Monera

Topic: Prokaryotic Cell Structure; Subtopic: Mesosomes and Cell Wall Formation

Keyword Definitions:

• Mesosomes: Infoldings of the bacterial plasma membrane that aid in cell wall formation, DNA replication, and respiration.

• Cell wall: A rigid outer layer made of peptidoglycan that maintains bacterial shape and protects against osmotic stress.

• Ribosomes: Small organelles responsible for protein synthesis in prokaryotic and eukaryotic cells.

• Golgi apparatus: Organelle involved in protein packaging and secretion in eukaryotic cells, absent in prokaryotes.

Lead Question - 2024 (Jhajjhar)
Cell wall formation in Bacteria is facilitated by:
1. Ribosomes
2. Mesosomes
3. Golgi Apparatus
4. Centrosomes

Explanation: Cell wall formation in bacteria is facilitated by Mesosomes. These are membrane infoldings that increase surface area for enzymatic activities and play a vital role in septum formation during cell division. Unlike Golgi bodies in eukaryotes, mesosomes function in distributing cell wall materials, DNA replication, and respiration, ensuring bacterial integrity and growth.

1. Which component is responsible for respiration in bacterial cells?
1. Ribosomes
2. Mesosomes
3. Nucleoid
4. Flagella

Explanation: In bacteria, mesosomes function as sites for cellular respiration, performing roles similar to mitochondria in eukaryotic cells. They contain respiratory enzymes that facilitate energy production through oxidative phosphorylation. Thus, mesosomes are essential for generating ATP required for bacterial metabolism and cellular processes.

2. Which structure is absent in prokaryotic cells?
1. Nucleoid
2. Ribosomes
3. Golgi apparatus
4. Plasma membrane

Explanation: Prokaryotic cells lack membrane-bound organelles such as the Golgi apparatus, mitochondria, and nucleus. They instead rely on structures like mesosomes for secretory and respiratory functions. The Golgi body’s absence differentiates prokaryotes from eukaryotes, emphasizing their simpler but efficient cellular organization for essential life processes.

3. What is the main component of the bacterial cell wall?
1. Cellulose
2. Chitin
3. Peptidoglycan
4. Pectin

Explanation: The bacterial cell wall is composed of peptidoglycan, a complex polymer of sugars and amino acids. It provides structural strength, protects against osmotic lysis, and maintains the cell’s shape. Gram-positive bacteria have thick peptidoglycan layers, while Gram-negative bacteria possess thinner layers with an outer lipid membrane.

4. In bacteria, genetic material is found in:
1. Nucleus
2. Nucleoid
3. Mesosome
4. Ribosome

Explanation: In bacteria, the genetic material is located in the nucleoid, a region containing circular DNA. It is not enclosed by a membrane. During cell division, mesosomes assist in distributing replicated DNA to daughter cells. This structure is unique to prokaryotes and is essential for inheritance and metabolic regulation.

5. Which structure performs a role similar to mitochondria in bacteria?
1. Mesosomes
2. Ribosomes
3. Nucleoid
4. Vacuoles

Explanation: Mesosomes in bacteria perform roles similar to mitochondria in eukaryotic cells. They provide a site for respiration and energy production through enzyme-mediated reactions. Their folded membrane structure maximizes surface area for metabolic activities essential for bacterial survival and efficient energy conversion within the cytoplasm.

6. Which of the following statements about mesosomes is incorrect?
1. They help in cell wall formation.
2. They are involved in respiration.
3. They are present in eukaryotic cells.
4. They assist in DNA replication.

Explanation: The statement “They are present in eukaryotic cells” is incorrect. Mesosomes are found exclusively in prokaryotic cells. They aid in cell wall formation, DNA replication, and respiration. Eukaryotes instead possess mitochondria and Golgi bodies for these functions, highlighting cellular structural differences between the two groups.

7. Assertion-Reason Type Question:
Assertion (A): Mesosomes are involved in bacterial cell wall formation.
Reason (R): They are invaginations of the plasma membrane that secrete enzymes necessary for peptidoglycan synthesis.
1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.

Explanation: Both statements are true, and the Reason correctly explains the Assertion. Mesosomes form vesicular structures that help secrete wall-forming enzymes. They ensure proper septum formation and cell division, performing crucial roles in the synthesis of peptidoglycan, essential for bacterial growth and stability.

8. Matching Type Question:
Match List-I with List-II
List-I List-II
A. Ribosomes I. Protein synthesis
B. Mesosomes II. Respiration
C. Nucleoid III. Genetic material
D. Flagella IV. Motility

Options:
1. A-I, B-II, C-III, D-IV
2. A-II, B-I, C-IV, D-III
3. A-III, B-IV, C-II, D-I
4. A-IV, B-II, C-I, D-III

Explanation: The correct match is A-I, B-II, C-III, D-IV. Ribosomes perform protein synthesis, mesosomes assist in respiration, nucleoid contains genetic material, and flagella provide motility. Each bacterial component plays a distinct functional role essential for maintaining cellular integrity and performing vital physiological processes.

9. Fill in the Blanks Type Question:
The bacterial cell wall is mainly composed of ________.
1. Peptidoglycan
2. Cellulose
3. Glycogen
4. Lignin

Explanation: The bacterial cell wall primarily consists of peptidoglycan, a strong and flexible polymer providing rigidity and protection. It forms a mesh-like structure surrounding the plasma membrane. Peptidoglycan synthesis involves enzymes produced by mesosomes, ensuring cell stability during growth and division, maintaining bacterial shape and resistance to lysis.

10. Choose the Correct Statements (Statement I & II):
Statement I: Mesosomes are artifacts of cell preparation.
Statement II: They play an important role in respiration and cell wall formation.
1. Both statements are true.
2. Both statements are false.
3. Statement I is true, Statement II is false.
4. Statement I is false, Statement II is true.

Explanation: Statement I is false and Statement II is true. Mesosomes are functional membrane invaginations in bacteria aiding in respiration and wall synthesis. Although some artificial structures appear during microscopy, genuine mesosomes serve real physiological functions essential for bacterial metabolism and division.

Topic: Prokaryotic Cell Structure; Subtopic: Mesosomes in Bacteria

Keyword Definitions:

• Bacteria: Unicellular prokaryotic microorganisms without a membrane-bound nucleus.

