Animal Kingdom - Class 11 NEET Biology Notes
Introduction:
The animal kingdom, or Kingdom Animalia, encompasses a vast array of multicellular, eukaryotic organisms that are predominantly heterotrophic, meaning they obtain their nutrition by consuming other organisms. These organisms exhibit diverse reproductive strategies, primarily sexual reproduction, and possess the ability to move voluntarily at some stage in their life cycle. This guide provides an in-depth look at the classification, characteristics, and significant examples of various phyla within the Animal Kingdom, essential for NEET Biology preparation.
Classification of Animal Kingdom
Basis of Classification:
To understand the complexity and diversity of the animal kingdom, biologists have developed several criteria to classify animals. These criteria include the level of organization, symmetry, germ layers, body cavity (coelom), segmentation, and the presence or absence of a notochord.
1. Level of Organization: Animals exhibit different levels of structural organization, which can be categorized into cellular, tissue, organ, and organ system levels.
Cellular Level: The simplest form of organization, where cells function independently (e.g., sponges).
Tissue Level: Cells with similar structures and functions group together to form tissues (e.g., cnidarians).
Organ Level: Tissues organize into organs with specific functions (e.g., flatworms).
Organ System Level: Organs form organ systems that perform complex functions (e.g., annelids, chordates).
2. Symmetry: Symmetry refers to the arrangement of body parts around a central axis.
Asymmetry: No symmetry; body parts are not arranged in a regular pattern (e.g., sponges).
Radial Symmetry: Body parts are arranged around a central axis, and any longitudinal cut through the central axis divides the organism into similar halves (e.g., cnidarians).
Bilateral Symmetry: Body has a left and right side that are mirror images of each other (e.g., humans, arthropods).
3. Germ Layers: Germ layers are layers of cells in the embryo that develop into various tissues and organs.
Diploblastic: Animals with two germ layers, the ectoderm and endoderm (e.g., cnidarians).
Triploblastic: Animals with three germ layers, the ectoderm, mesoderm, and endoderm (e.g., flatworms to chordates).
4. Body Cavity (Coelom): The body cavity, or coelom, is a fluid-filled space between the digestive tract and body wall.
Acoelomate: No body cavity; space between gut and body wall is filled with tissue (e.g., platyhelminthes).
Pseudocoelomate: False coelom; body cavity is not fully lined with mesoderm (e.g., nematodes).
Coelomate: True coelom; body cavity is completely lined with mesoderm (e.g., annelids, arthropods, mollusks, echinoderms, chordates).
5. Segmentation: Segmentation refers to the division of the body into repeated sections.
Metameric Segmentation: The body is divided into segments (e.g., annelids, arthropods).
6. Notochord: The notochord is a flexible rod that provides support in the embryo.
Chordates: Animals with a notochord at some stage in their development.
Non-chordates: Animals without a notochord.
Major Phyla of Animal Kingdom
1. Phylum Porifera
Common Name: Sponges
Characteristics:
Level of Organization: Cellular level
Symmetry: Asymmetrical or radially symmetrical
Germ Layers: Diploblastic
Body Cavity: Acoelomate
Features: Presence of pores (ostia) and canals; adults are sessile
Examples: Sycon, Spongilla, Euspongia
Description:
Sponges are primarily marine organisms that exhibit a simple body plan. They have a porous body with an internal canal system, allowing water to circulate through. Sponges possess specialized cells called choanocytes that help in feeding by filtering water for nutrients. They reproduce both sexually and asexually through budding and fragmentation.
2. Phylum Coelenterata (Cnidaria)
Common Name: Jellyfish, Corals, Sea Anemones
Characteristics:
Level of Organization: Tissue level
Symmetry: Radial symmetry
Germ Layers: Diploblastic
Body Cavity: Acoelomate
Features: Presence of cnidocytes (stinging cells)
Examples: Hydra, Jellyfish (Aurelia), Sea Anemone (Adamsia)
Description:
Cnidarians exhibit a more complex body plan than sponges, with specialized tissues. They have a central gastrovascular cavity and a simple nerve net. Their defining feature is the presence of cnidocytes, specialized cells used for capturing prey and defense. Cnidarians can exist in two forms: the sessile polyp (e.g., sea anemones) and the free-floating medusa (e.g., jellyfish).
3. Phylum Platyhelminthes
Common Name: Flatworms
Characteristics:
Level of Organization: Organ level
Symmetry: Bilateral symmetry
Germ Layers: Triploblastic
Body Cavity: Acoelomate
Features: Flat, ribbon-like body
Examples: Planaria (Dugesia), Liver fluke (Fasciola), Tapeworm (Taenia)
Description:
Platyhelminthes are the simplest triploblastic animals, with a dorsoventrally flattened body. They have a distinct head region and exhibit cephalization. Flatworms lack a body cavity, and their organs are embedded in the mesodermal tissue. They have a simple digestive system with a single opening. Many flatworms are parasitic, like the tapeworms and flukes.
