Viruses, Viroids, Prions and Lichens Questions in English

(B) The given figure represents a bacteriophage.
In the structure of a bacteriophage:
'a' points to the base plate.
'b' points to the pins.
'c' points to the tail fibers.
Therefore,'a' represents the plate and 'c' represents the tail fiber.

(D) The provided figure shows the structure of an Adenovirus.
Adenoviruses are medium-sized,non-enveloped viruses with a nucleocapsid containing a double-stranded $DNA$ genome.
They are characterized by their icosahedral shape,which is clearly visible in the provided image.

(B) The given figure shows rod-shaped viral particles.
These are characteristic of the Tobacco Mosaic Virus $(TMV)$.
$TMV$ is a plant virus with a helical symmetry and a rod-like structure.

(A) The Tobacco Mosaic Virus $(TMV)$ is a well-studied plant virus.
It possesses a helical symmetry and is characteristically rod-shaped.
Its structure consists of a single-stranded $RNA$ genome surrounded by a protein coat called a capsid,which is made up of capsomeres arranged in a helical fashion.

(D) Adenoviruses are a group of viruses that cause respiratory infections,conjunctivitis,or gastroenteritis.
They are characterized by a non-enveloped,icosahedral capsid containing a linear,double-stranded $DNA$ genome.
Therefore,the correct genetic material found in adenoviruses is double-stranded $DNA$.

(A) Lichens are a classic example of a symbiotic relationship,specifically mutualism,between two distinct organisms:
$1$. The algal component,known as phycobiont,which is autotrophic and prepares food.
$2$. The fungal component,known as mycobiont,which provides shelter,absorbs water,and provides minerals for the algae.
Therefore,lichens represent a symbiotic association between algae and fungi.

(B) Based on the provided biological diagrams:
$1$. Figure $A$ shows spherical bacteria,which are known as $Coccus$.
$2$. Figure $B$ shows rod-shaped bacteria,which are known as $Bacillus$.
$3$. Figure $C$ shows the structure of the $Tobacco \ mosaic \ virus$ $(TMV)$,which is a plant virus with a helical capsid.
Therefore,the correct matching is $A$ - $Coccus$,$B$ - $Bacillus$,$C$ - $Tobacco \ mosaic \ virus$. The correct option is $(B)$.

(C) The correct matching is as follows:
$(a)$ Potato spindle tuber is caused by a Viroid $(ii)$.
$(b)$ Creutzfeldt-Jakob disease $(CJD)$ is a neurodegenerative disorder caused by a Prion $(iii)$.
$(c)$ Cholera is a bacterial infection caused by Vibrio cholerae $(iv)$.
$(d)$ Leaf rolling and curling in plants is a common symptom of viral infection $(i)$.
Therefore,the correct sequence is $a-ii, b-iii, c-iv, d-i$,which corresponds to option $(C)$.

(C) The correct option is $(C)$.
$(a)$ Citrus canker is a plant disease caused by the bacterium $Xanthomonas \text{ citri}$. Thus,$(a)-(iv)$.
$(b)$ Spongiform encephalopathy (such as bovine spongiform encephalopathy or mad cow disease) is caused by infectious proteins known as prions. Thus,$(b)-(ii)$.
$(c)$ Herpes is a viral infection caused by the herpes simplex virus. Thus,$(c)-(iii)$.
$(d)$ Red rot of sugarcane is a fungal disease caused by $Colletotrichum \text{ falcatum}$. Thus,$(d)-(i)$.
Therefore,the correct matching is $a-iv, b-ii, c-iii, d-i$.

(A) The provided diagram represents an Adenovirus. Adenoviruses are a group of viruses that typically cause respiratory infections,such as the common cold,conjunctivitis,or bronchitis. Therefore,option $A$ is the correct statement.

(A) $(i)$ Viroid was discovered by $T.O. Diener$ in $1971$.
$(ii)$ The first living cell was observed and described by $Antonie van Leeuwenhoek$.
$(iii)$ Virus was discovered by $D.J. Ivanowsky$ in $1892$ while studying tobacco mosaic disease.
$(iv)$ The triple helical structure of collagen was proposed by $G.N. Ramachandran$.
Therefore, the correct matching is $(i)-(c), (ii)-(b), (iii)-(d), (iv)-(a)$.

(C) $TMV$ (Tobacco Mosaic Virus) is a rod-shaped helical virus containing single-stranded $RNA$. The provided image shows the characteristic rod-like structure of $TMV$ particles.

