1.Why are living organisms classified?
There are various kinds of plants, animals, and microbes on earth. All these living organisms differ many ways and have respective characteristics. As there are millions of living organisms on earth, studying each of them is very difficult. Therefore, scientists have devised way to classify all living organisms. These methods of classification are based on rules and principles that allow identification, nomenclature, and finally classification of an organism. For example, based on certain principles, if an organism is identified as an insect, it will be given a scientific name and then grouped with other similar organisms. Various groups or taxon include organisms based on their similarity and differences. Hence, the biological classification helps in studying the relationship between various organisms.
2. Why are the classification systems changing every now and then?
Earth has millions of plants, animals, and microorganisms. Many of these have been identified while many new species are still being discovered around the world. Therefore, to classify these newly discovered species, new systems of classification have to be devised every now and then. This creates the requirement to change the existing systems of classification.
3. What different criteria would you choose to classify people that you meet often?
To classify a class of fifty students, let us start the classification on the basis of gender of the students. This can be classified in to two major groups- boys and girls. Each of these two groups can be further classified on the basis of the names of the students. Since it is possible that more than one student can have a particular name, these names can be further divided based on the surnames. Since there is still some chance that more than one student can have the same surname, the final level of classification can be done based on the roll numbers of each student.
4. What do we learn from identification of individuals and populations?
The identification of individuals and populations help in classifying individuals into similar groups. It helps to study similarities and dissimilarities among the individuals of same kind or between different types of organisms.
5. Given below is the scientific name of Mango. Identify the correctly written name.
- Mangifera Indica
- Mangifera indica
According to binomial system of nomenclature, the generic name of a species always starts with a capital letter whereas the specific name starts with a small letter. Therefore, the correct scientific name of Mango is Mangifera indica.
6. Define a taxon. Give some examples of taxa at different hierarchical levels.
Each unit or category of classification is called as a taxon. It represents a rank.
For example, the basic level of Classification is species, followed by genus, family, order, Class, phylum or division, in ascending order. The highest level of Classification is known as kingdom.
7. Can you identify the correct sequence of taxonomical categories?
(a) Species → Order → Phylum → Kingdom
(b) Genus → Species → Order → Kingdom
(c) Species → Genus → Order → Phylum
The correct hierarchical arrangement of taxonomic categories in ascending order is Genus → Family → Order → Class → Phylum
Hence, both (a) and (c) represent correct sequences of taxonomic categories. In sequence (b), species should be followed by genus.Therefore, it does not represent the correct sequence.
8.Try to collect all the currently accepted meanings for the word ‘species’. Discuss with your teacher the meaning of species in case of higher plants and animals on one hand, and bacteria on the other hand.
ln biological terms, species is the basic taxonomic rank. It is defined as a group of similar organisms that are capable of interbreeding under natural conditions to produce fertile offsprings. Therefore, a group of similar individuals that are respectively isolated form a species. Species can also be defined as group of individuals that share the same gene pool.
9. Define and understand the following terms:
Classes comprising animals like fishes, amphibians, reptiles, birds along with mammals constitute the next higher category called Phylum. All these, based on the common features like presence of notochord and dorsal hollow neural system, are included in phylum Chordata. In case of plants, classes with a few similar characters are assigned to a higher category called Division
This category includes related orders. For example, order Primata comprising monkey, gorilla and gibbon is placed in class Mammalia along with order Carnivora that includes animals like tiger, cat and dog. Class Mammalia has other orders also.
Family, has a group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plant species. Among plants for example, three different genera Solanum, Petunia and Datura are placed in the family Solanaceae. Among animals for example, genus Panthera, comprising lion, tiger, leopard is put along with genus.
Order and other higher taxonomic categories are identified based on the aggregates of characters. Order being a higher category, is the assemblage of families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family. Plant families like Convolvulaceae, Solanaceae are included in the order Polymoniales mainly based on the floral characters. The animal order, Carnivora, includes families like Felidae and Cancidae.
Genus comprises a group of related species which has more characters in common in comparison to species of other genera. We can say that genera are aggregates of closely related species. For example, potato, tomato and brinjal are three different species but all belong to the genus Solanum. Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) with several common features, are all species of the genus Panthera. This genus differs from another genus Felis which includes cats.
10. How is a key helpful in the identification and classification of an organism?
Key is another taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities. The keys are based on the contrasting characters generally in a pair called couplet. It represents the choice made between two opposite options. This results in acceptance of only one and rejection of the other. Each statement in the key is called a lead. Separate taxonomic keys are required for each taxonomic category such as family, genus and species for identification purposes. Keys are generally analytical in nature.
11.Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Classification is not a single step process but involves hierarchy of steps in which each step represents a rank or category. Since the category is a part of overall taxonomic arrangement, it is called the taxonomic category and all categories together constitute the taxonomic hierarchy.
The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy.
Kingdom à phylum à classà order àfamilyà genus àspecies
Classification of a Plant: As an example, let us classify Solanum Melongena (Brinjal). Kingdom - Plantae Division - Angiospermae Class - Dicotyledonae Order - Solanales Family - Solanaceae Genus - Solanum Species – melongena
Classification of an Animal: As an example, let us classify Columba Livia (Blue Rock Dove). Kingdom - Animalia Phylum - chordata Class - Aves Order - Columbiformes Family - Columbidae Genus - columba Species – livia