CBSE Class 11 Biology Chapter 4 Animal Kingdom Revision Notes

In comparison to the plant kingdom, the animal kingdom has a much greater diversity of life. Metazoans are all animals (multicellular, eukaryotic, and heterotrophic animals).

4.1 Basis of Classification: 

Classification is based on characteristics such as:

• Cell arrangement 

• Level of body organization 

• Body symmetry 

• Nature of coelom 

• Patterns of digestive, circulatory, or reproductive systems

4.1.1 Levels of Organisation 

It varies significantly between animals. The major types are as follows:

• Cellular level. 

Cells are grouped together in loose cell aggregates. It demonstrates no coordination in the formation of tissues. Individual cells have the ability to perform specific functions. Sponge, for example.

• Tissue level. 

Tissues are formed by the accumulation of cells that perform similar functions. Coelenterates (hydra, for example)

• Organ level. 

Organs are made up of tissues that have been grouped together. Each organ is tasked with carrying out a specific function. Platyhelminthes and other higher phyla are examples.

• Organ system level. 

An organ system is a collection of organs that function as a single entity. The organ system is organised in a multitude of ways, as indicated in the diagram below.

Digestive system 

The digestive system in animals consists of the mouth, tongue, teeth, salivary glands, pharynx, oesophagus, stomach, small intestine, large intestine, liver, gallbladder, bile ducts, and pancreas. There are two kinds of it.

• Incomplete: The digestive system has only one exit to the outside world. It serves as both an anus and a mouth. Platyhelminthes and Coelenterates are two examples.

• Complete: The digestive system has two separate openings, the mouth and the anus, at each end. For instance: man

The circulatory system includes the following components: 

There are two kinds of it.

• Open type: The heart pumps blood to the tissues, which is bathed in it. Mollusks and arthropods are two examples.

• Closed type: Blood flows within blood vessels of varying diameters (arteries, veins, capillaries) without making direct contact with body cells. In many invertebrates (cephalopods) and all vertebrates, for example.

4.1.2 Symmetry 

Body parts are arranged on either side of the body's main median axis. Haeckel came up with this concept.

Animals have three types of symmetry.

• Asymmetry: The body cannot be divided into two equal halves by any plane that passes through the center. Sponge, for example

• Radial symmetry: Any plane which goes across the central axis can split the body into two equivalent halves. These creatures have two ends, the oral and aboral ends, but no left and right sides in the main body axis. Coelenterates, Ctenophora, and Echinodermata are a few examples.

• Bilateral symmetry: The body can only be divided into two identical halves by a single plane that passes through the central axis. There is a front end and a back end to such creatures. They have an upper and lower side as well. They have the same lateral sides on the left and right. Annelids, Arthropods, and so on.

Types of Symmetry

4.1.3 Diploblastic and Triploblastic Organisation 

This classification is divided into two categories based on the number of embryonic cell layers:

• Diploblastic: Cells are organized into two embryonic layers, outer ectoderm and inner endoderm, with a middle undifferentiated mesoglea in between. Coelenterates and Sponges, for example.

• Triploblastic: There are three embryonic layers present, namely the outer ectoderm, the middle mesoderm, and the inner endoderm. These three layers are responsible for the formation of all tissues and organs. Ectoderm gives rise to the epidermis and nervous system, for example, while mesoderm gives rise to muscles, endoskeleton, reproductive organs, coelom, and so on, and endoderm gives rise to the alimentary canal, lungs, and so on. 

• For example, platyhelminthes

Diploblastic and Triploblastic Organisation

4.1.4 Coelom 

The coelom is an animal's fluid-filled body cavity located between the body wall and the digestive tract. On either side of the coelom, mesodermal epithelium lines the space. The coelom contains all of the internal organs. The coelom enhances body flexibility. It is a shock absorber. It protects internal organs from external shocks in soft-bodied animals. It serves as an internal skeleton in some animals. As an example, consider the earthworm.

Animals are classified into three groups based on the nature of their coelom.

• Acoelomates: There is no body cavity, and the coelomic space is occupied by parenchyma-like cells. For instance, Platyhelminthes

• Pseudocoelomates: Animals with a false coelom. The mesodermal epithelium does not form the body cavity. Mesoderm appears as a smattering of pouches between the ectoderm and endoderm. Pseudocoelom develops in these animals from the embryonic cavity known as the blastocoel. As an example, consider Aschelminthes.

• Coelomates or Eucoelomates: Animals that have a true body cavity, such as annelids, mollusks, arthropods, echinoderms, hemichordates, and chordates.

4.1.5 Segmentation 

In some animals, the entire length of the body is divided transversely into a number of ring-like parts known as segments. This segmentation phenomenon is known as metamerism.

This pattern can be seen in annelids such as earthworms and arthropods such as millipedes and centipedes. Segmentation aids locomotion in earthworms.

Metameric segments in arthropods can be paired appendages for various functions such as legs for locomotion, antennae for sensory functions, and mouth for feeding, among others.

In insects, these metameric segments form body regions such as the head, thorax, and abdomen.

4.1.6 Notochord 

It is a rod-like structure derived from mesoderm that is present dorsally during embryonic development. It is a stiff and flexible tissue rod that runs along the dorsal side of the body, below the nerve cord and above the alimentary canal.

Animals are classified into two groups based on the presence or absence of a notochord.

• Chordates:  Animals that have a notochord. The notochord is present in chordates at some point in their lives. For example, fish, birds, mammals, and so on.

• Non-chordates: Animals that lack a notochord. They do not have the notochord at any stage of their life, for example, Porifera to Echinoderms.

4.2 Classification of Animals 

The animal kingdom is divided into three phyla, 11 of which are major phyla and the rest are minor phyla. Invertebrates make up nearly 99 percent of all animals.

