The Living World: common doubts, answered
The questions students ask most often about The Living World, each with a short answer. For the full chapter, read the The Living World notes.
Diversity and the need for naming
Read this section in the notes →Why do we need scientific names when every organism already has a local name?
Local names change from region to region, even inside one country, so people elsewhere cannot tell whether they are discussing the same organism. A scientific name is the same worldwide, belongs to only one organism, and is not reused for any other. That shared label lets scientists in different countries communicate without confusion.
What is the difference between nomenclature and identification?
Identification means describing an organism correctly so you know exactly which organism you have, while nomenclature means giving it its standard name. Identification comes first, because a name can only be attached once the organism has been recognised and described properly. Naming without correct identification would put the same name on different organisms.
What is the difference between ICBN and ICZN?
ICBN, the International Code for Botanical Nomenclature, governs how plants are named, whereas ICZN, the International Code of Zoological Nomenclature, governs how animals are named. Each code lays down the rules that make a scientific name valid, so that every organism ends up with one accepted name that nobody else can use.
How many species have been described so far?
About 1.7 to 1.8 million species of living organisms are known and described. The figure is not final, because new species are still being identified, both in poorly explored places and in regions that have been studied for a long time. So the number keeps rising as exploration and study continue.
Binomial nomenclature
Read this section in the notes →What is binomial nomenclature and who introduced it?
Binomial nomenclature is the system of giving every organism a two-part scientific name made of the genus name followed by the specific epithet. Carolus Linnaeus introduced it, and biologists everywhere still use it. For example, Mangifera indica is the name of mango, with Mangifera as the genus and indica as the epithet.
How do you write a scientific name correctly?
Write the genus with a capital first letter and the specific epithet entirely in small letters, as in Homo sapiens. In print the name is italicised. In handwriting, underline the two words separately instead of drawing one line under both. The words are Latin or Latinised, whatever language they were originally taken from.
Why is a handwritten scientific name underlined?
Underlining stands in for italics, which cannot be produced by hand. Printed names are italic, so a handwritten name is underlined to show that it is a scientific name. Each of the two words gets its own separate underline, because genus and epithet are distinct parts of the name and are not joined by a single line.
What does "Linn." mean in Mangifera indica Linn.?
Linn. is the abbreviated name of the author who first described the species, here Linnaeus. The author's name may be added after the epithet to show who published the original description. It is not part of the two-word scientific name itself, so the binomial remains Mangifera indica.
Classification, taxonomy and systematics
Read this section in the notes →What is the difference between classification and taxonomy?
Classification is the act of grouping organisms into convenient categories using easily observable characters, whereas taxonomy is the broader science of arranging organisms into taxa using many characteristics, such as external and internal structure, cell structure, development and ecology. Classification is therefore one of the processes that taxonomy includes.
What is a taxon, with examples?
A taxon is a group of organisms placed at any one rank of classification. Dogs, mammals, animals, rice and wheat are all taxa, though they sit at very different levels, because dogs are mammals and mammals are animals. So taxon refers to the group itself, whatever its rank happens to be.
Which four processes are basic to taxonomy?
The four basic processes are characterisation, identification, classification and nomenclature. First the characters of an organism are studied, then it is identified, then it is placed in a suitable group, and finally it is given a standard name. Together they let biologists describe and organise the diversity of living things.
What is the difference between taxonomy and systematics?
Systematics is the wider study of the kinds and diversity of organisms and the relationships among them, including evolutionary relationships. Taxonomy deals with characterising, identifying, classifying and naming organisms. The word systematics comes from the Latin systema, and Linnaeus used it in the title of his book Systema Naturae.
Taxonomic categories and hierarchy
Read this section in the notes →What is the correct order of taxonomic categories from lowest to highest?
The order from lowest to highest is species, genus, family, order, class, phylum and kingdom. For plants, the word division is used in place of phylum. Species is the lowest category for every organism and kingdom is the highest, so each step upward groups together several units from the step below.
What is the difference between phylum and division?
Both are the same rank in the hierarchy, a group of related classes; phylum is the term used for animals and division is the term used for plants. For instance, humans belong to the phylum Chordata, while mango and wheat belong to the division Angiospermae. Never write phylum for a plant in an answer.
Species and genus
Read this section in the notes →What is the difference between a species and a genus?
A species is a group of individuals with fundamental similarities that can be told apart from close relatives by distinct morphological differences. A genus is a higher group made of closely related species that share more characters with each other than with species of other genera. Potato and brinjal are different species of the genus Solanum.
Why are lion, tiger and leopard placed in the same genus?
They are in the genus Panthera because they share several characters with one another, more than they share with any other group. The lion is Panthera leo, the tiger is P. tigris and the leopard is P. pardus. Domestic cats are not included, since they belong to a different genus, Felis.
Family, order and class
Read this section in the notes →Which families do cats and dogs belong to?
Cats belong to the family Felidae and dogs belong to the family Canidae. They share some features but differ in others, so they are kept in separate families. Both families, however, are placed together in the order Carnivora, which also shows that an order groups families that share only a few characters.
Which order contains the families Solanaceae and Convolvulaceae?
Both families are placed in the order Polymoniales, mainly because of their floral characters. This is easy to confuse with Sapindales, which is the order of mango, and Poales, which is the order of wheat. Solanaceae itself includes Solanum, Petunia and Datura as genera.
In which class do both Primata and Carnivora fall?
Both fall in the class Mammalia. Order Primata includes monkey, gorilla and gibbon, while order Carnivora includes tiger, cat and dog. A class is a group of related orders, and Mammalia contains several other orders as well. Note the spelling Primata, as used in the NCERT table.
Phylum, kingdom and the hierarchy table
Read this section in the notes →What is the taxonomic classification of the housefly?
The housefly, Musca domestica, belongs to the genus Musca, family Muscidae, order Diptera, class Insecta and phylum Arthropoda, all within the animal kingdom. A quick way to remember it is that Muscidae comes from the genus Musca, and that insects form a class inside the very large phylum Arthropoda.
What features place fishes, birds and mammals in the phylum Chordata?
They all share a notochord and a dorsal hollow neural system. Fishes, amphibians, reptiles, birds and mammals have these features, so they are grouped together as the phylum Chordata. In humans the full chain is Homo sapiens, genus Homo, family Hominidae, order Primata, class Mammalia, phylum Chordata.
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