Prokaryotic Cell Structure Practice Questions
20 free Prokaryotic Cell Structure practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following represents the smallest living cells that lack a cell wall and can survive without oxygen?
- A Bacillus
- B Mycoplasma
- C Nostoc
- D Vibrio
Correct answer: Mycoplasma
Mycoplasmas are the smallest known living cells (about 0.3 micrometers). They are unique among prokaryotes because they completely lack a cell wall and are pathogenic to many animals and plants.
The genomic DNA of a bacterium is typically a single chromosome that is circular. Many bacteria also have smaller circular DNA outside the genomic DNA called:
- A Nucleoid
- B Plasmid
- C Mesosome
- D Episome
Correct answer: Plasmid
Plasmids are small, extrachromosomal, self-replicating circular DNA molecules. They often carry specific phenotypic characters such as resistance to antibiotics.
What is the correct sequence of the layers of a typical bacterial cell envelope from outermost to innermost?
- A Cell wall -> Glycocalyx -> Plasma membrane
- B Plasma membrane -> Cell wall -> Glycocalyx
- C Glycocalyx -> Cell wall -> Plasma membrane
- D Glycocalyx -> Plasma membrane -> Cell wall
Correct answer: Glycocalyx -> Cell wall -> Plasma membrane
Most prokaryotic cells have a chemically complex cell envelope consisting of three tightly bound layers: the outermost glycocalyx, followed by the cell wall, and then the plasma membrane.
A specialized differentiated form of cell membrane that is the characteristic of prokaryotes is the:
- A Plasmid
- B Mesosome
- C Nucleoid
- D Ribosome
Correct answer: Mesosome
Mesosomes are extensions of the plasma membrane into the cell in the form of vesicles, tubules, or lamellae. They help in cell wall formation, DNA replication, and respiration.
In some bacteria, the glycocalyx is a loose sheath called the ______, while in others it is thick and tough called the ______.
- A Capsule; Slime layer
- B Slime layer; Capsule
- C Cell wall; Capsule
- D Slime layer; Mesosome
Correct answer: Slime layer; Capsule
The glycocalyx differs in composition and thickness among bacteria. A loose sheath is called the slime layer, whereas a thick and tough layer is called a capsule.
Bacterial flagellum is composed of three parts. Which of the following is the longest portion?
- A Hook
- B Basal body
- C Filament
- D Pili
Correct answer: Filament
The bacterial flagellum consists of a basal body, a hook, and a filament. The filament is the longest portion and extends from the cell surface to the outside.
Which surface structures of bacteria do not play a role in motility but help in attachment to rocks or host tissues?
- A Pili and fimbriae
- B Flagella and fimbriae
- C Pili and mesosomes
- D Flagella and pili
Correct answer: Pili and fimbriae
Pili and fimbriae are surface structures that do not contribute to motility. Fimbriae are small bristle-like fibers used for attachment, while pili are elongated tubular structures used for conjugation.
The ribosomes of prokaryotes are of the 70S type. What are the two subunits of these ribosomes?
- A 60S and 40S
- B 50S and 30S
- C 50S and 20S
- D 40S and 30S
Correct answer: 50S and 30S
Prokaryotic ribosomes are about 15 nm by 20 nm in size. They are made of two subunits, 50S and 30S, which together form the 70S prokaryotic ribosome.
Several ribosomes may attach to a single mRNA and form a chain called:
- A Polyribosome
- B Mesosome
- C Inclusion body
- D Centrosome
Correct answer: Polyribosome
A polysome (polyribosome) consists of several ribosomes attached to a single mRNA strand. The ribosomes translate the mRNA simultaneously to produce multiple protein copies.
Reserve material in prokaryotic cells is stored in the cytoplasm in the form of:
- A Membrane vacuoles
- B Inclusion bodies
- C Mesosome vesicles
- D Nucleoid granules
Correct answer: Inclusion bodies
Inclusion bodies are not bound by any membrane system and lie free in the cytoplasm. Examples include phosphate granules, cyanophycean granules, and glycogen granules.
