NCERT Class 11 Biology Biology: Chapter 7 — Structural Organisation in Animals
This chapter, "Structural Organisation in Animals," from NCERT Class 11 Biology, delves into the hierarchical organization of multicellular animal bodies. It explains how cells group to form tissues, tissues to organs, and organs to organ systems, all contributing to specialized functions and survival through division of labor. The chapter introduces the four basic tissue types and their organization into organs like the stomach and heart. It also highlights the evolutionary trend in organ system complexity. The text then focuses on the frog (Rana tigrina) as an example, detailing its morphology, including its smooth, moist skin, coloration for camouflage (mimicry), ability to absorb water through the skin, and its adaptations for survival like aestivation and hibernation. The external features of the frog, such as the absence of neck and tail, presence of nostrils, bulged eyes with nictitating membranes, and tympanum for hearing, are described. This chapter provides a foundational understanding of animal anatomy and physiology relevant to CBSE curriculum.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Biology |
| Book | Biology |
| Chapter | Chapter 7 — Structural Organisation in Animals |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 4 minutes |
| Word count | 737 |
Learning outcomes
- Understand the hierarchical organization of animal bodies: cells, tissues, organs, and organ systems.
- Identify the four basic types of tissues found in complex animals.
- Explain the concept of division of labor in multicellular organisms.
- Describe the external morphology of a frog, including its adaptations.
- Differentiate between morphology and anatomy.
Vocabulary
| Word | Meaning |
|---|---|
| Tissue | A group of similar cells along with intercellular substances performing a specific function. |
| Organ | An organized group of tissues that performs a specific function. |
| Organ System | Two or more organs performing a common function through physical or chemical interaction. |
| Morphology | The study of externally visible features of an organism. |
| Anatomy | The study of the morphology of internal organs. |
| Poikilotherm | An animal whose body temperature varies with the temperature of its environment (cold-blooded). |
| Mimicry | The ability to change colour to hide from enemies (protective coloration). |
| Aestivation | Summer sleep; taking shelter in deep burrows to protect from extreme heat. |
| Hibernation | Winter sleep; taking shelter in deep burrows to protect from extreme cold. |
| Nictitating membrane | A transparent or translucent third eyelid that protects the eye while maintaining some visibility. |
| Tympanum | The eardrum; receives sound signals. |
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Practice questions
- What is the basic unit of organization in multicellular animals? Answer: Cells.
- Define an organ system. Answer: An organ system is formed when two or more organs perform a common function by their physical and/or chemical interaction.
- What is the scientific term for cold-blooded animals? Answer: Poikilotherms.
- What is mimicry in frogs? Answer: Mimicry is the ability of a frog to change its colour to hide from enemies.
- What are aestivation and hibernation? Answer: Aestivation is summer sleep, and hibernation is winter sleep, periods when frogs take shelter to escape extreme temperatures.
Frequently asked questions
What are the levels of structural organization in animals?
The levels are cells, tissues, organs, and organ systems.
What is the difference between morphology and anatomy?
Morphology studies the external appearance, while anatomy studies the internal organs.
Why are frogs called cold-blooded animals?
Frogs are called cold-blooded or poikilotherms because their body temperature varies with the environmental temperature.
How do frogs protect themselves from extreme temperatures?
They protect themselves by aestivation (summer sleep) and hibernation (winter sleep) in deep burrows.
What is the function of the nictitating membrane in frogs?
The nictitating membrane protects the frog's eyes while in water.
Can frogs drink water?
No, frogs absorb water through their skin.
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NCERT Class 11 Biology — Biology — Chapter 7 — Structural Organisation in Animals. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.