Viruses, Viroids, Prions and Lichens Questions in English

(A) Litmus, which is commonly used as an acid-base indicator in laboratories, is a natural dye extracted from certain species of lichens, specifically $Rocella$ $montagnei$ and $Lasallia$ $pustulata$.
Lichens are symbiotic organisms consisting of a fungal partner (mycobiont) and an algal or cyanobacterial partner (phycobiont).
Therefore, the correct option is $A$.

(B) Lichens represent a symbiotic association,which is a mutually beneficial relationship between algae (phycobiont) and fungi (mycobiont).
In this association,the alga prepares food through photosynthesis,while the fungus provides protection,anchorage,and absorbs water and minerals for the alga.
Therefore,the fungus has a symbiotic relationship with the alga.

(B) $Cladonia \ rangiferina$,commonly known as reindeer lichen,is a species of lichen belonging to the family $Cladoniaceae$.
Lichens are symbiotic associations between a fungus (mycobiont) and an alga or cyanobacterium (phycobiont).
Therefore,$Cladonia \ rangiferina$ is classified as a lichen.

(B) lichen is a symbiotic association between an alga (phycobiont) and a fungus (mycobiont).
In this association,the algal component is responsible for photosynthesis,providing food for the fungus.
The fungal component provides protection,anchorage,and absorption of water and minerals for the alga.
Therefore,the fungus acts as the protective and structural partner in this relationship.

(B) Lichens are symbiotic associations between algae and fungi.
$Cyphella$ are small,cup-like depressions found on the lower surface of the thallus in certain foliose lichens (e.g.,$Sticta$).
These structures facilitate gaseous exchange,thereby assisting in the respiration of the lichen thallus.

(B) $Usnea$ is a genus of fruticose lichens that grow hanging from tree branches,resembling a beard.
Due to this characteristic appearance,it is commonly referred to as 'old man's beard'.

(D) Viruses are considered an exception to the cell theory.
Cell theory states that all living organisms are composed of cells and products of cells.
Viruses are acellular entities consisting of genetic material ($DNA$ or $RNA$) enclosed within a protein coat (capsid).
They lack protoplasm,organelles,and metabolic machinery,which are essential characteristics of a true cell.

(D) . Viruses are acellular entities that lack their own metabolic machinery,including enzymes for independent biochemical reactions. They rely entirely on the host cell's machinery for replication and protein synthesis.

(B) Lichens are symbiotic associations between algae and fungi. They are known for their extreme resilience and can perform photosynthesis at very low temperatures,even as low as $-24^{\circ}C$.

(C) Photosynthesis is a metabolic process that is highly sensitive to temperature. While most plants cannot perform photosynthesis at freezing temperatures, certain organisms like lichens are extremophiles.
Lichens are symbiotic associations between algae and fungi, which allow them to survive and perform metabolic activities, including photosynthesis, at temperatures as low as $-20^{\circ}C$.

(D) Viruses are non-cellular infectious agents that consist of a genetic material core surrounded by a protein coat called a capsid.
The genetic material in viruses can be either $DNA$ or $RNA$,but never both.
Therefore,viruses are composed of proteins and nucleic acids ($DNA$ or $RNA$).

(D) Viroids are infectious agents that are smaller than viruses.
They consist solely of a short strand of circular,single-stranded $RNA$.
Unlike viruses,viroids lack a protein coat (capsid).
Therefore,the correct description is that they have single-stranded $RNA$ not enclosed by a protein coat.

(C) The correct answer is $C$. Viruses are obligate intracellular parasites,meaning they require a living host cell to replicate their genetic material and synthesize viral proteins.
They lack the metabolic machinery (such as ribosomes and enzymes for energy production) required for independent growth.
Therefore,they cannot be grown on artificial culture media like sugary solutions or agar plates,as these do not provide the necessary cellular machinery for viral replication.

(A) Host specificity is considered a living character of a virus.
Viruses are obligate parasites that require specific receptors on the surface of host cells to attach and enter.
Since each virus can only infect specific types of host cells or organisms,this selective interaction demonstrates the biological activity and specificity inherent to living systems.

(C) The sub-phylum $Deoxyvira$ (under the phylum $Vira$) consists of viruses that possess $DNA$ as their genetic material. Therefore,the virus of $Deoxyvira$ contains $DNA$.

(A) . Viruses consist of a genetic material ($DNA$ or $RNA$) enclosed within a protein coat called a capsid.
$B$. Viroids,discovered by $T.O. Diener$ in $1971$,are infectious agents that consist solely of a short strand of circular,single-stranded $RNA$ without any protein coat.
$C$. Therefore,viroids differ from viruses because they are naked $RNA$ molecules lacking the protein capsid found in viruses.

(D) The $Tobacco \text{ } mosaic \text{ } virus$ $(TMV)$ was the first virus to be crystallized by Wendell Stanley in $1935$.
He demonstrated that viruses could be crystallized and that these crystals consist largely of proteins.
This discovery provided significant evidence that viruses are not fully living organisms in the traditional sense, as they could be stored as inert crystals and still retain their infectivity when introduced into a host.

