Tissues
Introduction
A tissue is a group of similar cells that perform a specific function. ICSE Class 9 covers both plant and animal tissues, their types, structures, and functions.
Plant Tissues
Meristematic Tissue
Location: Found in growing regions of the plant (tips of roots and stems, cambium)
Characteristics:
- Cells are small, thin-walled, with dense cytoplasm
- Large nucleus, no vacuoles
- Capable of continuous division
Types:
| Type | Location | Function |
|---|---|---|
| Apical meristem | Root and shoot tips | Increases length |
| Lateral meristem | Cambium (sides) | Increases girth |
| Intercalary meristem | Base of leaves/nodes | Increases internode length |
Simple Permanent Tissue
Characteristics: Cells lose ability to divide; become specialised.
| Type | Structure | Function | Location |
|---|---|---|---|
| Parenchyma | Thin-walled, loosely packed, living cells | Storage, photosynthesis | Throughout plant |
| Collenchyma | Thickened corners, living cells | Flexibility and support | Stems, leaf stalks |
| Sclerenchyma | Thick lignified walls, dead cells | Mechanical support | Stems, seed coats, husks |
Complex Permanent Tissue (Conducting Tissues)
Xylem (Water Conduction)
- Tracheids: Elongated cells with tapered ends
- Vessels: Tube-like structures, wider than tracheids
- Xylem fibres: Provide mechanical support
- Xylem parenchyma: Storage
Function: Conducts water and minerals from roots to leaves (unidirectional)
Phloem (Food Conduction)
- Sieve tubes: Living cells with sieve plates at ends
- Companion cells: Help sieve tubes in function
- Phloem fibres: Support
- Phloem parenchyma: Storage
Function: Conducts food from leaves to other parts (bidirectional)
| Feature | Xylem | Phloem |
|---|---|---|
| Direction | Unidirectional (upward) | Bidirectional |
| Conducts | Water and minerals | Food (sucrose) |
| Living/Dead cells | Mostly dead at maturity | Mostly living |
| Cell types | Tracheids, vessels | Sieve tubes, companion cells |
Animal Tissues
Epithelial Tissue (Covering Tissue)
Covers body surfaces, lines cavities, and forms glands.
| Type | Structure | Location | Function |
|---|---|---|---|
| Squamous | Flat, thin cells | Skin, lung alveoli | Diffusion, protection |
| Cuboidal | Cube-shaped cells | Kidney tubules, glands | Secretion, absorption |
| Columnar | Tall, column-like cells | Intestine, stomach | Absorption, secretion |
| Ciliated | Columnar with cilia | Respiratory tract | Moves mucus |
| Stratified | Multiple layers | Skin, oesophagus | Protection against wear |
Connective Tissue
Characterised by cells scattered in an extracellular matrix.
| Type | Matrix | Cells | Location | Function |
|---|---|---|---|---|
| Blood | Fluid (plasma) | RBC, WBC, platelets | Blood vessels | Transport, immunity |
| Bone | Hard (calcium salts) | Osteocytes | Skeleton | Support, protection |
| Cartilage | Flexible (chondrin) | Chondrocytes | Nose, ears, joints | Flexibility, cushioning |
| Tendon | Dense fibrous | Fibroblasts | Muscle to bone | Connects muscle to bone |
| Ligament | Elastic fibrous | Fibroblasts | Bone to bone | Connects bone to bone |
| Areolar | Loose matrix | Various cells | Under skin | Fills spaces, support |
| Adipose | Fat-filled | Adipocytes | Under skin, organs | Fat storage, insulation |
Muscular Tissue
| Type | Structure | Location | Control | Function |
|---|---|---|---|---|
| Striated (skeletal) | Striped, multinucleated | Attached to bones | Voluntary | Body movement |
| Smooth (visceral) | Spindle-shaped, uninucleated | Stomach, intestines, blood vessels | Involuntary | Internal organ movement |
| Cardiac | Striated, branched, uninucleated | Heart | Involuntary | Heart contraction |
Nervous Tissue
- Neurons: Basic functional unit of nervous system
- Parts: Cell body (cyton), dendrites, axon
- Function: Conducts nerve impulses
- Neuroglia: Supporting cells that protect and nourish neurons
Comparison Table: Plant vs Animal Tissues
| Feature | Plant Tissues | Animal Tissues |
|---|---|---|
| Growth | Growth throughout life (meristems) | Growth limited to certain period |
| Cell division | Continues in meristems | Limited |
| Support | Cell wall provides support | Skeleton provides support |
| Dead cells | Many are dead at maturity | Most are living |
| Energy storage | Starch | Glycogen |
Common Mistakes With Fixes
| Mistake | Correction |
|---|---|
| Xylem carries food | Xylem carries WATER and MINERALS; phloem carries FOOD |
| Blood is not a connective tissue | Blood is considered a connective tissue (fluid matrix) |
| Cardiac muscle is voluntary | Cardiac muscle is INVOLUNTARY |
| All epithelial cells are cube-shaped | Epithelial cells come in squamous, cuboidal, columnar types |
ICSE Exam Focus
| Topic | Marks (approx.) | Frequency |
|---|---|---|
| Plant tissues (xylem and phloem) | 4-5 marks | Very common |
| Animal tissues (comparison) | 4-5 marks | Very common |
| Muscular tissue types | 3-4 marks | Common |
| Epithelial tissue | 3-4 marks | Frequently asked |
Self-Test
Q1: Distinguish between meristematic and permanent tissues.
Q2: Differentiate between xylem and phloem.
Q3: List the three types of muscular tissue and their locations.
Q4: What are the functions of: (i) Blood (ii) Bone (iii) Cartilage
Q5: Draw a labelled diagram of a neuron.
