EVENTS
CONVENT HIGH SCHOOL
18/08/2021 CLASS-11 SESSION2021-22(SLOT-1)
BIOLOGY
Chapter-1
DIVERSITY IN THE LIVING WORLD
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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) It bring sout similarities and dissimilarities.
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.