• Mesosome: Infoldings of the plasma membrane in bacteria, involved in cellular processes like DNA replication and cell division.

• Plasma membrane: The phospholipid bilayer that surrounds the cytoplasm of cells, regulating entry and exit of substances.

• DNA replication: The process of producing two identical copies of DNA from one original DNA molecule.

• Cell wall: A rigid layer outside the plasma membrane providing structural support and shape to bacterial cells.

• Prokaryotic cell: A cell lacking membrane-bound organelles, with genetic material in the nucleoid region.

• Nucleoid: Region in a prokaryotic cell where the DNA is localized.

• Infolding: The inward folding of a membrane to increase surface area or facilitate specific cellular functions.

• Cell division: The process by which a parent cell divides into two daughter cells.

• Replication: The biological process of copying genetic material.

• Organelle: Specialized structure within a cell performing distinct functions.

Lead Question - 2023 (Manipur)

Given below are two statements:

I: In bacteria, the mesosomes are formed by the extensions of the plasma membrane.

II: The mesosomes, in bacteria, help in DNA replication and cell wall formation.

In light of the above statements, choose the most appropriate answer from the options given below:

1. Statement I is correct but Statement II is incorrect

2. Statement I is incorrect but Statement II is correct

3. Both Statement I and Statement II are correct

4. Both Statement I and Statement II are incorrect

Explanation:

Mesosomes are folded extensions of the bacterial plasma membrane, increasing surface area for enzymatic activities. They play roles in DNA replication, segregation, and cell wall formation during division. Both statements I and II correctly describe their structure and functions. While their existence is debated in modern microscopy due to artifacts, traditionally, they are considered functional in bacterial cells. Correct answer is 3.

1. Single Correct Answer MCQ:

Mesosomes in bacteria are primarily composed of:

1. Proteins

2. Phospholipid bilayer

3. Peptidoglycan

4. Ribosomal RNA

Explanation:

Mesosomes are infoldings of the bacterial plasma membrane, which is a phospholipid bilayer with embedded proteins. They are not composed of peptidoglycan, proteins alone, or ribosomal RNA. Correct answer is 2.

2. Single Correct Answer MCQ:

The primary function of mesosomes is:

1. Energy production

2. DNA replication and cell wall synthesis

3. Protein synthesis

4. Photosynthesis

Explanation:

Mesosomes facilitate DNA replication, segregation, and cell wall formation in bacteria. They do not directly participate in protein synthesis, photosynthesis, or energy production. Correct answer is 2.

3. Single Correct Answer MCQ:

Mesosomes are considered artifacts because:

1. They are permanent structures

2. They result from chemical fixation during microscopy

3. They are part of the ribosome

4. They are extracellular structures

Explanation:

Modern microscopy suggests mesosomes may appear due to chemical fixation during electron microscopy, making them artifacts rather than permanent structures. They are intracellular, not ribosomes or extracellular. Correct answer is 2.

4. Single Correct Answer MCQ:

Which process is directly assisted by mesosomes?

1. Glycolysis

2. DNA replication

3. Protein folding

4. Photosynthesis

Explanation:

Mesosomes provide surface area for enzymes involved in DNA replication and segregation. They are not directly involved in glycolysis, protein folding, or photosynthesis. Correct answer is 2.

5. Single Correct Answer MCQ:

Mesosomes are located in:

1. Eukaryotic nucleus

2. Bacterial plasma membrane

3. Mitochondria

4. Cytoskeleton

Explanation:

Mesosomes are extensions of the bacterial plasma membrane in prokaryotes. They are absent in eukaryotic nuclei, mitochondria, or the cytoskeleton. Correct answer is 2.

6. Single Correct Answer MCQ:

Formation of mesosomes increases:

1. Cytoplasmic volume

2. Membrane surface area

3. Ribosomal density

4. Cell motility

Explanation:

Mesosomes are infoldings of the plasma membrane, increasing surface area for enzymatic reactions and DNA replication. They do not increase cytoplasmic volume, ribosome density, or motility. Correct answer is 2.

7. Assertion-Reason MCQ:

Assertion (A): Mesosomes assist in bacterial cell division.

Reason (R): Mesosomes provide sites for DNA replication and septum formation.

1. Both A and R are true and R explains A

2. Both A and R are true but R does not explain A

3. A is true but R is false

4. Both A and R are false

Explanation:

Mesosomes facilitate DNA replication and septum formation during bacterial cell division. Both the assertion and reason are correct, and the reason explains the function described. Correct answer is 1.

8. Matching Type MCQ:

Match the structure with its role:

A. Mesosome — (i) DNA replication

B. Ribosome — (ii) Protein synthesis

C. Peptidoglycan layer — (iii) Cell wall strength

D. Flagellum — (iv) Motility

1. A-(i), B-(ii), C-(iii), D-(iv)

2. A-(ii), B-(i), C-(iv), D-(iii)

3. A-(iii), B-(iv), C-(ii), D-(i)

4. A-(iv), B-(iii), C-(i), D-(ii)

Explanation:

Mesosomes assist DNA replication, ribosomes synthesize proteins, peptidoglycan provides cell wall strength, and flagella enable bacterial motility. Correct matching is A-(i), B-(ii), C-(iii), D-(iv), which is option 1.

9. Fill in the Blanks MCQ:

Mesosomes are formed by ______ of the plasma membrane.

1. Infoldings

2. Outgrowth

3. Fragmentation

4. Dissolution

Explanation:

Mesosomes are formed by infoldings of the bacterial plasma membrane, increasing surface area for enzymatic activity and DNA replication. Correct answer is 1.

10. Choose the correct statements MCQ:

Statement I: Mesosomes aid in bacterial DNA replication.

Statement II: Mesosomes are present in eukaryotic cells.

1. Statement I only

2. Statement II only

3. Both statements are true

4. Both statements are false

Explanation:

Mesosomes assist in DNA replication in bacteria (prokaryotes) but are not present in eukaryotic cells. Therefore, only Statement I is correct. Correct answer is 1.

Subtopic: Bacteria, Cyanobacteria, and Mycoplasma

Keyword Definitions:

• Bacteria: Single-celled prokaryotic microorganisms that can be autotrophic or heterotrophic.

• Slime Moulds: Fungus-like protists that are saprophytic in nature, feeding on decaying organic matter.

• Mycoplasma: Smallest bacteria-like organisms without a cell wall but containing DNA and ribosomes.