Animalia is divided into 11 phyla based on shared fundamental characteristics.

• Porifera 

• Coelenterata 

• Ctenophora 

• Platyhelminthes 

• Aschelminthes 

• Annelida 

• Arthropoda 

• Mollusca 

• Echinodermata 

• Hemichordata 

• Chordata. 

4.2.1 Phlyum Porifera 

(porus-to-bear; fere-to-bear)

• It is the sponges, a group of the most primitive animals.

• ELLIS identified these as animals.

• ROBERT GRANT coined the term "porifera."

• PARAZOOLOGY is the study of sponges.

• The majority of them are marine and remain affixed to rocks.

• Some people live in freshwater.

• Spongilla is a sponge that lives in freshwater.

Sponge Canal System

Important characteristic features: 

• They live in sedentary habitats and can be solitary or colonial. They are organized at the cellular level. Cells join together to form the body plan.

• The majority of them are asymmetrical, but some are radially symmetrical.

• They are pore-bearing animals, with numerous openings or pores called OSTIA perforating their bodies.

• Body wall: There are two loosely differentiated layers of cells in the body wall. An outer dermal layer of pinacocytes and an inner layer of flagellated cells known as collar cells or choanocytes. They have a diploblastic structure.

• Water transport system (water canal system): The body is a cylinder which envelopes a spongocoel, which is a huge cavity. Spongocoel is accessed through a narrow opening known as the osculum. This pathway aids them in food gathering, respiratory exchange, and waste removal. Ostia or pores (through which water enters) spongocoel (central cavity) osculum or pores (water goes out).

• Choanocytes: Each ostium connects to a canal, which connects to the spongocoel. Choanocytes, which are flagellated collar cells, line the canal. It transports food and oxygen as well as excretory and reproductive waste. Each choanocyte has a long flagellum that protrudes from the free end of the cell. A transparent collar surrounds the lower part of the flagellum. The canal is not well developed in simple sponges. In such cases, the ostia open into the spongocoel via porocytes, and the spongocoel is lined with choanocytes.

• Mesenchyme is a non-living gelatinous matrix that exists between the two layers of the body. There are amoeboid cells, spicules, and sponging fibers in the mesenchyme. Amoeboid cells: amoeboid cells that move through the matrix carrying food between them. Spicules: These are siliceous or calcareous structures made of silica or calcium carbonate. Sponging fibers are elastic structures made of silk.

• Spicules and sponging fibers make up the skeleton.

• Sponges are nutritionally holozoic (take solid food). The digestion takes place within the cell.

• Reproductive system: shemaphrodites (sexes are not separate) Reproduces sexually as well as asexually.

Asexual reproduction occurs through fragmentation and budding. During unfavorable conditions, freshwater sponges produce buds known as gemmules, which remain dormant until the next favorable season.

Sexual reproduction: Some amoeboid cells develop into eggs or sperm during sexual reproduction.

Internal fertilization occurs, and larval development occurs indirectly. The zygote develops into a larva after fertilization. Sponge larvae are ciliated and swim freely.

They are classified into two types: amphiblastula and parenchymula.

• All sponges have a high rate of regeneration.

• Examples of Common sponge species may include, Leucosolenia, Sycon (scypha), Euspongia (bath sponge), Spongilla (freshwater sponge), and Eupelectella (venus flower basket).

In Japan, its dried skeleton is given as a costly wedding gift. It is regarded as a symbol of union until death. More examples include Hyalonema (glass rope sponge), Cliona (sulphur sponge), Chalina (dead man finger sponge), and Proterion (neptunes cup).

Classification of Porifera 

Class I: Calcarea is a type of plant (calcareous sponges. eg: Sypha, Leucosolenia, etc.)

Class II: Demospongia (sponging fiber skeleton. Sponge class with the most members. For example, Euspongia, Spongilla, and so on.

Class III: Hexactinellida (glass sponges with siliceous spicules, such as Euplectella and Hyalonema)

4.2.2 Phylum Coelenterata 

Coelenterates or Cnidarians are the common names for animals in the phylum coelenterata. They have true tissues, which makes them more advanced than sponges. It contains approximately 9000 species.

They are aquatic in nature. The majority of them are sea creatures. Hydra is a type of freshwater.

Important Characteristic Features 

• They can swim sessile or free.

• They are organized at the tissue level.

• Acoelomates are a type of acoelomate.

• It is radially symmetrical. However, sea anemones are biradially symmetrical.

• Diploblastic body wall (outer ectoderm, inner endoderm and middle mesoglea)

• Body cavity: A central gastro-vascular cavity or coelenteron that exits through the mouth or hypostome. Anus is not present. The body cavity is responsible for both digestion and food circulation. Coelenterates are holozoic and carnivorous eaters.

• Digestion occurs both intracellularly and extracellularly. Tentacles are finger-like structures that surround the mouth. It is used for food capture as well as defense.

• Cnidoblasts: Cnidaria is derived from the transformation of certain ectodermal cells into stinging cells, cnidodoblasts, or cnidocytes. Each cnidoblast has a stinging capsule called a nematocyst, which contains poisonous fluid. Cnidoblasts are defensive cells that kill or paralyze prey and enemies. They're mostly found on tentacles. 

• Physalia's nematocyst poison is a neurotoxin

Polyp: Sedentary, with a tubular body and mouth encircled by a circlet of tentacles It denotes the asexual stage. Hydra and Adamsia are two examples.

Medusa: a free-floating creature with a soft, transparent bell-like body and tentacles on the rim. Like an umbrella. The mouth is located in the center of a concave surface that is directed downward. It symbolizes the sexual stage. Medusa can be thought of as an upside-down polyp. As an example, consider the word Aurelia. The hydra medusa stage does not exist. In the polyp stage, it reproduces sexually.