Gas vacuoles are found in which of the following organisms?
- A Green and purple photosynthetic bacteria
- B Mycoplasma and spirochetes only
- C Higher plants and mosses only
- D Decomposing saprophytic fungi
Correct answer: Green and purple photosynthetic bacteria
Gas vacuoles provide buoyancy to certain prokaryotes. They are commonly found in blue-green, purple, and green photosynthetic bacteria.
Which structure in prokaryotes is functionally similar to the mitochondria of eukaryotes?
- A Ribosome
- B Mesosome
- C Glycocalyx
- D Plasmid
Correct answer: Mesosome
Mesosomes increase the surface area of the plasma membrane and enzymatic content. They are involved in respiration and secretion, performing functions similar to eukaryotic mitochondria.
Bacteria are classified into Gram-positive and Gram-negative based on:
- A Fimbriae
- B Sex pili
- C Flagella
- D Mesosomes
Correct answer: Sex pili
Sex pili are specialized elongated tubular structures made of a protein called pilin. They facilitate the process of conjugation, which involves the transfer of DNA between bacteria.
The plasma membrane of a prokaryotic cell is best described as:
- A Selectively permeable, as in eukaryotes
- B Made of peptidoglycan rather than lipid
- C Absent in all Gram-negative bacteria types
- D Freely permeable to every dissolved molecule
Correct answer: Selectively permeable, as in eukaryotes
The plasma membrane of prokaryotes is a selectively permeable lipid bilayer that regulates the entry and exit of molecules. Structurally, it is very similar to the plasma membrane found in eukaryotes.
The 'S' in 70S ribosome stands for:
- A Small unit
- B Svedberg's unit
- C Structural unit
- D Solubility coefficient
Correct answer: Svedberg's unit
The S stands for Svedberg's unit, which is the sedimentation coefficient. It is indirectly a measure of density and size determined by the rate of sedimentation in an ultracentrifuge.
What is the primary function of the bacterial cell wall?
- A Their mode of reproduction
- B Their cell wall properties and response to Gram staining
- C Their shape and size
- D The presence or absence of flagella
Correct answer: Their cell wall properties and response to Gram staining
Christian Gram developed a staining method that differentiates bacteria based on their cell wall properties. Gram-positive bacteria retain the stain, while Gram-negative bacteria do not.
Which of the following prokaryotic structures is used for 'mating' or exchange of genetic material?
- A Mesosome folds
- B Chromatophores
- C Leucoplasts
- D Chloroplasts
Correct answer: Chromatophores
Chromatophores are internal membrane systems in photosynthetic prokaryotes like cyanobacteria. They contain photosynthetic pigments necessary for capturing light energy.
The plasma membrane of prokaryotes is:
- A Maintaining cell shape and preventing osmotic lysis
- B Carrying out protein synthesis
- C Storing reserve food materials
- D Providing resistance to antibiotics
Correct answer: Maintaining cell shape and preventing osmotic lysis
The cell wall provides strong structural support to the bacterium. It maintains the cell's shape and prevents it from collapsing or bursting (lysis) in a hypotonic medium.
A comma-shaped bacterium is known as:
- A Coccus
- B Bacillus
- C Vibrio
- D Spirillum
Correct answer: Vibrio
Bacteria are categorized by shape: spherical (Coccus), rod-shaped (Bacillus), comma-shaped (Vibrio), and spiral-shaped (Spirillum).
Which of the following lacks a membrane-bound nucleus and organelles?
- A Streptococcus
- B Saccharomyces
- C Chlamydomonas
- D Amoeba
Correct answer: Streptococcus
Streptococcus is a bacterium (prokaryote) and therefore lacks a nuclear envelope and membrane-bound organelles. The others listed are eukaryotes (fungi, algae, and protozoa).