• Cyanobacteria: Photosynthetic bacteria capable of producing oxygen and classified under Kingdom Monera.

• Autotrophic: Organisms that can synthesize their own food from inorganic sources.

• Heterotrophic: Organisms that depend on organic compounds for nutrition.

• Kingdom Monera: Taxonomic kingdom including prokaryotic microorganisms like bacteria and cyanobacteria.

Lead Question (2022):
Which of the following is a correct statement?
(1) Bacteria are exclusively heterotrophic organisms
(2) Slime moulds are saprophytic organisms classified under Kingdom Monera
(3) Mycoplasma have DNA, Ribosome and cell wall
(4) Cyanobacteria are a group of autotrophic organisms classified under Kingdom Monera

Explanation: Bacteria include both autotrophic and heterotrophic types, so option (1) is incorrect. Slime moulds are protists, not Monera, so option (2) is wrong. Mycoplasma lack a cell wall, so option (3) is incorrect. Cyanobacteria are autotrophic and prokaryotic, classified under Kingdom Monera, making option (4) correct.

1. Which of the following organisms is photosynthetic?
(1) Mycoplasma
(2) Cyanobacteria
(3) Slime mould
(4) Lactobacillus

Explanation: Cyanobacteria are prokaryotic autotrophs capable of photosynthesis, producing oxygen. Mycoplasma lack chlorophyll, slime moulds are saprophytic, and Lactobacillus are heterotrophic. Therefore, the correct answer is option (2).

2. Mycoplasma differ from typical bacteria because they:
(1) Have no DNA
(2) Lack ribosomes
(3) Lack cell wall
(4) Are eukaryotic

Explanation: Mycoplasma are prokaryotic but lack a rigid cell wall, making them unique among bacteria. They contain DNA and ribosomes but do not have a cell wall. Hence, the correct answer is option (3).

3. Slime moulds are classified under:
(1) Kingdom Monera
(2) Kingdom Protista
(3) Kingdom Fungi
(4) Kingdom Plantae

Explanation: Slime moulds are protist-like organisms that feed on decaying matter and exhibit amoeboid movement. They are not true fungi or bacteria. Therefore, they are classified under Kingdom Protista. Hence, the correct answer is option (2).

4. Which of the following bacteria is autotrophic?
(1) Escherichia coli
(2) Cyanobacteria
(3) Mycoplasma
(4) Staphylococcus aureus

Explanation: Cyanobacteria are photosynthetic prokaryotes capable of autotrophic nutrition. E. coli, Mycoplasma, and Staphylococcus aureus are heterotrophic. Therefore, the correct answer is option (2).

5. Which statement about bacteria is correct?
(1) All bacteria are heterotrophs
(2) Bacteria can be autotrophic or heterotrophic
(3) All bacteria are autotrophs
(4) Bacteria are eukaryotic

Explanation: Bacteria exhibit diverse nutritional modes, including autotrophy and heterotrophy. They are prokaryotic organisms, not eukaryotic. Hence, the correct answer is option (2).

6. Which of the following lacks a cell wall?
(1) Bacillus
(2) Mycoplasma
(3) Cyanobacteria
(4) Streptococcus

Explanation: Mycoplasma are unique among bacteria for their absence of a cell wall, while Bacillus, Cyanobacteria, and Streptococcus have cell walls. Hence, the correct answer is option (2).

7. Assertion-Reason:
Assertion (A): Cyanobacteria are autotrophic.
Reason (R): They contain chlorophyll and perform photosynthesis.
(1) Both A and R are true and R is the correct explanation
(2) Both A and R are true but R is not the correct explanation
(3) A is true, R is false
(4) A is false, R is true

Explanation: Cyanobacteria are autotrophs because they perform photosynthesis using chlorophyll. This photosynthetic capability explains their autotrophic nature. Therefore, both A and R are true, and R correctly explains A. Hence, the correct answer is option (1).

8. Matching Type: Match the organisms with their characteristics:
A. Mycoplasma – 1. Photosynthetic
B. Cyanobacteria – 2. Lacks cell wall
C. Slime mould – 3. Saprophytic protist
(1) A–2, B–1, C–3
(2) A–1, B–2, C–3
(3) A–3, B–1, C–2
(4) A–2, B–3, C–1

Explanation: Mycoplasma lack a cell wall (A–2), cyanobacteria are photosynthetic autotrophs (B–1), and slime moulds are saprophytic protists (C–3). Hence, the correct answer is option (1).

9. Fill in the blank:
________ are prokaryotic autotrophic organisms capable of oxygenic photosynthesis.

(1) Mycoplasma
(2) Cyanobacteria
(3) Slime mould
(4) Lactobacillus

Explanation: Cyanobacteria are prokaryotic, photosynthetic autotrophs capable of producing oxygen, unlike Mycoplasma, slime moulds, or Lactobacillus. Hence, the correct answer is option (2).

10. Choose the correct statements:
(a) Mycoplasma lack cell wall.
(b) Cyanobacteria are autotrophic.
(c) Slime moulds are bacteria.
(d) Bacteria can be heterotrophic or autotrophic.
(1) a, b,

Subtopic: Mycoplasma and Cell Wall Characteristics

Keyword Definitions:
• Mycoplasma: Smallest free-living bacteria lacking a cell wall.
• Cell wall: Rigid structure surrounding some bacterial cells providing shape and protection.
• Filterability: Ability of microorganisms to pass through filters of specific pore sizes.
• Bacteria: Prokaryotic, unicellular organisms without a membrane-bound nucleus.
• Gram-positive bacteria: Bacteria with thick peptidoglycan cell walls.
• Gram-negative bacteria: Bacteria with thin peptidoglycan and outer membrane.
• Pathogenicity: Ability of an organism to cause disease.
• Protoplasm: Living content of a cell including cytoplasm and nucleus.
• Antibiotic sensitivity: Susceptibility of bacteria to antibiotics.
• Culture medium: Nutrient solution supporting growth of microorganisms.

Lead Question (2022):
Given below are two statements:
Statement I: Mycoplasma can pass through less than micron filter size.
Statement II: Mycoplasma are bacteria with cell wall.
In the light of the above statements, choose the most appropriate answer from the options given below:
(1) Both Statement I and Statement II are incorrect
(2) Statement I is correct but Statement II is correct
(3) Statement I is incorrect but Statement II is correct
(4) Both Statement I and Statement II are correct

Explanation: The correct answer is (2). Statement I is correct because Mycoplasma are extremely small bacteria capable of passing through filters less than one micron. Statement II is incorrect as Mycoplasma lack a cell wall, making them unique among prokaryotic bacteria and resistant to antibiotics targeting cell wall synthesis.

