NCERT Solutions for Class 11th BIOLOGY
Chapter 1 THE LIVING WORLD
Question 1: Why are living organisms classified?
Answer: A large 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 millions 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.
For example, based on certain principles, once an organism is identified as an insect, it will be given a scientific name and then grouped with other similar organisms. Thus, various groups or taxon include organisms based on their similarity and differences.
Therefore, the biological classification helps in revealing the relationship between various organisms. It also helps in making study of organisms easy and organized.
Answer: A large 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 millions 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.
For example, based on certain principles, once an organism is identified as an insect, it will be given a scientific name and then grouped with other similar organisms. Thus, various groups or taxon include organisms based on their similarity and differences.
Therefore, the biological classification helps in revealing the relationship between various organisms. It also helps in making study of organisms easy and organized.
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.
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.
Question 3: What different criteria would you choose to classify people that you meet often?
Answer: To classify a class of forty students, let us start the classification on the basis of sexes of the students. This classification will result in the formation of two major groups- boys and girls. Each of these two groups can be further classified on the basis of the names of the students falling in these groups.
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 will be based on the roll numbers of each student.
DOWNLOAD APP FOR CLASS 11 BIOLOGY SOLUTION
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.
Question 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.
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.
Question 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.
(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.
DOWNLOAD APP FOR CLASS 11 BIOLOGY SOLUTION
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.
Question 9: Define and understand the following terms: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.
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Answer:(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 nigrum, melongena, tuberosum,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.
Question 10: How is a key helpful in the identification and classification of an organism?
Answer: Key is another taxonomical aid that helps in identification of plant and animal species. These keys are based on similarities and dissimilarities in characters, generally in a pair called couplet.
Each statement in a taxonomic key is referred to as a lead. For categorizing each taxonomic rank, such as family, genus, species, etc., different keys are used. It is also useful in identification of unknown organisms.
Keys are of two types- indented and bracketed keys. Indented key provides a sequence of choices between two or more statements while in bracketed key, a pair of contrasting characters are used.
(i) Indented key to identify different species of Rhododendron.
1. Leaves evergreen
2. leaves densely hairy below, orange or white hair; flower appears to have separate petals
………………………. Rhododendron groenlandicum
2. hair absent on leaves, flower has five petals fused in a shallow tube
………………………. Rhododendron maximus
1. Leaves deciduous
3. pink flowers with two free petals and three fused petals
………………………. Rhododendron canadense
3. white to pink flowers with all petals fused together
(ii) Bracketed key to identify different species of Rhododendron.
1. Leaves evergreen———————————————–2
1. Leaves deciduous———————————————–3
2. Leaves densely hairy below, orange or white hair; flower appears to have separate petals
……….………………………. Rhododendron groenlandicum
2. Hair absent on leaves, flower has five petals fused in shallow tube
………………………………..Rhododendron maximus
3. Pink flowers with two free petals and three fused petals
……………………………… Rhododendron canadense
3. White to pink flowers with all petals fused together—–4
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
DOWNLOAD APP FOR CLASS 11 BIOLOGY SOLUTION
Comments
Post a Comment