Viruses, Viroids, Prions and Lichens Questions in English

(B) Bacteriophages are viruses that infect bacteria. Most known bacteriophages contain double-stranded $DNA$ $(ds\,DNA)$ as their genetic material. Examples include the $T$-even bacteriophages like $T2$,$T4$,and $T6$.

(B) The Kingdom $Monera$ consists of unicellular prokaryotic organisms.
$Bacteria$,$Cyanobacteria$ (blue-green algae),and $Mycoplasma$ are all classified under the Kingdom $Monera$ as they are prokaryotic.
$Viruses$ are considered non-cellular entities that exist at the border of living and non-living things.
They do not possess a cellular structure,metabolism,or independent replication machinery,and therefore,they are not classified under the Kingdom $Monera$ or any other biological kingdom in the $Whittaker$ classification system.

(C) Viruses are considered to be at the border of living and non-living organisms. They lack their own metabolic machinery,including the enzymes required for protein synthesis,energy production,or replication. They rely entirely on the host cell's machinery to perform these functions. Therefore,enzymes are not found in viruses.

(C) In $1971$,$T.O. Diener$ discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease. This agent was named a viroid. Viroids consist of a short chain of circular,single-stranded $RNA$ without a protein coat.

(A) The term 'virus' means 'venom' or 'poisonous fluid'. This name was given by Louis Pasteur.
$D.J.$ Ivanowsky recognized certain microbes as causal organisms of the mosaic disease of tobacco.
$W$.$M$. Stanley showed that viruses could be crystallized and crystals consist largely of proteins.

(D) $1$. Viruses are obligate parasites because they require a living host cell to replicate their genetic material and produce new viral particles.
$2$. Lichens represent a symbiotic association between algae and fungi. The algal component is known as the phycobiont,which is autotrophic and provides food.
$3$. The fungal component is known as the mycobiont,which is heterotrophic and provides protection,anchorage,and absorption of minerals for the algae.
$4$. Since all three statements are scientifically accurate,the correct option is $D$.

(D) The five-kingdom system of classification,proposed by $R.H. Whittaker$,includes Monera,Protista,Fungi,Plantae,and Animalia.
Viruses,viroids,and prions are acellular entities and are not considered true organisms,hence they are not placed in any of these five kingdoms.
Lichens are symbiotic associations between algae and fungi,and while they are biological entities,they are not classified as a separate kingdom in this system.
Therefore,all of the mentioned entities ($Viruses$,$Viroids$,and $Lichens$) are not included in the five-kingdom classification system.

(A) Prions are infectious agents that are composed entirely of protein material.
They do not contain any nucleic acids like $DNA$ or $RNA$.
These proteins are misfolded forms of normal cellular proteins that can induce other normal proteins to adopt the same misfolded,infectious conformation.
Therefore,the correct option is $A$.

(A) $TMV$ stands for Tobacco Mosaic Virus. It is a plant virus that infects a wide range of plants,especially tobacco. The genetic material of $TMV$ is a single-stranded $RNA$ molecule. It does not contain $DNA$ as its genetic material.

(D) $1$. Mitochondria and Chloroplast are semi-autonomous organelles that contain their own circular $DNA$.
$2$. Bacteriophage is a virus that infects bacteria and contains $DNA$ as its genetic material.
$3$. $TMV$ (Tobacco Mosaic Virus) is a plant virus that contains $RNA$ as its genetic material,not $DNA$.
$4$. Therefore,$DNA$ is absent in $TMV$.

(B) $TMV$ stands for Tobacco Mosaic Virus. It is a plant virus that infects tobacco and other members of the Solanaceae family. Like all viruses,it consists of genetic material enclosed within a protein coat (capsid). The genetic material of $TMV$ is single-stranded $RNA$ $(ssRNA)$. Therefore,$TMV$ is composed of $RNA$ and protein.

(A) Lichens are symbiotic associations between algae and fungi.
They are very sensitive to sulfur dioxide $(SO_2)$ and do not grow in polluted areas,making them excellent bio-indicators for air pollution.
Additionally,they are known as pioneer species in primary succession on barren rocks,as they secrete acids to dissolve rocks and help in soil formation.
Since option $A$ covers both roles (bio-indicators and pioneers),it is the most comprehensive answer.