• Reproduction: both asexual and sexual.

Asexual reproduction: It occurs through polyp budding and gives rise to medusa. During sexual reproduction, medusa releases gametes into the surrounding water. The zygote develops into a larva after fertilization. Cnidarian larvae are ciliated and swim freely. They are known as planula. The planula transforms into a sessile polyp. Coelenterates exhibit generational alternation throughout their life cycle. Asexual polyp generation alternates with sexual medusa generation in coelenterates that exist in both forms (polyp and medusa). For instance, Obelia

• Polymorphism: This phenomenon is seen in many colonial cnidarians, where the individuals (zooids) of the colony show morphological and functional differentiation. For example, Halistemma and Physalia.

• Common coelenterates include Hydra, Obelia (sea fur), Aurelia (jellyfish), Physalia (portuguese man of war), Adamsia (sea anemone), Vallela (sail by wind), Fungia (mushroom coral), Astraea (star coral), Pennatula (sea pen), Gorgonian (sea fan), Madrepora (stag horn coral), Meandrina

Classification of Coelenterata 

Class I: Hydrozoa (both polyp and medusa forms are found). Hydra Obelia, Physalia, and so on)

Class II: Scyphozoa (only the medusa form is found. Aurelia, for example)

Class III: Anthozoa (only the polyp form is found. For example, Adamsia, Fungia, Astraea, Pennatula, Gorgonia, Madrepora, Meandrina, Corallium, and so on.

4.2.3 Phylum Ctenophora 

(Ktene-bearing; phors-bearing)

Eschololz identified this phylum for the first time in 1928. It only contains a small number of animals (50 species). The animals in this phylum are commonly referred to as sea walnuts or comb jellies.

Important characteristic features: 

• They are either free swimmers or pelagic.

• They are sea creatures.

• The body is transparent and soft gelatinous.

• They are acoelomates with the ability to emit bioluminescence.

Symmetry: They seem to be radially symmetrical (the comb plate arrangement provides the appearance of radial symmetry), while tentacles and gastrovascular cavity branching are symmetrical in both directions. According to some zoologists, it is a biradial symmetry Diploblastic organism with tissue level organization.

Comb plates: the animal's body has eight rows of cilia on the outside. Comb plates are formed when cilia in each row join together. Comb plate ciliary movements aid in locomotion.

Tentacles: A pair of long, retractile tentacles emerge from blind pouches on opposite sides of the body; the tentacles contain colloblast or collocytes that aid in food capture.

Digestion: It exists on both the extracellular and intracellular levels.

Statocyst: a strange sense organ seen at the opposite end of the mouth It aids in the maintenance of equilibrium.

Reproduction: Only sexually. They are both male and female. Fertilization is done externally. Cydipid larva are in development. Pleurobrachia (sea-gooseberry), Ctenoplana, Cestum (venus girdle), Hormiphora, and Beroe are examples of common ctenophores.

4.2.4 Phylum Platyhelminthes 

(Platys-flat; helmins-worms)

GEGENBAUR was the first to mention Platyhelminthes. They are commonly referred to as flatworms. Today, approximately 13,000 species of flatworms are known. The body is generally flat dorsi-ventrally, hence the name flatworm. This is the first animal group in which the anterior part develops into a head.

Important characteristic features: 

• The first animal group to have an organ system level of organization.

• Parasitic adaptations: hooks and suckers are present.

• Bilateral symmetry with dorsal and ventral surfaces The first group of animals with bilateral symmetry.

• Triploblastic animals: these are the first animals to have three germ layers.

• Acoelomate animals: The space between the body cavity and the alimentary canal is filled with mesoderm-derived loose parenchyma cells (mesenchymal cells).

• Alimentary canal: It has a number of branches. It has a single opening called the mouth that allows it to exit. Anus is not present. The alimentary canal is absent in parasitic flatworms. While living in the host intestine, they absorb nutrients through their body wall.

• Excretory system: it is made up of branching tubes that lead to specialized cells known as flame cells (protonephridia). These cells are responsible for osmoregulation and excretion.

• Reproduction: Hermaphrodites predominate. They can undergo reproduction in both asexual and sexual ways. Asexual reproduction is accomplished through fragmentation and regeneration. Some members have a high capacity for regeneration.

• Fertilisation: It occurs within the body and includes larval stages of development (amphiblastula and parenchymula).

• Tapeworm (Taenia or pork tapeworm), Liver fluke (Fasciola), Blood fluke (Schistosoma), Planaria, and Echinococcus are common examples of flatworms (Dog tapeworm).

Classification of Platyhelminthes 

Class I: Turbellaria (free living flatworms, eg : Planaria) 

Class II: Trematodes are parasitic worms (ecto or endoparasites with oral and ventral suckers, eg : liver fluke, blood fluke, etc). 

Class III: Cestoda (endoparasites with scolex, such as Taenia solium (pork tapeworm), Taenia saginata (beef tapeworm), and others).

4.2.5 Phylum Aschelminthes: 

Animals in this phylum are commonly referred to as roundworms, threadworms, bagworms, or nematodes. It contains approximately 15,000 species. Around 15 of these species are human parasites.

Important characteristic features: 

• Whether aquatic or terrestrial, free-living or parasitic in plants and animals.

• Bilaterally symmetrical, triploblastic, pseudocoelomate animals with organ system level.

• Body wall: It is tubular and tapered at both ends, with a thin cuticle covering it.

• The epidermis has multiple nuclei.

• Digestive system: They have a tubular and complete alimentary canal that includes the mouth, muscular pharynx, intestine, and anus. The mouth may have teeth that can cut and pierce the tissues. The muscular pharynx is well developed, assisting in the sucking of food from the host.

• The circulatory and respiratory systems are not present. 

