1. Why are living organisms
classified?
Soln. Living organisms
are classified because of the following reasons:
(i) Easy identification.
(ii)Study of organisms of other places.
(iii)Study of fossils
(iv)Grouping
helps in study of all types of organisms while it is impossible to study
individually all of them.
(v) Itbringsoutsimilaritiesanddissimilarities. They
help in knowing relationships among different groups.
(vi)Evolution of
various taxa can be known.
2. Why are the classification
systems changing every now and then?
Soln.
From very early days till now biologists use several characters for
classification system. These are morphology, anatomy, cytology, physiology,
ontogeny, phylogeny, reproduction, biochemistry, etc. But day by day biologists
are learning something new about organisms from their fossil records and using”
advanced study techniques such as molecular phylogeny, etc. So their point of
view about classification keeps changing. Thus the system of classification is
modified every now and then.
3. What different criteria
would you choose to classify people that you meet
often?
Soln. 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?
Soln.
The knowledge of characteristic of an individual or its whole population helps
in identification of similarities and dissimilarities among the individuals of
same 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
Soln.
The correctly written scientific name of mango is Mangifera indica.
6. Define a taxon. Give some
example of taxa at different hierarchical levels.
Slon. A taxonomic unit in
the biological system of classification of organism is called taxon (plural
taxa). 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—>
OrderKingdom
(c) Species —> Genus —>Order —> Phylum
Slon.
The correct sequence of taxonomical categories is
(c) i.e., Species
—>Genus —> Order —> Phylum.
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.
Slon.
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
Slon. (i) Phylum – Phylum
is a category higher than that of Class. The term Phylum is used for animals. A
Phylum is formed of one or more classes, e.g., the Phylum Chordata of animals
contains not only the class Mammalia but also Aves (birds), Reptilia (reptiles),
Amphibia (amphibians), etc. In plants the term Division is used in place of
Phylum.
(ii) Class – A Class is made of one or more related Orders. For
example, the Class Dicotyledoneae of flowering plants contains all dicots which
are grouped into several orders (e.g., Rosales, Sapindales, Ranales, etc.).
(iii) Family, – It is a taxonomic category which contains one or more related
genera. All the genera of a family have some common features or correlated
characters. They are separable from genera of a related family by important and
characteristic differences in both vegetative and reproductive features. E.g.,
the genera of cats (Fells) and leopard (Panthera) are included in the Family
Felidae. The members of Family Felidae are quite distinct from those of Family
Canidae (dogs, foxes, wolves).
Similarly, the family Solanaceae contains a
number of genera like Solanum, Datura, Petunia and Nicotiana. They are
distinguishable from the genera of the related family Convolvulaceae
(Convolvulus, Ipomoea).
(iv) Order – The category includes one or more
related families. E.g., the plant Family Solanaceae is placed in the Order
Polemoniales alongwith four other related families (Convolvulaceae,
Boraginaceae, Hydrophyllaceae and Polemoniaceae). Similarly, the animal families
Felidae and Canidae are included under the Order Carnivora alongwith Hyaenidae
(hyaenas) and Ursidae (bears).
(v) Genus – It is a group or assemblage of
related species which resemble one another in certain correlated characters.
Correlated characters are those similar or common features which are used in
delimitation of a taxon above the rank of species. All the species of genus are
presumed to have evolved from a common ancestor. A genus may have a single
living species e.g., Genus Homo. Its species is Homo sapiens – the living or
modem man. The Genus Felis has many species, e.g., F. domestica – common cat, F.
chaus (jungle cat) etc.
lO.How is a key helpful in
the identification and classification of an organism?
Slon.‘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 bebacked 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.
Slon. 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