Prokaryotic cell Questions in English

(B) In bacteria,the plasma membrane forms specialized invaginations known as $Mesosomes$.
These structures are rich in respiratory enzymes and are the primary sites for aerobic respiration,as bacteria lack mitochondria.

(B) $Escherichia$ $coli$ ($E.$ $coli$) is a prokaryotic organism.
Prokaryotes lack a well-defined,membrane-bound nucleus.
They possess a single,circular,double-stranded $DNA$ molecule that acts as their chromosome.
Therefore,the presence of one chromosome (which is essentially one $DNA$ molecule) is the correct characteristic among the given options.

(A) Bacteria are prokaryotic organisms. Prokaryotes lack membrane-bound cell organelles such as the endoplasmic reticulum,mitochondria,Golgi apparatus,and a well-defined nucleus. They only contain $70S$ ribosomes as non-membrane-bound organelles. Therefore,the endoplasmic reticulum is not found in bacteria.

(C) Bacteria are prokaryotic organisms,meaning they lack a well-defined nucleus and membrane-bound organelles.
Their genetic material consists of a single,circular,double-stranded $DNA$ molecule,which is not enclosed by a nuclear envelope.
Unlike eukaryotic cells,bacterial $DNA$ is not associated with histone proteins.
Therefore,the nuclear material,often referred to as the nucleoid or genophore,consists only of nucleic acid $(DNA)$.

(C) $genophore$ is the genetic material of a prokaryotic organism. Unlike eukaryotic cells,prokaryotes do not have a membrane-bound nucleus. Their genetic material consists of a single,circular,double-stranded $DNA$ molecule,which is often referred to as a $genophore$ or bacterial chromosome. Therefore,bacterial $DNA$ is the correct answer.

(A) The bacterial genome consists of a single,double-stranded,circular $DNA$ molecule.
It is not enclosed within a membrane-bound nucleus but is located in a region called the nucleoid.
Therefore,the correct description of the bacterial genome is circular.

(D) The term $DNA$ is considered 'naked' when it is not organized into nucleosomes by histone proteins. In prokaryotic cells,the $DNA$ is not associated with basic histone proteins,although it may be associated with other proteins like polyamines that help in maintaining its structure.

(A) Fimbriae are small,bristle-like fibers sprouting out of the cell. They are short,thin,and straight appendages that function as organs of adhesion,helping bacteria attach to rocks in streams and also to host tissues. Pili,on the other hand,are elongated tubular structures made of a special protein that form a conjugation tube for the transfer of genetic material. Therefore,the correct answer is $A$.

(C) Bacteria are prokaryotic organisms. Their genetic material is not enclosed within a nuclear envelope. The bacterial chromosome consists of a single,large,circular $DNA$ molecule,which is often referred to as the nucleoid. Therefore,the nucleic acid present in the bacterial chromosome is circular $DNA$.

(C) In many bacteria,the cell wall is covered with small,hair-like appendages known as $Pili$ and $Fimbriae$. $Pili$ are elongated,tubular structures made of a special protein called $pilin$,which are primarily involved in bacterial conjugation. $Fimbriae$ are small,bristle-like fibers sprouting out of the cell,which help bacteria attach to rocks in streams and also to host tissues. $Flagella$ are longer,whip-like structures used for motility,while $Cilia$ are typically found in eukaryotic cells,not bacteria.

(C) The infoldings of the plasma membrane in bacteria are known as mesosomes or chondrioids.
These structures are rich in respiratory enzymes and play a crucial role in cellular respiration,$DNA$ replication,and cell wall formation.
Therefore,the correct option is $C$.

(B) Circular $DNA$ is a characteristic feature of prokaryotic organisms like bacteria.
Additionally,eukaryotic organelles such as mitochondria and chloroplasts also contain circular $DNA$ molecules,which is evidence supporting the endosymbiotic theory.
Therefore,circular $DNA$ is found in bacteria,chloroplasts,and mitochondria.

(D) $E. coli$ (Escherichia coli) is a prokaryotic organism.
Prokaryotic $DNA$ is typically organized as a single,double-stranded,circular molecule located in the nucleoid region.
Therefore,the correct structure of $E. coli$ $DNA$ is double-stranded and circular.