• They have a nervous system and exhibit flexible body movements.

• Reproduction: Dioecious, with sexual dimorphism. Males are smaller than females. Copulatory spicules are found in males and aid in the process of copulation.

• Fertilization: It is an internal problem. To withstand harsh conditions, the zygote has a thick wall. Development can be either direct or indirect. Parasites in humans are common examples of this phylum, including Roundworms, Hookworms, Filarial worms, Pinworms, and Guinea worms. Other members of this phylum include the eye worm (Loaloa), the whip worm (Trichuristrichura), and the Trichina worm (Trichinella)

4.2.6 Phylum Annelida 

(annulus-small ring, lidos-shape)

Animals in this phylum are commonly referred to as annelids or segmented worms. Lamarck coined the term "Annelida'' in 1809. There are approximately 9,000 annelid species known today. They come in a variety of shapes and sizes, ranging from 1mm to 2.5m in length.

Important characteristic features: 

• They are terrestrial, marine, freshwater, or parasitic, and have organ system-level body organization.

• True coelomates that are bilaterally symmetrical and triploblastic.

• Metamerically segmented: the body is divided into segments called metameres on the outside. The true segmentation of annelids is a remarkable feature.

• A thick cuticle covers the body's surface. Both longitudinal and circular muscles tend to exist in the body wall.

• The organs of locomotion in aquatic annelids, such as Nereis, are setae or unjointed lateral appendages called parapodia, which aid in swimming.

• Digestive system: It is complete and includes the pharynx, oesophagus, stomach, intestine, and other organs.

• Typhlosole: A longitudinal fold in the intestine that increases the surface area available for secretion and absorption.

• Chloragogen cells: These are cells found in the cavity of the typhlosole that store food. They produce glycogen and store fat. They also have excretory functions.

• Excretory organs are paired segmentally arranged coiled tubes known as nephridia. They also assist with osmoregulation.

• Circulatory system: It is of the closed variety. Blood flows through a blood vessel that is closed. For the first time in animal evolution, a heart to move the oxygen-carrying blood is discovered.

• They demonstrate skin respiration.

• Nervous system: It is made up of a brain, segmented ganglia, and two ventral nerve cords.

• Reproduction: They have either dioecious or monoecious reproduction. They reproduce in a sexual manner. A trochopore larval stage has been observed in many members.

The common examples of this phylum are: 

Pheretima and Megascolex earthworms, Nereis, Hirudinaria (blood sucking leeches), Aphrodite (sea mouse), Tubifex, Chaetopterus, and Terebella

Classification of this phylum: 

Class I: Polychaeta (a large number of setae on the parapodia. Nereis, Aphordite, Chaetopterus, and so on)

Class II: Oligochaeta (setae are sparsely distributed throughout the body. As an example, consider the term "Earthworm."

Class III: Hirudinea (no parapodia or setae). There are two suckers present. As an example, consider the term "leech."

Class IV: Archiannelida (no setae or parapodia). Annelids in their primitive state. Polygordius, Bonelia, and others are examples).

4.2.7 Phlum Arthropoda 

(poda-appendages; arthros-joint)

They are the animals with appendages and jointed legs. Von Siebold made the first mention of it. It is the animal kingdom's largest phylum. It contains two-thirds of all named animal species on the planet. They first appeared around 600 million years ago. Trilobites are arthropod fossils that lived approximately 600 million years ago. TRILOBITES, the horse-shoe crab, an ancient relative of the Arachinds, can be found in warm estuarine zones such as Bengal's Sunderbans.

Important characteristic features. 

• Their distribution is cosmopolitan. They can be found in freshwater, marine water, on land, and in the air.

• They have two feet that are joined together. They are organized at the organ system level of the body.

• It is symmetrical on both sides.

• They are triploblastic creatures.

• They are segmented creatures.

• They share a dorm room. True coelom is diminished. The body cavity is called haemocoel because it is filled with blood.

• Insects, for example, have a segmented body divided into three regions: head, thorax, and abdomen. In some cases, the head and thorax fuse to form a single region known as the cephalothorax, as in Arachinds, Crustaceans, and so on. Some arthropods, such as myriapods, have only a head and a trunk.

• Exoskeleton: The chitinous jointed exoskeleton covers the entire body. The exoskeleton is light in weight, tough, and made up of proteins and chitin, a polysaccharide that results in a chitinous cuticle. Moulting, also known as ecdysis, is the casting of an old exoskeleton.

• Podomeres: These organisms have jointed appendages that are differentially modified to perform various functions. Each body segment is equipped with a pair of segmented appendages. Their segments are known as podomeres.

• Circulatory system: It is of the open variety and has a dorsal heart.

• Digestive system: It is fully developed and functional. The mouth is surrounded by mouth parts that have evolved into various types based on the feeding habits of various arthropods.

• Respiratory system: In aquatic forms, respiratory organs are gills (e.g., prawn) or gill books (e.g., horseshoe crab), while in terrestrial forms, respiratory organs are book lungs (e.g., scorpion) or tracheal system (e.g., insects).

• Excretion: Green glands or malpighian tubules are excretory organs. There is no nephridia.

• Cilia is not present.

• The presence of the brain.

• Sensory organs have matured. Simple or compound eyes are possible. The compound eye is made up of several independent visual units known as ommatidia, each with its own lens. Chirping crickets and cicadas have sound receptors. Many arthropods have feelers called antennae on their heads that allow them to detect odors and sensations of touch. Insects communicate using chemicals known as pheromones.

• Reproduction: most are dioecious. Fertilisation occurs externally in aquatic arthropods and internally in terrestrial arthropods.

• Most arthropods are oviparous. Some of them are viviparous. The eggs hatch within the female and the young are born in such arthropods.

