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Animal Kingdom Notes for Class 11 Biology

Following are Animal Kingdom Notes for Class 11 Biology. These revision notes have been prepared by expert teachers of Class 11 Biology as per the latest NCERT, CBSE, KVS books released for the current academic year. Students should go through Chapter 4 Animal Kingdom concepts and notes as these will help you to revise all important topics and help you to score more marks. We have provided Class 11 Biology notes for all chapters in your book. You can access it all free and download Pdf.

Chapter 4 Animal Kingdom Notes Class 11 Biology

1. Levels of Organisation
➤ All members of animalia are multicellular but all of them do not exhibit the same pattern of organisation of cells.

2. A complete digestive system has two openings, mouth and anus.
➤ Platyhelminthes has only a single opening to the outside of the body that serves as both mouth and anus, and is hence called incomplete.

3. Circulatory system may be of two types:
➤ Open type in which the blood is pumped out of the heart and the cells and tissues are directly bathed in it and
➤ Closed type in which the blood is circulated through a series of vessels of varying diameters (arteries, veins and capillaries).

4. Symmetry
➤ Sponges are mostly asymmetrical, i.e., any plane does not divide them into equal halves.
➤ When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. Coelenterates, ctenophores and echinoderms have this kind of body plan
➤ Animals like annelids, arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry 

5. Diploblastic and Triploblastic Organisation
➤ Two embryonic layers, an external ectoderm and an internal endoderm, are called diploblastic animals, e.g., coelenterates.
• An undifferentiated layer, mesoglea, is present in between the ectoderm and the endoderm
➤ Those animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm, are called triploblastic animals (Platyhelminthes to chordates).

6. Coelom → 
➤ Between the body wall and the gut wall → The body cavity
➤ Lined by mesoderm
➤ Animals possessing coelom → coelomates,
• e.g., annelids, molluscs, arthropods, echinoderms, hemichordates and chordates
➤ if the body cavity is not lined by mesoderm, (the mesoderm is present as scattered pouches) → Pseudocoelom
• The animals possessing them are called pseudocoelomates, o e.g., Aschelminthes
➤ The animals in which the body cavity is absent are called acoelomates, o e.g., Platyhelminthes

7. Segmentation
➤ In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs.
➤ This pattern called metameric segmentation
➤ Phenomenon is known as metamerism.
• For example, in earthworm

8. Notochord
➤ Mesodermally derived rod-like structure
➤ Formed on the dorsal side during embryonic development
➤ Animals with notochord are called chordates
➤ Animals which do not form this structure are called non-chordates, e.g., porifera to echinoderms.

➤ Commonly known as SPONGES.
➤ Generally marine
➤ Primitive multicellular animals
➤ Sponges have a water transport or canal system.
• Water enters through minute pores (ostia) in the body wall
• A central cavity, SPONGOCOEL,
• Water goes out through the osculum.
➤ This pathway of water transport is helpful in food gathering, respiratory exchange and removal of waste.
➤ Choanocytes or collar cells line the spongocoel and the canals.
➤ Digestion is intracellular.
➤ A skeleton made up of spicules or spongin fibres.
➤ Sexes are not separate (hermaphrodite),
• i.e., eggs and sperms are produced by the same individual.
➤ Sponges reproduce
• asexually by fragmentation
• sexually by formation of gametes.
• Fertilisation is internal
• development is indirect having a larval stage
• Larva is morphologically distinct from the adult.
➤ Examples:
• Sycon (Scypha),
• Spongilla (Fresh water sponge)
• Euspongia (Bath sponge).

10. Phylum – Coelenterata (Cnidaria)
➤ Aquatic, mostly marine,
➤ Sessile or free-swimming,
➤ Radially symmetrical animals
➤ The name cnidaria is derived from the cnidoblasts or cnidocytes
• Cnidoblasts or Cnidocytes (contain the stinging capsules or nematocytes) present on the tentacles and the body.
• Cnidoblasts are used for anchorage, defence and to capture prey
➤ Diploblastic.
➤ Central gastro-vascular cavity with a single opening, mouth on hypostome.
➤ Digestion is extracellular and intracellular.
➤ Some of the cnidarians, e.g., corals have a skeleton composed of calcium carbonate.
➤ Cnidarians exhibit two basic body forms called polyp and medusa
➤ Polyp is a sessile and cylindrical form like Hydra, Adamsia, etc.
➤ Medusa is umbrella-shaped and free-swimming like Aurelia or jelly fish.
➤ Those cnidarians which exist in both forms exhibit alternation of generation (Metagenesis), i.e., polyps produce medusae asexually and medusae form.

11. Phylum – Ctenophora
➤ Exclusively marine,
➤ Radially symmetrical,
➤ Diploblastic organisms
➤ Tissue level of organisation.
➤ The body bears eight external rows of ciliated comb plates, which help in locomotion
➤ Digestion is both extracellular and intracellular.
➤ Bioluminescence (the property of a living organism to emit light) is wellmarked in ctenophores.
➤ Sexes are not separate.
➤ Reproduction takes place only by sexual means.
➤ Fertilisation is external with indirect development.
➤ Examples: Pleurobrachia and Ctenoplana.
➤ Examples:
• Taenia (Tapeworm),
• Fasciola (Liver fluke).

12. Phylum – Platyhelminthes
➤ Dorso-ventrally flattened body, hence are called flatworms
➤ Mostly ENDOPARASITES found in animals including human beings.
➤ Bilaterally symmetrical,
➤ Triploblastic and acoelomate animals
➤ Hooks and suckers are present in the parasitic forms.
➤ Absorb nutrients from the host directly through their body surface.
➤ Specialised cells called FLAME CELLS help in osmoregulation and excretion.
➤ Sexes are not separate.
➤ Fertilisation is internal and development is through many larval stages.
➤ Some members like Planaria possess high regeneration capacity. the polyps sexually (e.g., Obelia).
➤ Examples:
• Physalia (Portuguese man-of-war),
• Adamsia (Sea anemone),
• Pennatula (Sea-pen),
• Gorgonia (Sea-fan) and
• Meandrina (Brain coral).

