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Basis of Classification Class 11 Biology | Animal Kingdom NEET Notes



Basis of classification

Introduction :
  • In this post, we will discuss the Basis of Classification of Animal Kingdom for Class 11 and NEET. We will cover Level of Organization, Symmetry, Coelom, and more with easy diagrams."
  • Animals are classified and placed on an appropriate group on the basis of observable characters. Some of the characters to classify the organism are being described below:

Doston mujhe kahte hue khuski ho rahi hai ki hum Plant kingdom ko poora complete kar liya hai . Isse pehle humne Gymnosperm ko bahut acchhe se jaana hai.

Levels of Organisation in Animals ( Animal Kingdom NCERT) 

  • All members of Animals  are multicellular but  all of them do not have  same pattern of organisation of cells. 
 "Sirf Notes hi nahi, is chapter ke Full Video Lectures aur MCQs ke liye hamara [NEET Biology Master Hub] visit karein — Jahan milega NEET 2026 ka complete study material ek hi jagah!
  • For example,  In sponges. the cells are arranged as lose aggregation and every cell perform specific function called as cellular level of organisation. The  division of labour is present among the cells. 

    📌 Video Key Moments (Timestamps)

    00:04 — Introduction: Basis of Classification

    00:54 — Level of Organisation kya hai?

    01:41 — Protozoa: Primitve Single Cell Animals

    03:09 — Porifera: Cellular Level & Division of Labour

    05:50 — Cellular Level: Loose cell aggregation

    06:23 — Coelenterata: Tissue Level of Organisation

    08:44 — Platyhelminthes: Organ Level

    10:06 — Aschelminthes to Mammals: Organ System Level

    11:43 — Conclusion & Summary

     
  • In coelenterates, the arrangement of cells is more complex. The cells  are arranged Into tissues to perform the same function.This  is called tissue level of organisation. 
  • Another  level of organisation called organ level of organisation has been first developed by members of Platyhelminthes. In this level of organisation, tissues are arranged in  form of  organs. Each specialised organ perform  a particular function. 
  • ln animals like Annelids. Arthropods. Molluscs. Echinoderms and Chordates. Number of organs have been organised in a functional systems. Each system is  associated  with  the specific physiological function. This pattern ls called organ system level of organisation. 

Digestive system  

  • The digestive system in which there is a single opening to the outside of the body that serves as both mouth and anus. This  type of digestive system is incomplete. 

📌 Is Video ke Mukhya Bindu (Timestamps)

00:03 — Intro: Basis of Classification (Part 2)

00:45 — Digestive System: Complete vs Incomplete

02:57 — Example: Hydra (Hypostome)

04:15 — Circulatory System: Open vs Closed

07:13 — Metamerism (Body Segmentation)

09:34 — Notochord: Origin and Importance

11:02 — Chordates vs Vertebrates (NEET Hotspot)

  •  A complete digestive system has two openings to serve as  mouth and anus separately. 

Circulatory system

  • In open type of Circulatory system,  the blood Is pumped out of the heart. The cells and tissues are directly bathed in blood.
  • In closed type of Circulatory system, the blood is circulated through a network  of  blood vessels  like arteries. veins and capillary.

Symmetry

  • Animals can be categorised on the basis of their symmetry. 
  • When , any plane is passed through the centre of body and it does not divide into equal halves than body is said to be asymmetrical. For Example - Poriferan or Songes.
  •  When any plane is passed through the central axis of the body and it is  divided  the organism Into two identical halves. This one is said to be radial symmetrical . For Example Coelenterates. Ctenophora
  • Animals like annelids. arthropods. etc.. where the body can be divided into Identical left and right halves in only one plane. This is a  bilateral symmetrical.

Diploblastic and Triploblastic Organisation

  • Those animals In which the developing embryo has a three germinal layer : outer ectoderm, middle  mesoderm and inner endoderm. Such  are called triploblastic animals For example : Platyhelminthes to chordates. 

Coelom

  • Presence or absence of a cavity between the body wall and the gut wall is very important feature  in classification. The body cavity which ls lined by mesoderm is called coelom .

Segmentation
  • In some animals, the body is externally and internally divided Into segments. 
  • But in earthworm,  the body is   metamerically  segmented in which external segments make correspondence to internal segments. This phenomenon is known as metamerism .
Notochord
  • Notochord is  derived from the mesoderm. Notochord is  rod- like structure present  on  dorsal side during embryonic development in some animals. 
  • Animals with  notochord are called chordates and those animals which do not have notochord  are called non-chordates, For example : Porifera to Echinoderms.
Feature Type/Condition Examples (Phylum)
Level of Organisation Cellular / Tissue / Organ / Organ System Porifera to Chordata
Symmetry Asymmetry / Radial / Bilateral Sponges, Coelenterata, Annelida, etc.
Germ Layers Diploblastic / Triploblastic Coelenterata (Diplo), Platyhelminthes (Triplo)
Coelom (Body Cavity) Acoelomate / Pseudo / Coelomate Platy (A-), Aschel (Pseudo), Annelida (True)
Segmentation Metamerism Annelida, Arthropoda, Chordata

*(Mobile users: Scroll left/right to see full table)*

  • In some chordates, Notochord is replaced by cartilaginous or bony vertebral column. Such chordates are called Vertebrates .
  • In some chordates, notochord is present as notochord in any stage of lifecycle but not replaced by  vertebral column. They are not vertebrates.
  • Therefore all vertebrates are chordates but all chordates are not vertebrates. 
Next post main hum baat karenge ek aise animal Phylum Porifera ki jinhe pehle multicellular animal hone ka gourav jaata hai.


