DIVERSITY IN THE LIVING WORLD: CLASS XI

 

DIVERSITY   IN  THE  LIVING  WORLD

Diversity in the Living World

1. Introduction to Biodiversity: When observing our surroundings, we encounter a diverse array of living organisms, ranging from potted plants, insects, and birds to various animals and plants, including many microscopic ones. The number of known species on Earth is estimated to be between 1.7-1.8 million, representing the concept of biodiversity.
2. Local Naming and Nomenclature: Local names for organisms vary from place to place, causing confusion when communicating about them. To establish a standardized naming system, or nomenclature, that ensures consistency across the globe, scientists have devised procedures for assigning scientific names to organisms.
3. Botanical Nomenclature: Plants are given scientific names based on principles outlined in the International Code for Botanical Nomenclature (ICBN). The scientific name for a plant consists of two components: the generic name (genus) and the specific epithet (species). This system, known as binomial nomenclature, was introduced by Carolus Linnaeus and is widely accepted.
4. Zoological Nomenclature: Animals are named following the rules of the International Code of Zoological Nomenclature (ICZN). Similar to plants, animal scientific names consist of two parts: the genus and the specific epithet. These names are typically in Latin and italicized, with the genus starting with a capital letter and the specific epithet with a lowercase letter. The name of the author who first described the species is often included, abbreviated, at the end of the biological name.
5. Purpose of Scientific Names: Scientific names ensure that each organism has a unique and consistent name worldwide, preventing confusion and facilitating accurate identification.
6. Classification and Taxonomy: Due to the vast number of living organisms, classification is essential. It involves grouping organisms into categories (taxa) based on observable characteristics. For example, we categorize organisms into groups like 'dogs,' 'cats,' 'mammals,' 'wheat,' and 'plants.' Taxa can represent different levels, with 'mammals' being a category under 'animals,' and 'dogs' being a subset of 'mammals.'
7. Taxonomy Defined: Taxonomy is the science of classifying organisms based on their external and internal structures, cell structure, development processes, and ecological roles. It encompasses characterization, identification, classification, and nomenclature.
8. Historical Perspective: The interest in understanding organisms and their relationships is not new. Early classifications were often based on the practical uses of organisms, such as food, clothing, and shelter. Systematics, a branch of study, emerged to focus on the systematic arrangement of organisms, including their identification, nomenclature, classification, and the consideration of evolutionary relationships.
9. Systematics and Evolution: Systematics, rooted in the Latin word 'systema,' meaning systematic arrangement, evolved to include the study of evolutionary relationships between organisms. It is a comprehensive approach to understanding the diversity of life on Earth.

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The study of biodiversity involves naming and categorizing organisms using scientific nomenclature and taxonomy, which encompasses classification, identification, and the consideration of evolutionary relationships among living organisms. This systematic approach allows scientists to better understand and communicate about the vast array of life on our planet.

TAXONOMIC   CATEGORIES   AND   HIERARCHY

Taxonomic Categories and Hierarchy

1. Introduction to Taxonomic Categories: Classification is not a single-step process; it involves a hierarchical arrangement of steps, where each step represents a rank or category. These categories collectively form the taxonomic hierarchy, and each category is referred to as a taxon (plural: taxa).
2. Example of Insects: Insects serve as an example of organisms that can be classified into taxonomic categories. Insects share common features like having three pairs of jointed legs, making them a distinct and recognizable group of organisms.
3. Identification of Other Organism Groups: Similar to insects, many other groups of organisms can also be categorized into taxonomic groups. These groups represent taxonomic categories and denote specific ranks within the classification system.
4. Distinct Biological Entities: These taxonomic groups or categories are not mere morphological collections but represent distinct biological entities with common characteristics.
5. Common Taxonomic Categories: Taxonomical studies of all known organisms have resulted in the establishment of common taxonomic categories, including:
• Kingdom
• Phylum (or Division for plants)
• Class
• Order
• Family
• Genus
• Species
6. Species as the Lowest Category: In the classification system, species is the lowest category. It represents a group of individuals that share the most similarities and can interbreed to produce fertile offspring.
7. Placing Organisms in Categories: Placing an organism in various taxonomic categories requires a thorough understanding of the characteristics of that organism or group of organisms. This knowledge helps in identifying both the similarities and differences among individuals within the same species and among different species.

Taxonomic categories form a hierarchical system used for classifying organisms, with each category representing a specific rank or taxon. These categories are based on the common features and characteristics of organisms, and they help scientists organize and understand the diversity of life on Earth.