➤ Body is circular in cross-section, hence, the name roundworms
➤ May be free living, aquatic and terrestrial or parasitic in plants and animals.
➤ Bilaterally symmetrical,
➤ Triploblastic
➤ Alimentary canal is complete with a well developed muscular pharynx.
➤ An excretory tube removes body wastes from the body cavity through the excretory pore.
➤ Sexes are separate (dioecious), i.e., males and females are distinct.
➤ Females are longer than males.
➤ Fertilisation is internal
➤ Development may be direct (the young ones resemble the adult) or indirect.
Examples :
• Ascaris (Round Worm),
• Wuchereria (Filaria worm),
• Ancylostoma (Hookworm).

14. Phylum – Annelida
➤ Aquatic (marine and fresh water) or terrestrial;
➤ Free-living, and sometimes parasitic.
➤ They exhibit organ-system level of body organisation a
➤ Bilateral symmetry.
➤ Triploblastic,
➤ Coelomate animals.
➤ Their body surface is distinctly marked out into segments or metameres
• hence, the phylum name Annelida (Latin, annulus : little ring)
➤ They possess longitudinal and circular muscles which help in locomotion.
➤ Aquatic annelids like Nereis possess lateral appendages, parapodia, which help in swimming.
➤ A closed circulatory system is present.
➤ Nephridia (sing. nephridium) help in osmoregulation and excretion.
➤ Neural system consists of paired ganglia (sing. ganglion) connected by lateral nerves to a double ventral nerve cord.
➤ Nereis, an aquatic form, is dioecious,
➤ earthworms and leeches are monoecious.
➤ Reproduction is sexual.
➤ Examples :
• Nereis,
• Pheretima (Earthworm) and
• Hirudinaria (Blood sucking leech).

15. Phylum – Arthropoda
➤ Largest phylum
➤ includes insects.
➤ Over two-thirds of all named species on earth are arthropods
➤ Organ-system level of organisation.
➤ Bilaterally symmetrical,
➤ Triploblastic,
➤ Segmented and Coelomate animals.
➤ The body covered by chitinous exoskeleton.
➤ The body consists of head, thorax and abdomen.
➤ They have jointed appendages (arthros-joint, poda-appendages).
➤ Respiratory organs are gills, book gills, book lungs or tracheal system.
➤ Circulatory system is of open type.
➤ Sensory organs like antennae, eyes (compound and simple), statocysts or balance organs are present.
➤ Excretion takes place through malpighian tubules.
➤ They are mostly dioecious.
➤ Fertilisation is usually internal.
➤ They are mostly oviparous.
➤ Development may be direct or indirect.
➤ Examples:
• Economically important insects –
o Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect)
• Vectors –
o Anopheles, Culex and Aedes (Mosquitoes)
• Gregarious pest –
o Locusta (Locust) Living fossil – Limulus (King crab).

16. Phylum – Mollusca
➤ Second largest animal phylum
➤ Terrestrial or aquatic (marine or fresh water)
➤ Organ-system level of organisation.
➤ Bilaterally symmetrical, triploblastic and coelomate animals.
➤ Body is covered by a calcareous shell
➤ unsegmented with a distinct head, muscular foot and visceral hump.
➤ A soft and spongy layer of skin forms a mantle over the visceral hump.
➤ The space between the hump and the mantle is called the MANTLE CAVITY in which feather like gills are present.
• They have respiratory and excretory functions.
➤ The anterior head region has sensory tentacles. The mouth contains a file-like rasping organ for feeding, called RADULA
➤ They are usually dioecious and oviparous with indirect development.
➤ Examples:
• Pila (Apple snail),
• Pinctada (Pearl oyster),
• Sepia (Cuttlefish),
• Loligo (Squid),
• Octopus (Devil fish),
• Aplysia (Seahare),
• Dentalium (Tusk shell) and
• Chaetopleura (Chiton).

17. Phylum – Echinodermata
➤ Have an endoskeleton of calcareous ossicles and, hence, the name Echinodermata (Spiny bodied). 
➤ All are marine
➤ Organ-system level of organisation.
➤ The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.
➤ They are triploblastic and coelomate animals.
➤ Digestive system is complete
• mouth on the lower (ventral) side
• anus on the upper (dorsal) side.
➤ The most distinctive feature → the presence of water vascular system
• helps in locomotion, capture and transport of food and respiration.
➤ An excretory system is absent.
➤ Sexes are separate.
➤ Reproduction is sexual.
➤ Fertilisation is usually external.
➤ Development is indirect with free-swimming larva.
➤ Examples:
• Asterias (Star fish),
• Echinus (Sea urchin),
• Antedon (Sea lily),
• Cucumaria (Sea cucumber) and
• Ophiura (Brittle star).

18. Phylum – Hemichordata
➤ Placed as a separate phylum under non-chordata.
➤ Small group of worm-like marine animals
➤ Organ-system level of organisation.
➤ Bilaterally symmetrical, triploblastic and coelomate animals.
➤ The body is cylindrical
• composed of an anterior proboscis, a collar and a long trunk
➤ Circulatory system is of open type.
➤ Respiration takes place through gills.
➤ Excretory organ is proboscis gland.
➤ Sexes are separate.
➤ Fertilisation is external; Development is indirect.
➤ Examples: Balanoglossus and Saccoglossus.

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