Viruses, Viroids, Prions and Lichens Questions in English

(D) Lichens are ecologically and economically important for several reasons:
$1$. Lichens contain a complex carbohydrate called lichenin,making them a food source for many animals,such as reindeer.
$2$. They are used in the production of various medicines,including antibiotics.
$3$. Lichens like $Roccella$ $tinctoria$,$Parmelia$,and $Omphalodes$ are used in the manufacturing of different types of dyes.
$4$. They are also well-known as pollution indicators,particularly for $SO_2$ (sulfur dioxide),as they do not grow in polluted areas.

(C) The characteristics of a virus that are similar to non-living objects are as follows:
$(a)$ They exist as an inert crystalline structure when outside a living host cell.
$(b)$ They lack cellular machinery,such as ribosomes,mitochondria,or other cell organelles,which are essential for independent metabolism.

(A) Lichens are symbiotic associations,i.e.,mutually useful associations,between algae and fungi.
The algal component is known as phycobiont (which is autotrophic) and the fungal component is known as mycobiont (which is heterotrophic).
The algae prepare food for fungi,and the fungi provide shelter and absorb mineral nutrients and water for their partner.

(A) Viruses are considered a connecting link between living and non-living organisms because they exhibit characteristics of both.
$1$. Non-living characteristics: They can be crystallized,lack metabolic machinery,and cannot reproduce outside a host cell.
$2$. Living characteristics: They possess genetic material ($DNA$ or $RNA$),can replicate inside a host cell,and can undergo mutations.
Therefore,option $A$ is the correct answer.

(D) In the $R.H. Whittaker$ five-kingdom classification system,viruses,viroids,prions,and lichens are not given any place or kingdom.
Viruses are considered non-cellular organisms that are characterized by having an inert crystalline structure outside the living cell.
Since they do not possess a cellular structure,they do not fit into the $Monera$,$Protista$,$Fungi$,$Plantae$,or $Animalia$ kingdoms.

(B) The image on the left represents the Tobacco Mosaic Virus $(TMV)$,which is a plant virus.
The image on the right represents a Bacteriophage,which is a virus that infects bacteria.
Therefore,the correct identification is Tobacco Mosaic Virus and Bacteriophage.

(A) Viruses are considered non-cellular organisms because they lack a true cellular structure (they do not have a cell membrane,cytoplasm,or organelles).
They consist only of genetic material ($DNA$ or $RNA$) enclosed in a protein coat.
Therefore,the statement that they have a cellular structure is incorrect.
All other statements are correct: they are inert outside a host,they are obligate parasites,and their small size allows them to pass through bacteria-proof filters.

(A) $D.J. Ivanowsky$ $(1892)$ 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.

(B) In $1892$, $D. J. Ivanowsky$ recognized certain microbes as causal organisms of the mosaic disease of tobacco. He demonstrated that these microbes could pass through bacteria-proof filters. Later, in $1898$, $M. W. Beijerinck$ demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and called the fluid as $Contagium \text{ } vivum \text{ } fluidum$ (infectious living fluid). Therefore, the correct answer is $M. W. Beijerinck$.

(C) nucleoprotein is any protein that is structurally associated with nucleic acid (either $DNA$ or $RNA$).
Viruses are composed of a genetic material ($DNA$ or $RNA$) enclosed within a protein coat called a capsid.
Because they consist of nucleic acid and protein,viruses are classified as nucleoproteins.
Ribosomes are also nucleoprotein complexes (rRNA and proteins),but in the context of biological classification and the study of infectious agents,viruses are the primary entities referred to as nucleoproteins.

(A) According to biological classification:
$1$. Animal viruses generally contain $dsRNA$,$dsDNA$,or $ssRNA$ as their genetic material $(P-II)$.
$2$. Plant viruses generally contain single-stranded $RNA$ $(ssRNA)$ as their genetic material $(Q-I)$.
$3$. Bacterial viruses (bacteriophages) generally contain double-stranded $DNA$ $(dsDNA)$ as their genetic material $(R-III)$.
Therefore,the correct matching is $P-II, Q-I, R-III$.

(A) The correct answer is $A$.
In virology,the capsid is the protein shell of a virus,which encloses its genetic material.
The capsid is composed of protein subunits called capsomeres.
Therefore,the statement '$A$' is incorrect because it reverses the relationship: a capsid is made of capsomeres,not the other way around.
Statements '$B$','$C$',and '$D$' are correct descriptions of viral structure.

(D) Viroids were discovered by $T.O. Diener$ in $1971$.
They are infectious agents that are smaller than viruses and consist of a free low molecular weight $RNA$ without a protein coat.

(C) The potato spindle tuber disease is caused by $Viroids$.
$Viroids$ are infectious agents that consist of a short strand of circular,single-stranded $RNA$ without a protein coat.
They were discovered by $T.O. Diener$ in $1971$.
Unlike viruses,they are much smaller and lack the capsid structure.

(B) Lichens are symbiotic associations between algae and fungi.
The algal component is known as the phycobiont,which is autotrophic and provides food through photosynthesis.
The fungal component is known as the mycobiont,which is heterotrophic and provides protection,anchorage,and absorption of minerals and water for the algae.
Therefore,phycobiont refers to the algal component and mycobiont refers to the fungal component.

(D) Lichens are symbiotic associations between fungi and algae. They are highly sensitive to sulfur dioxide $(SO_2)$ pollution. They do not grow in polluted areas,especially those with high levels of $SO_2$. Therefore,they are widely used as biological indicators of air pollution.

