Viruses, Viroids, Prions and Lichens Questions in English

(C) Lichens reproduce asexually primarily through the formation of specialized vegetative propagules called $Soredia$.
$Soredia$ are small,powdery clusters consisting of a few algal cells wrapped in fungal hyphae.
These structures are easily detached from the thallus and dispersed by wind or water to develop into new lichen colonies.
Fragmentation is also a common method,but $Soredia$ is the specific specialized asexual reproductive structure.

(C) $Strigula$ is a genus of foliicolous (leaf-dwelling) lichens. These lichens grow on the surface of living leaves in tropical and subtropical regions. They form a symbiotic association between a fungal partner (mycobiont) and an algal partner (photobiont,typically $Cephaleuros$).

(C) Lichenology is the branch of biology that deals with the scientific study of lichens. Lichens are composite organisms consisting of a symbiotic association between a fungus (mycobiont) and an alga or cyanobacterium (phycobiont).

(A) Lichens are symbiotic associations between fungi (mycobiont) and algae or cyanobacteria (phycobiont). In lichens,the fungal component is responsible for sexual reproduction. The fungal partner produces fruiting bodies,such as apothecia or perithecia,which contain asci and ascospores. Therefore,the sexual reproduction in lichens is mediated by the fungal fruiting bodies.

(D) The term $Virus$ means '$venom$' or '$poisonous$ fluid' in Latin.
$Louis$ $Pasteur$ gave the name '$Virus$' to these pathogens.
$Viruses$ are considered infectious agents that cause various diseases in living organisms.
They are often described as 'living chemicals' because they consist of genetic material ($DNA$ or $RNA$) enclosed in a protein coat and exhibit characteristics of both living and non-living entities.
Therefore, all the given options are correct descriptions of a virus.

(C) $D.J. Ivanowsky$ is famous for the discovery of the $Tobacco \text{ } Mosaic \text{ } Virus$ $(TMV)$ in $1892$. He recognized certain microbes as the causal organism of the mosaic disease of tobacco. These microbes were found to be smaller than bacteria because they could pass through bacteria-proof filters.

(C) bacteriophage is a type of virus that specifically infects and replicates within bacteria. The term 'bacteriophage' literally means 'bacteria eater' ($phage$ from the Greek word $phagein$ meaning 'to eat'). These viruses attach to the surface of a bacterium and inject their genetic material into the host cell to hijack its machinery for viral replication.

(A) Viruses are extremely small infectious agents,typically ranging from $20 \ nm$ to $300 \ nm$ in size.
Because of their minute size,they are capable of passing through standard bacteria-proof filters (such as $Chamberland$ filters),which are designed to retain bacteria but allow smaller particles like viruses to pass through.
Therefore,viruses can pass through bacteria-proof filters.

(D) Lichens are symbiotic associations between fungi and algae. The fungal component (mycobiont) produces fruiting bodies for sexual reproduction. These fruiting bodies are typically cup-shaped,known as $Apothecia$ (singular: $Apothecium$),or flask-shaped,known as $Perithecia$ (singular: $Perithecium$). Therefore,both $Perithecium$ and $Apothecium$ are types of fruiting bodies found in lichens.

(A) Viruses are considered obligate parasites because they lack the machinery required for independent metabolism and reproduction. They are inert outside a host cell and become active only when they enter a living host cell,where they hijack the host's cellular machinery to replicate. While other options like small size or nucleic acid content are true,the most defining biological characteristic that distinguishes them from other living organisms is their absolute dependence on a host cell for life processes.

(D) Viroids were discovered by $T.O. Diener$ in $1971$. They consist of a short,low molecular weight $RNA$ strand and lack a protein coat (capsid). They are known to cause potato spindle tuber disease. Prions,not viroids,are associated with certain neurological diseases like Alzheimer's or Creutzfeldt-Jakob disease. Therefore,the statement that viroids are responsible for Alzheimer's disease is incorrect,and the statement that they were discovered by Pasteur is also incorrect. However,in the context of standard biology questions,the discovery by $T.O. Diener$ is the primary fact to contrast with Pasteur. Since the question asks for the inconsistent characteristic,both $B$ and $D$ are technically incorrect,but $D$ is the most commonly cited historical error in this context.

(B) Viroids are infectious agents that are smaller than viruses. They consist of a short strand of circular,single-stranded $RNA$ without a protein coat (capsid). They were discovered by $T.O. Diener$ in $1971$ and are known to cause diseases in plants,such as potato spindle tuber disease.

