Chapter 1 : The Living World

1.Why are living organisms classified?

Answer: A huge variety of plants, animals, and microbes are found on earth. All these living organisms differ in size, shape, colour, habitat, and many other characteristics. As there are large number of living organisms on earth, studying each of them is impossible. Therefore, scientists have devised mechanisms 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.

2: Why are the classification systems changing every now and then?

Answer:  Huge numbers of plants, animals, and microorganisms are found on earth. Many of these have been identified by the scientists 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 derived 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?

Answer:The various criteria that may be chosen to classify people whom we meet often include behaviour, geographical location, morphology, family members, relatives, friends etc.

4. What do we learn from identification of individuals and populations?

Answer: The knowledge of characteristic of an individual or its whole population helps in identification of similarities and dissimilarities among the individuals of similar kind or between different types of organisms. It helps us to classify the organisms in various categories depending upon these similarities and dissimilarities.

5: Given below is the scientific name of Mango. Identify the correctly written name.

Mangifera Indica

Mangifera indica

Answer: In 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 example of taxa at different hierarchical levels.

Answer: Taxon can be defined as the taxonomic unit in the biological system of classification of organism. For example a phylum, order, family, genus or species represents taxon. It represents a rank. For example, all the insects form a taxon. Taxon of class category for birds is Aves and taxon of Phylum category for birds is Chordata. The degree of relationship and degree of similarity varies with the rank of the taxon. Individuals of a higher rank, say Order or Family, are less closely related than those of a lower rank, such as Genus or Species.

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

Answer:The correct hierarchical arrangement of taxonomic categories in ascending order is

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

Therefore, 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.

Answer. Species occupies a key position in classification. It is the lowest taxonomic category. It is a natural population of individuals or group of populations which resemble one another in all essential morphological and reproductive characters so that they are able to interbreed freely and produce fertile offsprings. Each species is also called genetically distinct and reproductively isolated natural population. Mayr (1964) has defined species as “a group of actually or potentially interbreeding populations that are reproductively isolated from other such groups”.
In higher plants and animals the term ‘species’ refers to a group of individuals that are able to interbreed freely and produce fertile offsprings. But, in case of bacteria interbreeding cannot serve as the best criteria for delimiting species because bacteria usually reproduce asexually. Conjugation, transformation and transduction, which are termed as sexual reproduction methods in bacteria, also do not correspond to true interbreeding. Thus, for bacteria many other characters such as molecular homology, biochemical, physiological, ecological and morphological characters are taken into consideration while classifying them.

9.  Define and understand the following terms:

(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus


(i) Phylum

Phylum is the primary division of kingdom. It includes one or more related classes of animals. In plants, instead of phylum, the term ‘division’ is used.

(ii) Class

Class is a taxonomic group consisting of one or more related orders.

For example, the class, Mammalia, includes many orders.

(iii) Family

Family is a taxonomic group containing one or more related genera. In plants, families are categorized on the basis of vegetative and reproductive features.

(iv) Order

Order is a taxonomic group containing one or more families.

For example, the order, carnivore, includes many families.

(v) Genus

Genus is a taxonomic group including closely related species.

For example, the genus, Solanum, includes many species such as nigrummelongenatuberosum, etc.

10. How is a key helpful in the identification and classification of an organism?

Answer. ‘Key is an artificial analytic device having a list of statements with dichotomic table of alternate characteristics. Taxonomic keys are aids for rapid identification of unknown plants and animals based on
the similarities and dissimilarities. Keys are primarily based on stable and reliable characters. The keys are helpful in a faster preliminary identification which can be backed up by confirmation through comparison with detailed description of the taxon provisionally identified with. Separate taxonomic keys are used for each taxonomic category like Family, Genus and Species.

11.Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.

Answer. The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy. The hierarchy indicates the various levels of kinship. The number of similar characters of categories decreases from lowest rank to highest rank. The hierarchical system of classification was introduced by Linnaeus.
The hierarchy of major categories is:
Species —►Genus-►Family —► Order—► Class
Kingdom -4— Phylum or Division
Increasing specificity – ► Decreasing specificity

Classification of a plant (Wheat):
Kingdom  –  Plantae
Division   –  Angiospermae
Class         –  Monocotyledonae
Order        –  Poales
Family      –  Poaceae
Genus       – Triticum
Species     –  aestivum

Classification of an animal (Housefly):
Kingdom  –   Animalia
Phylum    –   Chordata
Class        –   Insecta
Order       –   Diptera
Family     –  Muscidae
Genus      –   Musca
Species    –   domestica