-Dr Sanjaykumar Pawar
Class 11 Biology Ch 1 The Living World NCERT Solutions & Topper Notes
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CBSE Class 11 Biology
A vast variety of plants, animals, and microbes are found on Earth. These living organisms differ in size, shape, colour, habitat, and many other characteristics. Since millions of living organisms exist, studying each individual organism is practically impossible. Therefore, scientists have devised systematic classification methods.
These classification systems are based on established rules and principles that enable:
- Identification: Correctly determining the identity of an unknown organism.
- Nomenclature: Assigning a standardized scientific name.
- Classification: Grouping organisms into specific taxa based on their similarities and differences.
Significance: Biological classification helps reveal evolutionary relationships between various organisms and makes the study of life easy, logical, and organized.
Classification systems evolve continuously due to the following reasons:
- Millions of species exist on Earth, and scientists constantly discover new species worldwide.
- As newly discovered species exhibit unique morphological, anatomical, or genetic traits, existing classification systems must be adapted or revised to accommodate them.
- Advancements in biological tools (such as molecular biology, DNA sequencing, and electron microscopy) reveal new relationships among organisms, necessitating continuous refinements.
To classify a group of people (for example, a class of forty students), a hierarchical step-by-step approach can be used:
- Gender (Primary Criterion): Classifying students into two major groups — Boys and Girls.
- First Name: Grouping students within each gender group based on their first names.
- Surname: Sub-dividing individuals who share identical first names by using their surnames.
- Roll Number / Unique Identifier (Final Criterion): Assigning individual roll numbers to uniquely distinguish every single student without ambiguity.
Knowledge acquired from identifying an individual or a whole population helps us in:
- Understanding similarities and dissimilarities among individuals of the same species or between different species.
- Providing empirical data necessary for scientists to categorize organisms accurately into specific taxonomic ranks.
- Determining ecological roles, relationships, and evolutionary lineages.
- Mangifera Indica
- Mangifera indica
Answer: Mangifera indica is the correctly written name.
Definition: A taxon (plural: taxa) refers to any category, unit, or rank in a biological classification system.
Examples of Taxa at Hierarchical Levels (Ascending Order):
- Species: melongena
- Genus: Solanum
- Family: Solanaceae
- Order: Solanales
- Class: Dicotyledonae
- Phylum / Division: Angiospermae
- Kingdom: Plantae
(a) Species → Order → Phylum → Kingdom
(b) Genus → Species → Order → Kingdom
(c) Species → Genus → Order → Phylum
Answer: Both (a) and (c) represent valid ascending sequences of taxonomic categories.
Reason for (b) being incorrect: In sequence (b), species is placed after genus, whereas species should precede genus in ascending hierarchical order.
Biological Definition of Species: A species is the fundamental unit of taxonomic classification. It represents a group of closely related organisms capable of interbreeding naturally to produce fertile offspring and sharing a common gene pool
CBSE Class 11 Biology
- Phylum: Phylum is the primary division of kingdom. It includes one or more related classes of animals[span_0](start_span)[span_0](end_span). In plants, instead of phylum, the term 'division' is used[span_1](start_span)[span_1](end_span).
- Class: Class is a taxonomic group consisting of one or more related orders[span_2](start_span)[span_2](end_span). For example, the class, Mammalia, includes many orders[span_3](start_span)[span_3](end_span).
- Family: Family is a taxonomic group containing one or more related genera[span_4](start_span)[span_4](end_span). In plants, families are categorized on the basis of vegetative and reproductive features[span_5](start_span)[span_5](end_span).
- Order: Order is a taxonomic group containing one or more families[span_6](start_span)[span_6](end_span). For example, the order, carnivore, includes many families[span_7](start_span)[span_7](end_span).
- Genus: Genus is a taxonomic group including closely related species[span_8](start_span)[span_8](end_span). For example, the genus, Solanum, includes many species such as nigrum, melongena, tuberosum, etc.[span_9](start_span)[span_9](end_span).
Key is another taxonomical aid that helps in identification of plant and animal species[span_10](start_span)[span_10](end_span). These keys are based on similarities and dissimilarities in characters, generally in a pair called couplet[span_11](start_span)[span_11](end_span)[span_12](start_span)[span_12](end_span). Each statement in a taxonomic key is referred to as a lead[span_13](start_span)[span_13](end_span)[span_14](start_span)[span_14](end_span). For categorizing each taxonomic rank, such as family, genus, species, etc., different keys are used[span_15](start_span)[span_15](end_span)[span_16](start_span)[span_16](end_span). It is also useful in identification of unknown organisms[span_17](start_span)[span_17](end_span)[span_18](start_span)[span_18](end_span). Keys are of two types—indented and bracketed keys[span_19](start_span)[span_19](end_span)[span_20](start_span)[span_20](end_span). Indented key provides a sequence of choices between two or more statements while in bracketed key, a pair of contrasting characters are used[span_21](start_span)[span_21](end_span)[span_22](start_span)[span_22](end_span).
The arrangement of various taxa in a hierarchical order is called taxonomic hierarchy[span_23](start_span)[span_23](end_span)[span_24](start_span)[span_24](end_span). In this hierarchy, species is present at the lowest level whereas kingdom is present at the highest level[span_25](start_span)[span_25](end_span)[span_26](start_span)[span_26](end_span).
Classification of a Plant (Solanum melongena - Brinjal):[span_29](start_span)[span_29](end_span)[span_30](start_span)[span_30](end_span)
- Kingdom - Plantae[span_31](start_span)[span_31](end_span)[span_32](start_span)[span_32](end_span)
- Division - Angiospermae[span_33](start_span)[span_33](end_span)[span_34](start_span)[span_34](end_span)
- Class - Dicotyledonae[span_35](start_span)[span_35](end_span)[span_36](start_span)[span_36](end_span)
- Order - Solanales[span_37](start_span)[span_37](end_span)[span_38](start_span)[span_38](end_span)
- Family - Solanaceae[span_39](start_span)[span_39](end_span)[span_40](start_span)[span_40](end_span)
- Genus - Solanum[span_41](start_span)[span_41](end_span)[span_42](start_span)[span_42](end_span)
- Species - melongena[span_43](start_span)[span_43](end_span)[span_44](start_span)[span_44](end_span)
Classification of an Animal (Columba livia - Blue Rock Dove):[span_45](start_span)[span_45](end_span)
- Kingdom - Animalia[span_46](start_span)[span_46](end_span)
- Phylum - chordata[span_47](start_span)[span_47](end_span)
- Class - Aves[span_48](start_span)[span_48](end_span)
- Order - Columbiformes[span_49](start_span)[span_49](end_span)
- Family - Columbidae[span_50](start_span)[span_50](end_span)
- Genus - columba[span_51](start_span)[span_51](end_span)
- Species - livia[span_52](start_span)[span_52](end_span)
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