Guessed MCQs:

1. Single Correct Answer:
Which feature distinguishes Mycoplasma from most other bacteria?
(a) Presence of nucleus
(b) Lack of cell wall
(c) Photosynthetic ability
(d) Multicellularity
Explanation: The correct answer is (b). Mycoplasma are unique bacteria that lack a cell wall, which gives them flexibility in shape and resistance to antibiotics that target cell wall synthesis.

2. Single Correct Answer:
What is the approximate size of Mycoplasma bacteria?
(a) 100 microns
(b) 0.2–0.3 microns
(c) 10 microns
(d) 5 microns
Explanation: The correct answer is (b). Mycoplasma are extremely small bacteria, usually 0.2–0.3 microns in diameter, allowing them to pass through fine filters that trap larger bacteria.

3. Single Correct Answer:
Which antibiotic would be ineffective against Mycoplasma?
(a) Tetracycline
(b) Penicillin
(c) Macrolides
(d) Chloramphenicol
Explanation: The correct answer is (b). Penicillin targets cell wall synthesis, but Mycoplasma lack a cell wall, rendering beta-lactam antibiotics ineffective against these bacteria.

4. Assertion-Reason MCQ:
Assertion (A): Mycoplasma can pass through bacterial filters.
Reason (R): They are very small and lack a rigid cell wall.
(a) Both A and R are correct and R explains A
(b) Both A and R are correct but R does not explain A
(c) A is correct, R is incorrect
(d) A is incorrect, R is correct
Explanation: The correct answer is (a). Mycoplasma's tiny size and absence of a cell wall allow them to filter through membranes that block other bacteria.

5. Single Correct Answer:
Which type of culture medium is suitable for Mycoplasma?
(a) Nutrient agar
(b) Media enriched with sterols
(c) Minimal media
(d) MacConkey agar
Explanation: The correct answer is (b). Mycoplasma require sterols for membrane stability, so enriched media containing sterols are necessary for their growth in vitro.

6. Single Correct Answer:
Which disease is caused by Mycoplasma pneumoniae?
(a) Tuberculosis
(b) Walking pneumonia
(c) Cholera
(d) Typhoid
Explanation: The correct answer is (b). Mycoplasma pneumoniae is the causative agent of atypical or walking pneumonia, a mild form of respiratory infection.

7. Matching Type:
Match the Mycoplasma species with the disease it causes:
Column A
1. M. genitalium
2. M. hominis
3. M. pneumoniae
Column B
A. Genitourinary infections
B. Atypical pneumonia
C. Pelvic inflammatory disease
Options:
(a) 1-A, 2-C, 3-B
(b) 1-B, 2-A, 3-C
(c) 1-C, 2-B, 3-A
(d) 1-A, 2-B, 3-C
Explanation: The correct answer is (a). M. genitalium causes genitourinary infections, M. hominis is linked to pelvic inflammatory disease, and M. pneumoniae causes atypical pneumonia.

8. Fill in the Blanks:
Mycoplasma are bacteria that lack _______ and can pass through _______ filters.
(a) Nucleus, 5 micron
(b) Cell wall, 0.2 micron
(c) Ribosomes, 1 micron
(d) Membrane, 0.5 micron
Explanation: The correct answer is (b). Mycoplasma lack a cell wall and are extremely small, enabling them to pass through filters around 0.2 microns.

9. Single Correct Answer:
Which feature contributes to Mycoplasma's pleomorphic shape?
(a) Rigid peptidoglycan
(b) Absence of cell wall
(c) Thick outer membrane
(d) Capsule
Explanation: The correct answer is (b). The absence of a cell wall allows Mycoplasma cells to assume variable shapes, termed pleomorphism.

10. Choose the correct statements:
(a) Mycoplasma lack cell walls
(b) Mycoplasma can pass through submicron filters
(c) All bacteria have cell walls
(d) Mycoplasma require sterols for growth
Explanation: The correct answer is (a), (b), and (d). Statement (c) is incorrect because Mycoplasma are an exception among bacteria, lacking a cell wall.

Subtopic: Microorganisms and Cell Sizes

Keyword Definitions:

• PPLO: Pleuropneumonia-like organisms, the smallest self-replicating organisms, belonging to Mycoplasma group.

• Mycoplasma: Wall-less bacteria, smallest known prokaryotes, resistant to many antibiotics.

• Cell Size: Dimension of a living cell, varying from micrometers to millimeters depending on organism type.

• Virus: Infectious acellular agents smaller than bacteria, dependent on host machinery for replication.

• Prokaryotes: Single-celled organisms without a true nucleus or membrane-bound organelles.

• Eukaryotes: Organisms with true nucleus and membrane-bound organelles.

Lead Question - 2020 (COVID Reexam)

The size of Pleuropneumonia - like Organism (PPLO) is :
1. 0.02 m
2. 1-2 m
3. 10-20 m
4. 0.1 m

Explanation: PPLO or Mycoplasma are the smallest living prokaryotic organisms, measuring about 0.1 micrometer in size. They lack a cell wall, allowing them flexibility in shape. Options given in meters are misleading, as the correct unit is micrometer. Thus, the correct answer is option 4, 0.1 m (interpreted as micrometer).

Guessed Question 1. The smallest living cell is :
1. Virus
2. Mycoplasma
3. Bacteriophage
4. E.coli

Explanation: Mycoplasma, also called PPLO, is considered the smallest living cell with a size of about 0.1 µm. Viruses are smaller but not considered living without a host. Bacteriophage is a virus infecting bacteria. Hence, the correct answer is option 2, Mycoplasma.

Guessed Question 2. Which of the following lacks a cell wall?
1. Mycoplasma
2. Fungi
3. Bacteria
4. Algae

Explanation: Mycoplasma is unique among prokaryotes for lacking a cell wall, making it resistant to antibiotics like penicillin. Fungi have chitin walls, bacteria have peptidoglycan walls, and algae possess cellulose walls. Therefore, the correct answer is option 1, Mycoplasma.