(B) In prokaryotic cells like bacteria,the cell membrane undergoes invagination to form specialized structures known as $Mesosomes$.
These structures are formed by the extensions of the plasma membrane into the cell in the form of vesicles,tubules,and lamellae.
They play crucial roles in cell wall formation,$DNA$ replication,distribution to daughter cells,respiration,secretion processes,and increasing the surface area of the plasma membrane for enzymatic content.

(C) In many bacteria (especially Gram-positive bacteria),the plasma membrane gives rise to characteristic infoldings known as mesosomes.
These structures contain respiratory enzymes such as succinic dehydrogenase and cytochrome oxidase,which are essential for cellular respiration.

(A) Prokaryotes are organisms that lack a membrane-bound nucleus and membrane-bound organelles.
Specifically,they do not possess a true nucleus enclosed by a double-layered nuclear membrane.
Instead,their genetic material is found in a region called the nucleoid.
Therefore,the defining characteristic among the given options is the absence of a true nucleus with a double-layered nuclear membrane.

(D) Prokaryotic cells are characterized by the absence of a well-defined nucleus (nuclear membrane) and membrane-bound organelles such as mitochondria and chloroplasts.
However,all living cells,including prokaryotes,possess a cell membrane (plasma membrane) which acts as a selective barrier.
Therefore,the absence of a cell membrane is not a feature of prokaryotes; rather,they are identified by the presence of a cell membrane.

(D) Prokaryotic cells,such as bacteria,lack a well-defined nucleus.
Their genetic material consists of a single,circular $DNA$ molecule that is not enclosed within a nuclear membrane.
Unlike eukaryotes,prokaryotic $DNA$ is not associated with histone proteins,although it is organized by other proteins into a structure known as the nucleoid.

(B) $Pasteurella$ $pestis$ (now known as $Yersinia$ $pestis$) is a Gram-negative,non-motile,rod-shaped bacterium.
Its typical size ranges from $0.5$ $\mu m$ to $0.8$ $\mu m$ in width and $1$ $\mu m$ to $2$ $\mu m$ in length.
Therefore,the correct measurement for its length is $1$ to $2$ $\mu m$.

(C) The average weight of a single bacterial cell is estimated to be approximately $0.2 \times 10^{-12} \text{ g}$ (or $2 \times 10^{-13} \text{ g}$).
This value is derived from the typical mass of cellular components such as proteins,nucleic acids,and water content within a prokaryotic cell.

(B) The fundamental difference between prokaryotic and eukaryotic cells is the presence of a membrane-bound nucleus.
Prokaryotic cells lack a well-defined,membrane-bound nucleus,meaning their genetic material is not enclosed by a nuclear membrane.
In contrast,eukaryotic cells possess a well-organized nucleus that is enclosed by a distinct nuclear membrane.

(B) The correct answer is $B$.
Intracellular compartments refer to membrane-bound organelles such as the nucleus,mitochondria,endoplasmic reticulum,Golgi apparatus,etc.
These structures are characteristic of eukaryotic cells.
Prokaryotes,such as bacteria and cyanobacteria,lack a defined nucleus and other membrane-bound cell organelles,meaning they do not possess intracellular compartments.

(C) The term "Prokaryote" is derived from the Greek words "pro" (meaning primitive or before) and "karyon" (meaning nucleus).
Prokaryotic cells are characterized by the absence of a well-defined, membrane-bound nucleus.
Instead, their genetic material $(DNA)$ is found in a region called the nucleoid, which is not enclosed by a nuclear envelope, resulting in a diffused nucleus.

(D) Prokaryotic cells are characterized by the absence of a well-defined nucleus and membrane-bound organelles.
Specifically,they lack a nuclear membrane (the genetic material is present as a nucleoid).
They also lack membrane-bound cell organelles such as Golgi bodies,endoplasmic reticulum,mitochondria,and lysosomes.
Therefore,all the options listed are absent in prokaryotes.

(B) Cytoplasmic streaming,also known as cyclosis,is the directed flow of cytosol and organelles around the large central vacuole of a plant cell or along the cell membrane of other cells.
It is a characteristic feature of eukaryotic cells,which possess a well-developed cytoskeleton (microtubules and microfilaments) that facilitates this movement.
Prokaryotic cells,such as bacteria,lack a well-defined cytoskeleton and membrane-bound organelles,and therefore do not exhibit cytoplasmic streaming.

