Question
Classify animal tissues into four main types. For each type, describe the structure, subtypes, location in the body, and functions. Give a comparison table.
(NCERT Class 9, Tissues)
Solution — Step by Step
Epithelial tissue covers body surfaces and lines cavities. Cells are tightly packed with little or no intercellular space. It rests on a basement membrane.
| Subtype | Structure | Location | Function |
|---|---|---|---|
| Squamous | Flat, tile-like cells | Skin (outer layer), mouth lining, blood vessels | Protection, diffusion |
| Cuboidal | Cube-shaped cells | Kidney tubules, salivary gland ducts | Secretion, absorption |
| Columnar | Tall, pillar-like cells | Intestinal lining, stomach | Secretion, absorption |
| Ciliated columnar | Columnar + cilia on surface | Respiratory tract, oviducts | Movement of mucus/ova |
| Glandular | Modified columnar | Salivary glands, sweat glands | Secretion |
The most abundant tissue type. Cells are widely spaced in an extracellular matrix (ground substance + fibres).
| Subtype | Matrix | Location | Function |
|---|---|---|---|
| Areolar | Semi-fluid, fibres | Between skin and muscles, around organs | Packing, support |
| Adipose | Fat-filled cells | Below skin, around kidneys | Insulation, fat storage |
| Bone | Hard (calcium salts) | Skeleton | Structural framework |
| Cartilage | Semi-rigid (chondroitin) | Ear pinna, nose, tracheal rings | Flexible support |
| Blood | Fluid (plasma) | Blood vessels | Transport of O₂, nutrients, waste |
| Tendons | Dense, parallel fibres | Muscle-to-bone connection | Attach muscles to bones |
| Ligaments | Dense, elastic fibres | Bone-to-bone connection | Hold bones together at joints |
| Subtype | Appearance | Location | Control | Features |
|---|---|---|---|---|
| Striated (skeletal) | Long, cylindrical, multinucleate, striped | Limbs, body wall | Voluntary | Fatigues quickly |
| Smooth (visceral) | Spindle-shaped, uninucleate, no stripes | Stomach, intestine, blood vessels | Involuntary | Slow, sustained |
| Cardiac | Branched, uninucleate, faintly striped | Heart wall only | Involuntary | Never fatigues, intercalated discs |
Nervous tissue transmits electrical signals. The functional unit is the neuron:
- Cell body (soma): Contains nucleus and organelles
- Dendrites: Short, branched projections that receive signals
- Axon: Long, single projection that transmits signals away from the cell body
- Schwann cells and myelin sheath: Insulate the axon for faster signal transmission
Found in: brain, spinal cord, and nerves throughout the body. Function: detects stimuli, processes information, coordinates body responses.
Why This Works
Animal tissues are organised by function. Each tissue type is built for a specific job:
- Epithelial: barrier and exchange (tight cells = good barrier)
- Connective: support (matrix does the heavy lifting, not cells)
- Muscular: movement (specialised contractile proteins actin and myosin)
- Nervous: communication (electrochemical signalling)
The structure-function relationship is key. Blood is a connective tissue because its matrix (plasma) connects and transports between body parts — even though it doesn’t “connect” in the structural sense that tendons do.
Alternative Method
For exam recall, remember the “ECMN” classification and associate each with a key feature:
- Epithelial → no intercellular space, basement membrane
- Connective → extensive matrix (the matrix defines the tissue type)
- Muscular → contractile (actin-myosin)
- Nervous → excitable (can generate electrical impulses)
NEET commonly asks: “Blood is a type of _____ tissue” — answer: connective. “Cardiac muscle has ___” — answer: intercalated discs. “Which muscle type is voluntary?” — answer: striated/skeletal. “Tendons connect ___ to ___” — answer: muscle to bone. “Ligaments connect ___ to ___” — answer: bone to bone.
Common Mistake
Students swap tendons and ligaments. Tendons connect muscle to bone (think: T for “to bone”). Ligaments connect bone to bone (think: L for “links bones”). Another common error: writing that cardiac muscle is voluntary because we can feel our heartbeat. Cardiac muscle is strictly involuntary — it contracts rhythmically on its own, controlled by the SA node (pacemaker), not by conscious thought.