Guessed Question 3. The genome of Mycoplasma is made up of :
1. RNA only
2. DNA only
3. Protein only
4. RNA and Protein

Explanation: Mycoplasma possesses DNA as its genetic material, similar to other prokaryotes. Its small genome size supports self-replication and basic metabolic processes. RNA viruses differ in this aspect. Hence, the correct answer is option 2, DNA only, which directs all cellular functions.

Guessed Question 4. Assertion (A): Mycoplasma is the smallest free-living organism.
Reason (R): Mycoplasma can survive without a host cell.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Mycoplasma is the smallest free-living prokaryote capable of surviving without a host, unlike viruses. Both assertion and reason are correct, and reason justifies the assertion. Therefore, the correct answer is option 1.

Guessed Question 5. Match the following:
(a) Virus (i) Protein coat
(b) Mycoplasma (ii) Smallest living cell
(c) Bacteriophage (iii) Infects bacteria
(d) Fungi (iv) Chitin wall
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
3. (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
4. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)

Explanation: Viruses possess a protein coat called capsid, Mycoplasma is the smallest living cell, bacteriophage infects bacteria, and fungi have chitin cell walls. The correct match is option 1, which aligns the correct features with each organism.

Guessed Question 6. Fill in the blank: The genetic material of viruses can be either ______.
1. DNA or RNA
2. Only RNA
3. Only DNA
4. Only Protein

Explanation: Viruses are acellular infectious agents, and their genetic material can be either DNA or RNA, never both in a single virus. This diversity determines viral classification and replication strategy. Thus, the correct answer is option 1, DNA or RNA.

Guessed Question 7. Choose the correct statements:
(i) Viruses are acellular.
(ii) Mycoplasma lacks cell wall.
(iii) Bacteriophage infects fungi.
(iv) Fungi have cellulose walls.
1. (i) and (ii)
2. (i), (ii), and (iv)
3. (i), (ii), and (iii)
4. (ii) and (iii)

Explanation: Viruses are acellular particles, Mycoplasma lacks a cell wall, fungi have chitin walls not cellulose, and bacteriophage infects bacteria not fungi. Hence, only (i) and (ii) are correct. The correct answer is option 1, reflecting key distinctions among microbes.

Topic: Prokaryotic Cell
Subtopic: Inclusion Bodies in Bacteria

Keyword Definitions:

• Inclusion Bodies: Non-living reserve materials found in prokaryotic cells.

• Gas Vacuoles: Protein-covered structures providing buoyancy to photosynthetic bacteria.

• Contractile Vacuoles: Organelles regulating water balance, mostly in protists.

• Centrioles: Microtubule structures involved in cell division in animal cells.

• Microtubules: Cytoskeletal structures providing shape and transport inside eukaryotic cells.

• Photosynthetic Bacteria: Prokaryotes performing photosynthesis, like cyanobacteria and purple bacteria.

Lead Question - 2020 (COVID Reexam)

Inclusion bodies of blue-green, purple, and green photosynthetic bacteria are :
1. Contractile vacuoles
2. Gas vacuoles
3. Centrioles
4. Microtubules

Explanation: Inclusion bodies of blue-green, purple, and green photosynthetic bacteria are gas vacuoles. These provide buoyancy, helping bacteria float in water to receive optimal light for photosynthesis. Contractile vacuoles are found in protists, centrioles and microtubules are eukaryotic components. Hence, the correct answer is option 2, gas vacuoles.

Guessed Question 1. Which inclusion body stores phosphate in bacteria?
1. Sulphur granules
2. Phosphate granules
3. Gas vacuoles
4. Glycogen granules

Explanation: Phosphate granules serve as reserve storage of inorganic phosphate in bacteria. Sulphur granules store sulphur, gas vacuoles aid buoyancy, and glycogen granules store carbohydrates. Therefore, the correct answer is option 2, phosphate granules, as they provide essential phosphate for energy metabolism and biosynthesis in bacterial cells.

Guessed Question 2. Which of the following is a reserve material in prokaryotes?
1. Ribosomes
2. Glycogen granules
3. Mesosomes
4. Centrioles

Explanation: Glycogen granules are inclusion bodies acting as carbohydrate reserve in bacteria. Ribosomes are protein-synthesizing machinery, mesosomes are infoldings of plasma membrane, and centrioles are eukaryotic organelles. Thus, the correct answer is option 2, glycogen granules, storing energy reserves for bacterial survival and metabolism.

Guessed Question 3. Sulphur granules in bacteria serve as:
1. Reserve of sulphur
2. Gas vacuole
3. DNA storage
4. Protein synthesis site

Explanation: Sulphur granules act as storage form of elemental sulphur in certain bacteria. Gas vacuoles provide buoyancy, DNA is stored in nucleoid, and protein synthesis occurs in ribosomes. Therefore, the correct answer is option 1, sulphur granules, ensuring sulphur availability during metabolic requirements in bacteria.

Guessed Question 4. Assertion (A): Gas vacuoles help bacteria regulate buoyancy.
Reason (R): They are surrounded by protein membranes impermeable to gases.
1. Both A and R are true, R explains A
2. Both A and R are true, R does not explain A
3. A is true, R is false
4. A is false, R is true

Explanation: Gas vacuoles provide buoyancy to bacteria. They are protein-coated, but permeable to gases, not impermeable. Hence, assertion is true but reason is false. Correct answer is option 3. These vacuoles enable bacteria to position optimally in water for photosynthesis.

Guessed Question 5. Match the following:
(a) Gas vacuoles (i) Phosphate reserve
(b) Glycogen granules (ii) Buoyancy
(c) Polyphosphate granules (iii) Carbohydrate storage
(d) Sulphur granules (iv) Sulphur reserve
1. (a)-(ii), (b)-(iii), (c)-(i), (d)-(iv)
2. (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
3. (a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)
4. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)

Explanation: Gas vacuoles provide buoyancy, glycogen granules store carbohydrates, polyphosphate granules act as phosphate reserves, and sulphur granules store sulphur. Hence, the correct match is option 1. These bacterial inclusion bodies serve as non-living storage structures, aiding survival and adaptation in varied environments.