(D) Prokaryotic cells are characterized by the absence of a membrane-bound nucleus and membrane-bound organelles.
$DNA$ and $RNA$ are present in prokaryotes as genetic material.
The plasma membrane is present in all living cells,including prokaryotes,to regulate the transport of substances.
Mitochondria are membrane-bound organelles responsible for cellular respiration,which are absent in prokaryotic cells. Therefore,the correct option is $D$.

(A) Pinocytosis (cell drinking) and phagocytosis (cell eating) are types of endocytosis.
These processes involve the invagination of the plasma membrane to engulf extracellular materials.
In prokaryotic cells,the presence of a rigid cell wall and the lack of a complex endomembrane system (such as vesicles and lysosomes) prevent these processes from occurring.
Therefore,pinocytosis and phagocytosis are absent in prokaryotic cells.

(B) Mitochondria are membrane-bound cell organelles found in eukaryotic cells.
Prokaryotic cells,such as bacteria,lack membrane-bound organelles,including mitochondria.
Therefore,mitochondria are non-existent in bacteria.
Red algae,green algae,and brown algae are all eukaryotic organisms and possess mitochondria.

(B) Golgi bodies (or Golgi apparatus) are membrane-bound organelles found in eukaryotic cells.
Bacteria are prokaryotic organisms that lack membrane-bound organelles,including the Golgi apparatus.
Therefore,Golgi bodies are absent in bacteria.

(A) The flagella found in prokaryotes (such as bacteria) are structurally distinct from those in eukaryotes.
They consist of a single strand of the protein flagellin.
Unlike eukaryotic flagella,they do not possess the characteristic $9+2$ microtubule arrangement.
Therefore,the correct answer is $(a)$.

(A) Prokaryotic flagella are composed of a protein called flagellin.
These flagellin molecules are arranged in a helical manner to form a filament.
Unlike eukaryotic flagella,prokaryotic flagella are not enclosed by a cell membrane and do not possess the $9+2$ microtubular arrangement.

(B) Prokaryotic cells lack a well-defined,membrane-bound nucleus. Instead,their genetic material is present in an undefined,irregular-shaped region known as the nucleoid. This region contains a single circular chromosome and is often described as an undifferentiated or fibrillar nucleus.

(C) Prokaryotic cells,such as bacteria,lack a well-defined nucleus and complex spindle apparatus required for mitosis or meiosis. Instead,they undergo a simple form of cell division known as binary fission,which is a type of amitosis. In this process,the genetic material replicates and the cell divides into two daughter cells without the formation of chromosomes or a spindle.

(D) The correct answer is $D$. An episome is a genetic element that can exist either as a plasmid (free in the cytoplasm) or by integrating into the host cell's chromosome. This ability to replicate independently or as part of the chromosome is a characteristic feature of episomes,such as the $F$-plasmid in bacteria.

(A) Plasmids are small,circular,double-stranded $DNA$ molecules that are distinct from a cell's chromosomal $DNA$.
They are found in bacteria and some other microorganisms.
These molecules are physically separated from the chromosomal $DNA$ and can replicate independently.
Therefore,they are classified as extra-nuclear $DNA$.

(B) The genes that provide antibiotic resistance in bacteria are typically found on plasmids,which are small,circular,extrachromosomal $DNA$ molecules.
Specifically,these are known as $R$-factors or $R$-plasmids.
These plasmids carry genes that confer resistance to various antibiotics such as chloramphenicol,tetracycline,streptomycin,and sulfonamide.

(A) An episome is a genetic element that can exist either as a free,self-replicating plasmid or by integrating into the host cell's chromosome.
Therefore,it is essentially a type of plasmid that has the capability to integrate into the bacterial genome.

(A) Bacteria are prokaryotic organisms that contain genetic material in the form of a circular $DNA$ molecule,often referred to as the bacterial chromosome or nucleoid.
While bacteria contain both $DNA$ and $RNA$ for their cellular functions,the hereditary material that carries genetic information from one generation to the next is $DNA$.
Therefore,$DNA$ is the primary nucleic acid responsible for heredity in bacteria.
Option $A$ is the most appropriate choice as $DNA$ is a type of nucleic acid.