(C) virus is an infective agent that typically consists of a nucleic acid molecule in a protein coat. It is too small to be seen by light microscopy and is able to multiply only within the living cells of a host. It is considered a living organism because it possesses the ability to reproduce inside the host cell,which is a fundamental characteristic of life.

(B) $M. W. Beijerinck$ demonstrated in $1898$ that the extract of infected plants of tobacco could cause infection in healthy plants. He called the fluid as "Contagium vivum fluidum" (living infectious fluid).

(A) The given diagram represents a bacteriophage,which is a virus that infects bacteria.
It possesses a tadpole-like structure consisting of a head and a tail.
The head contains the genetic material,typically $DNA$.
The tail consists of a hollow core surrounded by a contractile tail sheath.
At the base of the tail,a base plate is present to which the tail fibres are attached.
Based on the provided diagram:
$A$ points to the Head.
$B$ points to the Sheath.
$C$ points to the Collar.
$D$ points to the Tail fibres.
Therefore,the correct identification is $A$-Head,$B$-Sheath,$C$-Collar,$D$-Tail fibres.

(A) The structures marked as $A, B, C$ and $D$ are respectively the head,collar,sheath,and tail fibres of a bacteriophage.
In the head (structure marked as $A$),the protein coat (called the capsid) is made of small subunits called capsomeres,which protect the enclosed nucleic acid ($DNA$ or $RNA$).

(D) The capsid is the protein shell of a virus,which encloses its genetic material.
This protein shell is composed of smaller structural units known as capsomeres.
These capsomeres self-assemble to form the protective capsid structure.

(A) The symbiotic association between fungi and algae is known as $Lichen$.
In $Lichen$,there are two components: the algal partner,which is called the $phycobiont$,and the fungal partner,which is called the $mycobiont$.
These two organisms live in a mutually beneficial relationship where the algae provide food through photosynthesis,and the fungi provide protection,anchorage,and absorption of minerals.

(D) Viruses are obligate intracellular parasites that can reproduce only by invading and taking over other cells,as they lack the cellular machinery for self-reproduction.
Viruses contain either $DNA$ or $RNA$ as their genetic material,but never both in the same virus.
Viruses having $RNA$ as the genetic material are often referred to as Retroviruses if they possess the enzyme reverse transcriptase.

(A) Tobacco mosaic virus $(TMV)$ is a single-stranded $RNA$ virus. Therefore,the statement that $TMV$ has a double-stranded $RNA$ molecule is incorrect. Most plant viruses contain $RNA$ as their genetic material. Bacteriophages (viruses that infect bacteria) usually contain double-stranded $DNA$. Animal viruses can contain either single or double-stranded $RNA$ or double-stranded $DNA$.

(B) In $1971$,$T. O.$ Diener discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease.
It was found to be a free $RNA$; it lacked the protein coat that is found in viruses,hence the name 'Viroid'.
The $RNA$ of the viroid was of low molecular weight.
Therefore,the infectious agent described is a Viroid.

(D) The five kingdom system of classification was proposed by $R$.$H$. Whittaker.
This system includes Monera,Protista,Fungi,Plantae,and Animalia.
Viruses,viroids,prions,and lichens are not placed in any of these kingdoms because they do not truly fit the definition of a living organism or have a unique cellular structure that does not align with the criteria used for these kingdoms.

(D) The correct answer is $D$. $TMV$ (Tobacco Mosaic Virus) is a plant virus that contains only $RNA$ as its genetic material,not both $RNA$ and $DNA$. Viruses are obligate parasites and never contain both types of nucleic acids simultaneously.

(B) Viruses that infect bacteria are known as $Bacteriophages$.
$Cyanophages$ are viruses that infect cyanobacteria.
$Mycophages$ are viruses that infect fungi.
Therefore,the correct term for viruses infecting bacteria is $Bacteriophages$.

(B) $M.W. Beijerinek$ demonstrated in $1898$ that the extract of the infected plants of tobacco could cause infection in healthy plants. He called the fluid as $Contagium \text{ } vivum \text{ } fluidum$ (infectious living fluid).

(A) Viruses consist of a genetic material ($DNA$ or $RNA$) enclosed within a protein coat known as a capsid. This capsid is composed of small protein subunits called capsomeres,which protect the viral genome.

(A) Based on the provided diagram of a bacteriophage:
$A$ represents the Head,which contains the genetic material.
$B$ represents the Collar,which connects the head to the tail.
$C$ represents the Sheath,which surrounds the central tail tube.
$D$ represents the Tail fibres,which are used for attachment to the host cell.
Therefore,the correct identification is $A$ - Head,$B$ - Collar,$C$ - Sheath,$D$ - Tail fibres.

