Tissues
Plant and animal tissues; structure–function links (NCERT Ch. 6).
Tissues
What you'll learn
- What a tissue is and why multicellular organisms need them.
- Plant tissues — meristematic and permanent (simple and complex).
- Animal tissues — epithelial, connective, muscular, nervous.
- How tissue structure relates to its function.
Key concepts
What is a tissue?
- Tissue: a group of cells that are similar in structure and work together to perform a specific function.
- Multicellular organisms have specialised tissues → division of labour → greater efficiency.
- Histology: the study of tissues.
Plant Tissues
Plants have two main categories:
1. Meristematic Tissue (Growing tissue)
- Cells are actively dividing (undergoing mitosis).
- Cells are small, thin-walled, no vacuole, dense cytoplasm.
- Found at growing tips of roots and shoots.
| Type | Location | Function |
|---|---|---|
| Apical meristem | Tips of roots and shoots | Increases length (primary growth) |
| Lateral meristem (cambium) | Sides of stem and root | Increases girth/width (secondary growth) — forms wood |
| Intercalary meristem | Nodes of grasses, at leaf bases | Allows grass to regrow after grazing |
2. Permanent Tissue
Made of cells that have stopped dividing and become specialised.
Simple Permanent Tissues
All cells are similar; one cell type:
| Tissue | Cell features | Function | Location |
|---|---|---|---|
| Parenchyma | Thin cell wall; large vacuole; loosely packed; living | Storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma in aquatic plants) | Leaves, stem cortex, fruit pulp |
| Collenchyma | Unevenly thickened corners; living | Mechanical support + flexibility (allows bending without breaking) | Leaf stalks, young stems |
| Sclerenchyma | Very thick walls; lignified; dead at maturity | Hard mechanical support | Seed coats, nut shells, coconut husk, jute fibres |
Complex Permanent Tissues
More than one cell type working together:
Xylem (water-conducting tissue):
| Component | Living/Dead | Function |
|---|---|---|
| Tracheids | Dead | Water transport; support |
| Vessels | Dead | Water + mineral transport (more efficient than tracheids) |
| Xylem fibres | Dead | Mechanical support |
| Xylem parenchyma | Living | Storage; lateral transport |
Phloem (food-conducting tissue):
| Component | Living/Dead | Function |
|---|---|---|
| Sieve tubes | Living (no nucleus) | Transport sugars (glucose) from leaves to rest of plant |
| Companion cells | Living | Support and control sieve tubes |
| Phloem fibres | Dead | Support |
| Phloem parenchyma | Living | Storage |
Key difference — xylem vs phloem:
| Xylem | Phloem | |
|---|---|---|
| What it transports | Water + minerals | Sugars (food) |
| Direction | Upward only (root → leaf) | Both directions |
| Cells | Mostly dead | Mostly living |
Animal Tissues
Four main types:
1. Epithelial Tissue
- Lines surfaces — skin, inside of mouth, lining of gut, kidney tubules.
- Tightly packed cells; very little intercellular material.
- Functions: protection, absorption, secretion, filtration.
| Type | Cell shape | Location | Function |
|---|---|---|---|
| Simple squamous | Flat, scale-like | Walls of blood vessels, air sacs (alveoli) | Diffusion; filtration |
| Simple cuboidal | Cube-shaped | Kidney tubules, salivary gland ducts | Absorption; secretion |
| Simple columnar | Column-shaped | Lining of intestine, stomach | Absorption; secretion; some have cilia |
| Stratified squamous | Multiple layers of flat cells | Skin, mouth, oesophagus | Protection from mechanical wear |
| Ciliated | Columns with hair-like cilia | Respiratory tract, fallopian tubes | Move mucus or eggs by cilia beating |
| Glandular | Secretory cells | Glands (sweat, mucus, digestive) | Produce and release secretions |
2. Connective Tissue
- Most abundant tissue in the body.
- Cells scattered in a matrix (extracellular material — can be fluid, semi-solid, or hard).
- Connects and supports other tissues.
| Type | Matrix | Location | Function |
|---|---|---|---|
| Areolar (loose) | Fluid; collagen + elastin fibres | Under skin; around organs | Fills spaces; supports; houses immune cells |
| Dense (fibrous) | Mostly collagen fibres packed tightly | Tendons (muscle→bone); ligaments (bone→bone) | Strong tensile connections |
| Adipose | Fat cells (adipocytes) in loose matrix | Under skin; around kidneys, heart | Energy storage; insulation; cushioning |
| Cartilage | Solid, flexible matrix (chondroitin) | Ear, nose, joints, trachea rings | Smooth surfaces at joints; flexible support |
| Bone | Hard matrix (calcium phosphate + collagen) | Skeleton | Rigid support; protection; blood cell production in marrow |
| Blood | Liquid matrix (plasma) | Blood vessels; heart | Transport of gases, nutrients, hormones, waste; immune function |
Blood components:
| Component | Description | Function |
|---|---|---|
| Plasma | Yellow liquid (92% water) | Carries dissolved substances |
| Red blood cells (RBCs) | No nucleus; biconcave; contain haemoglobin | Carry oxygen |
| White blood cells (WBCs) | Nucleated; several types | Immune defence |
| Platelets | Cell fragments; no nucleus | Blood clotting |
3. Muscular Tissue
- Cells called muscle fibres; contain actin and myosin proteins that slide past each other to contract.
| Type | Striated? | Voluntary? | Location | Feature |
|---|---|---|---|---|
| Skeletal (striated, voluntary) | Yes | Yes (we control it) | Attached to bones | Rapid, tiring; multinucleated |
| Smooth (non-striated, involuntary) | No | No (automatic) | Gut wall, blood vessels, uterus | Slow, sustained; spindle-shaped cells |
| Cardiac (striated, involuntary) | Yes | No | Heart wall only | Never tires; intercalated discs connect cells; self-stimulating |
4. Nervous Tissue
- Makes up the brain, spinal cord, nerves.
- Basic unit: neuron (nerve cell) — most specialised cell in the body.
- Parts of a neuron:
- Cell body (cyton): contains nucleus.
- Dendrites: short branching projections; receive signals.
- Axon: long single projection; carries signal away from cell body.
- Myelin sheath: insulating fatty layer around axon → speeds up signal.
- Synaptic terminals (axon terminals): pass signal to next neuron or muscle.
- Signal transmission: electrical impulse along neuron; chemical (neurotransmitter) across synapse (gap between neurons).
- Types of neurons: sensory (sense → brain), motor (brain → muscle), relay/interneuron (within brain/spinal cord).
Quick check
- What is the difference between meristematic and permanent tissue?
- What do xylem and phloem transport? In which direction?
- Name four types of animal tissue and one location for each.
- What are the three types of muscle tissue? Which is found in the heart?
- Draw and label a neuron; name the three types of neurons.
Open the Practice tab for graded questions on Tissues.
3 topics • Notes • Practice • AI explanations available
1. Plant Tissues
Meristematic and permanent tissues; xylem and phloem.
Read notes & practice →
2. Animal Tissues
Epithelial, connective, muscular, nervous tissues.
Read notes & practice →
3. Function
Structure adapted to function in plant and animal tissues.
Read notes & practice →
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