4. Phylum Nematoda
Common Name: Roundworms
Characteristics:
Level of Organization: Organ level
Symmetry: Bilateral symmetry
Germ Layers: Triploblastic
Body Cavity: Pseudocoelomate
Features: Unsegmented, cylindrical body
Examples: Ascaris (roundworm), Wuchereria (filarial worm)
Description:
Nematodes, or roundworms, have a cylindrical body covered with a tough cuticle. They possess a pseudocoelom, which acts as a hydrostatic skeleton. Nematodes have a complete digestive system with a distinct mouth and anus. They exhibit sexual dimorphism, with males and females being distinct. Many nematodes are parasitic and cause diseases in plants and animals.
5. Phylum Annelida
Common Name: Segmented worms
Characteristics:
Level of Organization: Organ system level
Symmetry: Bilateral symmetry
Germ Layers: Triploblastic
Body Cavity: Coelomate
Features: Metameric segmentation
Examples: Earthworm (Lumbricus), Leech (Hirudo), Nereis
Description:
Annelids are characterized by their segmented bodies, with each segment containing similar sets of organs. They have a true coelom, which is divided by septa. Annelids possess a closed circulatory system and exhibit a more developed nervous system with a ventral nerve cord. Their locomotion is facilitated by setae and, in some cases, parapodia.
6. Phylum Arthropoda
Common Name: Insects, Crustaceans, Arachnids
Characteristics:
Level of Organization: Organ system level
Symmetry: Bilateral symmetry
Germ Layers: Triploblastic
Body Cavity: Coelomate
Features: Jointed appendages, exoskeleton of chitin
Examples: Prawn, Butterfly, Spider, Cockroach
Description:
Arthropods are the largest phylum in the animal kingdom, encompassing a wide variety of organisms. They possess a segmented body divided into head, thorax, and abdomen, covered by an exoskeleton made of chitin. This exoskeleton provides protection and points of attachment for muscles but must be molted for growth. Arthropods have an open circulatory system and highly developed sensory organs.
7. Phylum Mollusca
Common Name: Mollusks
Characteristics:
Level of Organization: Organ system level
Symmetry: Bilateral symmetry
Germ Layers: Triploblastic
Body Cavity: Coelomate
Features: Soft body with a calcareous shell
Examples: Snail (Pila), Octopus, Oyster
Description:
Mollusks have a soft, unsegmented body, usually
enclosed within a calcareous shell. Their body is divided into three main parts: the head-foot, the visceral mass, and the mantle. The mantle secretes the shell and forms a cavity that houses the gills or lungs. Mollusk's exhibit a variety of feeding strategies, including filter-feeding, grazing, and predation. They have a complex nervous system and a well-developed circulatory system.
8. Phylum Echinodermata
Common Name: Starfish, Sea Urchins
Characteristics:
Level of Organization: Organ system level
Symmetry: Radial symmetry in adults, bilateral in larvae
Germ Layers: Triploblastic
Body Cavity: Coelomate
Features: Water vascular system
Examples: Starfish (Asterias), Sea urchin (Echinus)
Description:
Echinoderms are marine animals characterized by their unique water vascular system, which facilitates movement, feeding, and respiration. They have a calcareous endoskeleton made up of ossicles. Echinoderms exhibit pentaradial symmetry as adults, while their larvae are bilaterally symmetrical. They can regenerate lost body parts and have simple nervous and circulatory systems.
9. Phylum Chordata
Common Name: Vertebrates, Tunicates, Lancelets
Characteristics:
Level of Organization**: Organ system level
Symmetry: Bilateral symmetry
Germ Layers: Triploblastic
Body Cavity: Coelomate
Features: Presence of notochord, dorsal nerve cord, pharyngeal slits, post-anal tail
Subphyla:
Urochordata (Tunicates): Example - Ascidia
Cephalochordata (Lancelets): Example - Branchiostoma
Vertebrata: Divided into classes like Pisces, Amphibia, Reptilia, Aves, Mammalia
Description:
Chordates are distinguished by the presence of a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some stage of their development. Vertebrates, a major subphylum, possess a vertebral column that replaces the notochord during development. Vertebrates exhibit a high degree of cephalization and a complex nervous system. They are further classified into classes such as fishes (Pisces), amphibians, reptiles, birds (Aves), and mammals.
Key Points for NEET Preparation
1. Understand the Basis of Classification: Be familiar with the different criteria used to classify animals, such as the level of organization, symmetry, germ layers, body cavity, segmentation, and notochord.
2. Differentiate Between Levels of Organization: Recognize the differences between cellular, tissue, organ, and organ system levels of organization.
3. Focus on Unique Characteristics and Examples of Each Phylum: Memorize the defining features and representative examples of each phylum.
4. Understand Coelom Types and Their Significance: Know the distinctions between acoelomate, pseudocoelomate, and coelomate body plans and their evolutionary significance.
5. Study the Evolutionary Significance of Features: Pay attention to the evolutionary implications of features like segmentation and the notochord.
6. Familiarize with Physiological Systems: Learn the key physiological systems of each phylum, with particular emphasis on vertebrate systems.
Conclusion
The study of the animal kingdom reveals the immense diversity of life forms on Earth. A thorough understanding of the classification criteria and the unique characteristics of each phylum is crucial for mastering this topic in NEET Biology. These notes provide a comprehensive guide to the animal kingdom, essential for NEET success and a deeper appreciation of the complexity of