(C) $(i)$ Viroids are infectious agents consisting of a short strand of circular,single-stranded $RNA$ without a protein coat.
$(ii)$ The $RNA$ of viroids has a significantly lower molecular weight compared to the $RNA$ found in viruses.
$(iii)$ Mumps and Herpes are indeed caused by viruses,making this statement correct.
$(iv)$ The name '$virus$' (meaning venom or poisonous fluid) was given by Louis Pasteur,while $D$.$J$. Ivanowsky recognized certain microbes as causal organisms of the mosaic disease of tobacco.

(A) Lichens represent a symbiotic association,which is a mutually beneficial relationship between algae and fungi.
In this association,the algal component is known as phycobiont,and the fungal component is known as mycobiont.
The algae prepare food through photosynthesis,while the fungi provide protection,anchorage,and absorption of water and minerals for the algae.

(C) Lichens are symbiotic associations between algae and fungi. The algal component is called phycobiont (autotrophic),and the fungal component is called mycobiont (heterotrophic). Lichens are very sensitive to sulfur dioxide $(SO_2)$ pollution and therefore do not grow in polluted areas. Thus,they act as excellent indicators of air pollution.

(D) Viral infections in plants typically manifest as symptoms such as mosaic formation,leaf rolling,leaf curling,yellowing,and vein clearing.
- Mosaic formation,leaf rolling,curling,yellowing,and vein clearing are characteristic symptoms of viral diseases in plants.
- Root knot is a symptom typically caused by nematodes (e.g.,Meloidogyne incognita),not by viruses.
Therefore,the correct answer is $D$.

(B) Viruses are obligate parasites that contain either $DNA$ or $RNA$ as their genetic material,but never both. Therefore,the statement that they possess both $DNA$ and $RNA$ is incorrect.

(B) The image $A$ represents the Tobacco Mosaic Virus $(TMV)$,which is a well-known $RNA$ virus.
The image $B$ represents the $T_4$ bacteriophage,which is a virus that infects bacteria and contains $DNA$ as its genetic material.
Therefore,$A$ is an $RNA$ virus $(TMV)$ and $B$ is a $DNA$ virus ($T_4$ bacteriophage).

(D) $a.$ Lichens are sensitive to $SO_2$ pollution,making them good bioindicators. This is correct.
$b.$ Lichens are perennial,not annuals. This is incorrect.
$c.$ The fungal partner (mycobiont) in most lichens belongs to Ascomycetes. This is correct.
$d.$ Soredia are specialized structures for vegetative/asexual reproduction in lichens. This is correct.
$e.$ Orchids are associated with mycorrhiza,not lichens. This is incorrect.
$f.$ Crustose lichens (not foliose) are pioneers of succession on bare rocks. Foliose lichens are not pioneers in water bodies. This is incorrect.
Therefore,the correct statements are $a, c,$ and $d$.

(B) Assertion $(A)$ is correct because lichens are highly sensitive to sulfur dioxide $(SO_2)$ pollution and act as pollution indicators; they do not grow in areas with high $SO_2$ levels.
Reason $(R)$ is also correct because lichens are pioneer species that colonize barren rocks. They secrete organic acids like carbonic acid and oxalic acid,which help in the weathering of rocks and soil formation.
However,the Reason does not explain why lichens do not grow in polluted areas. Therefore,both are correct,but the Reason is not the correct explanation of the Assertion.

(D) In lichens,the fungal component is known as the mycobiont,and the algal component is known as the phycobiont.
The mycobiont is the dominant partner because it provides the structural framework,protection,and absorbs minerals and water for the lichen.
Therefore,the assertion that the phycobiont is the dominant parent is incorrect.
Regarding the reason,the algal component (phycobiont) can be either a prokaryote (like $Cyanobacteria$) or a eukaryote (like green algae).
Thus,the statement that the algal component can be eukaryotic only is also incorrect.
Since both the assertion and the reason are false,the correct option is $D$.

(A) The five-kingdom system of classification proposed by $R.H. Whittaker$ includes organisms that are cellular in nature (Monera,Protista,Fungi,Plantae,and Animalia).
Viroids are infectious agents that consist only of a short strand of circular single-stranded $RNA$ without a protein coat.
Because viroids are non-cellular entities (they lack a cell structure,organelles,and metabolic machinery),they do not fit into the five-kingdom classification system.
Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for why viroids are excluded from the system.

