Q.78 Which option(s) correctly match(es) the structures in a bacterial cell (Column I) with their corresponding functions (Column II).

Correct matches are: P – i, Q – ii, R – iii, and S – iv, so the correct option is (A).​

Question breakdown

Column I (structures) and Column II (functions):

• P. Cell wall → i. Protection from osmotic stress

• Q. Fimbriae → ii. Attachment to surfaces

• R. Flagella → iii. Motility

• S. Pili → iv. Transfer of genetic material

These are standard roles of bacterial surface structures in textbooks and competitive-exam syllabi.​

Why each match is correct

P. Cell wall – i. Protection from osmotic stress

• The bacterial cell wall is a rigid peptidoglycan-containing structure that provides mechanical strength and maintains cell shape.​

• Its rigidity prevents cell lysis when internal osmotic pressure exceeds that of the environment, giving protection from osmotic stress.​

Q. Fimbriae – ii. Attachment to surfaces

• Fimbriae are short, thin, hair-like appendages present in large numbers on many bacteria.​

• Their adhesive tips help bacteria attach to host tissues, abiotic surfaces, or other cells, playing a key role in colonisation and biofilm formation.​

R. Flagella – iii. Motility

• Flagella are long, whip-like helical filaments that rotate like propellers.​

• They enable motility, allowing bacteria to swim towards nutrients and away from harmful conditions (chemotaxis).​

S. Pili – iv. Transfer of genetic material

• Pili (especially sex pili) are longer, thicker appendages, usually 1–10 per cell, encoded by conjugative plasmids.​

• Sex pili form a conjugation bridge between donor and recipient bacteria, enabling transfer of genetic material such as plasmid DNA.​

Why other options are incorrect

• Option (B): P – i (correct); Q – iii (incorrect, fimbriae are mainly for attachment, not primary motility); R – iii (correct); S – iv (correct).​

• Option (C): P – i (correct); Q – iv (incorrect, fimbriae are not the main structures for genetic transfer); R – ii (incorrect, flagella do not mediate surface attachment as their primary role); S – iii (incorrect, pili are not the chief motility organelles).​

• Option (D): P – ii (incorrect, cell wall’s main role is structural and osmotic protection, not specific attachment); Q – iv (incorrect); R – i (incorrect); S – iii (incorrect).​

Introduction

Understanding bacterial cell wall, fimbriae, flagella and pili functions is essential for mastering microbiology questions in CSIR NET, NEET and other competitive exams. These external structures determine bacterial survival, motility, adhesion and gene transfer, and they frequently appear in matching-type MCQs.​

Bacterial cell wall function

• The bacterial cell wall is a rigid structure surrounding the cytoplasmic membrane, primarily composed of peptidoglycan in most species.​

• Its major role is to protect the cell from osmotic rupture and mechanical damage, thereby maintaining cell shape and integrity in varying environments.​

Fimbriae function

• Fimbriae are numerous, short, fine, hair-like projections on the bacterial surface composed of pilin protein.​

• They bear adhesins that allow specific attachment to host tissues or abiotic surfaces, aiding colonisation, biofilm formation and virulence.​

Flagella function

• Flagella are long helical filaments anchored in the cell envelope, capable of rapid rotation driven by a basal motor.​

• Their rotation propels the bacterium, providing motility and enabling chemotaxis towards nutrients or away from toxic substances.​

Pili function

• Pili are relatively long, sparse proteinaceous appendages; sex pili are encoded by conjugative plasmids such as the F plasmid in Escherichia coli.​

• Sex pili connect donor and recipient cells to form a conjugation bridge, mediating the transfer of plasmid DNA and other genes, including antibiotic resistance determinants.​

This conceptual clarity directly answers the given MCQ: the correctly matched option is (A) P – i; Q – ii; R – iii; S – iv.​