Question 2

   Question: A specialised membranous structure in a prokaryotic cell which helps in cell well wall formation, DNA replication and respiration is

   Options: 

       A. Cristae

       B. Endoplasmic Reticulum

       C. Mesosome

       D. Chromatophores

   Correct Answer: C

   Year: NEET 2025

   Solution: The correct answer is Mesosome (Option C). Key points about mesosomes in prokaryotes: They are infoldings of the plasma membrane. They house enzymes and machinery for: Cell-wall synthesis, DNA replication and segregation, and Respiratory processes (electron transport). No other prokaryotic structure (cristae, ER or chromatophores) performs all three functions together.

   Step Solution: 

    1.  Identify the cell type: The question specifies a prokaryotic cell.

    2.  Eliminate eukaryotic structures: Cristae and Endoplasmic Reticulum are membrane-bound organelles found only in eukaryotes.

    3.  Analyze remaining options: Chromatophores are used for photosynthesis, while mesosomes are general-purpose membrane extensions.

    4.  Match functions: Mesosomes are specifically documented to assist in cell wall synthesis, DNA replication, and respiration.

    5.  Select correct term: Mesosome is the specialized membranous structure described.

   Difficulty Level: Easy

   The Concept Name: Mesosome Functions

   Short cut solution: Prokaryote + Respiration/Replication = Mesosome.

Question 6

   Question: Mesosome in a cell is a :

   Options: 

       A. Membrane bound vesicular structure

       B. Chain of many ribosomes attached to a single mRNA

       C. Special structure formed by extension of plasma membrane

       D. Medium sized chromosome

   Correct Answer: C

   Year: [NEET 2024 Re]

   Solution: Mesosomes are formed by the extensions of plasma membrane into the cell. Lysosomes are membrane bound vesicular structures (incorrect). Several ribosomes may attach to a single mRNA and form a chain called polyribosomes (incorrect).

   Step Solution: 

    1.  Define Mesosome: It is a structural component of the bacterial cell envelope.

    2.  Analyze origin: It originates directly from the plasma membrane.

    3.  Determine structure type: It is formed by the extension or invagination of that membrane into the cytoplasm.

    4.  Eliminate decoys: It is not a ribosome chain (polyribosome) nor is it a chromosome.

    5.  Conclusion: Option C accurately describes its formation.

   Difficulty Level: Easy

   The Concept Name: Bacterial Cell Structure

   Short cut solution: Mesosome = Plasma membrane extension.

Question 18

   Question: Given below are two statements: 

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

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

   Options: 

       A. Statement I is correct but Statement II is incorrect.

       B. Statement I is incorrect but Statement II is correct.

       C. Both Statement I and Statement II are correct.

       D. Both Statement I and Statement II are incorrect.

   Correct Answer: C

   Year: [NEET 2023 mpr]

   Solution: Statement I: In bacteria, the mesosomes are indeed formed by the extensions of the plasma membrane into the cytoplasm. Statement II: Mesosomes in bacteria are thought to assist in several cellular processes including DNA replication, distribution of DNA during cell division, respiration, and cell wall formation. Hence, both are correct.

   Step Solution: 

    1.  Verify Statement I: Confirm if mesosomes are plasma membrane extensions (True).

    2.  Verify Statement II: Confirm if they assist in DNA replication and cell wall synthesis (True).

    3.  Evaluate consistency: Both statements align with established prokaryotic biology.

    4.  Select option: Option C represents "Both correct."

   Difficulty Level: Easy

   The Concept Name: Mesosome Properties

   Short cut solution: Both structure and function statements are standard textbook definitions for mesosomes.

Question 35

   Question: Select the wrong statement.

   Options: 

       A. Bacterial cell wall is made up of peptidoglycan.

       B. Pili and fimbriae are mainly involved in motility of bacterial cells.

       C. Cyanobacteria lack flagellated cells.

       D. Mycoplasma is a wall-less microorganism.

   Correct Answer: B

   Year: NEET II 2016

   Solution: (b) : Pili and fimbriae are bacterial appendages which are not involved in locomotion. Actually, pili are long outgrowths helpful in attaching to recipient cells for conjugation. Fimbriae are small bristle-like fibers involved in attaching bacteria to solid surfaces.

   Step Solution: 

    1.  Evaluate A: Bacterial walls typically contain peptidoglycan (True).

    2.  Evaluate B: Determine the function of pili/fimbriae. They are for attachment/conjugation, not motility (False).

    3.  Evaluate C: Cyanobacteria do not possess flagella (True).

    4.  Evaluate D: Mycoplasma is famous for lacking a cell wall (True).

    5.  Identify "Wrong": Statement B is the only incorrect fact.

   Difficulty Level: Medium

   The Concept Name: Bacterial Appendages

   Short cut solution: Motility in bacteria = Flagella. Pili/Fimbriae = Attachment.

