NCERT Class 11 Biology Biology: Chapter 4 — Animal Kingdom
Chapter 4 of the NCERT Class 11 Biology textbook introduces the Animal Kingdom, emphasizing the necessity of classification due to the vast diversity of over a million described animal species. It details the fundamental features used as the basis for animal classification, including levels of organization (cellular, tissue, organ, organ system), body symmetry (radial and bilateral), and germinal layers (diploblastic and triploblastic). The chapter explains concepts like incomplete and complete digestive systems, and open versus closed circulatory systems. Understanding these classification criteria is crucial for students to systematically study and comprehend the animal kingdom and its evolutionary relationships within the CBSE curriculum.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Biology |
| Book | Biology |
| Chapter | Chapter 4 — Animal Kingdom |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 537 |
Learning outcomes
- Understand the need for animal classification.
- Identify and differentiate between various levels of organization in animals.
- Distinguish between radial and bilateral symmetry.
- Explain the concepts of diploblastic and triploblastic organization.
- Recognize different types of digestive and circulatory systems.
Vocabulary
| Word | Meaning |
|---|---|
| Classification | The arrangement of organisms into groups based on their similarities and differences. |
| Cellular level of organisation | Cells are arranged as loose aggregates, with some division of labour. |
| Tissue level of organisation | Cells performing the same function are arranged into tissues. |
| Organ level of organisation | Tissues are grouped together to form organs, each specialised for a particular function. |
| Organ system level of organisation | Organs associated to form functional systems, each concerned with a specific physiological function. |
| Incomplete digestive system | A digestive system with a single opening serving as both mouth and anus. |
| Complete digestive system | A digestive system with two separate openings: mouth and anus. |
| Open circulatory system | Blood is pumped out of the heart and directly bathes cells and tissues. |
| Closed circulatory system | Blood is circulated through a network of vessels of varying diameters. |
| Radial symmetry | Body can be divided into two identical halves by any plane passing through the central axis. |
| Bilateral symmetry | Body can be divided into two identical left and right halves in only one plane. |
| Diploblastic | Animals with two embryonic layers: ectoderm and endoderm. |
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Practice questions
- Why is the classification of animals important? Answer: Classification is important due to the vast diversity of animal species (over a million described) and to assign a systematic position to newly described species.
- What are the different levels of organisation found in animals? Answer: The levels of organisation are cellular, tissue, organ, and organ system.
- Differentiate between radial and bilateral symmetry. Answer: Radial symmetry allows division into equal halves by any plane through the central axis, while bilateral symmetry allows division into equal halves by only one plane.
- What is the difference between an incomplete and a complete digestive system? Answer: An incomplete digestive system has one opening, while a complete digestive system has two openings (mouth and anus).
- Define diploblastic organisation. Answer: Diploblastic organisation refers to animals with two embryonic layers: an external ectoderm and an internal endoderm.
Frequently asked questions
What is the primary reason for classifying animals?
The vast number of animal species (over a million) necessitates classification for systematic study and identification.
Which animals exhibit the cellular level of organisation?
Sponges exhibit the cellular level of organisation.
Give examples of animals with radial symmetry.
Coelenterates, ctenophores, and echinoderms have radial symmetry.
What is the characteristic of bilateral symmetry?
Bilateral symmetry means the body can be divided into identical left and right halves in only one plane.
What distinguishes diploblastic from triploblastic animals?
Diploblastic animals have two embryonic layers (ectoderm and endoderm), while triploblastic animals have three (ectoderm, mesoderm, and endoderm).
What is an incomplete digestive system?
An incomplete digestive system has a single opening that functions as both mouth and anus.
What are the two types of circulatory systems mentioned?
The two types are open and closed circulatory systems.
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NCERT Class 11 Biology — Biology — Chapter 4 — Animal Kingdom. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.