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Biological Classification: questions with answers

Class 11 Biology, Chapter 2 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.

How to teach this chapter · Common misconceptions & worked visual for this chapter

Changing classification systems and five-kingdom criteria

Question 1

Which comparison of Aristotle, Linnaeus, and Whittaker is correct?

  1. (a)Each system is permanently correct, so their conflicting groupings cannot be revised.
  2. (b)All three used morphology alone, which is sufficient for the five kingdoms.
  3. (c)Their systems differ because later classifications incorporated additional biological distinctions and relationships.
  4. (d)Whittaker restored the same two kingdoms without adding criteria.
Show answer

(c) Their systems differ because later classifications incorporated additional biological distinctions and relationships.

Aristotle used simple morphology, Linnaeus used two kingdoms, and Whittaker used five kingdoms and several biological criteria.

Question 2

An old system places fungi with green plants because both have cell walls. What big problem does Whittaker's approach reveal?

  1. (a)Fungi differ only in colour, which is the sole five-kingdom criterion.
  2. (b)Cell-wall presence alone hides major differences in nutrition and wall composition.
  3. (c)The old system already separated all prokaryotes from eukaryotes.
  4. (d)There is no problem because every cell-walled organism belongs in Plantae.
Show answer

(b) Cell-wall presence alone hides major differences in nutrition and wall composition.

Fungi are absorptive heterotrophs with chitinous walls, whereas green plants are photosynthetic and mainly cellulose-walled.

Question 3

A wall-bearing organism once grouped with plants is shown to be a prokaryote with a very different mode of nutrition. Why can its classification change?

  1. (a)Only visible shape may be considered, so cell type and nutrition are irrelevant.
  2. (b)It cannot change because the first classification is permanent.
  3. (c)New biological evidence can justify replacing an older grouping with a more informative one.
  4. (d)Its scientific name changes automatically whenever its habitat changes.
Show answer

(c) New biological evidence can justify replacing an older grouping with a more informative one.

Classifications are revised when cell structure, nutrition, and evolutionary evidence reveal that an older grouping hides important differences.

Protist groups and their adaptations

Question 4

Organisms multiply rapidly in the sea, colour the water red, and release toxins that kill fish. Which organisms cause this red tide?

  1. (a)Diatoms
  2. (b)Euglenoids
  3. (c)Red dinoflagellates
  4. (d)Red algae
Show answer

(c) Red dinoflagellates

Red dinoflagellates such as Gonyaulax multiply rapidly and make the sea appear red. Toxins released by these organisms may kill fish.

Question 5

Which body covering allows Euglena to change its shape?

  1. (a)Rigid chitin cell wall
  2. (b)Silica cell wall
  3. (c)Protein-rich pellicle
  4. (d)Rigid cellulose cell wall
Show answer

(c) Protein-rich pellicle

Euglena has a protein-rich covering called a pellicle instead of a cell wall. The pellicle makes its body flexible, allowing it to change shape.

Question 6

Why can ancient diatom deposits be used for polishing and filtration?

  1. (a)Living diatom cytoplasm accumulates unchanged as the deposit.
  2. (b)A red algal toxin hardens into polishing powder.
  3. (c)All protists photosynthesise silica directly into food reserves.
  4. (d)Indestructible silica-rich wall remains accumulate into a gritty deposit.
Show answer

(d) Indestructible silica-rich wall remains accumulate into a gritty deposit.

Diatom walls contain durable silica and accumulate as gritty diatomaceous earth after the cells die.

Monera: diversity, nutrition, and reproduction

Question 7

By which process do bacteria mainly reproduce?

  1. (a)Fission
  2. (b)Budding
  3. (c)Spores formed by heterocysts
  4. (d)DNA transfer between bacteria
Show answer

(a) Fission

Bacteria reproduce mainly by fission. They also show a primitive sort of DNA transfer, but that is not their main way of reproducing. Heterocysts are the nitrogen-fixing cells of some cyanobacteria, not spores.

Question 8

What is the main function of heterocysts in a Nostoc filament?

  1. (a)Survival in unfavourable conditions
  2. (b)Production of new filaments
  3. (c)Fixation of atmospheric nitrogen
  4. (d)Photosynthesis
Show answer

(c) Fixation of atmospheric nitrogen

Heterocysts are specialised cells that fix atmospheric nitrogen. They are not reproductive spores. Resistant bacterial spores help bacteria survive unfavourable conditions.