(C) is the correct answer.
Lichens are highly sensitive to air pollution,particularly sulphur dioxide $(SO_2)$.
Cities typically have high levels of $SO_2$ due to vehicular emissions and industrial activities.
Therefore,lichens cannot survive or grow in urban environments,making them excellent bioindicators of air quality.

(D) The correct answer is $D$. Lichens are highly sensitive to atmospheric pollutants,particularly sulfur dioxide $(SO_2)$. They do not grow in areas with high levels of air pollution,making them excellent bioindicators for monitoring air quality.

(B) Lichens are symbiotic associations between algae and fungi. They are highly sensitive to atmospheric pollutants,particularly sulfur dioxide $(SO_2)$. Because they do not grow in polluted areas,they serve as excellent bioindicators for air quality and pollution levels.

(C) Lichens are symbiotic associations between fungi and algae. They are highly sensitive to sulfur dioxide $(SO_2)$ pollution in the atmosphere. Because they lack a protective cuticle and absorb nutrients directly from the air,they cannot survive in areas with high levels of $SO_2$. Therefore,they are widely used as bioindicators of air quality,specifically for $SO_2$ pollution.

(A) Lichens are considered excellent bio-indicators of air quality,particularly for sulfur dioxide $(SO_2)$ pollution. They do not grow in areas with high levels of air pollution because they absorb nutrients and water directly from the atmosphere through their surface. Therefore,their presence or absence serves as a reliable indicator of the surrounding air quality.

(D) Lichens,such as $Usnea$,are extremely sensitive to $SO_2$ and are widely regarded as bio-indicators of $SO_2$ pollution.
They are used to determine the Indices of Atmospheric Purity $(IAP)$.
Because they do not grow in areas with high levels of $SO_2$,their presence or absence serves as a reliable indicator of air quality.

(A) The symbiotic association between algae and fungi is known as $Lichens$. In this association, the algal component (phycobiont) provides food through photosynthesis, while the fungal component (mycobiont) provides protection, anchorage, and absorbs water and minerals for the algae.

(D) Lichens are symbiotic organisms consisting of a fungus and an alga or cyanobacterium. They are known for their extreme resilience and ability to survive in harsh environments, including polar regions and high-altitude mountains. Research has shown that lichens can maintain metabolic activity, including photosynthesis, at temperatures as low as $-20^{\circ}C$ or even lower, as they can remain physiologically active in a frozen state.

(B) The $3$-domain system of classification was proposed by $Carl$ $Woese$ in $1990$.
This system divides all living organisms into three domains: $Archaea$,$Bacteria$,and $Eukarya$.
Viruses are considered acellular entities and are not included in this classification system because they do not possess cellular machinery and are not considered true living organisms in the context of cellular life domains.
Therefore,the correct answer is $B$.

(D) Alzheimer's disease is a neurodegenerative disorder. It is not caused by viroids,viruses,or fungi. It is primarily associated with the accumulation of amyloid-beta plaques and tau protein tangles in the brain. Therefore,none of the options provided are the causative agents of Alzheimer's disease.

(B) Viruses are classified based on the type of host they infect.
$1$. Plant viruses typically contain single-stranded $RNA$ as their genetic material.
$2$. Tobacco mosaic virus $(TMV)$ is a well-known example of a plant virus that infects tobacco plants.
$3$. Polio virus is an animal virus.
$4$. Bacterial viruses (bacteriophages) infect bacteria.
Therefore,the correct option is $B$.

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

(A) The term 'virus' means 'venom' or 'poisonous fluid' (Pasteur). Viruses can be crystallized and stored in bottles like chemicals (Stanley). They are obligate parasites and require a host cell for replication; they cannot replicate on their own (not self-replicating). Parkinson's disease is a neurodegenerative disorder,not a viral disease.

(B) The Tobacco Mosaic Disease is caused by the Tobacco Mosaic Virus $(TMV)$.
$TMV$ was the first virus to be crystallized by $W.M. Stanley$ in $1935$.
It is a plant virus that infects tobacco plants,leading to mosaic patterns,mottling,and leaf curling.
Therefore,the correct option is $B$.

(C) Viroids are infectious agents that are smaller than viruses. They were discovered by $T.O. Diener$ in $1971$. $A$ viroid consists of a short strand of circular single-stranded $RNA$ without a protein coat (capsid). Because they lack a protein coat,they are smaller than viruses.

(A) $D.I.$ Ivanowsky discovered $TMV$ (Tobacco Mosaic Virus) in $1892$.
He demonstrated that the organisms causing mosaic disease in tobacco plants were smaller than bacteria because they could pass through bacteria-proof filters.

(D) virus is often described as a 'living chemical' because it exists at the boundary between living and non-living matter. Outside a host cell,a virus is inert and behaves like a chemical molecule (a nucleoprotein complex). Once it enters a living host cell,it utilizes the host's machinery to replicate,thereby exhibiting characteristics of life. Therefore,the term 'living chemical' is most appropriately used to describe a virus.