Guessed Question 6. Fill in the blank: In bacteria, ______ are sites of protein synthesis.
1. Ribosomes
2. Gas vacuoles
3. Inclusion bodies
4. Mesosomes

Explanation: Ribosomes are the sites of protein synthesis in bacteria. Gas vacuoles aid buoyancy, inclusion bodies are storage sites, and mesosomes are membrane infoldings. Prokaryotic ribosomes are 70S type, consisting of 50S and 30S subunits. Thus, the correct answer is option 1, ribosomes.

Guessed Question 7. Choose the correct statements:
(i) Gas vacuoles store proteins
(ii) Glycogen granules act as carbohydrate reserves
(iii) Polyphosphate granules provide energy reserves
(iv) Ribosomes are inclusion bodies
1. (i) and (iii)
2. (ii) and (iii)
3. (ii) and (iv)
4. (i) and (iv)

Explanation: Correct statements are (ii) glycogen granules act as carbohydrate reserves and (iii) polyphosphate granules serve as energy reserves. Gas vacuoles do not store proteins, and ribosomes are not inclusion bodies. Hence, the correct answer is option 2. Inclusion bodies are non-living reserves in bacterial cytoplasm.

Topic : Monera
Subtopic : Cyanobacteria

Keyword Definitions :

• Cyanobacteria : Photosynthetic prokaryotes, also called blue-green algae, capable of nitrogen fixation.

• Photoautotrophs : Organisms that use sunlight and inorganic substances to prepare food.

• Heterocysts : Thick-walled specialized cells in cyanobacteria responsible for nitrogen fixation.

• Algal bloom : Rapid increase of algae or cyanobacteria in polluted water bodies.

• Chlorophyll a : Primary pigment involved in photosynthesis, present in plants and cyanobacteria.

Lead Question - 2020 (COVID Reexam)

Which of the following is incorrect about Cyanobacteria?
1. They are photoautotrophs
2. They lack heterocysts
3. They often form blooms in polluted water bodies
4. They have chlorophyll A similar to green plants

Explanation : Cyanobacteria are photoautotrophs, possess heterocysts for nitrogen fixation, form blooms in polluted water bodies, and contain chlorophyll a like plants. The incorrect statement is that they lack heterocysts. Thus, option 2 is correct.

1) Which specialized cells in Cyanobacteria fix atmospheric nitrogen?
(1) Trichomes
(2) Heterocysts
(3) Mycelia
(4) Pyrenoids

Explanation : Nitrogen fixation in cyanobacteria occurs in thick-walled heterocysts that provide anaerobic conditions essential for nitrogenase enzyme activity. Trichomes are filaments, pyrenoids are in algae, and mycelia occur in fungi. Hence, option (2) is correct.

2) Algal blooms caused by cyanobacteria reduce water quality by
(1) Oxygen enrichment
(2) Oxygen depletion
(3) Decreasing carbon dioxide
(4) Providing nutrients to fish

Explanation : Cyanobacterial blooms consume dissolved oxygen during decomposition, leading to oxygen depletion and aquatic animal deaths. They also release toxins. Oxygen enrichment or nutrient supply does not occur. Thus, option (2) is correct.

3) Chlorophyll a in cyanobacteria functions in
(1) Protein synthesis
(2) Photosynthesis
(3) Nitrogen fixation
(4) Cell wall formation

Explanation : Chlorophyll a is the main photosynthetic pigment in cyanobacteria and green plants. It absorbs light energy and converts it into chemical energy during photosynthesis. It is not involved in protein synthesis, nitrogen fixation, or cell wall formation. Thus, option (2) is correct.

4) Which cyanobacterium is used as biofertilizer in paddy fields?
(1) Nostoc
(2) Anabaena
(3) Oscillatoria
(4) Gloeocapsa

Explanation : Anabaena, a symbiotic cyanobacterium living inside Azolla, is widely used as a biofertilizer in rice cultivation because of its nitrogen-fixing ability. Nostoc also fixes nitrogen but is less commonly used. Hence, option (2) is correct.

5) In cyanobacteria, the enzyme responsible for nitrogen fixation is
(1) Nitrogenase
(2) RuBisCO
(3) Dehydrogenase
(4) ATP synthase

Explanation : The nitrogenase enzyme in cyanobacteria fixes atmospheric nitrogen into ammonia under anaerobic conditions inside heterocysts. RuBisCO is for carbon fixation, ATP synthase produces ATP, and dehydrogenases act in respiration. Hence, option (1) is correct.

6) Cyanobacteria differ from true algae in having
(1) Prokaryotic cell structure
(2) Nucleus
(3) Membrane-bound organelles
(4) DNA in chromosomes

Explanation : Cyanobacteria are prokaryotic and lack a nucleus and membrane-bound organelles. Their DNA is circular and not organized into chromosomes. True algae are eukaryotic. Thus, option (1) is correct.

7) Assertion (A): Cyanobacteria form algal blooms in eutrophic water.
Reason (R): They grow rapidly in nutrient-rich polluted water bodies.
(1) Both (A) and (R) are true, and (R) is the correct explanation of (A)
(2) Both (A) and (R) are true, but (R) is not the correct explanation of (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false

Explanation : Cyanobacteria multiply rapidly in nutrient-rich eutrophic waters, causing algal blooms. The given reason correctly explains the assertion. Thus, option (1) is correct.

8) Match the following:
A. Nostoc – (i) Free-living nitrogen fixer
B. Anabaena – (ii) Symbiotic with Azolla
C. Oscillatoria – (iii) Water bloom
D. Rivularia – (iv) Filamentous cyanobacterium
(1) A-(iv), B-(ii), C-(iii), D-(i)
(2) A-(i), B-(ii), C-(iii), D-(iv)
(3) A-(iii), B-(iv), C-(i), D-(ii)
(4) A-(ii), B-(i), C-(iv), D-(iii)

Explanation : Nostoc is free-living, Anabaena is symbiotic with Azolla, Oscillatoria causes blooms, and Rivularia is filamentous. Thus, option (2) is correct.

9) Fill in the blank: Cyanobacteria store carbohydrates in the form of ______.
(1) Glycogen
(2) Starch
(3) Cellulose
(4) Amylose

Explanation : Cyanobacteria store food in the form of glycogen, unlike green plants that store starch. Hence, option (1) is correct.

10) Choose the correct statements:
A. Cyanobacteria are prokaryotic.
B. They contain chlorophyll a.
C. They lack heterocysts.
D. They act as biofertilizers.
(1) A, B, and D
(2) A, C, and D
(3) B, C, and D
(4) A, B, C, and D

Explanation : Cyanobacteria are prokaryotic, have chlorophyll a, and act as biofertilizers due to nitrogen fixation. They do not lack heterocysts, so statement C is false. Correct option is (1).

