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CHAPTER-04 ANIMAL KINGDOM
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CHAPTER-04 ANIMAL KINGDOM
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CBSE Quick Revision Notes (Class-11 Biology)CHAPTER-04 ANIMAL KINGDOM
Millions of species of animals have been described and it becomes more necessary to
classify them to assign a systematic position.
Animals are classified on the basis of arrangement of cells, body symmetry, nature of
coelom, pattern of digestive, circulatory and reproductive system.
Levels of organisation
Cellular Level Tissue Level Organ Level Oragn system Level
Sponges Cnidarians Platyhelminthes Arthropoda
Incomplete digestive system has one opening but in complete digestive system two opening
mouth and anus is present.
Open circulatory system- blood is pumped out of heart and cells and tissue are directly
bathed in it.
Closed circulatory system- blood is circulated through arteries, veins and capillaries.
Symmetry
Symmetrical Asymetrical
(can be divided into two equal (body is not divisible into equal
parts) halve)
eg.Amoeba, Sponges.
Radial Symmetry Bilateral Symmetry
(can be divided into eqaul halves by any plane (can be divided equal halves by only one plane)
passing through centre) eg. Star fish, hydra eg. all vertibrates.
The animals in which cells are arranged in two
embryonic layer, external ectoderm and internal
endoderm are called diploblastic. Eg. Porifera and
Cnidaria.
The animals in which developing embryo has a third
germinal layer, mesoderm besides ectoderm and
endoderm are called triploblastic. Eg. Platyhelminthes, Chordates.
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, The body cavity which is lined by mesoderm is called coelom.
Animals possessing coelom are called coelomate (Annelida,
Chordates, Mollusca). In some animals cavity is not lined by
mesoderm but scattered as pouches in between ectoderm and
endoderm, are called pseudo-coelomates (Aschelminthes).
The animals in which body cavity is absent are called
acoelomate (Platyhelminthes).
In some animals, body is externally and internally divided into
segments with serial repetition as in earthworm, called metameric segmentation.
CLASSIFICATION OF ANIMALS
1. Phylum Porifera-
• Members of this phylum are commonly known as sponges. Mostly marine, asymmetrical and
have cellular level of organization.
• They have water transport or canal system. Water enters through minute pores, Ostia into
central cavity Spongocoel, from where it goes out through Osculum.
• Nutrition, respiration and excretion is performed by pathway of water transport system.
• Skeleton made up of spicules or spongin fibres.
• Egg and sperms are produced by same organism (hermaphrodite). Asexual reproduction by
fragmentation and sexual reproduction by gametes formation.
• Fertilisation internal and development is indirect.
• Example- Sycon, Spongilla.
2. Phylum Cnidaria ( Coelenterate)-
• They are aquatic, mostly marine, sessile, free swimming, radially symmetrical animals.
• They exhibit tissue level of organization, diploblastic, coelomate with single opening.
• They show two types of body called polyp and medusa.
• Polyp is sessile, fixed, and cylindrical, without gonads such as Hydra, Adamsia and Medusa is
free swimming, umbrella like having four gonads like Aurelia and Jelly fish.
• Some cnidarians exhibits both forms (Obelia), polyp produce medusa asexually and medusa
produce polyp sexually.
3. Phylum Ctenophora-
Commonly known as the Comb Jellies or Sea Walnuts.
Exclusively marine, diploblastic, radially symmetrical, with tissue level of organization.
Body bears eight ciliated comb plates which help in locomotion.
Bioluminescence (to emit light) is present in Ctenophores.
Hermaphrodite, fertilisation external, development indirect,
Example- Ctenoplana, Pleurobranchia.
4. Phylum Platyhelminthes (The Flat worms)
Dorso-ventrally flattened body, bilaterally symmetrical, triploblastic, acoelomate with
organs levels of organization.
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