• In many arthropods, development is direct, and juveniles resemble adults. In several insect groups, development occurs in an indirect manner. In such arthropods, the egg hatches into a separate larva that is not related to the adult. The most common arthropods are: Araneus (garden spider), Limulus (king crab), Eupagurus (hermit crab), Cancer, Macrobrachium (prawn), Lepisma (silver fish), Periplanata (cockroach), Apis (bee), Anopheles (mosquito), Musca (housefly), Triops (tadpolefish), Daphnia (water flea), Xensops (Lepas and Balanus)

Classification of phylum Arthropoda: 

Class I: Crustacea-Aquatic animals with gills as respiratory organs (eg: prawn, crab, hermit crab, barnacles, etc.) 

Class II: Myriaopoda- a terrestrial, air-breathing, multi-legged animal (eg : millipede, centipede, etc)

ClassIII: Arachnids are air-breathing creatures with four pairs of legs (eg: spider, scorpion, king crab, etc.)

Class IV: Insecta – air breathing creatures with three pairs of legs (eg: cockroach, butterfly, Lepisma, Oryctes, Leptocorisa, Musca, Apis silkworm, etc.) 

Class V: Onychopora – a terrestrial, air-breathing creature with clawed legs (eg: Peripatus, a living fossil)

4.2.8 Phylum Mollusca 

It is the animal kingdom's second largest phylum. Johnston coined the term "mollusca." They have a soft body as well as a shell. Malacology is the study of mollusks, and chonochology is the study of molluscan shells.

Important characteristic features 

• They are mostly aquatic in nature. The majority of them are marine, but some are freshwater and a few are terrestrial. A grey slug is a type of terrestrial mollusk that lacks a shell.

• Molluscs are all soft-bodied, unsegmented animals.

• They have organ system level body organization and are bilaterally symmetrical, with the exception of univalves.

• They are triploblastic creatures.

• They are true coelomates, but the coelom in adults is reduced. 

• Their soft body is protected by an unsegmented external shell, which is a haemocoel. The shell is made of calcium carbonate and can be one piece (univalve) or two pieces (dualvalve) (bivalve). In some cases, the shell is internal or not present at all.

• The body is divided into four sections: the head, mantle, visceral hump, and foot. Sensory tentacles can be found in the head region. The vital internal organs are housed in the visceral hump. It is protected by a soft, spongy layer of skin known as the mantle or pallium. Shell is secreted by the mantle. Gills can be found in the mantle cavity. It has a soft and muscular foot. It is known as the locomotory organ.

• Digestive system: It is fully developed, complete with salivary glands and a liver.

• The circulatory system is of the open variety. The heart has chambers and is valvular.

• Excretion: Nephridia is present.

• Nervous system: A network of nerves connects paired ganglia. Tentacles and eyes are examples of sense organs.

• Respiration: Ctenidia (gills) in aquatic forms. Pulmonary sacs in a terrestrial setting.

• Reproduction: Dioecious. Fertilization can be external or internal, oviparous or viviparous. Glochidium, Trocophere, and Veliger are the larval forms. Pila (apple snail), Achatina (land snail), Lamellidens (mussel), Pinctada (pearl oyster), Sepia (cuttlefish), Loligo (squid), and other common molluscans.

Classification 

Class I: Polyplacophora- shell made up of 8 pieces. Chilton, for example.

Class II: Monoplacophora- a single-piece shell. As an example, consider the word neopilina.

Class III: Aplacophora-shell is missing. As an example, consider the term neomenia.

Class IV: Tubulr of Scaphopoda. As an example, consider dentalium.

Class V: Pelecypoda- shell in two pieces For example, Mussel, Oyster, Teredo, and so on.

Class VI: Gastropoda- a spirally coiled shell made of one piece. For example, Pila, Snail, Slug, and so on.

Class VII: Cephalopoda- internal or reduced shell. Loligo, Cuttlefish, Devil fish, and so on.

4.2.9 Phylum Echinodermata 

(Echinos/spines; derm/skin)

They have a spiny skin or a spiny body. J.Klein coined the term "echinodermata."

Important characteristic features: 

• They are exclusively marine animals. 

• The body is covered by a large number of spines, most of which are immovable and serve a protective function, but some spines are movable and aid in locomotion. A few spines are also modified to form defense organs known as pedicellaria. For example, sea urchins, starfish, and so on.

• They have organ system-level body organization. They are triploblastic creatures.

• They are unsegmented and pentamerous in the adult, radially symmetrical, but bilaterally symmetrical in the larval forms.

• They have an endoskeleton made up of calcareous plates called ossicles that are embedded in the skin.

• They are true coelomates, but a large portion of the coelom has been modified to form the water-vascular system, which aids in locomotion, food capture and transport, and respiration.

• A water vascular or ambulacral system in which sea water enters through a porous plate known as madreporite.

• Tube feet: The water vascular system is made up of radiating canals and tube-like appendages that contain water. Tube feet are the name given to these appendages (podia). Their primary function is locomotion and food capture.

• Digestive system: Includes a mouth on the ventral (lower) side and an anus on the dorsal side (upper side).

• Respiration: It is carried out by skin gills that protrude from the coelom over the skin.

• Circulatory system: It has been slowed.

• Excretory system: It is not present. Nitrogenous wastes are expelled through the gills.

• Nervous system: It consists of a central nerve ring with radial nerves that extend to each arm.

• Reproduction: Sexes are distinct. External fertilization. The larva develops in an indirect manner as it swims freely.

• Echinoderms have a high capacity for automy and regeneration. Asterias (star fish or sea star), Echinus (sea urchin), Echinocardium (heart urchin), Antedon (feather star or sea silly), Cucumaria (sea cucumber), and Ophiura are the most common echinoderms (brittle star).