Question 9

A bacterium breaks down dead leaves in soil. What ecological role does it perform in this process?

  1. (a)Producing food by photosynthesis
  2. (b)Fixing atmospheric nitrogen
  3. (c)Recycling nutrients
  4. (d)Causing disease
Show answer

(c) Recycling nutrients

Decomposer bacteria break down dead matter and return nutrients to the soil. Many bacteria perform useful roles rather than causing disease.

Fungal structure, reproduction, and classes

Question 10

Which comparison of fungal body organisation is correct?

  1. (a)Plasmogamy and karyogamy describe the same cross wall.
  2. (b)Every fungus is multicellular and every hypha is divided by septa.
  3. (c)All fungal forms are photosynthetic plants with cellulose walls.
  4. (d)Fungal organisation ranges from unicellular yeast to septate or coenocytic hyphae.
Show answer

(d) Fungal organisation ranges from unicellular yeast to septate or coenocytic hyphae.

Yeast is unicellular; many fungi form septate hyphae, while phycomycetes can have aseptate coenocytic hyphae with multinucleate cytoplasm.

Question 11

Which statement correctly locates fungal spores?

  1. (a)All three spores are formed only inside sporangia.
  2. (b)Conidia—external on conidiophores; ascospores—inside asci; basidiospores—external on basidia.
  3. (c)Conidia are produced endogenously inside asci.
  4. (d)These locations define a permanent sexual stage unique to Deuteromycetes.
Show answer

(b) Conidia—external on conidiophores; ascospores—inside asci; basidiospores—external on basidia.

Conidia are produced exogenously on conidiophores, ascospores endogenously in asci, and basidiospores exogenously on basidia.

Plantae, Animalia, and alternation of generations

Question 12

Which comparison of cell boundaries is correct?

  1. (a)Plants—cellulose wall; fungi—chitinous wall; animals—no cell wall.
  2. (b)Plants have chitinous walls like fungi.
  3. (c)All three groups lack cell walls.
  4. (d)Animals have cellulose walls for support.
Show answer

(a) Plants—cellulose wall; fungi—chitinous wall; animals—no cell wall.

Plant walls are mainly cellulose, fungal walls contain chitin, and animal cells lack cell walls.

Question 13

Which combination of stored food and cell wall status is characteristic of animals?

  1. (a)Starch; chitinous cell wall present
  2. (b)Starch; cellulose cell wall present
  3. (c)Glycogen or fat; cell wall absent
  4. (d)Glycogen or fat; supporting cell wall present
Show answer

(c) Glycogen or fat; cell wall absent

Animals store food reserves as glycogen or fat, and their cells lack cell walls. Plants typically store starch and have mainly cellulose cell walls.

Viruses, viroids, prions, and lichens

Question 14

Which comparison of a virus, viroid, and prion is correct?

  1. (a)A prion is infectious RNA that lacks a protein coat.
  2. (b)A viroid is simply a smaller virus enclosed by a capsid.
  3. (c)Both partners in a lichen are infectious autotrophs.
  4. (d)Virus—nucleic acid with capsid; viroid—free RNA; prion—infectious protein.
Show answer

(d) Virus—nucleic acid with capsid; viroid—free RNA; prion—infectious protein.

A virus has nucleic acid plus capsid, a viroid is uncoated RNA, and a prion is infectious misfolded protein.

Question 15

A virus can be crystallised outside a host but makes many copies after entering a living cell. Which viral characteristics do these observations demonstrate?

  1. (a)Inertness outside hosts and dependence on living cells for replication
  2. (b)Independence from hosts after capsid formation
  3. (c)Independent reproduction outside living cells
  4. (d)Cellular organisation with both DNA and RNA
Show answer

(a) Inertness outside hosts and dependence on living cells for replication

Crystallisation provides evidence of inertness outside hosts. Viruses replicate only inside living host cells by using the host-cell machinery.

Common misconception in Biological Classification

Open full misconception guide →

Can a virus multiply on nutrient medium by itself?

Wrong

A virus grows on nutrient agar like bacteria.

Why it feels right. Both are microscopic infectious agents.

Right

A virus uses a suitable host cell to produce new virus particles.

Worked example

Bacterium
Suitable nutrient agar→Colony
Virus
Suitable living cell→Uses host machinery→New virus particles
Nutrient agar supports many bacteria. A virus needs a suitable living cell to reproduce.
  1. Compare a bacterial colony on agar with a virus grown in suitable living cells.
  2. The latter relies on the cell’s machinery.