Quick Summary
Plant tissues are of two main types: meristematic (dividing) and permanent (differentiated). Permanent tissues include simple tissues (parenchyma, collenchyma, sclerenchyma) and complex tissues (xylem, phloem). The three tissue systems — epidermal, vascular, and ground — organise these tissues in the plant body. Xylem and phloem structure is heavily tested in NEET.
Meristematic Tissue
Actively dividing cells that give rise to all other tissues.
Types by Location
| Type | Location | Function |
|---|---|---|
| Apical meristem | Shoot and root tips | Primary growth (increase in length) |
| Lateral meristem | Sides (vascular cambium, cork cambium) | Secondary growth (increase in girth) |
| Intercalary meristem | Between mature tissues (leaf base, internodes) | Regrowth after grazing |
Characteristics
- Thin-walled, isodiametric cells
- Dense cytoplasm, prominent nucleus
- No or small vacuoles
- No intercellular spaces
Permanent Tissues
Simple Tissues (one cell type)
| Tissue | Cell Type | Wall | Function |
|---|---|---|---|
| Parenchyma | Living, thin-walled, isodiametric | Thin, cellulose | Storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma) |
| Collenchyma | Living, unevenly thickened walls | Cellulose + pectin at corners | Mechanical support in young stems and petioles |
| Sclerenchyma | Dead, uniformly thick walls | Lignin | Mechanical support |
Sclerenchyma types:
- Fibres: Long, narrow (jute, hemp, flax)
- Sclereids (stone cells): Irregular, gritty texture (pear, seed coat)
Complex Tissues (multiple cell types)
Xylem (water and mineral conduction — upward)
| Component | Living/Dead | Function |
|---|---|---|
| Tracheids | Dead | Water conduction + support |
| Vessels (Tracheae) | Dead | Main water conduction (wider) |
| Xylem fibres | Dead | Mechanical support |
| Xylem parenchyma | Living | Storage, lateral conduction |
Protoxylem: First formed; smaller diameter Metaxylem: Later formed; larger diameter
Phloem (sugar conduction — bidirectional)
| Component | Living/Dead | Function |
|---|---|---|
| Sieve tubes | Living (no nucleus) | Sugar translocation |
| Companion cells | Living (with nucleus) | Metabolic support to sieve tubes |
| Phloem fibres (bast fibres) | Dead | Mechanical support |
| Phloem parenchyma | Living | Storage |
Tissue Systems
The three tissue systems organise all tissues in the plant body:
| System | Tissues Included | Location | Function |
|---|---|---|---|
| Epidermal tissue system | Epidermis, stomata, trichomes | Outermost layer | Protection, gas exchange, absorption |
| Vascular tissue system | Xylem + Phloem (in vascular bundles) | Throughout plant | Conduction |
| Ground tissue system | Parenchyma, collenchyma, sclerenchyma | Between epidermis and vascular tissue | Storage, support, photosynthesis |
Vascular Bundle Types
| Type | Xylem/Phloem arrangement | Cambium | Example |
|---|---|---|---|
| Collateral | Phloem outside, xylem inside | Open (dicot) / Closed (monocot) | Sunflower stem (open), Maize (closed) |
| Bicollateral | Phloem on both sides of xylem | Open | Cucurbit stem |
| Concentric amphivasal | Xylem surrounds phloem | — | Dracaena |
| Concentric amphicribal | Phloem surrounds xylem | — | Ferns |
| Radial | Xylem and phloem alternate | — | Roots |
Important Questions
One Mark
- Name the tissue that provides mechanical support in young stems.
- What is the conducting element for water in angiosperms?
- Define intercalary meristem. Where is it located?
- What are sclereids? Give one example.
Short Answer (3 marks)
- Compare parenchyma, collenchyma, and sclerenchyma on the basis of cell wall, contents, and function.
- Describe the components of phloem with their functions.
- What is the difference between open and closed vascular bundles?
Long Answer (5 marks)
- Describe the structure and functions of xylem. How does it differ from phloem?
- Explain the three tissue systems in plants with their components and functions.
Common Mistakes
- Sieve tubes are living but have NO nucleus in mature state — companion cells have the nucleus and support them.
- Collenchyma: unevenly thickened (corners) — NOT uniformly thickened (that is sclerenchyma).
- Vessels are found in angiosperms; tracheids are found in all vascular plants including gymnosperms and ferns.
- Phloem conducts in both directions (bidirectional); xylem conducts only upward.
Board Exam Tips
- Xylem vs phloem comparison (components, living/dead, function) is a standard 5-mark question.
- Vascular bundle types with diagrams appear as 3-mark or 5-mark questions.
- "Distinguish meristematic from permanent tissue" is a reliable 3-mark question.
- NEET: Xylem components (especially difference between tracheids and vessels), phloem sieve tubes, and tissue types contribute 2–3 questions per paper.
Frequently Asked Questions
Meristematic tissue: actively dividing cells, thin walls, no vacuoles, dense cytoplasm, no intercellular spaces. Permanent tissue: non-dividing, differentiated, may be living or dead, have vacuoles and intercellular spaces.