Structural Organisation in Animals
'The body of an animal is a community of cells organised into tissues, organs, and organ systems.' — Animal Physiology
1. Chapter Overview
Just as plants have tissues and tissue systems, animals are organised into TISSUES, ORGANS, and ORGAN SYSTEMS. This chapter covers the FOUR BASIC TISSUES of animals — EPITHELIAL, CONNECTIVE, MUSCULAR, and NERVOUS — their TYPES, STRUCTURE, and FUNCTION. It also includes a DETAILED study of the COCKROACH as a representative animal to illustrate how tissues are ORGANISED into systems.
2. Epithelial Tissue
Characteristics
- Covers BODY surfaces and lines CAVITIES
- Cells are TIGHTLY PACKED (minimal intercellular matrix)
- BASEMENT MEMBRANE (separates epithelium from underlying connective tissue)
- AVASCULAR (no blood vessels; nutrients from diffusion)
- REGENERATES rapidly
Classification
Based on Number of Layers
- Simple epithelium: SINGLE layer of cells (function: absorption, secretion, filtration)
- Stratified epithelium: MULTIPLE layers (function: protection)
Based on Cell Shape
| Type | Shape | Location | Function |
|---|---|---|---|
| Squamous | Flat, thin | Blood vessels, lung alveoli | Diffusion, filtration |
| Cuboidal | Cube-shaped | Kidney tubules, glands | Secretion, absorption |
| Columnar | Tall, column | Stomach, intestine | Secretion, absorption |
| Ciliated columnar | With CILIA | Respiratory tract, oviduct | Move mucus/egg |
| Pseudostratified | Appears layered | Trachea | Protection + secretion |
Glandular Epithelium
- Unicellular glands: Goblet cells (secrete mucus)
- Multicellular glands: Salivary glands, sweat glands
3. Connective Tissue (MOST ABUNDANT)
Characteristics
- CELLS scattered in an EXTRACELLULAR MATRIX (fibres + ground substance)
- Matrix determines the PROPERTIES of the tissue
- GOOD blood supply (except cartilage and tendons)
Types of Connective Tissue
| Type | Matrix | Cells | Location | Function |
|---|---|---|---|---|
| Loose (Areolar) | Loose fibres (collagen, elastin) | Fibroblasts, macrophages | Under skin, between organs | FILLER, binds organs |
| Adipose | Fat cells | Adipocytes | Under skin, around organs | STORAGE (fat), insulation |
| Dense regular | Parallel collagen fibres | Fibroblasts | Tendons, ligaments | STRONG connection |
| Dense irregular | Random collagen fibres | Fibroblasts | Dermis of skin | STRENGTH (all directions) |
| Cartilage | Firm, flexible; chondrin | Chondrocytes | Nose, ears, joints | SMOOTH surface, support |
| Bone | HARD, mineralised (Ca, P) | Osteocytes | Skeleton | SUPPORT, protection |
| Blood (Fluid CT) | PLASMA (liquid) | RBC, WBC, platelets | Blood vessels | TRANSPORT |
Special Connective Tissues
- Tendon: Cord-like, connects MUSCLE to BONE (dense regular)
- Ligament: Elastic, connects BONE to BONE
4. Muscular Tissue
Characteristics
- CONTRACTILE cells (myofibrils — actin + myosin)
- Excitability, contractility, extensibility, elasticity
| Type | Structure | Nuclei | Control | Location |
|---|---|---|---|---|
| Skeletal (Striated, Voluntary) | Long, cylindrical, STRIATED (sarcomeres) | MULTI-nucleate (peripheral) | VoluntarY | Attached to bones |
| Smooth (Non-striated, Involuntary) | Spindle-shaped, NO striations | SINGLE nucleus (central) | INVOLUNTARy | Walls of organs, blood vessels |
| Cardiac | Branched, STRIATED, INTERCALATED DISCS | SINGLE or BINUCLEATE | INVOLUNTARy (myogenic) | Heart wall (myocardium) |
5. Nervous Tissue
- Neuron: Structural and functional UNIT
- Dendrites: RECEIVE signals
- Cell body (Soma): Contains NUCLEUS
- Axon: TRANSMITS impulses AWAY
- Synapse: Junction between neurons
Types of Neurons
- Unipolar: Single process (embryonic)
- Bipolar: One axon + one dendrite (retina, ear)
- Multipolar: ONE axon + MANY dendrites (MOST common in brain/spinal cord)
Neuroglial Cells