(C) Assertion $(A)$ is correct: Animal viruses typically contain either single-stranded $RNA$ $(ssRNA)$,double-stranded $RNA$ $(dsRNA)$,or double-stranded $DNA$ $(dsDNA)$ as their genetic material.
Reason $(R)$ is incorrect: Phytophagineae (plant viruses) generally contain $ssRNA$ as their genetic material,not $dsDNA$.

(A) Tobacco mosaic virus $(TMV)$ is a well-studied plant virus.
Its genetic material consists of a single-stranded $RNA$ $(ssRNA)$ molecule,which is enclosed within a protein coat called a capsid.

(C) Viruses are often considered at the borderline between living and non-living entities. The primary characteristic that classifies them as living is their ability to replicate or reproduce,but this process can only occur inside a living host cell. Outside the host,they are inert and behave like non-living chemicals. Therefore,the ability to reproduce is the key biological trait that links them to living organisms.

(A) Lichens are symbiotic organisms consisting of algae and fungi. They are highly sensitive to air pollution,particularly sulfur dioxide $(SO_2)$. Because they cannot survive in environments with high levels of industrial pollutants,they are widely used as bio-indicators to assess air quality in industrial regions.

(D) Virus consists of protein and nucleic acid ($DNA$ or $RNA$).
Bacteria are prokaryotic organisms with a cell envelope,cytoplasm,and nucleoid.
Viroids are infectious agents consisting only of short strands of low molecular weight $RNA$ without a protein coat.
Prions are infectious agents composed entirely of abnormally folded protein,lacking any nucleic acid.

(A) Viroids are infectious agents that consist only of a short strand of circular,single-stranded $RNA$ without a protein coat. They are smaller than viruses and are known to cause diseases in plants.

(C) The given diagram represents a bacteriophage,which is a virus that infects bacteria. The labels correspond to the following structures:
$A$ - Head (contains the genetic material)
$B$ - Collar
$C$ - Tail
$D$ - Base plate (or end plate,to which tail fibers are attached)
Comparing these with the given options,option $C$ correctly identifies the parts as: $A$ - Head,$B$ - Collar,$C$ - Tail,and $D$ - Plate.

(A) Based on the provided images:
$a$. Adenovirus (shows a geometric viral structure).
$b$. Tobacco Mosaic Virus $(TMV)$ (shows rod-shaped viral particles).
$c$. Bacillus (shows rod-shaped bacteria).
$d$. Cocci (shows spherical bacteria).
Therefore,the correct matching is: $a(iv), b(iii), c(i), d(ii)$.

(C) Bovine spongiform encephalopathy $(BSE)$,commonly known as 'mad cow disease',is a progressive neurological disorder of cattle.
It is caused by an infectious protein particle called a prion.
In humans,a similar disease caused by prions is known as Creutzfeldt-Jacob disease $(CJD)$.
Both conditions are characterized by the accumulation of misfolded proteins in the brain,leading to spongiform degeneration of brain tissue.

(B) $\rightarrow$ In $1971$,$T.O. Diener$ discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease.
$\rightarrow$ It was found to be a free $RNA$; it lacked the protein coat that is found in viruses,hence the name viroid.
$\rightarrow$ The $RNA$ of the viroid was of low molecular weight.

(N/A) $\rightarrow$ $D. J. Ivanowsky (1892)$ recognized certain microbes as the causal organisms of the mosaic disease of tobacco.
$\rightarrow$ These were found to be smaller than bacteria because they passed through bacteria-proof filters.
$\rightarrow$ $M. W. Beijerinck (1898)$ demonstrated that the extract of infected tobacco plants could cause infection in healthy plants and called the fluid $Contagium$ $\text{vivum}$ $\text{fluidum}$ (infectious living fluid).
$\rightarrow$ $W. M. Stanley (1935)$ showed that viruses could be crystallized and crystals consist largely of proteins.

(N/A) $\rightarrow$ Lichens growing on rocks secrete organic acids,such as oxalic acid.
These acids penetrate the rock surface and create numerous crevices.
Dust and organic matter accumulate within these crevices.
Moss spores are then able to germinate and grow in these crevices,initiating the process of biological succession and contributing to soil formation.

(A) The full form of $TMV$ is Tobacco Mosaic Virus.
It is a positive-sense single-stranded $RNA$ virus that infects a wide range of plants,especially tobacco and other members of the family Solanaceae.
It was the first virus to be discovered and crystallized.