Classification of Phylum Echinodermata 

Class I: Asteroidean (a star with five arms. As an example, consider the starfish.)

Class II: Ophiuroidea (slender and flexible arms. Brittle fish, for example)

Class III: Echinoidea has no arms and a globular body with long spines. For example, sea urchin) 

Class IV: Holothuroidea (armless, long body with long spines. For example, sea cucumber) 

Class V: Crinoidea (slender, forked arms with branches. As an example, consider the sea lily.)

4.2.10 Phylum Hemichordata : 

Have small worm-like sea creatures. Previously classified as a sub-phylum of Phylum Chordata. Triploblastic, bilaterally symmetrical, and coelomate. The body is cylindrical, with a proboscis, collar, and trunk. The circulation is of the open type. Respiration via the gills Proboscis gland excretion The sexes are distinct. Fertilization from outside sources Development that is done indirectly. Balanoglossus and Saccoglossus are two examples.

4.2.11 Phylum Chordata: 

The presence of a Notochord (between gut and nerve cord) Have a hollow nerve chord on the dorsal side. There are two pharyngeal gill slits. The heart is located ventral. There is a postanal tail present. Organ system level of organization is bilaterally symmetrical, triploblastic, and coelomate. Circulation is of the closed variety. The distinctions between Chordata and Non-chordata are shown below.

Chordata 

1. Notochord is found in the embryonic stage Absent 

2. Central nervous system is dorsal, hollow and single Ventral, solid and double 

3. Pharyngeal gill slits present Absent 

4. Ventral heart Dorsal heart (if present) 

5. Post-anal tail present Absent 

The phylum Chordata is divided into three sections: 

1.Urochordata or Tunicata, 

2.Cephalochordata, 

3.Vertebrata.

Sub-Phyla Urochordata: 

The notochord is only found in the larval stage's tail. The body is covered by test or a tunic made entirely of tunicin. Metamorphosis that regresses Ascidia, Salpa, and Doliolium are examples of hermaphrodites.

Subphylum Cephalochordata: 

The segmented notochord is a persistent structure that extends from head to tail. The body has a pharynx-like sac with gill slits for filter feeding and respiration. Fish-like only in the sea There is no clear coelom. The sexes are distinct. Branchiostoma, for example (Amphioxus or Lancelet)

Sub-Phyla Vertebrata: 

Only during the embryonic period do you have a notochord. The notochord is replaced by the vertebral column, which can be bony or cartilaginous. A ventral muscular heart with two, three, or four chambers is preferred. Fins or limbs with paired appendages. Kidneys are responsible for excretion and osmoregulation. Vertebrata: Agnatha and Gnathostomata are the two divisions. Agnatha (Toothless): There is one class included: Cyclostomata

4.2.11.1 Class: Cyclostomata: 

Suction and a circular mouth without jaws Some fishes host ectoparasites. There are no scales and no paired fins. The cranium and spinal column are cartilaginous. Although it lives in the sea, it migrates to freshwater to spawn and dies afterward. After metamorphosis, larvae of Petromyzon (Lamprey) and Myxine return to the ocean (Hagfish).

Division Gnathostomata (Bear Jaws) 

SUPER-CLASS: PISCES 

4.2.11.2 Class 1: Chondrichthyes : 

Marine animals that have a stream-lined body and a cartilaginous endoskeleton. The mouth is located ventrally. The notochord is present throughout life. Gill slits are distinct and lack an operculum. The skin is covered in placoid scales. Teeth are modified placoid scales found in the jaw. Predaceous in most cases. There is no swim bladder. The heart has two chambers. (One auricle and one ventricle) certain of them possess electric organs (for example, Torpedo) and few carry poison stings. (For example, Trygon) Poikilotherms are people who are cold-blooded. Dioecious. The male's pelvic fin bears claspers, indicating sexual dimorphism. Internal fertilization. Many are viviparous. Torpedo (Electric ray) and Rhinobatus are two examples (Guitar fish).

4.2.11.3 Class 2: Osteichthyes: 

Fish from both salt and freshwater are included. Endoskeleton made of bone. Usually, the mouth is the last stop. The operculum covers four pairs of gill slits. Scales on the skin are cycloid/ctenoid. For buoyancy, an air bladder is present. The heart has two chambers. Animals with cold blood. Dioecious. Monomorphic in both sexes. Fertilization is done externally. The majority of them are oviparous. Development is a two-way street. Exocoetus (flying fish) and Hippocampus are two marine examples (Sea horse). Labeo (freshwater) (Rohu). Clarias, Catla (Katla) (Magur). Betta (fighting fish) aquarium, Pterophyllum (Angel fish).

SUPER CLASS: TETRAPODA – 

4.2.11.4 Class-1: Amphibia 

It is a type of terrestrial tetrapod that lives in both water and on moist land because the skin lacks protective scales and the larval stage is aquatic. The creature has two pairs of jointed pentadactyl limbs. Their digits lack claws, nails, and hoofs. The body is categorised into two major parts: the head and the trunk. Skin that is moist and free of scales. Tympanum is a symbol for the ear. The cloaca is the common chamber through which the alimentary, urinary, and reproductive tracts emerge. Respiration via the gills, lungs, or skin Cold blooded animals have a three-chambered heart (two auricles and one ventricle). The sexes are separated. Fertilization is an external process that necessitates the use of water. Indirect development, oviparous. Ichthyophis, Necturus, Siren, Amphiuma, Salamandra, Rana, Bufo, Hyla, and other genera are examples.