- SUPPORT, PROTECT, and NOURISH neurons
- Outnumber neurons 10:1
6. Cockroach (Periplaneta americana) — Morphology
Classification
- Phylum: Arthropoda; Class: Insecta; Order: Blattodea
External Features
- Body: Elongated, FLATTENED, SEGMENTED
- Colour: Brown/Brownish-black
- Size: 34-53 mm
- Three Body Regions: HEAD, THORAX, ABDOMEN
- Head: Compound eyes, antenna (sensory), mouthparts (chewing/biting)
- Thorax: 3 segments (pro, meso, meta); 2 PAIRS of wings + 3 PAIRS of jointed legs
- Abdomen: 10 segments, anal cerci (sensory)
7. Cockroach — Internal Systems
Digestive System
- Foregut: Mouth → oesophagus → crop (storage) → gizzard (grinding)
- Midgut: Hepatic caecae (secrete digestive enzymes)
- Hindgut: Ileum, colon, rectum → reabsorption of water
Circulatory System
- OPEN type (blood = HAEMOLYMPH)
- Heart: Tubular, 13 chambers with OSTIA
- Haemolymph colourless (NO haemoglobin)
Respiratory System
- TRACHEAL system: Network of tubes (tracheae)
- Spiracles: 10 pairs (openings on body surface)
- Direct O₂ delivery to cells (EFICIENT)
Excretory System
- Malpighian tubules: 100-150, attached at junction of midgut and hindgut
Nervous System
- Ventral nerve cord: Ganglia in each segment
- Sense organs: Compound eyes, antenna, maxillary palps, cerci
Reproductive System
- Male: Testes → seminal vesicles → ejaculatory duct → phallomere
- Female: Ovaries → oviduct → vagina → genital pouch
8. Common Mistakes
- Blood is a CONNECTIVE tissue: Even though it's liquid, it fits the definition (cells in matrix)
- Cardiac muscle is STRIATED but INVOLUNTARY: The only muscle with this combination
- Cartilage is AVASCULAR: That is why cartilage injuries HEAL SLOWLY
- Cockroach heart is TUBULAR, not chambered like the human heart: Open circulation
- Epithelial tissue is AVASCULAR and relies on DIFFUSION from underlying connective tissue
9. CBSE Exam Focus
- Epithelial tissue — types, locations, functions (3/5-mark)
- Connective tissue — classification and features (5-mark)
- Muscle tissue — types and comparison (3-mark)
- Cockroach — digestive and respiratory systems (5-mark)
- Neuron structure and function (3-mark)
10. Self-Test (5+ Q&A)
Q1: What are intercalated discs? Where are they found? A: INTERCALATED DISCS are specialised junctions between CARDIAC muscle cells. They connect cells mechanically and electrically (gap junctions), enabling SYNCHRONISED contraction.
Q2: Why is blood considered a connective tissue? A: Blood has CELLS (RBC, WBC) suspended in a FLUID MATRIX (plasma) — fitting the definition of connective tissue (cells separated by extracellular matrix). It CONNECTS different parts of the body through transport.
Q3: Describe the respiratory system of cockroach. A: TRACHEAL system — air enters through 10 PAIRS OF SPIRACLES, passes through tracheae and tracheoles, delivering O₂ DIRECTLY to tissues. NO blood involvement in gas transport.
Q4: Differentiate between tendon and ligament. A: Tendon: Connects MUSCLE to BONE; DENSE REGULAR connective tissue; STRONG and INELASTIC. Ligament: Connects BONE to BONE; ELASTIC fibres; ALLOWS flexibility at joints.
Q5: How many Malpighian tubules does a cockroach have and what is their function? A: 100-150 Malpighian tubules. They EXCRETE nitrogenous waste (mainly uric acid) from haemolymph into the hindgut — function as the KIDNEY equivalent.
11. Conclusion
Animal tissues are ORGANISED in a hierarchy: cells → tissues → organs → systems. The FOUR tissues coordinate to perform all body functions. Epithelial tissue provides BARRIERS. Connective tissue PROVIDES framework and transport. Muscular tissue ENABLES movement. Nervous tissue COORDINATES responses. The cockroach is an EXCELLENT model for understanding how these tissues integrate into functioning organ systems. This knowledge is the FOUNDATION for understanding animal physiology and human biology.