(D) Viruses are considered to be at the border of living and non-living organisms. Outside a host cell,they are inert or inactive crystalline structures. However,once they enter a host cell,they take over the machinery of the host cell to replicate themselves,thereby exhibiting the characteristics of living organisms. Therefore,inside a host cell,a virus is considered active and living.

(D) Viruses exhibit several unique characteristics:
$1$. They are obligate parasites that require a living host cell to replicate (self-replicate).
$2$. They are ultramicroscopic,meaning they are smaller than bacteria and can be crystallized,a property typical of non-living matter.
$3$. Because they lack independent metabolic machinery but possess genetic material and can evolve,they are considered to be at the threshold or intermediate between living and non-living entities.
Therefore,all the given options are correct.

(D) Lichens are classified based on their growth forms into three main types:
$1$. Crustose lichen: These form a thin,crust-like layer on the substrate.
$2$. Foliose lichen: These have leaf-like,flattened,lobed structures.
$3$. Fruticose lichen: These are branched,shrub-like,or hair-like structures.
'Crystalline lichen' is not a recognized morphological classification of lichens. Therefore,option $D$ is the incorrect type.

(D) Plant viruses typically have single-stranded $RNA$ as their genetic material.
$Tobacco$ $mosaic$ $virus$ $(TMV)$ is a well-known example of a plant virus that infects tobacco plants.
$Potato$ $spindle$ $tuber$ $virus$ $(PSTV)$ is also a plant pathogen,specifically a viroid,which is a type of infectious agent that infects plants.
Therefore,both $Potato$ $spindle$ $tuber$ $virus$ and $Tobacco$ $mosaic$ $virus$ are examples associated with plant infections.

(A) Viroids were discovered by $T.O. Diener$ in $1971$.
They are infectious agents that are smaller than viruses and consist of a short strand of circular,single-stranded $RNA$ without a protein coat.

(A) virus is an obligate parasite that requires a living host cell to replicate and perform metabolic activities.
When a virus is not inside a host cell,it exists in an inert or 'free' state.
In this free state,it is essentially a non-living particle (virion) that cannot reproduce or carry out any biological processes.
Therefore,the habitat of a virus in its free state is outside a living cell.

(B) Viruses are considered to be at the border between living and non-living organisms.
They behave as non-living entities because they can be crystallized and stored in bottles like chemicals.
They lack their own metabolic machinery and can only replicate when they infect a host cell.

(B) Viruses are considered acellular organisms because they lack a cellular structure.
They do not possess a cell membrane,cytoplasm,organelles,or metabolic machinery of their own.
They consist only of genetic material ($DNA$ or $RNA$) enclosed within a protein coat called a capsid.
Because they cannot reproduce or perform metabolic activities independently,they are considered to be on the borderline between living and non-living entities.

(B) Viruses are classified based on their host. Viruses that infect animals are called animal viruses. The Polio virus is a well-known example of an animal virus that infects humans. Alzheimer's is a neurodegenerative disease,not a viral infection. Bacterial viruses are known as bacteriophages. Therefore,the correct option is $B$.

(C) Viruses are nucleoprotein entities that contain genetic material.
This genetic material can be either $DNA$ or $RNA$,but never both in the same virus.
Therefore,a virus contains either $DNA$ or $RNA$ as its hereditary material.

(C) Lichens are symbiotic associations between algae and fungi.
In this association,the algal component is known as the $Phycobiont$ (or $Photobiont$),which is autotrophic.
The fungal component is known as the $Mycobiont$,which is heterotrophic and provides protection,anchorage,and absorption of minerals for the algae.
Therefore,the correct answer is $Mycobiont$.

(A) Lichens are symbiotic associations between algae and fungi.
The algal component of a lichen is known as the $Phycobiont$.
The fungal component of a lichen is known as the $Mycobiont$.
$Phycobionts$ are usually green algae or cyanobacteria,which provide food through photosynthesis.
$Mycobionts$ are usually $Ascomycetes$ or $Basidiomycetes$,which provide protection and absorb water and minerals for the algae.

(B) Viruses are considered to be at the border of living and non-living organisms. When they are outside a host cell (in a free-living state),they do not possess any metabolic machinery of their own. Therefore,they remain in an inactive and non-living state. They only exhibit characteristics of living organisms when they enter a host cell and hijack its machinery to replicate.

(A) The potato spindle tuber disease is caused by $Viroids$.
$Viroids$ are infectious agents that are smaller than viruses and consist only of a short strand of circular,single-stranded $RNA$ without a protein coat.
They were discovered by $T.O. Diener$ in $1971$.