4.2.11.5 Class - 2: Reptilia 

The crawling or creeping mode of locomotion. The skin on the body is dry and cornified, with epidermal scales or scutes. Tympanum is a symbol for the ear. When limbs are present, they are in pairs. Crocodiles have a four-chambered heart, which is unusual for a three-chambered heart. Scales shed by snakes and lizards as skin cast. Poikilotherm. The sexes are distinct. Internal fertilization occurs. Direct development, oviparous. Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator), Hemidactylus (Wall lizard), Poisonous Snakes – Naja (Cobra), Bangarus (Krait), Vipera (Wall lizard) (Viper).

4.2.11.6 Class - 3: Aves 

The presence of feathers, and the majority of them fly, with the exception of flightless birds such as the ostrich. Jaws reshaped to form a beak with no teeth. Wings are formed from the forelimbs. Scales cover the hind limbs. Except for an oil gland at the base of the tail, there are no glands on the skin. The endoskeleton has nearly completely ossified. Spongy or pneumatic bones Long bones are hollow and contain air cavities. There are no epiphyses. The skull has a monocondylic shape. The digestive tract contains additional chambers such as the crop and gizzard. The heart has four chambers. Homoiothermous, or warm-blooded, with the ability to maintain a constant body temperature. To supplement respiration, air sacs are connected to the lungs. Oviparous. Direct advancement. Examples include pigeons, crows, sparrows, and peacocks.

4.2.11.7 Class- 4: Mammalia 

Mammary glands secrete milk to nourish young ones. You have two sets of limbs. Hairs can be found on skin. There are external ears or a pinna present. Jaw teeth come in a variety of shapes and sizes. The heart has four chambers. Homoiothermous. Respiration via the lungs. Sexes separate, and fertilization occurs internally. It is either viviparous or oviparous. Direct advancement. Examples: Ornithorhynchus ovary-Ornithorhynchus ovary-Ornithorhynchus (Platypus). Viviparous - Macropus (Kangaroo), Camelus (Camel), Pteropus (Flying Fox), Rattus (Rat), Macaca (Monkey), Felis (Cat), Canis (Dog), Equus (Horse), Elephas (Elephant), Balaenoptera (Blue whale), Delphinus (Common dolphin), Panthera leo (Tiger), Panthera tigris (Tiger), Panther (Lion).

Fast Track Revision: 

1. Animals are multicellular, heterotrophic eukaryotes with a variety of cell-organization patterns. Structural Organization Levels: a. Cellular level b. Tissue level c. Organ level d. Organ system level

2. Animals can be asymmetrical or symmetrical based on symmetry.

3. Diploblastic animals exist.

4. The coelom is the body cavity lined by mesoderm. The presence or absence of coelom is also used to classify organisms, as shown below 

a. Coelomates Pseudocoelomates 

b. Pseudocoelomates 

c. Acoelomates

5. Animalia is divided into five kingdoms based on the presence or absence of a vertebral column.

a. Invertebrate 

b. Vertebrate. 

6. During embryonic development, mesodermal cells form the notochord, a rod-like structure on the dorsal surface. Chordates are animals that have a notochord and non-chordates are animals that do not have a notochord.

7. Non-chordates include

a. Phylum Porifera 

b. Phylum Cnidaria 

c. Phylum Ctenophora 

d. Phylum Platyhelminthes 

e. Phylum Aschelminthes 

f. Phylum Annelida 

g. Phylum AArthropoda 

h. Phylum Mollusca 

i. Phylum Echinodermata 

j. Phylum Hemichordata 

k. Phylum Chordata. 

8. Phylum Chordata is further subdivided into the following subphyla:

a. Urochrodata 

b. Cephalochordata 

c. Vertebrata.

Animal Kingdom Basic Subjective Questions - Class 11 Revision Notes

Section–A (1 Mark Questions)

1. Animals of which class do not have jaws in their mouth?

Ans. Animals of Class Cyclostomata are called jawless fishes as these animals do not possess jaws in their mouth.

2. Name an animal which belongs to Class Chondrichthyes.

Ans. Trygon (Stingray) is a cartilaginous fish that belong to Class Chondrichthyes.

3. Name an animal which has both the following characteristics.

a. Radial symmetry

b. Freshwater habitat

Ans. Hydra is an animal which has radial symmetry and freshwater habitat. 

4. Animals considered as the connecting link between chordates and non-chordates belong to phylum ……….

Ans. Animals of Phylum Hemichordata are considered as a connecting link between chordates and non-chordates. 

5. Animals of which phylum developed the organ system level of organization for the first time?

Ans. Animals of Phylum Aschelminths were the first to show the organ system level of organization. 

Section–B (2 Mark Questions)

6. Name two oviparous animals which belong to class Mammalia.

Ans. Oviparous mammals are egg laying mammals. Viviparous animals give direct birth to the young ones. Animals of Class Mammalia are viviparous with few exceptions. Platypus (Ornithorhynchus) and Echidna (Tachyglossus) are oviparous mammals.

7. Answer the following questions.

(i) Segmentation in the body is first observed in phylum ………. .

(ii) Name all the phyla where segmentation occurs.  

Ans. (i) Segmentation was first observed in animals of Phylum Annelida. 

(ii) Other than annelids, animals of Phylum Arthropoda and Phylum Chordata also have segmentation. 

8. How important is the presence of air bladder in Pisces? 

Ans. The air bladder is found to be present in the members of Class Osteichthyes, the bony fishes.  The main function of air bladder is to regulate the buoyancy and it helps the fishes to float in the water preventing sinking. Air bladder is absent in cartilaginous fishes (Class Chondrichthyes). Since cartilaginous fishes do not have air bladder they have to swim continuously to avoid sinking.

9. Name the animals which have the following structures along with their respective functions.

(a) Flame cells

(b) Ambulacral system

Ans. (a) Flame cells: Flame cells are found in the excretory system of flatworms (Phylum Platyhelminthes). They also help in osmoregulation. Planaria has flame cells and it belongs to Phylum Platyhelminthes.

