The Living WorldClass 11 Biology NCERT Solutions
10 Solutions
Generated by KedovoAI
Solution 1 of 10
Q1Exercises
Why are living organisms classified?
Solution
Living organisms are classified for the following reasons:
- Convenient Study: The vast diversity of life, with millions of species, makes it impossible to study each organism individually. Classification groups organisms into convenient categories (taxa) based on shared characteristics, making their study systematic and organized.
- Identification: Classification provides a framework that helps in the correct identification of a newly discovered organism by comparing it to known organisms in the system.
- Understanding Relationships: It helps us understand the interrelationships among different groups of organisms. By placing them in a hierarchy, we can see the evolutionary connections (phylogeny) between them.
- Universal System: It provides a standardized and universally accepted system of naming and grouping organisms, allowing scientists worldwide to communicate about a specific organism without confusion.
Q2Exercises
Why are the classification systems changing every now and then?
Solution
Classification systems are dynamic and change over time because our understanding of organisms and their interrelationships is constantly improving. The factors contributing to these changes are:
- New Discoveries: As new species are discovered, they need to be placed appropriately within the existing framework, which may sometimes require adjustments to the system.
- Advancements in Science: New tools and techniques from fields like cytology, biochemistry, and molecular biology provide new information. For instance, DNA sequencing allows us to understand the genetic and evolutionary relationships between organisms more accurately.
- Shift in Criteria: Early classification systems were based on a few superficial morphological characters or habitat ('uses' of organisms). Modern systems, known as systematics, are based on a wider range of characteristics, including cell structure, developmental processes, ecological information, and most importantly, evolutionary relationships. As our understanding of these relationships becomes clearer, the classification system is modified to reflect this new knowledge.
Q3Exercises
What different criteria would you choose to classify people that you meet often?
Solution
To classify people I meet often, I could use various criteria based on easily observable characters, similar to the principles of taxonomy. The choice of criteria would depend on the purpose of the classification. Some possible criteria are:
- Relationship: Grouping them as family, friends, colleagues, or acquaintances.
- Age Group: Classifying them into categories like children, teenagers, adults, and senior citizens.
- Profession: Grouping them based on their occupation, such as students, teachers, doctors, engineers, etc.
- Geographical Location: Classifying them based on where they live, for example, people from the same neighborhood, city, or state.
- Shared Interests/Activities: Grouping them based on common hobbies or activities, such as members of a sports team, a book club, or a music class. Each of these criteria helps in organizing and understanding my social connections in a systematic way.
Q4Exercises
What do we learn from identification of individuals and populations?
Solution
From the identification of individuals, we learn the specific identity of an organism. Identification is the process of determining the correct name and placement of an organism within the established system of classification. This allows us to know its species, genus, family, and other taxonomic ranks. It is the first step in gathering information about its specific characteristics, such as morphology, anatomy, and ecological role.
From the identification of populations (groups of individuals of the same species), we learn about:
- Biodiversity: The variety and range of organisms present in a particular habitat or geographical area.
- Species Distribution: The geographical area where a particular species is found.
- Bio-resources: It helps in knowing our bio-resources and their diversity, which is useful in fields like agriculture, forestry, and industry.
- Ecological Studies: Understanding the composition of populations is essential for studying interactions within a community and the overall health of an ecosystem.
Q5Exercises
Given below is the scientific name of Mango. Identify the correctly written name. Mangifera Indica Mangifera indica
Solution
The correctly written scientific name of Mango is Mangifera indica.
This is based on the universally accepted rules of binomial nomenclature:
- The first word represents the genus and starts with a capital letter (e.g., Mangifera).
- The second word represents the specific epithet and starts with a small letter (e.g., indica).
- When printed, the biological name is written in italics.
The name Mangifera Indica is incorrect because the specific epithet 'Indica' starts with a capital letter, which violates the rules.
Q6Exercises
Define a taxon. Give some examples of taxa at different hierarchical levels.
Solution
A taxon (plural: taxa) is the scientific term for any unit or category in the system of biological classification. It represents a group of one or more organisms that are considered to form a unit at a particular level in the taxonomic hierarchy. Each taxon represents a rank in classification.
Examples of taxa at different hierarchical levels include:
- Kingdom: Animalia (a taxon that includes all animals), Plantae (a taxon that includes all plants).
- Phylum/Division: Chordata (a taxon for animals with a notochord), Angiospermae (a taxon for flowering plants).
- Class: Mammalia (a taxon for animals with hair and mammary glands), Dicotyledonae (a taxon for plants with two cotyledons).
- Order: Primata, Carnivora, Sapindales.
- Family: Hominidae, Felidae, Anacardiaceae.
- Genus: Homo, Panthera, Mangifera.