(C) Prions are abnormally folded proteins that can induce normal proteins to misfold into the same infectious shape.
They are known to cause several neurological diseases in animals,such as bovine spongiform encephalopathy $(BSE)$ in cattle and its analogous variant in humans.
Unlike viruses or viroids,prions do not contain any nucleic acids ($DNA$ or $RNA$).

(D) $Prions$ are abnormally folded proteins that act as infectious pathogens.
$1$. They cause $Mad$ $Cow$ $Disease$ ($Bovine$ $Spongiform$ $Encephalopathy$) in cattle.
$2$. They are responsible for serious diseases like $Creutzfeldt-Jakob$ $Disease$ $(CJD)$ in humans.
$3$. These diseases primarily affect the central nervous system,hence they are classified as neurological disorders.
Therefore,all the given options are correct.

(A) Lichens represent a symbiotic association between an algal component $(Phycobiont)$ and a fungal component $(Mycobiont)$.
In this relationship, the algae prepare food through photosynthesis, while the fungi provide protection, anchorage, and absorption of water and minerals for the algae.
Therefore, the correct answer is $Algae + Fungi$.

(A) Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein.
They are known as proteinaceous infectious agents because they lack nucleic acids ($DNA$ or $RNA$) and consist entirely of protein.
Viruses contain genetic material ($DNA$ or $RNA$) enclosed in a protein coat.
Viroids consist only of a short strand of circular,single-stranded $RNA$ without a protein coat.
Bacteria are unicellular prokaryotic organisms with a complex cell structure.
Therefore,the correct option is $A$.

(C) Based on the provided images:
$P$ represents a Bacteriophage,which is a virus that infects bacteria.
$Q$ represents an Adenovirus,which causes respiratory infections.
$R$ represents the Tobacco Mosaic Virus $(TMV)$,which is a rod-shaped virus that infects tobacco plants.
Therefore,the correct matching is $(P-II), (Q-III), (R-I)$.

(D) Mad cow disease (Bovine Spongiform Encephalopathy) in cattle and $Creutzfeldt-Jakob$ disease $(CJD)$ in humans are caused by prions.
Prions are abnormally folded proteins that can induce abnormal folding in normal proteins.
They are infectious agents that lack nucleic acids ($DNA$ or $RNA$) and are smaller than viruses.
Therefore,the correct option is $D$.

(B) Prions are abnormally folded proteins that can induce abnormal folding in normal proteins.
They are known to cause several neurological diseases in animals,such as bovine spongiform encephalopathy $(BSE)$ or mad cow disease,and its analogous variant in humans,Creutzfeldt-Jakob disease $(CJD)$.
Unlike viruses,prions do not contain nucleic acids ($DNA$ or $RNA$).
Therefore,they are defined as infectious proteins.

(D) Viruses are non-cellular organisms that are characterized by having an inert crystalline structure outside the living cell.
They are obligate parasites.
$\text{M.W. Beijerinck}$ $(1898)$ demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and called the fluid as "contagium vivum fluidum" (infectious living fluid).
$A$ virus is a nucleoprotein, meaning it contains genetic material (either $\text{RNA}$ or $\text{DNA}$) and a protein coat.
No virus contains both $\text{RNA}$ and $\text{DNA}$ as its genetic material.
Therefore, the statement that viruses contain both $\text{RNA}$ and $\text{DNA}$ is incorrect.

(C) Lichens are symbiotic associations between algae and fungi.
They are highly sensitive to atmospheric pollutants,especially sulfur dioxide $(SO_2)$.
Because they do not grow in polluted areas,they serve as excellent bio-indicators of air pollution.

(C) The correct matches are as follows:
$1$. $DJ$ Ivanowsky $(1892)$ discovered the causal organism of the mosaic disease of tobacco,which was smaller than bacteria.
$2$. $MW$ 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' (infectious living fluid).
$3$. $WM$ Stanley $(1935)$ showed that viruses could be crystallised and crystals consist largely of proteins.
$4$. $TO$ Diener $(1971)$ discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease,which was named as Viroids.
Therefore,the correct matching is: $A \longrightarrow (iv), B \longrightarrow (iii), C \longrightarrow (ii), D \longrightarrow (i)$.

(A) The infectious and free $\text{RNA}$ particles with low molecular weight are known as $\text{Viroids}$.
They were discovered by $T.O. \text{Diener}$ in $1971$.
These particles lack the protein coat that is found in viruses,which is why they are called 'free' $\text{RNA}$ particles.
Therefore,the correct answer is $A$.

(C) The correct matches are as follows:
$(i)$ Viroids are infectious $RNA$ particles that cause diseases like Potato spindle tuber disease $(c)$.
$(ii)$ Viruses are infectious agents that cause various diseases,including Mumps $(d)$.
$(iii)$ Bacteria are prokaryotic organisms that cause diseases such as Citrus canker $(b)$.
$(iv)$ Prions are misfolded proteins that cause neurodegenerative diseases like $\text{CJD}$ (Creutzfeldt-Jakob disease) $(a)$.
Therefore,the correct matching is $(i-c, ii-d, iii-b, iv-a)$.

(C) The correct answer is $C$.
In $1898$, the Dutch microbiologist $M. W. Beijerinck$ demonstrated that the extract of infected tobacco plants could cause infection in healthy plants.
He called this fluid extract "Contagium vivum fluidum", which translates to "infectious living fluid".