 

SPECIES    IN   TAXONOMY

Species in Taxonomy

1. Definition of a Species: In taxonomic studies, a species is a group of individual organisms that share fundamental similarities. The ability to distinguish one species from closely related species is based on distinct morphological differences.
2. Specific Epithets: Specific epithets are names given to species and are represented by words such as "indica" in Mangifera indica, "tuberosum" in Solanum tuberosum (potato), and "leo" in Panthera leo (lion).
3. Genera in Taxonomy: The first words in scientific names, such as Mangifera, Solanum, and Panthera, represent genera. Genera are a higher level of taxon or category than species. A genus may include one or more specific epithets, each representing different organisms within that genus but sharing morphological similarities.
4. Examples of Genera with Multiple Species: For instance, the genus Panthera includes the specific epithet "tigris," representing a different species (tiger), and Solanum includes species like "nigrum" (black nightshade) and "melongena" (eggplant).
5. Human Classification: Human beings belong to the species "sapiens," which is grouped in the genus "Homo." Therefore, the scientific name for humans is written as "Homo sapiens."

A species represents a group of organisms with fundamental similarities, and their distinct morphological differences allow for differentiation between closely related species. Taxonomical classification involves the use of specific epithets and genera to name and categorize different species based on their shared characteristics.

GENUS  IN  TAXONOMY

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Genus in Taxonomy

1. Definition of a Genus: A genus is a taxonomic category that comprises a group of related species. These species within a genus share more common characteristics with each other in comparison to species belonging to other genera.
2. Genera as Closely Related Aggregates: Genera can be thought of as aggregates of closely related species. This means that species within the same genus have more similarities than they do with species from different genera.
3. Example with Solanum: For example, consider the two different species, potato and brinjal (eggplant). Both of these species belong to the same genus, Solanum. While they are distinct species, they share common characteristics that place them within the Solanum genus.
4. Example with Panthera: Another example is the genus Panthera, which includes species like lion (Panthera leo), leopard (Panthera pardus), and tiger (Panthera tigris). These species share several common features and are grouped within the genus Panthera. However, this genus differs from another genus called Felis, which includes domestic cats.

A  genus in taxonomy is a category that encompasses a group of closely related species. The species within a genus share more common characteristics with each other than they do with species from other genera, making genera an important level of classification in understanding the diversity of life.

FAMILY  IN  TAXONOMY

Family in Taxonomy

1. Introduction to the Family Category: The category of "Family" is another level in the taxonomic hierarchy. Families consist of related genera, and the level of similarity within families is less compared to that within genera and species.
2. Characteristics Used for Family Classification in Plants: Families among plants are characterized based on both vegetative (structural) and reproductive features of plant species. This comprehensive assessment helps in placing plant genera into the appropriate families.
3. Example in Plant Taxonomy: To illustrate this, consider three different genera—Solanum, Petunia, and Datura. These genera are placed within the same family, known as Solanaceae. This classification is made based on shared features among these genera.
4. Example in Animal Taxonomy: In the context of animal taxonomy, let's look at the genera Panthera and Felis. The genus Panthera includes species like the lion, tiger, and leopard, while the genus Felis comprises domestic cats. These two genera are placed within the same family called Felidae because they share certain common characteristics.
5. Comparison of Cat and Dog Families: If you observe the features of a cat and a dog, you'll notice some similarities and differences. These distinctions lead to the classification of cats under the family Felidae and dogs under the family Canidae, highlighting the diversity within the animal kingdom.

The taxonomic category of "Family" represents a higher level in the classification system, grouping together related genera. The criteria for classification into families vary among different organisms, whether in the plant kingdom, as seen with Solanaceae, or the animal kingdom, as seen with Felidae and Canidae. Families serve as an intermediate level in the taxonomic hierarchy, helping organize and categorize diverse groups of species.

ORDER  IN  TAXONOMY

Order in Taxonomy

1. Introduction to Higher Taxonomic Categories: In the taxonomy system, categories like species, genus, and families are primarily based on the presence of a number of similar characteristics among organisms.
2. Characteristics Used for Higher Categories: Generally, higher taxonomic categories such as "Order" are identified based on the aggregation of characters or traits exhibited by a group of related families. In this context, the focus is on similarities among families rather than individual species.
3. Order as an Assemblage of Families: "Order" serves as a higher category in the taxonomic hierarchy and represents an assemblage of families that exhibit a limited number of shared characteristics. These shared characteristics are fewer in number compared to the range of different genera included within a family.
4. Example in Plant Taxonomy: In the plant kingdom, certain plant families, such as Convolvulaceae and Solanaceae, are included in the order Polymoniales. This classification is primarily based on floral characters shared by the families in this order. These floral characteristics help group families into a common order.
5. Example in Animal Taxonomy: In the context of animal taxonomy, the order Carnivora includes families like Felidae and Canidae. The presence of carnivorous characteristics and certain anatomical features shared by these families justifies their placement within the same order, Carnivora.

