🧫 Chapter 05 — Tissue

General Science · Biology · BPSC / BSSC Exam Preparation
📖 What is Tissue?
  • Group of cells similar in origin and basic structure, functioning together as a unit
  • Division of Labour in multicellular organisms
Level:Cell → Tissue → Organ → Organ System → Animal
🌿 Plant Tissue — Overview
1. Meristematic Tissue
  • Capable of continuous cell division
  • Immature / undifferentiated tissue
  • Present in developing parts of plant
  • No intercellular space, no vacuole
  • Prominent nucleus, dense cytoplasm
  • Thin cell wall of cellulose
2. Permanent Tissue
  • Living and dead tissues — no dividing capacity
  • Fundamental and structural tissues
  • Formed by differentiation of meristematic tissues
  • Defined shape and size
  • Thin cytoplasm, large central vacuole
  • Intercellular space may be present or absent
🐾 Animal Tissue — Overview
Epithelial
Protective / Lining tissue
Connective
Connects organs
Muscular
Movement & locomotion
Nervous
Sensitivity & coordination
⚡ Quick Recall
Animal tissues are mostly living. The four types are: Epithelial · Connective · Muscular · Nervous → ECMN
🌱 Types of Meristematic Tissue
(i) Apical Meristem
  • Location: Developing tips of shoots and roots
  • Function: Elongation of shoots and roots
(ii) Intercalary Meristem
  • Location: Base of leaves and nodes/internodes of branches
  • Function: Growth in length of stems and leaves
(iii) Lateral Meristem
  • Location: Along the sides of stems and roots
  • Function: Increases thickness of stems and roots
⚠ Exam Trap
Apical = Length (tips) | Intercalary = Length (nodes/base of leaves) | Lateral = Thickness (girth/width). These have three distinct functions and locations.

Protoderm = part of apical meristem found in roots.
⚡ Quick Recall
Cork (secondary meristem) is also a meristematic tissue, but it is distinct from the lateral meristem. Cork cells are dead and contain deposits of suberin.
🍃 Simple Permanent Tissue (Same cell types)
1. Parenchyma
  • Simplest permanent tissue
  • Location: Cortex & pith of stem/root, Mesophyll of leaves
  • Living, isodiametric cells
  • Thin wall, intercellular space present
  • Function: Storage of food and water
Modifications:
  • Chlorenchyma: Has chloroplast → photosynthesis (leaves, herbaceous stem)
  • Aerenchyma: Large air spaces → buoyancy in aquatic plants
2. Collenchyma
  • Location: Petiole below epidermis, hypodermis of dicot stems
  • Cells: Living and elongated
  • Intercellular space usually absent
  • Deposition of stiff thick cellulose-hemicellulose-pectin at corners of cell
  • Function: Mechanical support and flexibility
3. Sclerenchyma
  • Location: Stem, leaf veins, seed coat, outer fibrous husk of coconut
  • Cells: Dead, elongated, narrow, pointed at both edges
  • Thick wall: Cellulose + Lignin
  • Intercellular space absent
  • Function: Safety, strength and mechanical support
⚠ Exam Trap
Parenchyma = Living | Collenchyma = Living | Sclerenchyma = Dead. Coconut husk = Sclerenchyma. Aerenchyma helps aquatic plants float.
🔀 Complex Permanent Tissue (Different cell types)
Xylem (Water conducting)
  • Unidirectional transport
  • Water & minerals: Roots → Stem → Leaves
  • Components:
    • Tracheids
    • Vessels
    • Xylem Parenchyma (Living)
    • Xylem Fibre
Phloem (Food conducting)
  • Bidirectional transport
  • Food: Usually leaves → other parts
⚠ Exam Trap
Xylem = Unidirectional (water, roots to leaves). Phloem = Bidirectional (food). Xylem parenchyma = Living component of xylem; this is a common exam trap.
🛡️ Protective Tissue — Overview
  • Provides safety against mechanical injury, infection and extra water loss
  • Two types: Epidermis and Cork
1. Epidermis
  • Outermost, continuous, single-layered protective layer
  • Usually waxy waterproof layer present
  • Protects from water loss and mechanical damage
  • Cuticle: Waterproof thick waxy layer — found in desert plants
  • Small pores called Stomata present on epidermis of leaf
  • Stomata regulate: Transpiration + Gaseous exchange
  • Stomata opening/closing by Guard cells
  • Dicots: Bean-shaped guard cells
  • Monocots: Dumbbell-shaped guard cells
  • Root epidermis modified into Root hair → increases surface area for water absorption
💧 Stomata Guard Cell Mechanism
Condition Guard Cell State Stomata
Water enters guard cell Turgid (swells) Opens
Water exits guard cell Loose / Relaxed (shrinks) Closes
⚠ Exam Trap
Guard cells: Dicot = Bean-shaped | Monocot = Dumbbell-shaped. This difference in shape is frequently tested directly in MCQs.
2. Cork
  • Multilayered thick, dead cells formed from secondary meristem
  • Intercellular space absent, arranged densely
  • Suberin deposition in cell walls (makes it waterproof)
⚡ Quick Recall
Cork cells = Dead + Suberin = Waterproof + No intercellular space. Robert Hooke observed cork cells and named them “Cellula.”