(B) The polio virus is a human pathogen that belongs to the genus $Enterovirus$ within the family $Picornaviridae$. Since it infects humans,it is classified as an animal virus. Plant viruses typically infect plants,bacteriophages infect bacteria,and nodule-forming bacteria are prokaryotes,not viruses.

(D) Viruses are nucleoprotein entities. The genetic material of a virus consists of nucleic acids,which can be either $RNA$ or $DNA$. No virus contains both $RNA$ and $DNA$ as its genetic material. Therefore,the nucleic acid present in a virus is either $RNA$ or $DNA$.

(A) The term 'virus' means 'venom' or 'poisonous fluid'. This name was coined by Louis Pasteur. Among the given options,none of the scientists listed (Diener,Ivanowsky,Iyengar) coined the term 'virus'. Louis Pasteur is the correct scientist who gave the name 'virus',but he is not listed correctly in the options provided. In many standard biology textbooks,this question is often presented with Louis Pasteur as the intended answer. Therefore,the question is technically flawed as the correct answer is not among the choices.

(B) Based on their external morphology or growth form,lichens are primarily classified into three main types:
$1$. Crustose lichens: These form a thin crust-like layer on the substrate.
$2$. Foliose lichens: These have a leaf-like,flattened,and lobed structure.
$3$. Fruticose lichens: These have a branched,shrub-like,or hanging structure.
Therefore,the correct answer is $B$ (three).

(B) Lichens are symbiotic associations between algae and fungi. In lichens,the fungal component (mycobiont) is responsible for sexual reproduction. The sexual reproductive structures produced by the fungal partner are known as fruiting bodies. Specifically,in many lichens,these fruiting bodies are often in the form of an $Apothecium$ (a cup-shaped structure) or $Perithecium$ (a flask-shaped structure). Among the given options,$Apothecium$ is the specific type of fruiting body commonly associated with sexual reproduction in lichens.

(D) Lichens are classified based on their growth forms into three main types:
$1$. $Crustose$ $lichens$: These grow as a thin crust on rocks or bark.
$2$. $Foliose$ $lichens$: These have a leaf-like,flattened thallus.
$3$. $Fruticose$ $lichens$: These have a branched,shrub-like,or hanging thallus.
Since all three are recognized growth forms of lichens,the correct answer is $D$.

(A) Lichens are symbiotic associations between algae and fungi.
In this association,the fungal component is known as the $Mycobiont$,while the algal component is known as the $Phycobiont$.
The $Mycobiont$ provides protection,anchorage,and absorption of minerals for the algae,while the $Phycobiont$ prepares food through photosynthesis.

(A) Lichens represent a symbiotic association between algae $(phycobiont)$ and fungi $(mycobiont)$.
In this association,the algal component is photosynthetic and is responsible for preparing food for both partners.
The fungal component provides protection,anchorage,and absorbs water and minerals from the surroundings for the algae.

(B) In lichens,the fungal component (mycobiont) produces reproductive structures called ascocarps.
An $Apothecium$ is a cup-shaped or saucer-shaped ascocarp.
$A$ $Perithecium$ is a flask-shaped ascocarp with a small opening called an ostiole at the top.
Therefore,the flask-shaped fruiting body of a lichen is known as a $Perithecium$.

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

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

(B) Lichens are symbiotic associations between fungi and algae. $Strigula$ is a well-known genus of foliicolous lichens,which grow on the surface of leaves. Bread mold $(Rhizopus)$ and $Penicillium$ are fungi,while $Anthoceros$ is a bryophyte (hornwort).

(C) Lichens are classified into three main types based on their growth form or morphology: $1$. Crustose (crust-like),$2$. Foliose (leaf-like),and $3$. Fruticose (shrub-like). Therefore,the classification is based on their external appearance or morphology.

(D) Lichens are symbiotic associations between fungi and algae. They reproduce asexually primarily through vegetative propagules.
$1$. $Soredia$ are small,powdery,bud-like structures consisting of a few algal cells wrapped in fungal hyphae.
$2$. $Isidia$ are small,stalked,outgrowths on the thallus surface that contain both algal and fungal components.
Both $Soredia$ and $Isidia$ serve as vegetative reproductive units in lichens. Therefore,the correct answer is $(D)$.

(A) The fruiting bodies of lichens,which are formed by the fungal component (mycobiont),are known as ascocarps.
Among these,the cup-shaped or saucer-shaped fruiting body is specifically called an $Apothecium$.
$Perithecium$ is flask-shaped,while $Androthecium$ is not a standard term for lichen fruiting bodies.
$Phycocyanin$ is a pigment found in cyanobacteria,not a fruiting body.

(A) Lichens are symbiotic associations between algae and fungi.
The algal component is known as the $Phycobiont$,which is autotrophic and prepares food.
The fungal component is known as the $Mycobiont$,which provides protection,anchorage,and absorbs water and minerals for the partner.
Therefore,the correct term for the algal component is $Phycobiont$.