"Order" is a higher taxonomic category that groups together related families based on a limited set of shared characteristics. These shared characteristics are fewer in number compared to the diverse genera found within families. Orders provide a way to organize and categorize families with some common features, facilitating the classification of organisms in a hierarchical manner.

 

CLASS  IN  TAXONOMY

Class in Taxonomy

1. Introduction to Class Category: "Class" is a higher taxonomic category that includes related orders. It serves as an intermediate level in the taxonomic hierarchy, grouping together orders that share certain common characteristics.
2. Example in Animal Taxonomy: To illustrate this, consider the class Mammalia. Within this class, you find various orders, including Primata, which comprises animals like monkeys, gorillas, and gibbons. Additionally, the order Carnivora, which includes animals such as tigers, cats, and dogs, is also placed in the class Mammalia.
3. Variety of Orders: The class Mammalia encompasses a range of orders beyond just Primata and Carnivora. This class accommodates numerous orders that exhibit a wide variety of characteristics but share the fundamental trait of being mammals.

The taxonomic category of "Class" is a higher level that groups related orders together. Classifications within this category are based on shared characteristics among the orders, allowing for the organization and categorization of diverse groups of organisms in a systematic manner.

PHYLUM  IN  TAXONOMY

Phylum in Taxonomy

1. Introduction to Phylum Category: "Phylum" represents a higher taxonomic category in the classification hierarchy. It encompasses a group of classes that share certain fundamental characteristics.
2. Example in Animal Taxonomy: In the animal kingdom, classes like fishes, amphibians, reptiles, birds, and mammals belong to the next higher taxonomic category known as Phylum. These classes are grouped together based on common features such as the presence of a notochord and a dorsal hollow neural system. This categorization helps scientists organize and categorize diverse groups of animals.
3. Phylum Chordata: The grouping of classes like fishes, amphibians, reptiles, birds, and mammals falls under the Phylum Chordata. This phylum is characterized by the presence of a notochord and a dorsal hollow neural system, which are key defining features of chordates.
4. Example in Plant Taxonomy: In the plant kingdom, higher taxonomic categories called "Division" are used instead of phyla. Classes with some shared characteristics are assigned to a higher category known as Division. This system is employed to organize and categorize plant groups based on their common traits.

"Phylum" is a higher taxonomic category that consists of related classes sharing fundamental characteristics. In animals, classes like fishes, amphibians, reptiles, birds, and mammals are grouped under the Phylum Chordata based on the presence of a notochord and a dorsal hollow neural system. In plant taxonomy, the equivalent higher category is "Division," where classes with certain similarities are grouped together for classification and organization.

KINGDOM   IN  TAXONOMY

Kingdom in Taxonomy

1. Introduction to Kingdom Category: In the taxonomic classification system, the highest category is known as the "Kingdom." This category serves as the broadest and most inclusive level in the hierarchy.
2. Kingdom Animalia: In the context of animals, all organisms belonging to various phyla are grouped together under the highest category called "Kingdom Animalia." This kingdom encompasses the entire animal kingdom, including diverse phyla.
3. Kingdom Plantae: Conversely, in the plant kingdom, there is a separate and distinct category known as "Kingdom Plantae." This kingdom includes all plants from various divisions within the plant kingdom.
4. Animal and Plant Kingdoms: For convenience, we commonly refer to these two major groups as the "animal kingdom" and the "plant kingdom." These kingdoms are characterized by the vast diversity of organisms they encompass.
5. Ascending Taxonomic Categories: The taxonomic categories, from species to kingdom, are depicted in ascending order in Figure 1.1. These categories represent progressively broader classifications.
6. Basis of Arrangement: The arrangement within the taxonomic hierarchy is based on the concept that as we ascend from species to kingdom, the number of common characteristics shared by organisms within each taxon decreases. In other words, lower taxa, such as species, have a higher number of shared characteristics among their members, while higher categories, like kingdom, have fewer shared characteristics.
7. Complexity of Classification: As we move up the taxonomic hierarchy, the difficulty of determining the relationships between taxa at the same level increases. This complexity arises because higher-level categories encompass a greater diversity of organisms, making it challenging to establish clear relationships among them.

"Kingdom" represents the highest level in the taxonomic classification system. The concept underlying this hierarchy is that lower taxa, like species, share more common characteristics, while higher categories, such as kingdom, encompass a wider range of organisms, making classification more complex at those levels.