🛡️ Epithelial Tissue
  • Protective tissue of animal body
  • Forms lining of body surfaces, organs and organ-system cavities
  • Continuous and dense cellular level
📋 Types of Epithelial Tissue
Type Description Location
Squamous — Simple Thin, flat, single layer Blood vessels, Alveoli, Mouth, Alimentary canal
Squamous — Stratified Multilayered Skin
Cuboidal Cube-shaped cells Kidney tubules, Sweat glands, Salivary glands, Thyroid glands
Columnar Column-shaped cells Stomach, Intestines, Gall bladder, Bile duct
Ciliated Columnar Multiple hair-like protrusions on free surface Trachea, Oviduct, Vas deferens
Glandular — Single cell Goblet cells —
Glandular — Multi cell Glands Salivary glands, Thyroid glands
⚠ Exam Trap
Ciliated columnar = Trachea, Oviduct, Vas deferens; the cilia move particles. Cuboidal = Kidney tubules. Skin = Stratified squamous.
⚡ Quick Recall
Simple epithelial types: Squamous · Cuboidal · Columnar · Ciliated columnar → SC³
🔗 Connective Tissue — Overview
  • Connects different organs of body with each other
  • Cells embedded in intercellular matrix
🦴 Fibrous Connective Tissue
Tendon
  • Connects Bone to Muscle
  • Strong, limited flexibility
  • Has White collagen filaments
Ligament
  • Connects Bone to Bone
  • More flexibility
  • Has Yellow elastin filaments
⚠ Exam Trap
Tendon = Bone ↔ Muscle (White collagen, less flexible) | Ligament = Bone ↔ Bone (Yellow elastin, more flexible). These two should not be confused.
🩸 Fluid Connective Tissue — Blood
  • Fluid filled vascular tissue
  • Transports: Nutrients, Gases (CO₂ & O₂), Hormones, Excretory materials
55%
Plasma (Fluid part)
45%
Cells (Solid part)
Plasma (55%)
  • Fluid matrix
  • 90% Water
  • 8% Protein
  • 2% Minerals / Ions
Blood Cells (45%)
  • RBC: Red (Fe), Biconcave, Formed in Bone Marrow, Destroyed in Spleen ("Graveyard of RBC")
  • WBC: Neutrophil, Eosinophil, Basophil, Lymphocyte, Monocyte
  • Platelets: Blood clotting
⚠ Exam Trap
RBC formed in Bone Marrow, destroyed in Spleen ("Graveyard of RBC"). Lymph = Colourless liquid, RBC absent.
🧊 Original / Proper Connective Tissue
Adipose Tissue
  • Fat storage cells
  • Shock absorption + insulation regulation
  • Present in: Bone marrow, organs, below skin
Areolar Tissue
  • Loose connective tissue
  • Matrix: Jelly-like
  • Present below skin, in blank spaces of hollow organs, near muscles and blood vessels
  • Function: Repairing and filling of blank spaces
🦴 Skeletal Connective Tissue
Bone
  • Hard and stiff
  • Matrix hard due to: CaPO₄ & CaCO₃ salts
  • Osteoblasts = bone-forming cells
  • Provides safety, support to soft organs; gives shape to body
Cartilage
  • Flexible and strong
  • Matrix: Chondrin protein, sugar, collagen and elastin fiber
  • Location: Joints, tip of nose, outer ear, trachea, throat
⚠ Exam Trap
Bone matrix = CaPO₄ + CaCO₃. Cartilage = Flexible (Chondrin). Bone-forming cells = Osteoblasts. Stem cells present in Bone marrow.
💪 Muscular Tissue
  • Contains contractile protein: Actin and Myosin
  • Elongated, large contractile muscle fibres
  • Movement due to contraction and relaxation
Feature Striated (Skeletal) Smooth (Visceral) Cardiac
Also called Voluntary / Skeletal / Somatic muscles Involuntary / Smooth / Visceral muscles Heart muscles
Branching Unbranched Unbranched Branched
Shape Elongated, Cylindrical Elongated, Spindle-shaped (narrow edges) Branched, Cylindrical, Striated
Nucleus Multi-nucleate Uni-nucleate Uni-nucleate
Bands (Striations) Present Absent Present (but involuntary)
Control Voluntary Involuntary Involuntary
Fatigue Fast fatigue Slow, fatigue resistant No fatigue (lifelong)
Location / Special Attached to skeleton (movement) Walls of internal organs Intercalated discs present
⚠ Exam Trap
Cardiac muscle is both striated and involuntary. Intercalated discs = only in cardiac muscle. Striated = Multi-nucleate. Smooth = Spindle-shaped, Uni-nucleate.
⚡ Quick Recall
Bands present: Striated + Cardiac. Bands absent: Smooth. Voluntary: only Striated. Branched: only Cardiac. No fatigue: only Cardiac.
🧠 Nervous Tissue
  • Responsible for sensitivity and excitability
  • Coordinates between different organ systems
  • Neuron = Functional and Structural unit of nervous tissue
  • Neuron can be up to 1 m long
  • Dividing capability absent
  • Present in brain, spinal cord and nerves
  • Schwann cells of nerve tissue = Neurilemma cells
⚠ Exam Trap
Nervous tissue cells cannot divide (dividing capacity is absent). Schwann cells = Neurilemma cells. This fact is frequently tested directly in MCQs.
📌 Important Additional Facts
  • Eosine: Luminous red, acidic dye — stains cytoplasm, RBC, collagen and muscle fibres
  • Stem cells: Present in bone marrow
  • Schwann cells of nerve tissue = Neurilemma cells
  • Lymph = Colourless liquid, RBC absent
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