Atul Sharma

teacher | Chemistry Biology


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Summary Animal Kingdom on Basis of Classification

1.      Levels of organization

2.      Symmetry

3.      Number of Embryonic cell layers

4.      Nature of Coleom

5.      Segmentation (Metamerism)

6.      Notochord

7.      Body Plan


Organ system level shows various patterns in digestive system and circulatory system.


Digestive system:

·         Incomplete Eg. Platyhelminthes

·         Complete Eg. Aschelminthes to chordata


Circulatory system:

·         Open Eg. Arthropoda Most mollusks & Tunicates

·         Closed Eg. Vertebrates Cephalochordata Annelida & Cephalopoda

Classification of Animal Kingdom on basis of Arrangements of cells in germ layers

Some organisms have two kinds of tissues that develop in embryonic life. These tissues are the primary germ layers.


Diploblastic: The organism has two germ layers; an external ectoderm and internal mesoderm. An undifferentiated layer of cells called mesoglea is seen in between these two layers. Eg: Coelenterates.


Triploblastic: The organism has three germ layers, the third germ layer being the middle mesoderm. E.g. Platyhelminthes to chordata.

Classification of Animal Kingdom on basis of Notochord and Segmentation

Notochord: Notochord is a mesodermally derived rod-like structure on the dorsal side during the embryonic stage in some animals.

o Animals with notochord → Chordates

o Animals without notochord → Non Chordates (Porifera to echinoderms).


Segmentation: Segmentation, also called metamerism, or metameric segmentation, is the condition of being constructed of a linear series of repeating parts, each being a metamere (body segment, or somite) E.g. annelids.

Classification of Animal Kingdom on basis of Arrangement of cells

Every organism in Animal kingdom is multicellular.


The types of cellular organisations found in animals are:


1.      Cellular level of organization: The organisms are made of cells which are formed or arranged as loose lumps. This is mainly seen in Sponges.


2.      Tissue level of organization: A tissue refers to a group of cells performing a similar function. In this organisation cells cooperate with each other performing same function. It is mainly seen in coelenterate.


3.      Organ level of organization: In this organisation the tissues are organised into organs to perform specific functions. It is mainly seen in platyheliminthes.


4.      Organ system level of organisation: In this system of organisation, the organs associate and co-ordinate with each other to form functional systems. Each system is concerned with a specific physiological function. It is seen from Annelids to Chordates.


Patterns in circulatory, digestive and reproductive system:


1. Circulatory System:

·         Open type: Blood is pumped out of the heart and cells and tissues are bathed in it. E.g. Arthropods, Mollusca.

·         Closed type: Blood is circulated through series of vessels of different size and diameters. E.g. Vertebrates.


2. Digestive System:

·         Complete: There are 2 openings to the outside of the body, the mouth and anus. E.g. Arthropods, Chordates.

·         Incomplete: They have only one opening towards the outside of the body and it serves as both mouth and anus. E.g. Platyhelminthes.


3. Reproductive System:

·         Internal fertilisation: Fertilisation takes place inside the body of some organisms. E.g. Platyhelminthes.

·         External fertilisation: Fertilisation takes place outside the body of some organisms. E.g. Ctenophora.


1. Direct development: Embryo develops into a mature individual without involving a larval

stage. Metamorphosis is absent E.g. fishes, reptiles, birds etc.


2. Indirect development: Involves sexually immature larval stage, having different food requirements than adults. Metamorphosis is present. E.g. most of invertebrates and amphibians.


·         Oviparous animals: They lay fertilised or unfertilised eggs. The chances of survival of young one is less.

·         Viviparous animals: They give birth to young ones. The chances of survival of young one is more.

·         Ovoviviparous animals: They produce eggs, but instead of laying eggs, the eggs develop within the maternal body and hatch within or immediately after release from the parent. E.g. Some sharks, snakes etc.

Classification of Animal Kingdom on basis of Nature of coelom

Coelom refers to a fluid filled body cavity present between the body wall and the intestine and is lined with mesodermal epithelium. It is present in bilaterally symmetrical



Organisms are classified into three categories based on the nature of coelom:


1. Acoelomates – Acoelomates are those which do not possess any coelom.

E.g: Platyhelminthes.


2. Pseudo-coelomates – Pseudo-coelomates are those which possess coelom but not lined by mesoderm. Instead mesoderm is present as scattered pouches.

E.g: Aschelminthes.


3. True coelomates or Entero-coelomates – Coelomates are those which possess a proper fluid filled body cavity lined by mesoderm.

E.g: annelids, molluscs, arthropods, echinoderms, hemichordates and chordates.

Classification of Animal Kingdom on basis of Body Symmetry

Animals can be divided based on their symmetry or overall shape of the organism.


A. Bilateral symmetry

B. Radial symmetry


In bilateral symmetry the animals can be divided into identical right and left parts in only one plane.


In radial symmetry body can be divided into identical parts through any plane passing through the central axis of the body. E.g.: Coelenterates, ctenophores and echinoderms.


In A symmetrical organism, the body cannot be divided into equal halves through any axis of the body.


Animal Kingdom and its Classifications

R.H. Whittaker in 1969 proposed a five kingdom classification in which all the eukaryotic, multicellular animal species are grouped into a kingdom named as Animal kingdom.


Classification based on their characteristics.

1. Body symmetry

2. Nature of coelom

3. Arrangement of cells

4. Notochord

5. Segmentation

6. Arrangements of cells in germ layers.

7. Patterns in circulatory, digestive and reproductive system.

Chemistry - Solid State

Important Topics:
1. Number of octahedral voids = Number of atoms and Number of tetrahedral voids = Twice the number of atoms
2. For unit cell dimension the important formula is M = dNaa3/ z
3. Imperfections in solids:

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