Biological Classification

Biological Classification

Lichens are ecologically highly significant because they are notoriously good indicators of environmental:

The NCERT text highlights a very practical ecological application of lichens. They are exceptionally sensitive to toxic air pollutants, particularly sulphur dioxide (SO2) from industrial emissions. Because they lack roots and absorb everything directly from the air, they rapidly die in polluted areas. Thus, they act as highly effective, natural biological 'pollution indicators'—they simply 'do not grow in polluted areas'.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

In the symbiotic association known as lichens, what is the fungal component biologically termed?

Lichens represent a brilliantly successful, intimate, mutually beneficial symbiotic association between an alga and a fungus. The NCERT textbook specifies that the autotrophic, photosynthetic algal component is termed the phycobiont (which prepares food). Conversely, the heterotrophic fungal component is formally termed the 'mycobiont'. The fungus provides structural shelter, absorbs vital mineral nutrients, and retains water for its algal partner.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

In modern medicine, certain severe neurological diseases, like Bovine Spongiform Encephalopathy (BSE), were found to be

According to the latest additions in NCERT biology, 'prions' represent a highly unusual class of infectious agents. Unlike viruses or viroids which rely on nucleic acids, prions consist entirely of 'abnormally folded proteins' with no genetic material. When they enter a healthy brain, they induce normal proteins to misfold, leading to fatal neurodegenerative diseases like BSE (mad cow disease) in cattle and CJD in humans.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

Which of the following is a key distinguishing characteristic of the RNA found in viroids?

Viroids are primitive, naked strands of infectious RNA. Beyond lacking a protein capsid, specifies an important biochemical characteristic: the free RNA of the viroid is consistently of 'low molecular weight' compared to the massive RNA genomes found in typical RNA viruses. This tiny strand of RNA is nonetheless sufficient to hijack plant cellular machinery and cause severe diseases.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

In 1971, T.O. Diener discovered a novel infectious agent that lacked a protein coat and caused potato spindle tuber dise

The NCERT textbook highlights a critical discovery by 'T.O. Diener in 1971'. He isolated a completely new type of infectious agent that was significantly smaller than a standard virus. It uniquely caused 'potato spindle tuber disease'. Because this agent consisted solely of free, naked RNA and completely lacked the standard protective protein coat (capsid) found in viruses, Diener appropriately named it a 'viroid'.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

The protective protein coat of a virus is called a capsid. This capsid is made of smaller, repeating protein subunits kn

To protect their delicate internal nucleic acid genome, viruses are enveloped in a robust protein coat called a capsid. According to the NCERT text, this capsid is structurally composed of many small, repeating, interlocking protein subunits called 'capsomeres'. These capsomeres are typically arranged in highly precise geometric patterns, such as helical or complex polyhedral forms, depending on the specific virus species.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

Bacteriophages (viruses that uniquely infect bacteria) generally possess which type of genetic material?

Viruses exhibit patterns in their genetic material based on their host. The NCERT textbook specifies that viruses infecting plants generally have single-stranded RNA, and those infecting animals have single/double-stranded RNA or double-stranded DNA. However, 'bacteriophages' (viruses infecting bacteria) are definitively and 'usually double-stranded DNA viruses', which they inject directly into the bacterial host cell for replication.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

Which of the following statements about the genetic material of a virus is strictly correct?

Viruses consist of a protein coat shielding genetic material. According to the NCERT Class 11 Biology text, a fundamental biological rule regarding viral genomes is that 'no virus contains both RNA and DNA'. A virus is either an RNA virus or a DNA virus. The genetic material is the sole infectious component that hijacks the host's cellular machinery to replicate itself.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

W.M. Stanley (1935) showed a major breakthrough in virology by proving that viruses could be:

The physical nature of viruses was a mystery until 'W.M. Stanley' in 1935 biochemically manipulated them. The NCERT textbook highlights his discovery that viruses could actually be 'crystallised', and these biological crystals consisted almost entirely of tightly packed proteins. This proved they were inert outside a host, cementing their status as non-cellular obligate parasites lying on the boundary of living and non-living.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

Who demonstrated that the extract of infected tobacco plants could cause infection in healthy plants and coined the phra

In 1898, 'M.W. Beijerinck' made a monumental biological discovery. According to NCERT, he demonstrated that the filtered, cell-free extract from tobacco plants infected with the mosaic disease could actively cause the same infection in completely healthy plants. To describe this mysterious, soluble infectious agent, he famously coined the descriptive Latin phrase 'Contagium vivum fluidum' (infectious living fluid).

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

Who formally recognised certain microbes as the causal organism of the mosaic disease of tobacco in 1892, noticing they

The history of virology is detailed in the NCERT text. It specifically credits 'D.J. Ivanowsky (1892)' with the formal recognition of certain microscopic infectious agents as the causal organisms of tobacco mosaic disease. He astutely observed that these agents were capable of passing through standard bacteria-proof filters, conclusively proving that they were significantly smaller than conventional bacteria.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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Biological Classification

In the five-kingdom classification system proposed by Whittaker, which of the following entities were NOT given any plac

R.H. Whittaker's robust five-kingdom classification system (Monera, Protista, Fungi, Plantae, Animalia) is based on cellular structure and physiology. According to NCERT, truly acellular entities like 'viruses, viroids, and prions' (as well as the symbiotic lichens) were totally excluded and found no place in this system. This is because they are not considered truly 'living' cellular organisms in the traditional biological sense.

Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.6 Viruses, Viroids, Prions and Lichens

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