(C) Lichens represent a classic example of $Mutualism$ or $Symbiosis$. In this association,the fungal component (mycobiont) and the algal component (phycobiont) live together in a mutually beneficial relationship. The fungus provides protection,anchorage,and absorbs water and minerals from the environment,while the algae perform photosynthesis to provide food for both. Therefore,they share a $Symbiotic$ relationship.

(D) Lichens are highly sensitive to air pollutants,especially sulfur dioxide $(SO_2)$. They do not grow in polluted areas,making them excellent bio-indicators of air pollution. Therefore,their presence or absence indicates the level of air quality in a given habitat.

(C) Pox viruses,such as the Vaccinia virus,are complex $DNA$ viruses. Scientific studies have demonstrated that these viruses contain certain vitamins,specifically Riboflavin and Biotin,within their viral structure. Therefore,both $(A)$ and $(B)$ are correct.

(B) The figure shows the Tobacco Mosaic Virus $(TMV)$.
$D$.$J$. Ivanowsky $(1892)$ recognized certain microbes as causal organisms of the mosaic disease of tobacco.
These were found to be smaller than bacteria because they passed through bacteria-proof filters.
Therefore,the correct association with the discovery of the virus is Ivanowsky.

(A) Lichens are symbiotic associations between algae and fungi.
In the cross-section of a foliose lichen,the algal component is known as the phycobiont,while the fungal component is the mycobiont.
The part labeled '$A$' represents the algal cells located just below the upper cortex,which is the phycobiont layer.

(C) The given figure represents a bacteriophage,a virus that infects bacteria.
In the diagram,the labels represent the following parts:
$A$ = Head (Capsid)
$B$ = Collar
$C$ = Tail fibers
$D$ = Genetic material $(DNA)$
Therefore,the part labeled '$C$' represents the tail fibers,which are used by the bacteriophage to attach to the surface of the host bacterium.

(A) The given figure represents a bacteriophage,which is a virus that infects bacteria.
In the diagram:
- $'A'$ represents the head.
- $'B'$ represents the capsid (protein coat).
- $'C'$ represents the tail fibers.
- $'D'$ represents the genetic material,which is $DNA$ in this specific bacteriophage.

(B) The figure represents a bacteriophage,which is a virus that infects bacteria.
In the structure of a bacteriophage:
- '$A$' represents the head.
- '$B$' represents the protein coat known as the capsid,which encloses the genetic material.
- '$C$' represents the tail fibers.
- '$D$' represents the genetic material $(DNA)$.
Therefore,the part labeled '$B$' is the capsid.

(A) The figure shows an open,cup-shaped fruiting body of a lichen,which is characteristic of an apothecium.
An apothecium is a wide,open,disc-shaped or cup-shaped ascocarp in which the hymenium is exposed at maturity.
Phycobiont refers to the algal component of the lichen,not a fruiting body.
Perithecium is a flask-shaped fruiting body with a small pore.
Capitulum is a different type of structure found in some fungi.

(B) The figure shows a foliose lichen,which is a symbiotic association between an alga and a fungus. Among the given options,$Parmelia$ is a well-known genus of foliose lichen,characterized by its leaf-like,flattened thallus that attaches to the substrate. $Usnea$ is a fruticose lichen,$Riccia$ is a liverwort (bryophyte),and $Strigula$ is a crustose lichen. Therefore,the correct identification is $Parmelia$.

(A) The given figure represents the internal structure of a lichen. Lichens are symbiotic associations between algae and fungi. The algal component is known as the phycobiont,while the fungal component is known as the mycobiont. In the diagram,the fungal hyphae (mycobiont) are shown surrounding the algal cells (phycobiont). The label '$A$' points to the fungal hyphae,which constitute the mycobiont.

(A) The given figure represents a bacteriophage,which is a virus that infects bacteria.
In the structure of a bacteriophage,the polyhedral protein coat that encloses the genetic material is known as the head.
The part labeled as $''X''$ points to this polyhedral head structure.
Therefore,the correct option is $A$.

(B) The given diagram represents a bacteriophage,which is a virus that infects bacteria.
In the diagram:
- '$A$' represents the overall structure or the sheath/tail region.
- '$B$' represents the head of the bacteriophage,which contains the genetic material.
- '$C$' represents the tail fibers.
- '$D$' represents the genetic material,which is $DNA$.
Therefore,'$B$' is the head.

