Animal Kingdom — NCERT Solutions

Given/Concept: Classification requires common fundamental features such as level of organisation, symmetry, coelom, segmentation, notochord, etc.

Answer:
If common fundamental features are not taken into account, the following difficulties would arise:

1. No systematic grouping: Animals could not be placed into logical, hierarchical groups. Every animal would have to be treated as a separate entity.
2. Confusion due to superficial similarities: Animals that look alike but are fundamentally different (e.g., a whale and a fish) might be grouped together incorrectly.
3. Inability to identify evolutionary relationships: Phylogenetic (evolutionary) relationships among animals could not be established.
4. Lack of universal system: Different scientists would use different criteria, making communication and comparison impossible.
5. Difficulty in studying millions of species: With over a million animal species, without common features it would be impossible to study, remember, or compare them systematically.
6. Misidentification: Animals with convergent evolution (similar adaptations but different ancestry) would be misclassified.

Conclusion: Common fundamental features provide the scientific basis for a natural, logical, and universally accepted classification system.

Given/Concept: Classification is based on a hierarchy of fundamental characters observed in the specimen.

Steps to classify a given specimen:

Step 1 – Level of Organisation:
Determine whether the organism is unicellular or multicellular. If multicellular, identify the level — cellular, tissue, organ, or organ-system level.

Step 2 – Symmetry:
Observe the body symmetry — is it asymmetrical, radially symmetrical, or bilaterally symmetrical?

Step 3 – Diploblastic or Triploblastic:
Determine the number of embryonic germ layers — two (diploblastic) or three (triploblastic).

Step 4 – Nature of Coelom:
Check whether the animal is acoelomate, pseudocoelomate, or eucoelomate (true coelomate).

Step 5 – Segmentation:
Observe whether the body shows segmentation (metamerism) or not.

Step 6 – Presence/Absence of Notochord:
Check for the presence of a notochord — this distinguishes chordates from non-chordates.

Step 7 – Other specific features:
Look for features like jointed appendages, exoskeleton, water vascular system, gill slits, dorsal hollow nerve cord, etc.

Step 8 – Assign to Phylum, Class, Order, Family, Genus, Species based on the above observations.

Conclusion: By following these steps in a systematic manner, any animal specimen can be correctly classified.

Given/Concept: Coelom is the fluid-filled body cavity present between the body wall and the gut wall. It is lined by mesoderm.

Usefulness in Classification:

The nature of the body cavity divides animals into three major groups:

Significance:

• The coelom provides space for organ development and complexity.
• It helps in determining the evolutionary advancement of an animal.
• It is a key character used to separate major phyla.
• The presence of a true coelom is associated with higher complexity of organ systems.

Conclusion: The study of coelom is extremely useful as it is one of the most fundamental criteria for classifying the animal kingdom into major groups.

Given/Concept: Digestion is the process of breaking down complex food molecules into simpler absorbable forms.

Conclusion: Extracellular digestion is more efficient and is seen in evolutionarily advanced animals, while intracellular digestion is a primitive feature seen in lower animals like sponges.

Given/Concept: Development refers to the changes an organism undergoes from fertilised egg to adult.

Conclusion: In direct development, the juvenile is a miniature adult, whereas in indirect development, a larval stage with metamorphosis is involved before the adult form is attained.

Given/Concept: Platyhelminthes (flatworms) include both free-living (e.g., Planaria) and parasitic forms (e.g., Taenia, Fasciola).

Peculiar features of parasitic Platyhelminthes:

1. Suckers and Hooks: Presence of suckers (acetabula) and hooks (in tapeworms) for attachment to the host's body.
2. Loss of digestive system: In tapeworms (e.g., Taenia solium), the digestive system is completely absent. Nutrients are absorbed directly through the body surface (tegument).
3. Tegument: The body is covered by a thick, syncytial tegument that protects against host's digestive enzymes and immune responses.
4. High reproductive capacity: Hermaphroditic (both male and female reproductive organs in the same individual); produce enormous numbers of eggs to ensure transmission.
5. Proglottids: In tapeworms, the body is divided into proglottids, each containing a complete set of reproductive organs.
6. Scolex: The head region (scolex) bears hooks and suckers for attachment.
7. Reduced sense organs: Sense organs are greatly reduced or absent as they live in a stable internal environment.
8. Complex life cycle: Involve one or more intermediate hosts (e.g., pig in Taenia solium).

Conclusion: These adaptations are specifically suited for a parasitic mode of life — attachment, nutrient absorption, protection from host defences, and efficient reproduction.

Given/Concept: Arthropoda is the largest phylum in the animal kingdom, comprising more than two-thirds of all known animal species.

Reasons for their success and dominance:

1. Jointed appendages: Highly versatile jointed legs and appendages allow locomotion, feeding, sensory perception, and reproduction — adaptable to diverse functions.
2. Exoskeleton of chitin: Provides protection against predators, desiccation, and mechanical injury. It also serves as a site for muscle attachment.
3. Moulting (Ecdysis): Periodic shedding of the exoskeleton allows growth and adaptation.
4. Adaptability: Found in almost every habitat — land, water, air, soil, deserts, polar regions.
5. Flight in insects: Wings in insects (Class Insecta) gave them access to aerial habitat, reducing competition and predation.
6. Small body size: Requires less food and space; can exploit microhabitats unavailable to larger animals.
7. High reproductive rate: Produce large numbers of offspring in a short time, ensuring survival of the species.
8. Metamorphosis: Different larval and adult stages exploit different food sources, reducing intraspecific competition.
9. Well-developed sensory organs: Compound eyes, antennae, etc., help in efficient detection of food and mates.
10. Efficient respiratory and circulatory systems: Tracheal system in insects allows efficient gas exchange.

Conclusion: The combination of structural versatility, adaptability, efficient reproduction, and ability to colonise diverse habitats has made Arthropoda the most species-rich group in the animal kingdom.

Correct Answer: (c) Echinodermata

Justification:
The water vascular system (ambulacral system) is the most distinctive feature of Phylum Echinodermata (e.g., starfish, sea urchin, sea cucumber). It is a network of water-filled canals derived from the coelom. It helps in:

• Locomotion (via tube feet)
• Capture and transport of food
• Respiration and excretion

None of the other options (Porifera, Ctenophora, Chordata) possess a water vascular system.