The study of the structural organisation in animals is one of the foundational topics in zoology. It helps us understand how cells, tissues, and organ systems are arranged in different animals and how these structures work together to support life. For NEET and other competitive exams, this chapter carries high weightage, often with direct and conceptual questions.
Introduction to Structural Organisation in Animals
Every multicellular organism displays a hierarchy of structural organisation. In animals, this starts from the cellular level, progresses through tissues, and reaches the organ and organ-system level. Studying this structural organisation helps in understanding physiology, adaptations, and evolutionary significance.
Levels of Organisation in Animals
- Cellular Level – Seen in sponges where cells function independently.
- Tissue Level – Found in cnidarians, with division of labour among tissues.
- Organ Level – Platyhelminthes exhibit distinct organs performing specialized functions.
- Organ System Level – Higher animals like annelids, arthropods, chordates show complex organ systems.
Animal Tissues
Animal tissues are broadly divided into four types:
1. Epithelial Tissue
Forms the covering and lining of body surfaces. It protects underlying tissues and aids in absorption, secretion, and excretion. Types include:
- Simple squamous, cuboidal, columnar
- Ciliated epithelium
- Glandular epithelium
2. Connective Tissue
Supports and binds other tissues. It has fewer cells and abundant extracellular matrix. Major types:
- Loose Connective Tissue – Areolar, adipose
- Dense Connective Tissue – Tendons, ligaments
- Skeletal Connective Tissue – Cartilage, bone
- Fluid Connective Tissue – Blood, lymph
3. Muscular Tissue
Responsible for movement. It consists of contractile proteins (actin, myosin). Types include:
- Skeletal (voluntary)
- Smooth (involuntary)
- Cardiac (involuntary, rhythmic)
4. Nervous Tissue
Made up of neurons and supporting cells. It helps in transmission of impulses and coordination of body functions.
Organ Systems in Animals
Structural organisation also extends to major organ systems, such as:
- Digestive system (earthworm, cockroach, frog)
- Circulatory system
- Respiratory system
- Excretory system
- Reproductive system
Each organism studied in this chapter (earthworm, cockroach, frog) serves as a representative model to understand comparative anatomy.
Study of Earthworm, Cockroach, and Frog
Earthworm (Pheretima posthuma)
- Segmented, bilaterally symmetrical, coelomate animal.
- Closed circulatory system, nephridia for excretion.
- Hermaphrodite with cross-fertilization.
Cockroach (Periplaneta americana)
- Segmented body divided into head, thorax, abdomen.
- Open circulatory system, tracheal respiration.
- Reproduction is sexual with separate sexes.
Frog (Rana tigrina)
- Amphibian with moist skin for cutaneous respiration.
- Three-chambered heart, kidneys for excretion.
- Dioecious, external fertilization.
These examples highlight evolutionary advancement from invertebrates to vertebrates.
Comparative Table of Tissues
| Tissue Type | Key Features | Examples |
|---|---|---|
| Epithelial | Protective covering, absorption, secretion | Skin epithelium, intestinal lining |
| Connective | Binding, support, transport | Bone, cartilage, blood |
| Muscular | Contraction, movement | Skeletal, cardiac muscles |
| Nervous | Impulse conduction, coordination | Brain, spinal cord |
Importance of Studying Structural Organisation
- NEET and Exams: Frequently asked MCQs from tissues and model organisms.
- Medical Relevance: Tissue studies form the basis for histology and pathology.
- Evolutionary Insight: Understanding progression from simple to complex body plans.
FAQs on Structural Organisation in Animals
Q1. What are the four types of animal tissues?
The four major types are epithelial, connective, muscular, and nervous tissues.
Q2. Why is earthworm studied in structural organisation?
Earthworm serves as a model to study organ-system level organisation in invertebrates.
Q3. Which tissue is responsible for impulse conduction?
Nervous tissue, composed of neurons, transmits impulses.
Q4. How do frogs respire?
Frogs respire through lungs, skin (cutaneous), and buccal cavity.
Q5. Which type of circulatory system does cockroach have?
Cockroach has an open circulatory system.