishelsoni
• B. Pseudomonas aeruginosa
• C. Escherichia coli
• D. Streptococcus pneumoniae

Explanation: The correct answer is Epulopiscium fishelsoni, which is one of the largest known bacteria, reaching lengths up to 0.5 millimeters, approximately the size of a hyphen. This makes it unique among bacteria, which are typically much smaller. Pseudomonas aeruginosa, Escherichia coli, and Streptococcus pneumoniae are all much smaller, generally in the range of 1-2 micrometers in size, and thus do not match the size comparison to a hyphen.

2855. What is the main role of bacteria?

• A. CO2 cycle
• B. Nitrogen cycle
• C. Phosphorus cycle
• D. All of the above

Explanation: Bacteria are indispensable in various biogeochemical cycles. In the carbon cycle, they decompose organic matter, releasing carbon dioxide. In the nitrogen cycle, they perform nitrogen fixation, ammonification, and denitrification, all crucial for nitrogen availability. In the phosphorus cycle, they transform phosphorus into forms usable by plants. Therefore, the correct answer is 'All of the above' as bacteria contribute to all these cycles significantly. The other options are too narrow, focusing on only one specific role.

2856. DNA replication in bacteria occurs:

• A. Within nucleolus
• B. Prior to fission
• C. Just before transcription
• D. During S phase

Explanation: In bacteria, DNA replication occurs just prior to binary fission, ensuring that each daughter cell receives a complete set of genetic material. This is a crucial step for bacterial reproduction, as it allows for genetic continuity.

2857. Why is a capsule advantageous to a bacterium?

• A. It protects the bacterium from desiccation
• B. Provides pathogenicity to bacteria
• C. It allows bacterium to "hide" from host's immune system
• D. It allows the bacterium to attach to the surface
• E. All

Explanation: A bacterial capsule is advantageous to a bacterium, particularly in terms of pathogenicity, for the following reasons:1. **It protects the bacterium from desiccation:** This protective capsule helps pathogens survive outside of a host. When a bacterium is expelled from a host, it may face harsh environmental conditions, including drying out (desiccation). The capsule acts as a shield, retaining moisture and preventing the bacterium from drying up, enhancing its ability to persist in the environment and potentially infect new hosts.2. **It allows the bacterium to "hide" from the host's immune system:** Pathogenic bacteria often possess capsules composed of materials that are not easily recognized by the host's immune system. This camouflage effect makes it difficult for immune cells to detect and eliminate the bacterium. By "hiding" from the immune system, the bacterium can establish infections and continue to cause disease.3. **It allows the bacterium to attach to a surface:** Bacterial capsules can aid in adhesion to host tissues and surfaces. This is a critical step in the pathogenic process. For instance, many pathogenic bacteria need to adhere to host cells or tissues to initiate an infection. The capsule can facilitate this attachment, allowing the bacterium to colonize and establish infections in the host.In the context of pathogenicity, these advantages of a bacterial capsule contribute to the bacterium's ability to evade host defenses, survive in various environments, and initiate infections within the host's body.

2858. Which of the following is false about conjugation?

• A. It forms a bridge between two bacterial cells
• B. It involves the transport of genetic material via vectors
• C. It is a form of sexual reproduction
• D. None of these

Explanation: Bacterial conjugation is a mechanism of horizontal gene transfer where genetic material, typically plasmid DNA, is directly transferred between two bacterial cells via a conjugation bridge. Option A is true because the formation of this bridge is essential for conjugation. Option B is the correct answer because vectors are not involved in this process. Option C is also true, as the process introduces genetic diversity similar to sexual reproduction. Option D is incorrect, as Option B provides a false statement about conjugation.

2859. African sleeping sickness is caused by which of these human parasites?

• A. Choanoflagellates
• B. Trypanosoma
• C. Trichonymphas
• D. Paramecium

Explanation: Trypanosoma is a protozoan that causes African sleeping sickness, transmitted by the tsetse fly.

2860. To which group does Pinnularia belong?

• A. Chrysophyta
• B. Pyrophyta
• C. Rhodophyta
• D. Phaeophyta

Explanation: Pinnularia is part of the diatom group, which falls under the Chrysophyta division. Diatoms are a type of golden-brown algae known for their silica cell walls and aquatic habitat.