Question 41

   Question: Which of the following structures is not found in a prokaryotic cell?

   Options: 

       A. Mesosome

       B. Plasma membrane

       C. Nuclear envelope

       D. Ribosome

   Correct Answer: C

   Year: NEET 2015

   Solution: (c) : A prokaryotic cell is characterised by absence of an organised nucleus and membrane bound cell organelles. DNA is naked i.e., without a nuclear envelope and lies variously coiled in the cytoplasm.

   Step Solution: 

    1.  Define Prokaryote: Organisms lacking a membrane-bound nucleus.

    2.  Analyze Option C: A "nuclear envelope" is the membrane that creates a nucleus.

    3.  Compare: If a cell has no membrane-bound nucleus, it cannot have a nuclear envelope.

    4.  Confirm A, B, D: Mesosomes, membranes, and 70S ribosomes are standard prokaryotic features.

    5.  Select C: Correct answer for "not found."

   Difficulty Level: Easy

   The Concept Name: Prokaryotic Cell Characteristics

   Short cut solution: Prokaryote = No Nucleus = No Nuclear Envelope.

Question 56

   Question: The term 'glycocalyx' is used for

   Options: 

       A. a layer present between cell wall and membrane of bacteria

       B. cell wall of bacteria

       C. bacterial cell glyco-engineered to possess N-glycosylated proteins

       D. a layer surrounding the cell wall of bacteria.

   Correct Answer: D

   Year: KN NEET 2013

   Solution: (d) : Glycocalyx is a sticky, gelatinous material that collects outside the cell wall of bacteria to form an additional surface layer. When firmly attached, it is a capsule; when loose, it is a slime layer.

   Step Solution: 

    1.  Locate Glycocalyx: It is the outermost component of the bacterial cell envelope.

    2.  Identify position: It sits outside the cell wall.

    3.  Determine composition: It is often a sticky or gelatinous layer.

    4.  Verify options: Option D correctly describes its position relative to the cell wall.

   Difficulty Level: Easy

   The Concept Name: Bacterial Cell Envelope

   Short cut solution: Glycocalyx = Outermost coating (Capsule/Slime layer).

Question 113

   Question: The prokaryotic flagella possess

   Options: 

       A. helically arranged protein molecule

       B. " 9 + 2 " membrane enclosed structure

       C. unit membrane enclosed fibre

       D. protein membrane enclosed fibre

   Correct Answer: A

   Year: 1995

   Solution: (a) : Prokaryotic flagellum is not surrounded by any membrane. It consists of a single thread made of numerous identical spherical protein sub-units called flagellin. These sub-units are arranged in helical spirals to form a hollow cylinder.

   Step Solution: 

    1.  Recall structure: Prokaryotic flagella are simple and lack a membrane.

    2.  Contrast with eukaryotes: Eukaryotic flagella have a "9+2" microtubule arrangement (Eliminate B).

    3.  Identify the protein: Bacteria use "flagellin" protein.

    4.  Analyze arrangement: These protein subunits are organized into helical spirals.

    5.  Match: Option A matches this structural description.

   Difficulty Level: Hard

   The Concept Name: Prokaryotic Flagella Structure

   Short cut solution: Prokaryote flagella = Naked helical flagellin. Eukaryote = 9+2 tubulin.

Question 125

   Question: Golgi apparatus is absent in

   Options: 

       A. higher plants

       B. yeast

       C. bacteria and blue-green algae

       D. none

   Correct Answer: C

   Year: 1993

   Solution: (c) : Golgi apparatus is absent in bacteria and blue-green algae (prokaryotes). It is generally absent in prokaryotic cells and present in eukaryotic cells.

   Step Solution: 

    1.  Categorize Golgi: It is a membrane-bound organelle.

    2.  Apply general rule: Prokaryotes lack membrane-bound organelles.

    3.  Identify Prokaryotes: Bacteria and blue-green algae are prokaryotic.

    4.  Identify Eukaryotes: Yeast and higher plants are eukaryotic (and thus have Golgi).

    5.  Select C: The groups where it is absent.

   Difficulty Level: Easy

   The Concept Name: Absence of Organelles in Prokaryotes

   Short cut solution: Prokaryote = No membrane-bound organelles (No Golgi/Mito/ER).