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Class 9 Science · Chapter 3 · Part 1 of 2
Tissues in Action
Plant Tissues — Meristematic, Permanent, Xylem & Phloem
🌱 Meristematic Tissue
🌿 Permanent Tissue
💧 Xylem & Phloem
🛡️ Epidermis
PART 1
This part covers: Introduction → Why Different → Meristematic Tissues → Permanent Tissues → Xylem & Phloem → Tissue Systems. Part 2 covers Animal Tissues, Joints & Skeletal System.
📌 Jump to Section
Introduction
Why Different?
Meristematic
Permanent Tissues
Epidermis
Simple Tissues
Xylem & Phloem
Tissue Systems
Definitions
Exam FAQs
🧬 Introduction — Tissues in Action
Life begins when a single cell divides several times, giving rise to many cells. These gradually form skin (protection), muscles (movement), bones (support), nerves (control), and all other organs.
In all multicellular organisms there is a hierarchy of organisation:
- Similar cells performing similar functions → Tissue
- More than one type of tissues → Organ
- Different organs → Organ Systems → Organism
📖 Definition — Tissue
Tissue — A group of cells (similar in structure) that work together to perform a specific function. The formation of different tissues leads to division of labour, which increases efficiency and enables complex life processes.
⭐ Examples of Division of Labour
- In animals: muscle tissue enables movement; nervous tissue carries messages.
- In plants: xylem transports water and minerals; phloem transports food.
- In unicellular organisms (like Amoeba): a single cell performs ALL life functions.
🌿 3.1 Why are Plant and Animal Tissues Different?
- Plants are fixed in one place — need rigid support → have cell wall providing rigidity and strength.
- Animals can move — no rigid cell wall → animal cells can change shape easily → cellular flexibility supports locomotion.
- Plants have tissues for photosynthesis; animals have tissues for digestion.
- Both have distinct tissues for transporting food and water.
- Growth patterns differ — tissues responsible for growth differ in structure and function.
🌿
B. G. L. Swamy — Meet a Scientist
Renowned Indian botanist known for contributions to plant morphology and anatomy. His book Hasuru Honnu (Kannada) is a blend of science, satire and culture — describing botanical excursions in the Western Ghats forests. Won the Kendra Sahitya Akademi Award in 1978.
🌱 3.2 Tissues for Growth — Meristematic Tissues
Plants grow in different ways:
- Increase in length (height of stem, depth of roots)
- Increase in girth (thickness of stem)
- Regrowth after cutting or grazing
This growth requires actively dividing cells — forming meristematic tissue.
📖 Characteristics of Meristematic Cells
- Cells are small with thin cell walls
- Large and prominent nucleus
- Dense cytoplasm with many organelles
- Vacuoles absent — all energy goes to division, no storage needed
- Cells are tightly packed with little or no intercellular space
- These features allow continuous and rapid cell division
Three Types of Meristematic Tissues
⬆️
Apical Meristem
📍 Tips of roots and shoots
Responsible for increase in length. Present at root apical meristem and shoot apical meristem. Roots grow only from their tips.
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Lateral Meristem
📍 Along circumference of stems
Responsible for increase in girth. Cells arranged in a ring — divide to produce new cells inside and outside. Causes annual growth rings.
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Intercalary Meristem
📍 Base of internode / just above node
Responsible for regrowth after cutting. Present in grasses — grass grows back after mowing! Node = point where branch/leaf arises. Internode = stem between two nodes.
🧪 Activity 3.1 — Observing Growth of Onion Roots
Aim
To show that roots grow from their tips (apical meristem).
Setup
Two jars of water with one onion each. Jar A = control. Jar B = root tips cut on Day 3.
Observation
Jar A: Roots continue to grow. Jar B: Roots stop growing after tip is cut.
Conclusion
Roots grow only from their tips. Tips contain actively dividing cells = apical meristem.
🔩 Annual Growth Rings
Ring-like patterns on the cut surface of a tree trunk are called annual growth rings — formed by lateral meristem activity, one ring per year. Wide rings = favourable year. Narrow rings = unfavourable year. By counting rings, scientists can estimate the age of a tree and understand past climate.