 

QUESTIONS  AND  ANSWERS

1. Why are living organisms classified?
• Living organisms are classified to organize the immense diversity of life on Earth. Classification helps scientists study and understand the relationships between different species.
• It simplifies the study of organisms by categorizing them into groups with shared characteristics.
• It aids in the identification, naming, and communication about different species.
• Classification provides insights into the evolutionary history and ancestry of organisms.
2. Why are the classification systems changing every now and then?
• Classification systems change as new scientific discoveries and advancements are made.
• Advances in molecular biology and genetics have led to revisions in classification based on genetic relationships.
• Fossil discoveries and new ecological information can also alter the classification of certain organisms.
• As our understanding of life evolves, taxonomists update classification systems to reflect more accurate and meaningful relationships among organisms.
3. What different criteria would you choose to classify people that you meet often?
• Criteria for classifying people might include age, gender, occupation, nationality, interests, or physical characteristics. For a more scientific classification, genetic factors, such as DNA analysis, could be used.
4. What do we learn from the identification of individuals and populations?
• Identification of individuals and populations helps us understand genetic diversity within a species.
• It provides insights into geographical distribution and adaptation of organisms.
• It aids in conservation efforts by tracking endangered species and monitoring their populations.
5. Given below is the scientific name of Mango. Identify the correctly written name.
• The correctly written name is "Mangifera indica."
6. Define a taxon. Give some examples of taxa at different hierarchical levels.
• A taxon is a category or rank in the biological classification system. It can represent a group of organisms at various hierarchical levels. Examples include:
• Species: Homo sapiens (human)
• Genus: Panthera (genus of big cats)
• Family: Felidae (family of cats)
• Order: Carnivora (order of carnivorous mammals)
• Class: Mammalia (class of mammals)
• Phylum: Chordata (phylum of animals with a notochord)
• Kingdom: Animalia (animal kingdom)
7. Can you identify the correct sequence of taxonomical categories?
• The correct sequence is (c) 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 the case of higher plants and animals on one hand, and bacteria on the other hand.
• The term "species" can have various meanings, including:
• Biological Species Concept: Defines a species as a group of organisms that can interbreed and produce fertile offspring.
• Morphological Species Concept: Defines a species based on physical characteristics.
• Phylogenetic Species Concept: Defines a species based on evolutionary relationships and common ancestry.
• In higher plants and animals, the biological species concept is often applicable, emphasizing interbreeding and reproductive isolation as key factors.
• In bacteria, where reproduction is primarily asexual, the morphological and phylogenetic species concepts may be more relevant.
9. Define and understand the following terms:
• Phylum: A taxonomic rank or category that includes related classes. For example, Chordata is a phylum that includes classes like Mammalia and Aves.
• Class: A higher taxonomic category that includes related orders. For instance, Mammalia is a class that includes orders like Primata.
• Family: A taxonomic rank comprising related genera. An example is Felidae, the family that includes the genera Panthera and Felis.
• Order: A higher taxonomic category that includes related families. For example, Carnivora is an order that includes families like Felidae and Canidae.
• Genus: A taxonomic rank representing closely related species. Panthera is a genus that includes species like lion and tiger.

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

Plant Example - Mango (Mangifera indica):

1. Kingdom: Plantae (Plant Kingdom)
• Mango belongs to the plant kingdom, along with all other plants.
2. Division (in plants) or Phylum (in animals): Angiosperms (Division in plants)
• Mango is classified under the division Angiosperms, which includes all flowering plants.
3. Class: Magnoliopsida (Class in plants)
• Mango falls into the class Magnoliopsida, a category of flowering plants with two cotyledons in their seeds.
4. Order: Sapindales (Order)
• Mango is part of the order Sapindales, which includes various plants like citrus fruits.
5. Family: Anacardiaceae (Family)
• Mango belongs to the family Anacardiaceae, which also includes cashew and pistachio.
6. Genus: Mangifera (Genus)
• The genus of mango is Mangifera, and this category includes several species of mango.
7. Species: indica (Species)
• The specific epithet for mango is "indica." So, its scientific name is Mangifera indica.

Animal Example - Lion (Panthera leo):

1. Kingdom: Animalia (Animal Kingdom)
• Lions, like all animals, belong to the animal kingdom.
2. Phylum: Chordata (Phylum)
• Lions fall under the phylum Chordata, as they possess a notochord at some stage in their development.
3. Class: Mammalia (Class)
• Lions are mammals, and they belong to the class Mammalia.
4. Order: Carnivora (Order)
• Lions are part of the order Carnivora, which includes various carnivorous mammals.
5. Family: Felidae (Family)
• Lions are in the family Felidae, which comprises big cats.
6. Genus: Panthera (Genus)
• The genus of lions is Panthera, a group of big cat species.
7. Species: leo (Species)
• The specific epithet for lions is "leo," so their scientific name is Panthera leo.

This illustration shows the taxonomic hierarchy for both a plant (mango) and an animal (lion) with examples at each taxonomic level