Topic: Bacteria and Related Microorganisms

Subtopic: Mycoplasma and Pathogenic Bacteria

Keyword Definitions:

• Mycoplasma – Smallest free-living cells lacking a cell wall, can be pathogenic.

• Cell wall – Rigid layer providing shape and protection to most bacteria.

• Nostoc – Filamentous cyanobacterium, photosynthetic, with a cell wall.

• Bacillus – Rod-shaped, spore-forming bacterium with a cell wall.

• Pseudomonas – Gram-negative bacterium with cell wall, aerobic.

• Obligate aerobe – Organism requiring oxygen for survival.

• Facultative anaerobe – Organism that can survive with or without oxygen.

• Pathogenic – Ability to cause disease in plants or animals.

• Prokaryote – Single-celled organism without a nucleus.

• Smallest cell – Cell with minimal size and genome capable of independent life.

Lead Question – 2017:

Which among the following are the smallest living cells known without a definite cell wall, pathogenic to plants as well as animals and can survive without oxygen:

(A) Nostoc

(B) Bacillus

(C) Pseudomonas

(D) Mycoplasma

Explanation:

The smallest living cells without a cell wall, capable of causing disease in plants and animals, and able to survive without oxygen are Mycoplasma. Other options have cell walls and different metabolic requirements, making Mycoplasma unique among prokaryotes. (Answer: D)

1) Single Correct Answer MCQ:

Which characteristic distinguishes Mycoplasma from Bacillus and Pseudomonas?

(A) Presence of cell wall

(B) Ability to form spores

(C) Absence of cell wall

(D) Photosynthetic ability

Explanation:

Mycoplasma are unique because they lack a cell wall, unlike Bacillus and Pseudomonas, which have rigid cell walls, allowing them flexibility in shape and resistance to antibiotics targeting cell walls. (Answer: C)

2) Single Correct Answer MCQ:

Which of the following can survive without oxygen?

(A) Bacillus

(B) Pseudomonas

(C) Mycoplasma

(D) Nostoc

Explanation:

< b>Mycoplasma

can survive without oxygen (facultative anaerobic), while Bacillus and Pseudomonas are obligate or facultative aerobes, and Nostoc is photosynthetic, requiring light and oxygen for energy production. (Answer: C)

3) Single Correct Answer MCQ:

Which bacteria are pathogenic to both plants and animals?

(A) Nostoc

(B) Mycoplasma

(C) Pseudomonas

(D) Bacillus

Explanation:

< b>Mycoplasma can infect multiple hosts, including plants and animals. Nostoc is non-pathogenic, Pseudomonas and Bacillus have limited host specificity. Pathogenicity and lack of cell wall distinguish Mycoplasma. (Answer: B)

4) Single Correct Answer MCQ:

Which is the smallest self-replicating cell known?

(A) Nostoc

(B) Bacillus

(C) Pseudomonas

(D) Mycoplasma

Explanation:

< b>Mycoplasma are the smallest self-replicating cells capable of independent life. Their minimal genome allows basic metabolic functions without a cell wall. (Answer: D)

5) Single Correct Answer MCQ:

Which cell lacks peptidoglycan in its cell wall?

(A) Bacillus

(B) Mycoplasma

(C) Pseudomonas

(D) Nostoc

Explanation:

< b>Mycoplasma entirely lack a peptidoglycan cell wall, making them resistant to antibiotics targeting cell wall synthesis, unlike Bacillus, Pseudomonas, and Nostoc, which have cell walls containing peptidoglycan. (Answer: B)

6) Single Correct Answer MCQ:

Which of the following is pleomorphic?

(A) Mycoplasma

(B) Bacillus

(C) Pseudomonas

(D) Nostoc

Explanation:

< b>Mycoplasma are pleomorphic because of the absence of a rigid cell wall, allowing variable shapes. Other bacteria have rigid walls, maintaining a fixed shape. (Answer: A)

7) Assertion-Reason MCQ:

Assertion (A): Mycoplasma can survive without oxygen.

Reason (R): They have flexible membranes and minimal metabolic requirements.

(A) Both A and R true, R explains A

(B) Both A and R true, R does not explain A

(C) A true, R false

(D) A false, R true

Explanation:

Both assertion and reason are true. Mycoplasma have flexible membranes and minimal metabolic needs, allowing survival in anaerobic conditions. (Answer: A)

8) Matching Type MCQ:

Match the organism with its feature:

1. Mycoplasma – (i) Photosynthetic

2. Nostoc – (ii) Lacks cell wall

3. Bacillus – (iii) Spore-forming

4. Pseudomonas – (iv) Gram-negative aerobic

Options:

(A) 1-ii, 2-i, 3-iii, 4-iv

(B) 1-i, 2-ii, 3-iii, 4-iv

(C) 1-iii, 2-i, 3-ii, 4-iv

(D) 1-ii, 2-iv, 3-iii, 4-i

Explanation:

Correct matching: Mycoplasma – lacks cell wall, Nostoc – photosynthetic, Bacillus – spore-forming, Pseudomonas – Gram-negative aerobic. (Answer: A)

9) Fill in the Blanks MCQ:

Mycoplasma are the smallest living cells without _________ and can survive without oxygen.

(A) Nucleus

(B) Cell wall

(C) Ribosomes

(D) DNA

Explanation:

< b>Mycoplasma lack a cell wall, have minimal size, and can survive anaerobically, making them distinct among bacteria. (Answer: B)

10) Choose the correct statements MCQ:

1. Mycoplasma lack cell wall.

2. Bacillus is spore-forming.

3. Nostoc is photosynthetic.

4. Pseudomonas is obligate anaerobe.

Options:

(A) 1, 2, 3

(B) 2, 3, 4

(C) 1, 3, 4

(D) 1, 2, 4

Explanation:

Statements 1, 2, 3 are correct. Pseudomonas is an obligate aerobe, not anaerobe. Mycoplasma is unique for lacking cell wall, Bacillus forms spores, Nostoc performs photosynthesis. (Answer: A)

Chapter: Microbiology

Topic: Extremophiles and Bacterial Diversity

Subtopic: Archaebacteria and Environmental Adaptations

Keyword Definitions:

• Extremophiles – Organisms thriving in extreme environmental conditions like high salinity, temperature, or pH.

