Question
Classify plant tissues into meristematic and permanent tissues. Compare their characteristics. Describe the types and functions of simple permanent tissues — parenchyma, collenchyma, and sclerenchyma.
(NCERT Class 9, Tissues)
Solution — Step by Step
| Feature | Meristematic Tissue | Permanent Tissue |
|---|---|---|
| Cell division | Actively dividing | Do not divide (lost ability) |
| Cell shape | Small, round, thin-walled | Variable, may have thick walls |
| Vacuoles | Absent or very small | Large central vacuole |
| Intercellular spaces | Absent (tightly packed) | May be present |
| Nucleus | Prominent, large | May be less prominent |
| Function | Growth (new cells) | Support, storage, conduction |
Meristematic tissues are found at growing points: root tips, shoot tips (apical meristem), cambium (lateral meristem), and base of internodes in grasses (intercalary meristem).
Parenchyma is the most common and versatile tissue:
- Cells are thin-walled, living, isodiametric (roughly spherical)
- Large intercellular spaces present
- Functions: storage (store starch, water), photosynthesis (when containing chloroplasts, called chlorenchyma), buoyancy in aquatic plants (when containing air spaces, called aerenchyma)
- Found in: cortex of stems and roots, mesophyll of leaves, fruit pulp
Collenchyma provides flexible support:
- Cells are living with unevenly thickened walls (thickened at corners due to pectin/cellulose deposits)
- Some intercellular spaces present
- Functions: provides mechanical support with flexibility — allows the organ to bend without breaking
- Found in: leaf stalks (petioles), stems of herbaceous plants, below the epidermis
Sclerenchyma provides rigid support:
- Cells are dead at maturity with uniformly thick, lignified walls
- No intercellular spaces
- Two types: fibres (long, narrow cells — in jute, hemp) and sclereids (stone cells — in nut shells, pear grit)
- Functions: provides rigidity and strength, protects inner tissues
- Found in: seed coats, bark, nut shells, around vascular bundles
Why This Works
Plants need three things from their tissues: growth, support, and metabolic functions. Meristematic tissue handles growth — it’s the only tissue that keeps dividing throughout the plant’s life. Permanent tissues handle everything else.
Among permanent tissues, the three simple types form a spectrum of rigidity: parenchyma (soft, flexible) → collenchyma (flexible but stronger) → sclerenchyma (rigid, hard). This parallels their wall thickness and the state of cells — living to dead.
Think of it like building materials: parenchyma is foam (soft filler), collenchyma is flexible rubber (bends but supports), and sclerenchyma is steel rebar (rigid strength).
Alternative Method
For quick recall, remember the “P-C-S” sequence by wall thickness:
- Parenchyma: Paper-thin walls
- Collenchyma: Corner thickening
- Sclerenchyma: Solid (uniformly thick) + dead
NEET and CBSE both frequently ask: “Which tissue provides flexibility to plants?” — Collenchyma. “Which tissue has dead cells?” — Sclerenchyma. “Husk of coconut is made of?” — Sclerenchyma (sclereids). These are direct 1-mark questions that appear almost every year.
Common Mistake
Students confuse collenchyma and sclerenchyma because both provide mechanical support. The key difference: collenchyma cells are living with uneven wall thickening and provide flexible support. Sclerenchyma cells are dead with uniform wall thickening (lignified) and provide rigid support. If the question says “flexibility” — the answer is collenchyma. If it says “rigidity” — the answer is sclerenchyma.