(C) The term 'lichen' was first used by Theophrastus,but the dual nature of lichens (symbiotic association between algae and fungi) was discovered by Louis René Tulasne in $1852$. Therefore,Tulasne is credited with the discovery of the nature of lichens.

(D) virus consists of genetic material ($DNA$ or $RNA$) enclosed within a protective protein shell called the $Capsid$.
The $Capsid$ is composed of smaller protein subunits known as $Capsomeres$.
Therefore,the entire protective protein coat structure is referred to as the $Capsid$.

(B) The first virus to be discovered was the $TMV$ (Tobacco Mosaic Virus). It was discovered by Dmitri Ivanovsky in $1892$ when he demonstrated that the causative agent of tobacco mosaic disease could pass through bacteria-proof filters.

(C) Viruses are considered to be at the border of living and non-living things. They are non-cellular organisms that are characterized by having an inert crystalline structure outside the living cell. However,once they infect a host cell,they take over the machinery of the host cell to replicate themselves. Therefore,they are known as the connecting link between living and non-living organisms.

(C) virus consists of a genetic material (either $DNA$ or $RNA$) enclosed within a protein coat called a capsid.
The capsid is composed of small protein subunits known as capsomeres.
Since capsomeres are protein subunits,they are made of polypeptide chains.
Therefore,the correct option is $C$.

(A) Lichens are symbiotic associations between algae and fungi. Asexual reproduction in lichens primarily occurs through specialized structures or spores. The common methods include the formation of $Oidia$ (small,thin-walled cells),$Pycniospores$ (produced in pycnidia),and sometimes $Soredia$ or $Isidia$. Among the given options,$Oidia$ and $Pycniospores$ are recognized methods of asexual reproduction in the fungal component of lichens. Therefore,the correct answer is $A$.

(A) Viruses are sub-microscopic infectious agents that are much smaller than bacteria.
Because of their extremely small size (typically ranging from $20-300 \ nm$),they can easily pass through filters that are designed to trap bacteria (bacteria-proof filters).
Therefore,both statement $S$ and statement $R$ are true,and $R$ provides the correct scientific explanation for why $S$ occurs.

(C) Viroids are infectious agents that consist only of a short strand of low molecular weight $RNA$ without a protein coat (capsid).
Therefore,statement $A$ is true because viroids lack a capsid.
Statement $R$ is false because viroids contain $RNA$,not $DNA$.
Thus,the correct option is $C$.

(B) $S$ is true: Lichens are symbiotic associations,i.e.,mutually useful associations,between algae and fungi. The algal component is known as phycobiont and the fungal component as mycobiont.
$R$ is true: The scientific study of lichens is indeed known as lichenology.
Since $R$ provides a definition of the study of lichens and does not explain why the association is called a lichen,$R$ is not the correct explanation of $S$.

(A) Viruses are considered to be at the boundary of living and non-living organisms because they lack independent metabolic machinery.
In a free state (outside the host),viruses are inert and behave like non-living chemical particles (crystalline structure).
However,once they enter a host cell,they hijack the host's machinery to replicate,thus exhibiting characteristics of living organisms.
Therefore,$R$ correctly explains why $A$ is true.

(D) Assertion $A$ is false because Parkinson's disease is a neurodegenerative disorder,not caused by viroids. Viroids are infectious agents consisting only of a short strand of circular,single-stranded $RNA$ without a protein coat,primarily known to cause diseases in plants (e.g.,Potato Spindle Tuber disease).
Reason $R$ is true because viroids are indeed smaller than viruses. While viruses consist of genetic material enclosed in a protein coat (capsid),viroids lack this protein coat and have a much lower molecular weight than viruses.

(C) $A.$ The protein coat of a virus is known as the capsid,which is composed of small subunits called capsomeres. This statement is true.
$R.$ Viruses are inert outside their specific host cells. They do not exhibit any living characteristics or active behavior in a virus-free (non-host) environment. They only replicate when they enter a living host cell. Therefore,the statement that they exhibit active and living behavior in a virus-free state is false.
Thus,$A$ is true and $R$ is false.

(D) $1$. $TMV$ $(Tobacco Mosaic Virus)$ is a plant virus,not a bacterial virus (bacteriophage).
$2$. Capsid is the protein coat of a virus,made of capsomeres (proteins),not polynucleotides.
$3$. Viroids are infectious agents consisting only of a short strand of circular $RNA$,lacking a protein coat. They cause diseases like potato spindle tuber disease,not mosaic disease in tomato.
$4$. Viruses are obligate parasites consisting of genetic material ($DNA$ or $RNA$) enclosed in a protein coat called a capsid. Thus,their main structural component is nucleoprotein.