NEET MULTIPLE CHOICE  QUESTIONS 
100 % Challenge 

Questions yahi se aayaga

1. In which level of  organisation,  cells are arranged in loose aggregation and have divison of labour  in
A. Porifera (sponges)
B. Platyhelminthes
C. Aschelminthes(round worm)
D. Coelentrata 
Answer : A  

2. In coelentrata, the arrangement of cell  is more complex & performing some function as
A. Cellular level of Organisation
B. Organ level of Organisation
C . Tissue leve Organisation
D. Organ system level of organisation 
Answer: C  


3. Organ Level of organisation  was first appeared in
A.Annelida  
B.Arthropoda
C.Platyhelmenthes
D.Aschelminnthes
Answer : C  

4. Match the list -
Level of               Phylum
organisation

A.Cellular     1. Porifera 
B.Tissue      2.Cnidaria
C.Organ      3.Platyhelminthes
D.Organ      4.Aschelminthes
System

              A.       B        C          D 
A.          1         2         3          4
B.          2         3         1          4
C.          4         3         2          1
D.         4          2         3          1
Answer : A 

5. Which of the following statement is not correct.
A. In complete digestive system,a single opening is present that serves as both anus and mouth.

B. When the blood is pumped in network of blood  vessel called as closed vascular system.

C. All the cells and tissue are directly bathed in blood in body cavity sinus in open circulatory system.

D. A single opening in digestive system form incomplete digestive system.
Answer : A  

6. In Diploblastic animals,which of the following embryonic layer is are responsible for formation of all tissue or organs.
A. Mesoderm 
B. Ectoderm & Endoderm
C. Mesoderm  & Endoderm
D. Mesoderm & Ectoderm
Answer: A  

7. Which of the following phylum is / are Diploblastic.
A. Porifera
B. Coelentreta 
C. Ctenophora
D. All of the above.
Answer : D  

8. Triploblastic condition, In which all tissue and organs are developed from the ectoderm, Endoderm and mesoderm found from 
A. Porifera to Platyhelminthes
B. Porifera to ctenophora
C. Platyhelminthes to choradates
D. Fish to mammals.
Answer : C 

9. Coelom is a space between 
A. Pelvic wall and bodywall
B. Body wall and gut
C. Pelvic wall and gut
D. Pelvic wall and abdomen
Answer : B 

10. Coelom or body cavity is lined by 
A. Ecto - mesoderm
B. Endoderm
C. Mesoderm
D. Ectoderm
Answer : C 

11. In which type of Coelom, body cavity is not lined by the mesoderm but present in form of scattered pouch .
A. A coelom
B. Pseudocoelom
C. Coelom
D. Entero coelom
Answer : B 

13. Which of the following pair is not correct.
A.Acoelomate:
Platyhelminthes
B.Pseudocoelomate:
Aschelminthes 
C. Coelomate :Porifera
D. Acoelomate : Cnidaria
Answer : A 

14. When a body is divided into identical left and right halves when passing a plane vertically than body is said to be 
A. Asymmetrical    
B. Bilateral  symmetrical
C. Radial symmetrical 
D. Iso Symmetrical
Answer : B 

15. Bilateral symmetrical condition has been started from the 
A. Cnidaria 
B. Platyhelminthes 
C. Annelida
D. Aschelminthes
Answer : B 
              
16. When a plane is passed from central axis of body and divided it into two equal halves called 
A. Asymmetrical    
B. Bilateral  symmetrical
C. Radial symmetrical 
D. Iso symmetrical
Answer : C 


17. Redial symmetry is not present in 
A. Porifera 
B. Coelentreta 
C. Ctenophora 
D. Echinodermata
Answer : A 

18. Sponges have 
A. Diploblastic 
B. Asymmetrical 
C. Cellular level of organisation 
D. All of the above
Answer : D 

19. Consider the following features for the members of Aschelminthes and select the correct code 
1. Pseudocoelomate
2. Organ system level of organisation 
3. Acoelomate
4. Bilateral symmetrical 
5. Triploblastic 
A. 1,3,4,and 5
B. 1,2,4 and 5
C. 1,2,3 and 4
D. 2,3,4 and 5
Answers: B 

20. First Coelomate animals belong to 
A. Annelida
B. Platyhelminthes 
C. Aschelminthes
D. Arthropoda
Answer : A 

21. Which of the following features are first appeared in members of platyhelminthes.
A. Triploblastic and Bilateral symmetry
B. Organ level of system and Triploblastic
C. Organ level of system and Triploblastic 
D. Triploblastic , Bilateral symmetry and organ level of system
Answer : D 

22. In which of the following phylum, the larva is bilateral symmetrical and adult is radial symmetrical.
A. Mollusca 
B. Echinodermata
C. Hemichordata
D. Ctenophora
Answer : B 

23. Metameric segmentation in which external segments make correspondence to internal segments, found in 
A. Annelida
B. Platyhelminthes 
C. Aschelminthes
D. Arthropoda
Answer : A 

24. Which of the following statement is not correct with respect to the Notochord.
A. It is rod like tubular structure present on dorsal side of body of choradates.
B. An animal  with the notochord is called as Choradates.
C. It is endodermal in origin.
D. Notochord is absent from Porifera to Echinodermata.
Answer: C 


Next Topic: Now that you have learned  about Basis of classification, let's explore the porous body animals in : Phylum  Porifera ( sponge) notes

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