Chapter 7: Structural Organisation in Animals – Study Modules with Revision Notes
CBSE Class 11 Biology Study Module: Structural Organisation in Animals (NCERT-Based Revision Notes)
Course Details and Examination Framework
Course: CBSE Class 11 Biology
Board: Central Board of Secondary Education
Syllabus: Strictly Based on NCERT
Unit II: Structural Organisation in Animals and Plants
Chapter 7: Structural Organisation in Animals
Assessment Focus: Structure–Function Relationships
Examination Level: CBSE Class 11 Annual & School-Based Assessments
Introduction to Structural Organisation in Animals
Animals exhibit a high degree of structural complexity that supports diverse physiological functions. This complexity arises from the systematic organization of cells into tissues, tissues into organs, and organs into organ systems. Structural Organisation in Animals explores how microscopic and macroscopic structures are intricately linked to their biological roles.
This chapter builds foundational knowledge essential for understanding physiology, anatomy, and evolutionary adaptations, making it a high-weightage unit in CBSE Class 11 Biology.
Section I: Animal Tissues
A tissue is a group of similar cells, along with their intercellular substances, performing a specific function. Animal tissues are broadly classified into four main types.
1. Epithelial Tissue
Key Features
- Forms protective covering and lining
- Cells are tightly packed with minimal intercellular matrix
- Rests on a basement membrane
- Lacks blood vessels (avascular)
- High regenerative capacity
Types of Epithelial Tissue
a) Simple Epithelium
- Single layer of cells
- Found where absorption, diffusion, or filtration occurs
Types:
- Squamous Epithelium: Thin, flat cells; diffusion and filtration (alveoli, capillaries)
- Cuboidal Epithelium: Cube-shaped cells; secretion and absorption (kidney tubules)
- Columnar Epithelium: Tall cells; absorption and secretion (intestine)
- Ciliated Epithelium: Moves substances (respiratory tract)
b) Stratified Epithelium
- Multiple layers of cells
- Protection against mechanical stress (skin)
c) Glandular Epithelium
- Specialized for secretion
- Forms endocrine and exocrine glands
Structure–Function Link:
Thin epithelial layers facilitate diffusion, while thick stratified layers provide protection.
2. Connective Tissue
Connective tissues bind, support, and protect organs. They consist of cells embedded in an extracellular matrix.
Types of Connective Tissue
a) Loose Connective Tissue
- Areolar Tissue: Packing tissue; holds organs
- Adipose Tissue: Fat storage; insulation and energy reserve
b) Dense Connective Tissue
- Tendons: Connect muscle to bone
- Ligaments: Connect bone to bone
c) Skeletal Tissue
- Cartilage: Flexible support (nose, ear)
- Bone: Rigid support, protection, mineral storage
d) Fluid Connective Tissue
- Blood: Transport of gases, nutrients, hormones
- Lymph: Immune function, fluid balance
Structure–Function Link:
Rigid matrix in bones supports weight, while fluid matrix in blood enables transport.
3. Muscular Tissue
Muscle tissues are responsible for movement and locomotion.
Types of Muscular Tissue
- Skeletal Muscle: Voluntary, striated; attached to bones
- Smooth Muscle: Involuntary, non-striated; internal organs
- Cardiac Muscle: Involuntary, striated; heart
Structure–Function Link:
Striations allow rapid contraction in skeletal muscles, while smooth muscles enable slow, sustained movements.
4. Nervous Tissue
- Composed of neurons and neuroglial cells
- Found in brain, spinal cord, and nerves
- Capable of excitation and impulse conduction
Structure–Function Link:
Long axons allow rapid transmission of nerve impulses.
Section II: Earthworm – Morphology and Anatomy
General Characteristics
- Scientific Name: Pheretima posthuma
- Habitat: Moist soil
- Body is long, cylindrical, and metamerically segmented
External Morphology
- Segments called metameres
- Clitellum: Thickened glandular region for cocoon formation
- Setae: Help in locomotion
Anatomy of Earthworm
Digestive System
- Mouth → Pharynx → Oesophagus → Gizzard → Intestine
- Gizzard grinds food
Circulatory System
- Closed type
- Dorsal, ventral, and lateral hearts
Respiratory System
- Cutaneous respiration through moist skin
Excretory System
- Nephridia remove nitrogenous wastes
Nervous System
- Nerve ring and ventral nerve cord
Structure–Function Link:
Segmented body enhances flexibility and efficient locomotion.
Section III: Cockroach – Morphology and Anatomy
General Characteristics
- Scientific Name: Periplaneta americana
- Terrestrial insect
- Body divided into head, thorax, and abdomen
External Morphology
- Exoskeleton made of chitin
- Jointed appendages
- Compound eyes and antennae
Anatomy of Cockroach
Digestive System
- Foregut, midgut, hindgut
- Gastric caeca increase surface area for digestion
Respiratory System
- Tracheal system with spiracles
Circulatory System
- Open type
- Haemolymph without respiratory pigment
Excretory System
- Malpighian tubules
Nervous System
- Ventral nerve cord with segmental ganglia
Structure–Function Link:
Tracheal system ensures direct oxygen supply to tissues.
Section IV: Frog – Morphology and Anatomy
General Characteristics
- Scientific Name: Rana tigrina
- Amphibian; lives on land and in water
External Morphology
- Streamlined body
- Moist, scaleless skin
- Webbed hind limbs for swimming
Anatomy of Frog
Digestive System
- Mouth → Oesophagus → Stomach → Intestine → Cloaca
Respiratory System
- Skin, lungs, and buccopharyngeal cavity
Circulatory System
- Closed type
- Three-chambered heart
Excretory System
- Kidneys and urinary bladder
Nervous System
- Brain, spinal cord, cranial and spinal nerves
Structure–Function Link:
Webbed feet aid swimming; moist skin enables cutaneous respiration.
Revision Notes: Key Exam Highlights
- Animal tissues are classified into epithelial, connective, muscular, and nervous tissues
- Earthworm shows metameric segmentation
- Cockroach has an open circulatory system
- Frog has a three-chambered heart
- Structure always determines function in biological systems
Conclusion
The chapter Structural Organisation in Animals establishes a clear understanding of how cells organize into tissues and organs to perform specialized functions. Comparative study of earthworm, cockroach, and frog highlights evolutionary adaptations and functional efficiency. Mastery of this chapter is essential for scoring well in CBSE Class 11 Biology examinations, as it strengthens conceptual clarity and analytical skills.
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