• Archaebacteria – Prokaryotic microorganisms often found in extreme environments, distinct from eubacteria.

• Halophiles – Organisms adapted to high-salt environments.

• Mycobacteria – Actinobacteria, some pathogenic, typically not halophilic.

• Cyanobacteria – Photosynthetic bacteria, mostly freshwater or marine.

• Eubacteria – True bacteria, wide range of habitats, not all extremophiles.

• Clinical relevance – Studying extremophiles aids biotechnology, industrial enzymes, and understanding microbial survival.

Lead Question – 2017:

Which of the following are found in extreme saline conditions ?

(A) Mycobacteria

(B) Archaebacteria

(C) Eubacteria

(D) Cyanobacteria

Explanation:

Archaebacteria, particularly halophilic archaea, thrive in extreme saline conditions like salt lakes and salt pans. Mycobacteria, eubacteria, and cyanobacteria generally inhabit normal or moderately saline environments. Halophiles possess specialized adaptations for osmotic balance and protein stability, making archaebacteria ideal models for extremophile studies. (Answer: B)

1) Which archaebacteria are halophilic?

(A) Methanogens

(B) Halophiles

(C) Thermoacidophiles

(D) Cyanobacteria

Explanation:

Halophiles are archaebacteria adapted to high-salt environments, maintaining osmotic balance using compatible solutes and specialized proteins. Methanogens produce methane, thermoacidophiles tolerate heat and acidity, while cyanobacteria are photosynthetic. Understanding halophiles aids biotechnology, saline agriculture, and enzyme research. (Answer: B)

2) Extremophiles that produce methane belong to:

(A) Halophiles

(B) Methanogens

(C) Thermoacidophiles

(D) Mycobacteria

Explanation:

Methanogens are archaebacteria that generate methane in anaerobic environments. They are extremophiles but not halophilic. Halophiles tolerate high salinity. Extremophiles’ study informs renewable energy, waste treatment, and microbial ecology. (Answer: B)

3) Which organism is photosynthetic but rarely halophilic?

(A) Cyanobacteria

(B) Halophiles

(C) Archaebacteria

(D) Methanogens

Explanation:

Cyanobacteria are photosynthetic bacteria, usually in freshwater or marine habitats. Only few tolerate moderate salinity; extreme halophilic cyanobacteria are rare. Halophilic archaebacteria are specialized for high salt. Cyanobacteria contribute to oxygen production and nitrogen fixation. (Answer: A)

4) Clinical/biotechnological relevance of halophiles:

(A) Enzyme production

(B) Salt-tolerant crops

(C) Osmoprotectant studies

(D) All of the above

Explanation:

Halophiles produce salt-tolerant enzymes, compatible solutes, and osmoprotectants. They inform biotechnology, industrial processes, and saline agriculture. Their study enhances understanding of microbial adaptation in extreme environments and can lead to novel bioproducts. (Answer: D)

5) Which group can survive in salt-saturated ponds?

(A) Mycobacteria

(B) Halophilic archaebacteria

(C) Eubacteria

(D) Cyanobacteria

Explanation:

Halophilic archaebacteria survive in salt-saturated ponds due to osmotic adaptation and stable proteins. Eubacteria, mycobacteria, and cyanobacteria are less tolerant of extreme salinity. Studying halophiles helps understand microbial ecology and extremophile adaptations. (Answer: B)

6) Adaptation mechanism in halophiles:

(A) Osmotic balance using compatible solutes

(B) Thick peptidoglycan

(C) Spore formation

(D) Photosynthesis

Explanation:

Halophiles maintain osmotic balance with compatible solutes like potassium ions and organic molecules. Thick peptidoglycan and spores are structural or survival features in other bacteria. Photosynthesis is not a primary halophilic adaptation. These strategies prevent desiccation and protein denaturation in extreme saline habitats. (Answer: A)

7) Assertion-Reason type:

Assertion (A): Archaebacteria are found in extreme saline conditions.

Reason (R): They have specialized osmotic adaptations and salt-tolerant proteins.

(A) Both A and R are true, and R is the correct explanation of A

(B) Both A and R are true, but R is not the correct explanation

(C) A is true, R is false

(D) A is false, R is true

Explanation:

Both assertion and reason are correct; halophilic archaebacteria survive high salinity due to specialized osmotic adaptations and salt-stable proteins. This enables them to thrive in extreme saline habitats like salt lakes and salt pans. (Answer: A)

8) Matching type:

Match bacteria with environment:

(A) Halophiles – (i) Salt lakes

(B) Thermoacidophiles – (ii) Hot acidic springs

(C) Methanogens – (iii) Anaerobic mud

(D) Cyanobacteria – (iv) Freshwater/marine

Options:

(A) A-i, B-ii, C-iii, D-iv

(B) A-ii, B-i, C-iv, D-iii

(C) A-iii, B-iv, C-i, D-ii

(D) A-iv, B-iii, C-ii, D-i

Explanation:

Correct matches: Halophiles – salt lakes, Thermoacidophiles – hot acidic springs, Methanogens – anaerobic mud, Cyanobacteria – freshwater/marine. These adaptations allow survival in extreme conditions, aiding biotechnological and ecological studies. (Answer: A)

9) Fill in the blanks:

_______ are extremophiles that thrive in high-salt environments.

(A) Halophiles

(B) Methanogens

(C) Cyanobacteria

(D) Eubacteria

Explanation:

Halophiles, mostly archaebacteria, thrive in high-salt environments due to osmotic adaptations and salt-stable proteins. They are models for extremophile research and industrial enzyme applications. Other bacteria may tolerate mild salinity but not extreme levels. (Answer: A)

10) Choose the correct statements:

1. Archaebacteria include halophiles and methanogens.

2. Halophiles survive in extreme saline conditions.

3. Cyanobacteria are mostly freshwater or marine.

4. Mycobacteria are extreme halophiles.

(A) 1, 2, 3 only

(B) 2, 3, 4 only

(C) 1, 3, 4 only

(D) All are correct

Explanation:

Statements 1, 2, and 3 are correct. Statement 4 is false; Mycobacteria are not extreme halophiles. Recognizing extremophiles and their habitats is essential for microbial ecology, industrial applications, and biotechnological research. (Answer: A)