(C) The figure shows the structure of the Tobacco Mosaic Virus $(TMV)$.
$TMV$ is a rod-shaped virus with a helical symmetry.
It consists of a single-stranded $RNA$ molecule surrounded by a protein coat called a capsid,which is made up of capsomeres.
This specific helical structure is a classic representation of $TMV$ found in biology textbooks.

(D) The given figure represents a bacteriophage,which is a virus that infects bacteria.
In the diagram,the part labeled $''A''$ points to the tail fibers.
These tail fibers are essential for the attachment of the bacteriophage to the specific receptor sites on the surface of the host bacterial cell.

(B) The given figure represents a bacteriophage.
In the diagram,'$A$' points to the entire upper portion of the virus,which is the 'Head' (or capsid-containing region).
'$B$' represents the capsid,'$C$' represents the tail fibers,and '$D$' represents the genetic material $(DNA)$.
Therefore,'$A$' represents the Head.

(B) The figure represents a $Bacteriophage$.
Bacteriophages are viruses that infect bacteria.
The structure consists of a head containing genetic material $(D)$,a collar,a tail $(A)$,and tail fibers $(C)$.
The head is protected by a protein coat called a capsid $(B)$.
This specific structure is characteristic of a $Bacteriophage$.

(D) The figure shows the Tobacco Mosaic Virus $(TMV)$.
Dmitri Ivanowsky $(1892)$ recognized certain microbes as causal organisms of the mosaic disease of tobacco. These were found to be smaller than bacteria because they passed through bacteria-proof filters.

(C) The provided figure shows a cross-section of a lichen thallus.
Based on the structural organization,specifically the radial symmetry and the arrangement of algal and fungal components,this represents a Fruticose lichen.
Fruticose lichens are branched,shrub-like,and often grow attached to a substrate at a single point.
In the cross-section,the algal cells are distributed throughout the medulla,which is characteristic of this type.

(C) The correct answer is $C$ (Virus).
Viruses are considered to be at the border of living and non-living organisms because they lack a cellular structure and cannot replicate independently without a host cell.
Protozoa,Bacteria,and Spirogyra are all considered true living organisms as they possess cellular machinery and can perform metabolic activities independently.

(D) $R$.$H$. Whittaker proposed the five-kingdom classification system,which includes Monera,Protista,Fungi,Plantae,and Animalia.
Viruses,viroids,prions,and bacteriophages are acellular entities that lack a cellular structure and metabolic machinery of their own.
Because they do not possess the characteristics of living cells,they were not placed in any of the five kingdoms by Whittaker.

(A) Bacteriophages are viruses that infect bacteria. The term 'phage' means 'to eat',hence they are known as bacteria-eating viruses. This makes Assertion $A$ true.
Bacteriophages are obligate intracellular parasites,meaning they require a living bacterial host cell to replicate and survive. They inject their genetic material into the bacterial cell,hijack the host's machinery,and produce more viral particles. This makes Reason $R$ true.
Since the definition of a bacteriophage as a 'bacteria-eating virus' is directly based on its nature as an obligate parasite of bacteria,Reason $R$ is the correct explanation for Assertion $A$.

(A) $Viroid$ is an infectious agent that consists solely of a short strand of circular, single-stranded $RNA$ without a protein coat.
Unlike viruses, they lack a capsid.
$E. coli$ and other bacteria are prokaryotic organisms with double-stranded $DNA$ genomes.
$Amoeba$ is a eukaryotic protist with a complex cellular structure containing $DNA$ within a nucleus.
Therefore, the correct answer is $Viroid$.

(C) Viruses are obligate parasites that consist of genetic material ($DNA$ or $RNA$) enclosed within a protein coat called a capsid. Statement $C$ is incorrect because viruses possess a protein coat known as a capsid,which protects the genetic material. Statements $A$,$B$,and $D$ are correct characteristics of viruses.

(B) In $1892$,$D.J. Ivanowsky$ recognized certain microbes as causal organisms of the mosaic disease of tobacco. These were found to be smaller than bacteria because they passed through bacteria-proof filters. Hence,the correct answer is tobacco.

