Introduction

Structural organisation in animals is a key NEET Biology topic. It deals with the hierarchical organization of body structures, starting from cells, tissues, organs, to organ systems. Understanding this helps students answer questions on animal physiology, organ functions, and tissue types.

Animals show different levels of organisation depending on their complexity: cellular, tissue, organ, and organ-system level. NEET emphasizes tissue types, organ systems, and examples.

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1. Levels of Structural Organisation in Animals

a. Cellular Organisation

• Found in unicellular animals (e.g., Paramecium, Amoeba)

• Single cell performs all life functions (nutrition, respiration, excretion, reproduction)

b. Tissue Organisation

• Found in simple multicellular animals (e.g., Hydra, Coelenterates)

• Similar cells are grouped to perform a specific function → called tissues

c. Organ Organisation

• Found in complex animals (e.g., Flatworms)

• Tissues are grouped to form organs with specialized functions

d. Organ-System Organisation

• Found in higher animals (e.g., Humans, Mammals)

• Organs performing related functions form organ systems

• Examples: Digestive system, Circulatory system

NEET Tips:

• Levels of organisation = Cell → Tissue → Organ → Organ system

• Simpler animals → Lower organisation, Complex animals → Higher organisation

2. Animal Tissues

Animal tissues are groups of cells performing similar functions.

Types of Animal Tissues:

a. Epithelial Tissue

• Covers body surfaces and cavities

• Types:

  • Squamous → Lungs, Kidney

  • Cuboidal → Glands

  • Columnar → Intestine lining

• Function: Protection, absorption, secretion

b. Connective Tissue

• Connects, supports, and binds tissues and organs

• Types:

  • Loose (Areolar) → Under skin, around organs

  • Dense (Tendons, Ligaments)

  • Cartilage (Hyaline, Elastic) → Support

  • Bone → Skeleton

  • Blood → Transport

c. Muscular Tissue

• Responsible for movement

• Types:

  • Skeletal → Voluntary, striated

  • Cardiac → Involuntary, striated, heart

  • Smooth → Involuntary, unstriated, gut, blood vessels

d. Nervous Tissue

• Controls body activities

• Composed of neurons (cell body, dendrites, axon)

• Function: Receive stimuli, conduct impulses

NEET Tips:

• Epithelial → Covering, Connective → Support, Muscular → Movement, Nervous → Control

• Important for MCQs: Examples, structure, function

3. Organs and Organ Systems in Animals

Major Organ Systems (with functions):

a. Digestive System

• Organs: Mouth → Esophagus → Stomach → Intestine → Accessory glands

• Function: Digestion and absorption

• Formula (Simplified NEET): Food → Digestion → Absorption → Assimilation → Egestion

b. Circulatory System

• Organs: Heart, Blood vessels, Blood

• Function: Transport of gases, nutrients, and wastes

• Types: Open (Insects), Closed (Vertebrates)

• NEET Formula: Heart → Arteries → Capillaries → Veins

c. Respiratory System

• Organs: Lungs (Mammals), Gills (Fish), Trachea (Insects)

• Function: Exchange of gases (O₂ in, CO₂ out)

• NEET Tip: Fish → gills, Amphibians → lungs + skin

d. Excretory System

• Organs: Kidney, Ureter, Urinary bladder, Urethra

• Function: Removal of nitrogenous wastes

• NEET Tip: Nephrons → Functional unit of kidney

e. Nervous System

• Organs: Brain, Spinal cord, Nerves

• Function: Coordination and control

• Formula: Stimulus → Receptor → CNS → Effector → Response

f. Reproductive System

• Male → Testes, Vas deferens, Penis

• Female → Ovaries, Oviduct, Uterus, Vagina

• Function: Sexual reproduction

g. Skeletal and Muscular System

• Function: Support, protection, movement

• Skeleton → Axial (skull, vertebral column) + Appendicular (limbs)

4. Structural Organisation in Invertebrates vs Vertebrates

NEET Tip:

• Focus on body cavity, skeleton, and circulation type for invertebrates vs vertebrates MCQs.

5. NEET Formulas / Memory Aids

1. Levels of Organisation → Cell → Tissue → Organ → Organ System

2. Tissue Types → Epithelial (cover), Connective (support), Muscular (movement), Nervous (control)

3. Digestive System Formula → Food → Digestion → Absorption → Assimilation → Egestion

4. Circulatory System Formula → Heart → Arteries → Capillaries → Veins

5. Nervous System → Stimulus → Receptor → CNS → Effector → Response

Mnemonic for Animal Tissues:
“Every Cool Man Needs” → Epithelial, Connective, Muscular, Nervous

6. NEET Exam Tips

• Draw diagrams of tissue types and organ systems for better retention.

• Compare invertebrates and vertebrates for key MCQs.

• Remember functional units: Neuron (nervous), Nephron (excretory), Alveoli (respiratory), Heart chambers (circulatory).

• Use tables for quick revision of organ systems and examples.

Conclusion

Structural Organisation in Animals is a high-yield topic in NEET Biology. Understanding levels of organisation, tissue types, and organ systems is essential for scoring in MCQs and diagram-based questions.

With this StudentBro.in guide, students can efficiently revise tissues, organ systems, and structural organisation formulas, enhancing speed and accuracy during NEET exams.

Remember: Linking cell → tissue → organ → system and structure → function → example is the key to mastering this topic.