Prokaryotic cell Questions in English

(B) Prokaryotic cells lack a well-defined nucleus and are characterized by the absence of a nuclear membrane surrounding their genetic material.
In contrast,eukaryotic cells possess a well-organized nucleus enclosed by a distinct nuclear membrane.

(A) In prokaryotic cells,such as bacteria,the plasma membrane undergoes special modifications to form extensions called mesosomes.
These extensions are formed by the invagination of the plasma membrane into the cell.
Mesosomes can be in the form of vesicles,tubules,and lamellae.
They play crucial roles in cell wall formation,$DNA$ replication,and distribution to daughter cells,as well as in respiration and secretion processes.

(B) The correct answer is $B$. Pili are elongated tubular structures made of a special protein called pilin. They are primarily involved in the attachment of bacteria to surfaces or to other bacteria (conjugation),rather than reproduction itself. While they play a role in the transfer of genetic material during conjugation,they are not reproductive organs. Glycocalyx,cell wall,and the classification of flagella,pili,and fimbriae as surface structures are all correctly described.

(A) Statement $(i)$ is correct: Mesosomes are indeed infoldings or extensions of the plasma membrane into the cell.
Statement $(ii)$ is correct: Pili are elongated tubular structures made of a special protein called pilin.
Statement $(iii)$ is correct: The bacterial flagellum consists of three parts: filament,hook,and basal body.
Statement $(iv)$ is incorrect: Ribosomes in prokaryotes are $70S$ type,and their size is approximately $15 \; nm$ by $20 \; nm$,not $30 \; nm$ by $50 \; nm$.
Therefore,statements $(i), (ii),$ and $(iii)$ are correct.

(C) Statement $(i)$ is correct: The glycocalyx is the outermost layer of the bacterial cell envelope.
Statement $(ii)$ is incorrect: $A$ loose sheath of glycocalyx is called a slime layer,not a capsule.
Statement $(iii)$ is incorrect: $A$ thick and tough layer of glycocalyx is called a capsule,not a slime layer.
Statement $(iv)$ is correct: Mesosomes are specialized membranous structures formed by the extensions of the plasma membrane into the cell.
Statement $(v)$ is correct: Fimbriae are small bristle-like fibers sprouting out of the cell that help bacteria attach to rocks in streams and also to host tissues.
Therefore,statements $(ii)$ and $(iii)$ are wrong.

(A) $Plasmid$ is a small, circular, double-stranded $DNA$ molecule that is distinct from a cell's chromosomal $DNA$. It is primarily found in prokaryotic cells, such as bacteria. While most eukaryotes lack plasmids, $Saccharomyces \text{ } cerevisiae$ (yeast) is a notable exception that contains them. Nuclei, mitochondria, and ribosomes are found in eukaryotic cells, and ribosomes are also present in prokaryotes.

(A) The genomic $DNA$ of a bacterium is typically a single,circular,double-stranded molecule. Unlike eukaryotic cells,which have linear chromosomes contained within a nucleus,the bacterial genome is not enclosed in a membrane-bound nucleus and exists as a closed loop,often referred to as the nucleoid.

(C) In prokaryotic cells,the genetic material is not enclosed by a nuclear envelope. This region containing the genetic material is referred to as the $Nucleoid$.

(B) The prokaryotic flagellum is composed of three main parts: the filament,the hook,and the basal body.
$1$. The filament is the long,tubular structure that extends from the cell surface.
$2$. The hook is a curved structure that connects the filament to the basal body.
$3$. The basal body is a complex structure embedded in the cell envelope that acts as a motor.
Centrioles are microtubule-based structures found in eukaryotic cells,typically involved in spindle formation during cell division,and are not part of the prokaryotic flagellum.

(D) Fimbriae are small bristle-like fibres sprouting out of the bacterial cell. They are known to help attach bacteria to rocks in streams and also to the host tissues.
$Pili$ are elongated tubular structures made of a special protein called $pilin$.
$Mesosomes$ are infoldings of the plasma membrane into the cell,which help in respiration,secretion,and $DNA$ replication.
$Cilia$ are fine hair-like outgrowths of the cell membrane,primarily found in eukaryotic cells.

(D) The features associated with a prokaryotic cell are:
$1$. Gas vacuole: Present in many prokaryotes.
$2$. Single envelope system: Prokaryotes typically have a single envelope system (cell wall and plasma membrane).
$3$. Non-cellulosic wall: Prokaryotic cell walls are made of peptidoglycan,not cellulose.
Features like cytoskeleton,microfilaments,cytoplasmic streaming,and the presence of membrane-bound cell organelles are characteristic of eukaryotic cells.
Therefore,there are $3$ features associated with a prokaryotic cell.

(B) In the given diagram of a dividing bacterium:
$P$ points to the outermost protective layer,which is the Cell wall.
$Q$ points to the layer just inside the cell wall,which is the Cell membrane.
$R$ points to the central genetic material,which is the bacterial $DNA$ (nucleoid).
Therefore,the correct sequence is Cell wall,Cell membrane,and $DNA$.

(A) The statement in option $A$ is incorrect because viruses are not considered cells. They are acellular entities that lack the cellular machinery required for independent life and reproduction,thus they are not classified as prokaryotic cells. Prokaryotic cells include bacteria,blue-green algae,mycoplasma,and $PPLO$. Options $B$,$C$,and $D$ are correct characteristics of prokaryotic cells: they are smaller,divide faster,and exhibit four basic shapes (bacillus,coccus,vibrio,and spirillum).