(C) The genetic system of prokaryotes,such as bacteria,contains a circular $DNA$ molecule but lacks histone proteins.
Histone proteins are characteristic structural proteins found in eukaryotic cells that help in the packaging of $DNA$ into chromatin.
In prokaryotes,the $DNA$ is organized into a structure called the nucleoid,which is not associated with histones.

(D) Cells that lack a membrane-bound nucleus and membrane-bound organelles like mitochondria are classified as prokaryotic cells.
Among the given options,$Bacteria$ are prokaryotic organisms.
Primitive protozoans and algae are eukaryotic,and the term $Eubiont$ refers to a hypothetical early living system,not a specific cell type lacking these organelles.

(C) In photosynthetic bacteria,the photosynthetic pigments are associated with membrane systems known as $Chromatophores$. These are internal membrane systems that are extensions of the plasma membrane,which contain the necessary pigments for photosynthesis. Unlike higher plants,bacteria do not possess membrane-bound organelles like $Chloroplasts$.

(A) Prokaryotic organisms (such as bacteria) are characterized by the absence of a well-defined nucleus and membrane-bound organelles. Their genetic material is typically present as a naked circular $DNA$ molecule known as the nucleoid. They possess a rigid cell wall (except in Mycoplasma) that provides structural support. Option $A$ is correct because prokaryotes lack a true nucleus and possess a rigid cell wall. Option $B$ is incorrect as their cell wall is made of peptidoglycan,not cellulose. Option $C$ is incorrect as it describes a eukaryotic cell. Option $D$ is incorrect because many prokaryotes are heterotrophic.

(D) The fundamental distinction between prokaryotic and eukaryotic organisms lies in their cellular organization.
Prokaryotes (e.g.,bacteria) lack a well-defined nucleus and membrane-bound organelles.
Eukaryotes (e.g.,plants,animals,fungi) possess a distinct nucleus enclosed by a nuclear envelope and various membrane-bound organelles like mitochondria and chloroplasts.
Therefore,this classification is primarily based on the complexity of cell structure.

(C) Prokaryotic cells are characterized by the absence of a well-defined nucleus and membrane-bound organelles.
$1$. They lack a nuclear membrane,meaning their genetic material $(DNA)$ is not enclosed within a nucleus but exists as a nucleoid.
$2$. They also lack membrane-bound organelles such as mitochondria,endoplasmic reticulum,Golgi apparatus,and lysosomes.
$3$. However,they do possess a cell membrane,ribosomes (of the $70S$ type),and genetic material ($DNA$/$RNA$).
Therefore,the correct answer is $C$.

(A) Prokaryotic cells,such as bacteria,lack a well-defined nucleus. Their genetic material is not organized into chromosomes with histone proteins. Instead,the $DNA$ exists as a circular,double-stranded molecule that is not associated with histones,often referred to as the nucleoid. Therefore,the correct description is histone-free double-stranded $DNA$.

(C) Prokaryotic cells are characterized by the absence of membrane-bound organelles and a well-defined nucleus.
$1$. They lack a membrane-bound nucleus; instead,they have a nucleoid region.
$2$. They contain $70S$ ribosomes,which are smaller than the $80S$ ribosomes found in eukaryotic cells.
$3$. They possess a cell membrane (plasma membrane) that regulates the transport of substances.
$4$. They lack membrane-bound organelles such as the endoplasmic reticulum,Golgi apparatus,mitochondria,and lysosomes.
Therefore,the presence of the endoplasmic reticulum is $NOT$ a characteristic of a prokaryotic cell.

(D) In prokaryotic cells like bacteria,the cell membrane undergoes characteristic infoldings into the cytoplasm. These structures are known as $Mesosomes$. They 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 $DNA$ replication,cell wall formation,respiration,and secretion processes.

(D) Prokaryotic cells are primitive cells that lack a well-defined membrane-bound nucleus and membrane-bound cell organelles.
Specifically,they lack organelles such as the endoplasmic reticulum,Golgi apparatus,mitochondria,lysosomes,and vacuoles.
They also do not form spindle fibers during cell division.
Therefore,the absence of endoplasmic reticulum,Golgi bodies,and spindle fibers is a characteristic feature of prokaryotic cells.