(A) Lichens are symbiotic associations between algae and fungi.
$1$. The algal component is known as the phycobiont,and the fungal component is known as the mycobiont.
$2$. Aplanospores are non-motile spores involved in asexual reproduction in some lichens.
$3$. Fructicose is a morphological growth form of lichens (shrub-like),not a mode of sexual reproduction. Therefore,the pair 'Fructicose - Sexual reproduction' is incorrect.

(D) The correct pair is Tobacco - Mosaic disease.
$TMV$ stands for Tobacco Mosaic Virus,which causes mosaic disease in tobacco plants.
Option $A$ is incorrect as 'Diver' is not a biological term related to viruses.
Option $B$ is incorrect as Alzheimer is a human neurological disorder,not a potato disease.
Option $C$ is incorrect because $TMV$ is a plant virus,not an animal virus.

(D) The discovery of Lichens is attributed to $Simon Schwendener$,who proposed the dual nature of lichens in $1867$. $Tulasne$ (Louis René Tulasne) worked extensively on the structure and reproduction of lichens,but the term 'Lichens' and the concept of their symbiotic nature were established by $Schwendener$. Therefore,the pair 'Discovery of Lichens - $Tulasne$' is considered incorrect in the context of identifying the primary discoverer of their dual nature.

(A) The correct answer is $A$.
$1$. Potato tuber disease is not a standard biological term; potatoes are tubers themselves, and they suffer from diseases like late blight caused by $Phytophthora infestans$.
$2$. Tobacco mosaic disease is a well-known viral disease caused by the Tobacco Mosaic Virus $(TMV)$.
$3$. Alzheimer's disease is a chronic neurodegenerative disease affecting humans.
$4$. Fungi were historically classified as primitive plants in older taxonomic systems, though they are now placed in their own kingdom, $Fungi$.

(B) $soredium$ (plural: $soredia$) is a small,asexual reproductive unit found in lichens. It consists of a few algal cells (photobiont) wrapped in fungal hyphae (mycobiont). These structures break off from the parent lichen and are dispersed by wind or water to form a new lichen colony. Therefore,it is a specialized mechanism for asexual reproduction in lichens.

(B) Viruses are considered to have a 'dubious' or 'borderline' status because they do not truly fit into the definition of living organisms.
They lack a cellular structure,metabolic machinery,and the ability to reproduce independently.
They behave like inert chemicals outside a host cell but exhibit characteristics of living organisms (such as replication) only when they infect a host cell.
Therefore,they are not included in the five-kingdom classification system.

(D) $R.H. \text{Whittaker}$ proposed the five-kingdom classification system, which includes Monera, Protista, Fungi, Plantae, and Animalia.
Viruses, viroids, and prions are acellular entities that lack a cellular structure and metabolic machinery.
Since they do not possess a cell, they are not considered true living organisms in the context of the five-kingdom classification system.
Bacteriophages are viruses that infect bacteria.
Therefore, viruses, viroids, prions, and bacteriophages are not included in any of the five kingdoms.

(C) Viruses are considered to be at the borderline between living and non-living organisms. They lack a cellular structure and metabolic machinery of their own. They can only replicate and exhibit characteristics of life when they infect a host cell,utilizing the host's machinery. Therefore,they are obligate intracellular parasites that are considered living only inside host cells.

(A) The Tobacco Mosaic Virus $(TMV)$ is a well-studied plant virus.
Its structure consists of a single-stranded $RNA$ molecule encapsulated within a protein coat called a capsid.
Unlike many other organisms,$TMV$ does not contain $DNA$ as its genetic material.
Therefore,the correct genetic material for $TMV$ is $RNA$.

(C) The correct matches are as follows:
$(A)$ Tobacco Mosaic Virus is a plant virus that infects tobacco plants: $(A-r, s)$.
$(B)$ Potato Spindle Tuber Disease is caused by viroids in potatoes: $(B-t)$.
$(C)$ Alzheimer's disease is a neurodegenerative disorder affecting humans: $(C-p)$.
$(D)$ Bacteriophage is a virus that infects bacteria: $(D-q)$.
$(E)$ Polio virus is an animal virus that infects humans: $(E-u)$.
Combining these, the correct sequence is $(A-r), (B-t), (C-p), (D-q), (E-u)$.
Looking at the options, option $(C)$ provides the most accurate mapping: $(A-r), (B-t), (C-p), (D-q), (E-u)$.