(A) Prokaryotic cells (such as bacteria,blue-green algae,mycoplasma,and $PPLO$) represent a group of organisms that share a fundamentally similar organization,despite showing wide variations in shape and function.
They lack a well-defined nucleus and membrane-bound organelles.
Therefore,the statement that they have a fundamentally similar organization is correct.

(D) Bacteria often contain small,circular,double-stranded $DNA$ molecules that are distinct from their chromosomal $DNA$.
These molecules are known as plasmids.
Plasmids are extra-chromosomal and can replicate independently within the bacterial cell.
They often carry genes that provide advantages,such as antibiotic resistance.

(C) Mesosomes are specialized membranous structures formed by the extensions of the plasma membrane into the cell in the form of vesicles,tubules,and lamellae. These extensions are essentially infoldings of the plasma membrane in prokaryotic cells.

(A) In prokaryotic cells,specifically bacteria,the cell envelope consists of a tightly linked three-layered structure.
From the outermost layer to the innermost layer,the sequence is as follows:
$1$. Glycocalyx (outermost layer).
$2$. Cell wall (middle layer).
$3$. Plasma membrane (innermost layer).
Therefore,the correct sequence from outside to inside is Glycocalyx $\rightarrow$ Cell wall $\rightarrow$ Plasma membrane.

(A) In prokaryotic cells, the glycocalyx is an outer envelope that varies in composition and thickness.
$1$. When the glycocalyx is loose and sheath-like, it is known as the $\text{Slime layer}$.
$2$. When the glycocalyx is thick and tough, it is known as the $\text{Capsule}$.
Therefore, $P$ corresponds to the $\text{Slime layer}$ and $Q$ corresponds to the $\text{Capsule}$.

(B) Mesosomes are characteristic structures found in prokaryotic cells,specifically bacteria.
$1.$ They are formed by the extensions of the plasma membrane into the cell,not the cell wall. Thus,statement $II$ is incorrect.
$2.$ They exist in the form of vesicles,tubules,and lamellae. Thus,statement $I$ is correct.
$3.$ They help in increasing the surface area of the plasma membrane,which in turn helps in enzymatic content increase and metabolic activities. Thus,statement $III$ is correct.
$4.$ They are involved in cell wall formation,$DNA$ replication,distribution to daughter cells,respiration,and secretion processes. Thus,statement $IV$ is correct.
Therefore,statements $I, III,$ and $IV$ are correct.

(B) Inclusion bodies are reserve materials in prokaryotic cells which are stored in the cytoplasm in the form of particles.
These are not bound by any membrane system and lie free in the cytoplasm.
Examples include phosphate granules,cyanophycean granules,and glycogen granules.
Therefore,the statement that they are membrane-bound organelles is incorrect.

(C) In bacteria,$Mesosomes$ are specialized membranous structures formed by the extensions of the plasma membrane into the cell. These extensions are in the form of vesicles,tubules,and lamellae. $Mesosomes$ play a crucial role in cell wall formation,$DNA$ replication,and distribution to daughter cells. They also help in respiration,secretion processes,and increasing the surface area of the plasma membrane and enzymatic content. Therefore,they are essential for cell division in prokaryotes like bacteria.

(D) In prokaryotic cells,such as bacteria,the genetic material is not enclosed within a nuclear membrane.
Instead,the $DNA$ is organized in large loops and held by proteins in a specific region of the cytoplasm known as the nucleoid.
Therefore,all the given statements correctly describe the nucleoid.

(A) In prokaryotic cells,the plasma membrane undergoes infoldings to form specialised structures called $Mesosomes$.
These structures are formed by the extensions of the plasma membrane into the cell in the form of vesicles,tubules,and lamellae.
$Mesosomes$ play a crucial role in various cellular processes,including cell wall formation,$\text{DNA}$ replication,and the distribution of daughter cells.
They also help in respiration,secretion processes,and increasing the surface area of the plasma membrane for enzymatic content.

(D) Inclusion bodies.
In prokaryotic cells,reserve materials are stored in the cytoplasm in the form of inclusion bodies. These are not bound by any membrane system and lie free in the cytoplasm. Examples include phosphate granules,cyanophycean granules,and glycogen granules.

(A) The correct answer is $A$.
$A$ bacterial flagellum is composed of three distinct parts:
$1$. The basal body: This is the structure that anchors the flagellum into the cell wall and plasma membrane.
$2$. The hook: This is a curved structure that connects the basal body to the filament.
$3$. The filament: This is the longest portion that extends from the cell surface into the surrounding medium and is responsible for bacterial motility.

(A) The correct answer is $A$ (capsule).
$Glycocalyx$ varies in composition and thickness among different bacteria.
If the $glycocalyx$ is loose and thin,it is known as the $slime$ $layer$.
If the $glycocalyx$ is thick and tough,it is known as the $capsule$.

(A) The correct statement is $A$.
Prokaryotes are unicellular organisms that lack membrane-bound cell organelles such as mitochondria,chloroplasts,and the endoplasmic reticulum.
Option $B$ is incorrect because prokaryotic cells lack a true nucleus.
Option $C$ is incorrect because cells arise from pre-existing cells (Omnis cellula-e cellula).
Option $D$ is incorrect because animal cells lack a cell wall.