13. The correct hierarchy of taxa in the Linnaean classification of eukaryotes is

(A) kingdom, class, phylum, order, family, genus

(B) kingdom, order, class, phylum, family, genus

(C) kingdom, phylum, order, family, class, genus

(D) kingdom, phylum, class, order, family, genus

Correct Hierarchy of Taxa in Linnaean Classification of Eukaryotes

Detailed Explanation of the Correct Hierarchy of Taxa

The correct hierarchy of taxa in the Linnaean classification of eukaryotes is Kingdom → Phylum → Class → Order → Family → Genus. Therefore, option (D) is the correct answer.

Biological classification is a systematic method used to arrange organisms into different groups based on their similarities, differences, and evolutionary relationships. The Linnaean system of classification organizes living organisms into a series of hierarchical taxonomic categories. A broader category contains many organisms, while each successive category becomes more specific.

In the hierarchy given in this question, kingdom is the broadest taxonomic category and genus is the most specific category. The correct sequence moves from the broadest rank toward increasingly specific ranks as follows:

Kingdom → Phylum → Class → Order → Family → Genus

A complete modern taxonomic hierarchy generally continues further to the species level:

Kingdom → Phylum → Class → Order → Family → Genus → Species

The question, however, asks only for the correct arrangement of the ranks provided in the options. Since option (D) places every taxonomic rank in its correct hierarchical position, it is the correct choice.

Understanding Each Taxonomic Rank in Detail

Kingdom

Kingdom is the highest and broadest taxonomic rank among the categories listed in this question. It includes a very large number of organisms that share certain fundamental characteristics. Organisms within the same kingdom may differ greatly in their structure, physiology, mode of nutrition, and habitat, but they share broad biological features.

For example, animals are placed in the kingdom Animalia, while plants belong to the kingdom Plantae. Because kingdom is a broad taxonomic category, it contains many phyla.

Thus, the hierarchy begins with:

Kingdom → Phylum

Phylum

Phylum is the taxonomic category immediately below kingdom and above class. A kingdom is divided into different phyla based on major structural and organizational features.

For example, within the animal kingdom, organisms possessing a notochord at some stage of their life cycle are placed in the phylum Chordata. Similarly, animals with jointed appendages and an exoskeleton are placed in the phylum Arthropoda.

A single phylum contains one or more classes. Therefore, the correct position of phylum is:

Kingdom → Phylum → Class

Class

Class is the taxonomic rank below phylum and above order. Members of a class share more specific characteristics than members grouped together at the phylum level.

For example, the phylum Chordata contains several classes. Mammals belong to the class Mammalia, while birds belong to the class Aves. Organisms within the same class show a greater degree of similarity than organisms that merely belong to the same phylum.

A class is further divided into different orders. Therefore, the correct relationship is:

Phylum → Class → Order

Order

Order is the taxonomic category below class and above family. It brings together related families that share important structural, biological, or evolutionary characteristics.

For example, within the class Mammalia, primates are placed in the order Primates. Other mammalian groups are placed into different orders based on their distinguishing characteristics.

Since an order contains one or more related families, its correct position is:

Class → Order → Family

Family

Family is the taxonomic rank below order and above genus. Members of the same family are more closely related to one another than members of the same order.

A family contains one or more closely related genera. For example, the family Felidae includes genera containing cats and other closely related feline animals. At the family level, organisms show a relatively high degree of similarity.

Therefore, the correct position of family is:

Order → Family → Genus

Genus

Genus is the most specific taxonomic rank mentioned in the question. It is placed below family and above species. A genus contains one or more closely related species.

For example, humans belong to the genus Homo. The species name of modern humans is Homo sapiens, where Homo represents the genus and sapiens represents the specific epithet.

Thus, among the ranks listed in the question, genus appears last:

Family → Genus

Why Option (A) Is Incorrect

Option (A) gives the sequence:

Kingdom → Class → Phylum → Order → Family → Genus

This option is incorrect because it reverses the positions of phylum and class. In the correct Linnaean classification hierarchy, phylum is a broader taxonomic category than class. A kingdom is divided into phyla, and each phylum is further divided into classes.

The correct relationship is:

Kingdom → Phylum → Class

not:

Kingdom → Class → Phylum

Therefore, option (A) does not represent the correct taxonomic hierarchy.

Why Option (B) Is Incorrect

Option (B) gives the sequence:

Kingdom → Order → Class → Phylum → Family → Genus

This option is incorrect because several taxonomic categories are placed in the wrong order. Order cannot come immediately after kingdom because order is a much more specific taxonomic category.

The correct sequence must place phylum and class before order:

Kingdom → Phylum → Class → Order

Since option (B) incorrectly places order above class and phylum, it fails to represent the Linnaean taxonomic hierarchy.

Why Option (C) Is Incorrect

Option (C) gives the sequence:

Kingdom → Phylum → Order → Family → Class → Genus

The beginning of this sequence is partly correct because kingdom is followed by phylum. However, the remaining categories are incorrectly arranged.

After phylum, the next taxonomic rank must be class, not order. Furthermore, class cannot be placed between family and genus because class is a much broader taxonomic category than both family and genus.

The correct relationship is:

Phylum → Class → Order → Family → Genus

Therefore, option (C) is incorrect.

Why Option (D) Is Correct

Option (D) gives the sequence:

Kingdom → Phylum → Class → Order → Family → Genus

This is the correct hierarchy of taxa in the Linnaean classification of eukaryotes. Each category is placed in the correct order from the broadest taxonomic rank to the more specific taxonomic rank.

A kingdom contains phyla, a phylum contains classes, a class contains orders, an order contains families, and a family contains genera. Therefore, the sequence in option (D) accurately represents the hierarchical organization used in biological classification.

Complete Taxonomic Hierarchy

The complete commonly used hierarchy of major taxonomic ranks is:

Kingdom → Phylum → Class → Order → Family → Genus → Species

As we move from kingdom toward species, the number of organisms included in each category generally decreases, while the similarities and relatedness among the organisms increase.

At the kingdom level, organisms share only broad characteristics. At the genus and species levels, organisms are much more closely related and share many specific features.

Final Answer

The correct hierarchy of taxa in the Linnaean classification of eukaryotes is:

Kingdom → Phylum → Class → Order → Family → Genus

Therefore, the correct answer is (D) kingdom, phylum, class, order, family, genus.