Which one among the following is the correct scheme followed for classification of animals?

Correct — D, Phylum → Class → Order → Family → Genus → Species. Classification proceeds by narrowing: each step down the ladder is a smaller group whose members share more characters with one another. NCERT names the categories in exactly this sequence — kingdom, phylum or division for plants, class, order, family, genus and species — with species as the lowest category for every organism, plant or animal. The stem starts the list at phylum because it asks specifically about animals, and kingdom, the step above, would be Animalia in every case and so carries no information. Take a familiar animal and the ladder becomes concrete: a tiger belongs to phylum Chordata, class Mammalia, order Carnivora, family Felidae, genus Panthera and species tigris. The other three options can be dismissed by two quick checks — does phylum come before class, and does genus come before species? Only option (d) passes both. It is worth knowing that plants use division where animals use phylum, and that ranks are often subdivided further into sub-phyla, super-orders and the like without changing this backbone.

• (a)Class → Phylum → Order → Genus → Family → Species — Begins with class above phylum, which inverts the top of the ladder, and then places genus before family. Both errors run the sequence in the wrong direction at once.
• (b)Phylum → Class → Family → Genus → Order → Species — Starts correctly with phylum and class, then puts family straight after and leaves order until second-last. Order is the assemblage of families and therefore sits above family, not below genus.
• (c)Order → Class → Phylum → Family → Species → Genus — Almost completely inverted: order is placed at the top, above class and phylum, and species is put above genus. Species is the lowest category of all, and a genus is a group of related species.

Taxonomy arranges living things in a hierarchy of ranks, each rank called a taxon. Working downwards the standard categories are kingdom, phylum for animals or division for plants, class, order, family, genus and species. Each step is defined by an increasing number of shared characters, so a family shares more with itself than an order does, and a genus more again. Species is the basic and lowest unit — a group of individuals with fundamental similarities that can interbreed — and the two-word scientific name of any organism is built from its genus and its species, a convention that goes back to Carl Linnaeus.

Sequence questions are best answered from two ends rather than by trying to recall the whole chain in one go. At the bottom, genus must come immediately before species, because the scientific name is genus plus species; any option that reverses them is out, which disposes of option (c). At the top, phylum must precede class, since a phylum such as Chordata contains many classes; that disposes of option (a). The remaining decision is whether order or family comes first, and the rule is that an order is an assemblage of families — order Carnivora contains the families Felidae and Canidae — so order sits above family, which disposes of option (b). The common mnemonic runs king, phylum, class, order, family, genus, species; whichever memory aid you use, anchoring it to a real animal is what makes it stick.

• The taxonomic categories in descending order are kingdom, phylum or division, class, order, family, genus and species.
• Species is the lowest category, and every organism in both the plant and animal kingdoms has one.
• An order is an assemblage of families, and a class includes related orders — which fixes the relative position of those two ranks.
• The binomial name of an organism is its genus followed by its species, which is why those two ranks are adjacent at the bottom.
• Animals are divided into phyla while plants are divided into divisions; the rest of the ladder is common to both.

• Reversing genus and species; the binomial name gives the order away.
• Placing family above order — an order contains families, not the other way round.
• Forgetting that plants use division in place of phylum, which matters when a question mixes plant and animal examples.

Either as an ordering item like this one, or by naming a rank and asking what lies immediately above or below it, or by giving an organism's full classification and asking which rank is misplaced.

• practice — not a real PYQ

  Which one of the following is the lowest taxonomic category?

  • (a)Genus
  • (b)Family
  • (c)Species
  • (d)Order

  Answer(c) Species — every organism, plant or animal, has species as its lowest category, and a genus is a group of related species.

• practice — not a real PYQ

  In the classification of plants, which category takes the place occupied by phylum in animals?

  • (a)Order
  • (b)Division
  • (c)Family
  • (d)Class

  Answer(b) Division — plants are grouped into divisions where animals are grouped into phyla; the remaining ranks are the same for both.