- Species: sapiens, tigris, indica.
Q7Exercises
Can you identify the correct sequence of taxonomical categories?
(a)
Species → Order → Phylum → Kingdom
(b)
Genus → Species → Order → Kingdom
(c)
Species → Genus → Order → Phylum
Solution
The correct sequence of taxonomical categories in ascending order is:
(a) Species → Order → Phylum → Kingdom
Explanation:
The taxonomic hierarchy is an arrangement of categories in a definite sequence from lower to higher ranks. The standard ascending order is: Species → Genus → Family → Order → Class → Phylum → Kingdom.
- (a) Species → Order → Phylum → Kingdom: This sequence is correct as it follows the ascending order of the hierarchy (even though some intermediate ranks like Genus, Family, and Class are skipped).
- (b) Genus → Species → Order → Kingdom: This sequence is incorrect because Species is a lower rank than Genus.
- (c) Species → Genus → Order → Phylum: This sequence is also in the correct ascending order. However, option (a) represents a wider progression up to the highest rank, Kingdom.
Q8Exercises
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.
Solution
The term 'species' is a fundamental unit of classification. Two currently accepted meanings are:
-
Morphological Species Concept: This defines a species as a group of individual organisms with fundamental morphological similarities. Based on distinct observable structural differences, one can distinguish one species from another. The textbook refers to this concept.
-
Biological Species Concept: Proposed by Ernst Mayr, this is the most widely used definition. It defines a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are reproductively isolated from other such groups.
Meaning of Species in Different Organisms:
-
Higher Plants and Animals: The biological species concept is largely applicable to higher plants and animals as they primarily reproduce sexually. Reproductive isolation is the key criterion that separates one species from another. For example, a lion (Panthera leo) and a tiger (Panthera tigris) are considered different species because although they can be made to interbreed in captivity to produce a liger, they do not do so in their natural habitats and are thus reproductively isolated.
-
Bacteria: The biological species concept cannot be applied to bacteria and other prokaryotes. This is because:
- They reproduce asexually (e.g., by binary fission), so the concept of 'interbreeding' is not relevant.
- They can exchange genetic material through horizontal gene transfer with even distantly related organisms, which breaks down the barriers of reproductive isolation.
Therefore, for bacteria, a species is defined as a collection of strains sharing a high degree of similarity based on a combination of criteria (polyphasic approach), including:- Morphological and Biochemical Traits: Cell shape, metabolic pathways, etc.
- Genetic Similarity: Criteria such as having over 70% DNA-DNA hybridization or over 97% similarity in 16S rRNA gene sequence are used to group strains into the same species.
Q9Exercises
Define and understand the following terms:
(i)
Phylum
(ii)
Class
(iii)
Family
(iv)
Order
(v)
Genus
Solution
(i) Phylum: Phylum is a taxonomic category placed below Kingdom and above Class. It consists of related classes sharing common fundamental features. For example, Phylum Chordata includes classes like Amphibia, Reptilia, and Mammalia, all of which share features like the presence of a notochord and a dorsal hollow neural system. In plants, the category 'Division' is used instead of Phylum.
(ii) Class: This category includes related orders. It is placed below Phylum and above Order. For example, Order Primata (monkey, gorilla) and Order Carnivora (tiger, cat, dog) are placed together in the Class Mammalia because they share features like having body hair and mammary glands.
(iii) Family: A family is a group of related genera with fewer similarities as compared to genus and species. It is placed below Order and above Genus. Families are characterized by both vegetative and reproductive features in plants. For example, the family Felidae includes the genus Panthera (lion, tiger) and the genus Felis (cat).
(iv) Order: An order is an assemblage of related families that exhibit a few similar characters. It is a higher category placed below Class and above Family. For example, the plant families Convolvulaceae and Solanaceae are included in the Order Polymoniales based on floral characters. Similarly, animal families Felidae and Canidae are included in the Order Carnivora.
(v) Genus: A genus comprises a group of related species which have more characters in common in comparison to species of other genera. It is placed below Family and above Species. For example, the genus Panthera includes the species leo (lion), tigris (tiger), and pardus (leopard).
Q10Exercises
Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Solution
The taxonomical hierarchy is the arrangement of various taxonomic categories in descending order, from kingdom to species. As we move down the hierarchy, the number of common characteristics increases.
Example of a Plant (Mango):
- Kingdom: Plantae
- Division: Angiospermae
- Class: Dicotyledonae
- Order: Sapindales
- Family: Anacardiaceae
- Genus: Mangifera
- Species: indica
Biological Name: Mangifera indica
Example of an Animal (Man):
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Primata
- Family: Hominidae
- Genus: Homo
- Species: sapiens
Biological Name: Homo sapiens