(C) The name 'virus' which means 'venom' or 'poisonous fluid' was given by Louis Pasteur.
$D.J. Ivanowsky$ $(1892)$ recognized certain microbes as causal organisms of the mosaic disease of tobacco.
$M.W. Beijerinck$ $(1898)$ demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and called the fluid as 'Contagium vivum fluidum'.
However,the term 'virus' itself is attributed to Louis Pasteur.

(C) Figure $I$ represents the Tobacco Mosaic Virus $(TMV)$,which is a well-known plant virus characterized by its helical symmetry.
Figure $II$ represents a Bacteriophage,which is a virus that infects bacteria,characterized by its complex structure consisting of a head and a tail.
Therefore,the correct identification is $I$ as a plant virus and $II$ as a bacteriophage.

(B) Viroids are infectious agents that are smaller than viruses. They consist solely of a short strand of circular,single-stranded $RNA$ without a protein coat (capsid). In contrast,viruses consist of genetic material ($DNA$ or $RNA$) enclosed in a protein coat. Protozoa,$E$. coli (a bacterium),and Mucor (a fungus) are all significantly larger than viruses.

(B) In $1971$,$T.O. Diener$ discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease. This infectious agent was named 'viroid'. Viroids consist of a short strand of low molecular weight $RNA$ and lack a protein coat.

(A) virus is a nucleoprotein entity,which means it consists of a genetic material core surrounded by a protein coat called a capsid.
The genetic material can be either $DNA$ or $RNA$,but never both in the same virus.
Therefore,the basic composition of a virus is proteins and $DNA$ or $RNA$.

(NONE) Alzheimer's disease is a progressive neurodegenerative disorder characterized by the accumulation of misfolded proteins,specifically $amyloid-beta$ plaques and $tau$ tangles in the brain.
None of the options provided ($Viroids$,$Viruses$,$Fungi$,or $Bacteria$) are the primary causative agents of Alzheimer's disease.
$Viroids$ are small circular $RNA$ molecules that infect plants.
$Viruses$,$Fungi$,and $Bacteria$ are infectious pathogens that cause various diseases,but they are not the cause of Alzheimer's.
Neurodegenerative diseases like $Creutzfeldt-Jakob$ disease are caused by $Prions$ (misfolded proteins),which are distinct from the options listed.
Therefore,this question is technically inaccurate as none of the provided options are responsible for Alzheimer's disease.

(B) Viruses are unique biological entities that contain either $DNA$ or $RNA$ as their genetic material,but never both.
In contrast,all cellular organisms like moss (plants),fungi,and lichens contain both $DNA$ and $RNA$ within their cells.
Therefore,the correct answer is $B$ (Virus).

(C) capsomere is a subunit of the capsid,which is the outer protein shell of a virus particle.
These capsomeres are composed of protein molecules that self-assemble to protect the viral genetic material ($DNA$ or $RNA$).
Therefore,a capsomere is essentially a protein subunit.

(B) In $1892$,$D.I. Ivanowsky$ recognized certain microbes as causal organisms of the mosaic disease of tobacco. These were found to be smaller than bacteria because they passed through bacteria-proof filters. Thus,$Ivanowsky$ is credited with the discovery of the Tobacco Mosaic Virus $(TMV)$.

(C) The Tobacco Mosaic Virus $(TMV)$ is a well-known plant virus that infects a wide range of plants,especially tobacco.
It was the first virus to be discovered and crystallized.
It consists of a single-stranded $RNA$ genome enclosed in a protein coat (capsid).
Since it specifically infects plants,it is classified as a plant virus.

(C) capsid is the protein shell of a virus.
It consists of several oligomeric structural subunits made of protein called protomers.
The capsid encloses the genetic material of the virus,which can be either $DNA$ or $RNA$.

(A) Assertion $A$ is true because viruses exhibit characteristics of both living (e.g.,replication,genetic material) and non-living (e.g.,lack of cellular structure,inert outside host) entities.
Reason $R$ is also true. Viruses are considered non-living outside a host because they lack metabolic machinery. However,they become active and replicate only when they enter a living host cell,making them obligate parasites.
Since the reason explains why viruses are considered a link (because they are inert outside but active inside),$R$ is the correct explanation of $A$.

(C) The Tobacco Mosaic Virus $(TMV)$ is a plant virus that infects a wide range of plants,especially tobacco.
It causes the characteristic 'mosaic' pattern of mottling and discoloration on the leaves.
Therefore,the disease caused by $TMV$ is known as Mosaic disease.