(b) Ambulacral system: Ambulacral system or the water vascular system is the characteristic feature of Phylum Echinodermata. The water vascular system helps in locomotion, capture of food and respiration. Astarias (Starfish) possess an ambulacral system.

10. Why are hemichordates not classified as chordates? Name an animal which is placed in Phylum Hemichordata.

Ans. Hemichordates were initially grouped under Phylum Chordata because both chordates and hemichordates are enterocoelus. Later on, more studies proved that none of the animals of Phylum Hemichordata have a notochord, which is a distinguishing feature of chordates. Hence, these animals have been given a separate phylum, called the Hemichordata. 

Balanoglossus (Acorn) belongs to Phylum Hemichordata. 

11. Give an example of the following animals with their scientific name.

(i) A freshwater poriferan

(ii) A flightless bird

(iii) A limbless reptile

Ans. (i) A freshwater poriferan- Fresh water sponge (Spongilla)

(ii) A flightless bird – Ostrich (Struthio)

(iii) A limbless reptile – Indian Cobra (Naja naja)

Overview of Class 11 Chapter 4 Animal Kingdom

Biology Notes for Class 11 Chapter 4 gives a brief comprehension of eukaryotic, multicellular species belonging to the Kingdom Animalia. The chapter presents the unique characteristics of every animal classification. The animals enlisted under the Animal Kingdom obtain their energy either by feeding on other animals or from plants. Kingdom Animalia holds millions of identified species. While a few species share similar characteristics, others differ drastically.

Class 11 Biology Chapter 4 Animal Kingdom Notes presents a brief on Phylum Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, and Chordata. 

Basis of Classification

The Animal Kingdom classification is based on the different critical and essential characteristics such as the level of organisation, symmetry, habitat, and pattern of organ systems.

Levels of Organisation

There are four levels of the organisation, and they are as follows.

• Cellular Level of Organisation

• Tissue Level of Organisation

• Organ Level of Organisation

• Organ System Level of Organisation

1. Cellular Level of Organisation

At the Cellular Level of Organisation, the cells are arranged as loose aggregates. An example of a Cellular Level of Organisation is Sponges.

2. Tissue Level of Organisation

At the Tissue Level of Organisation, the cells that perform the same function are arranged into tissues. An example of the Tissue Level of Organisation is Coelenterates.

3. Organ Level of Organisation

At the Organ Level of Organisation, the tissues are grouped to form organs. Each organ is specialised for a particular function. An example of an Organ Level of Organisation is Platyhelminthes.

4. Organ System Level of Organisation:

In the Organ System Level of Organisation, the organs associate to form some functional systems like Arthropods, Annelids, Chordates, Echinoderms, and Molluscs. An example of an Organ System Level Organisation is the Circulatory System.

Body Symmetry

There are three levels of Body symmetry:

• Asymmetrical

• Radial symmetry

• Bilateral symmetry

1. Asymmetrical Body Symmetry

Those organisms falling under the asymmetrical body symmetry cannot be divided into two halves through a median plane. An example of asymmetrical body symmetry is Sponges.

2. Radial Body Symmetry

Those organisms falling under the radial body symmetry can be divided into two identical halves through any plane passing through the central axis. An example of radial body symmetry is coelenterates, echinoderms and ctenophores.

3. Bilateral Body Symmetry

Those organisms falling under the bilateral body symmetry can be divided into two identical left and right halves through only one plane. An example of bilateral body symmetry is annelids and arthropods.

Germ Layers

Based on the germ layers, the animals are classified as follows:

1. Diploblastic

Here, the cells are arranged in two embryonic layers—an external ectoderm and an internal endoderm. Besides, an undifferentiated layer known as mesoglea is present. 

2. Triploblastic

Here, the developing embryo possesses a third germinal layer, mesoderm, between the ectoderm and endoderm.

Important Questions on Class 11 Biology Chapter 4 Animal Kingdom

1. Give 5 examples of Arthropoda.

2. Why are air sacs and pneumatic bones essential for aves?

3. What is the role of feathers in birds?

4. Give 5 differences between open and closed circulatory systems.

5. What are sponges?

6. Differentiate between complete and incomplete digestive systems.

7. Give examples of limbless reptiles and oviparous mammals.

8. What are coelomates?

9. How many types of patterns are there in the organ system?

10. What are the functions of the coelom and body cavity in animals? Support your answer with relevant diagrams.

Benefits of Studying Vedantu’s Class 11 Biology Revision Notes for Chapter 4 - Animal Kingdom

There are several advantages of studying Vedantu’s Class 11 Biology Revision Notes for Chapter 4 Animal Kingdom. However, the following are the ones that help students the most during their revision before the exam. 

1. Vedantu’s revision notes are precise and comprehensive, and they help students gain knowledge of all the important concepts and areas covered in Class 11 Animal Kingdom before the exam without wasting much time. 

2. Our subject experts have created these revision notes in a manner that students find these notes extremely easy to read and understand, without allowing any missing out on any information due to great readability and easy language. 

3. Our revision notes are in line with the latest Class 11 CBSE syllabus and guidelines. Therefore students can get a clear idea of the question patterns and the weightage of marks for their CBSE Class 11 Biology exam.
   
   

Students can prepare the CBSE Class 11 Biology Chapter 4 with the help of our study materials. They can download and refer to the Animal Kingdom Important Questions, NCERT Solutions for Class 11 Biology Chapter 4, and NCERT Exemplar Solutions for Class 11 Animal Kingdom. They can also refer to the topic-wise notes for a better understanding of the topics. Vedantu provides previous years’ question papers, sample papers, and solutions for NCERT and other reference books for Class 11 Biology and other subjects. Students can access and download the study materials for free and prepare for the Class 11 Biology exam as well as the NEET exam.