SolveItClass 9 · NCERT

NCERT Solutions · Class 9 Science Patterns in Life: Diversity and Classification

25 questions · 25 still being checked

Revise, Reflect, Refine 12.8–12.9 (part 12 of 14)

  1. Exercise 12.8

    Viruses were studied in earlier classes. Why are they not placed in any of the five kingdoms? Give reasons.

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    Because viruses are acellular — they are not made of cells, and every criterion of the five kingdom system is a criterion about cells.
    No cell type to record. The first branch of Fig. $\displaystyle 12.5$ asks prokaryote or eukaryote. A virus is neither: it has no nucleus, primitive or true.
    No cell structure to record. There is no cell wall to be present or absent, and none to be made of cellulose or chitin.
    No level of organisation. It is neither unicellular nor multicellular, because it has no cells to count.
    No mode of nutrition. It does not take in, absorb or make food, so it cannot be called autotrophic or heterotrophic, and it has no ecological role as producer, consumer or decomposer.
    It shows no life processes on its own. Outside a host cell it remains inactive; it can only multiply inside a living cell.
    Yet it is not plainly non-living either — it contains genetic material, like every living organism. It sits between the two categories.
    So Whittaker's system has no box for it. The system was designed to sort cellular life, and NCERT's own key puts it in one line: there is no place for acellular entities.
    NCERT_Solution_Class9_Science_Ch12_RRR_Q12-8

  2. Exercise 12.9

    If you were asked to revise the five kingdom classification, would you create a separate category for viruses or keep them outside the system? Justify your answer and explain what this indicates about the evolving nature of scientific classification.

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    My stand: create a separate category for viruses rather than leaving them outside — but make it a category alongside the five kingdoms, not one of them.
    Why not inside the five kingdoms. Every one of Whittaker's criteria — cell type, cell wall, unicellular or multicellular, mode of nutrition — assumes a cell. A virus has none, so forcing it into Monera or Protista would break the very rules the system runs on.
    Why not simply ignore them. Viruses contain genetic material, they multiply, they evolve, and they cause disease in every kingdom. A classification meant to help scientists identify, name and discuss organisms using a common system cannot leave out something so widespread.
    What the separate category would be built on. Non-cellular organisation, the type of genetic material carried, and complete dependence on a host cell for reproduction — criteria a virus can actually be tested against.
    The honest alternative view: keep them outside, on the ground that the five kingdom system classifies living organisms and a virus shows no life processes outside a host. This is a defensible answer too, provided the reasoning is stated.
    What this tells us about scientific classification: it is not fixed — it is an ongoing process of reasoning and change.
    The chapter's own timeline proves it. Aristotle grouped by habitat in the 4th century BCE; two kingdoms in \(\displaystyle 1758\); Protista added in \(\displaystyle 1866\); Monera in \(\displaystyle 1938\); Whittaker's five kingdoms in \(\displaystyle 1969\); Woese's three domains in \(\displaystyle 1977\).
    Each change followed a new tool or a new fact — better microscopes, staining techniques, then DNA comparison. Viruses are simply the next case pressing on the boundary, and a system that can be revised is a strength of science, not a flaw.