Differentiation — From Meristematic to Permanent
Meristematic tissue adds new cells. Some cells remain meristematic; others lose the ability to divide and change in structure and function → they become permanent tissues.
This process — by which meristematic tissue becomes specialised — is called differentiation.
✅ Check Your Understanding — Meristematic Tissues
Q1. Which meristematic tissue is responsible for increase in girth of the stem?
AApical meristem
BLateral meristem
CIntercalary meristem
DGround meristem
Q2. Grass grows back after mowing because of:
AApical meristem
BLateral meristem
CIntercalary meristem
DPermanent tissue
Q3. Meristematic cells do NOT have vacuoles because:
AThey are dead cells
BAll energy goes to rapid cell division; no storage needed
CThey have thick cell walls
DThey lack a nucleus
📋 Answer Key
Q1B — Lateral meristem — Located along the circumference of stems, it divides to increase girth and forms annual rings.
Q2C — Intercalary meristem — Located at nodes/base of grasses, it helps them regenerate after cutting or grazing.
Q3B — No storage needed — Meristematic cells use all space and energy for rapid division. Vacuoles are for storage which these cells don’t need.
🛡️ 3.2.4 Permanent Tissues — Epidermis (Protective Tissue)
📖 Definition — Permanent Tissue
Permanent Tissues — Formed from meristematic tissues after differentiation. Cells have lost the ability to divide and are specialised for specific functions. Can be Simple (one type of cell) or Complex (more than one type of cell).
The epidermis forms the outermost layer of the plant body — a tightly packed, single layer of flat and rectangular cells.
- Covered with a waxy layer called cuticle — protects against mechanical injury and parasites.
- In dry habitats, a thick cuticle reduces water loss through transpiration.
- In roots, epidermal cells form root hair — increase surface area for absorption of water and minerals.
- In leaves, epidermis has pores called stomata — for gaseous exchange and transpiration.
- Transpiration creates a transpiration pull in xylem, helping water rise in tall trees.
- Transpiration also helps in elimination of wastes from the plant body.
💡 Cork — Ready to Go Beyond
In older plants, some cells below the epidermis form cork cambium → produces cork cells (dead, compactly arranged, impermeable to water and gases). This forms the bark of the tree.
🏗️ Simple Permanent Tissues — Supporting Tissues
Three types: Parenchyma, Collenchyma, Sclerenchyma
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Parenchyma
Storage Tissue
Living cells with thin walls. Loosely packed with intercellular spaces. Mainly stores food. Performs photosynthesis in green parts. In aquatic plants, forms air spaces to help them float.
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Collenchyma
Flexibility Tissue
Living cells with unevenly thickened corners due to pectin deposition. Provides support and flexibility. Allows stems and tendrils to bend without breaking.
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Sclerenchyma
Hard & Strong Tissue
Dead cells with thick walls due to lignin deposition. Hard, strong and woody. Found in stems, leaf veins, coconut husk, walnut shell.
🎯 Exam Point
A fresh twig bends (collenchyma — flexible, pectin). A dry twig breaks (sclerenchyma — dead, lignified). Coconut husk fibres (sclerenchyma) = hard and brittle. Coriander leaf stalks (collenchyma) = soft and flexible.
✅ Check Your Understanding — Simple Permanent Tissues
Q4. Sclerenchyma cells have thick walls due to deposition of:
APectin
BCellulose
CLignin
DStarch
Q5. Aquatic plants float because of specialised:
AParenchyma forming air spaces
BSclerenchyma with lignin
CXylem vessels
DCollenchyma with pectin
Q6. Which tissue provides support and flexibility to stems and tendrils?
AParenchyma
BCollenchyma
CSclerenchyma
DXylem
📋 Answer Key
Q4C — Lignin — Lignin deposition makes sclerenchyma cells hard, strong and woody (dead). Pectin causes collenchyma thickening.
Q5A — Parenchyma forming air spaces — Specialised parenchyma in aquatic plants creates air spaces providing buoyancy.
Q6B — Collenchyma — Has pectin-thickened corners, giving flexibility. Allows bending without breaking. Found in young stems and tendrils.
🔗 Complex Permanent Tissues — Xylem and Phloem
📖 Definition
Complex Permanent Tissues — Made up of more than one type of cells working together. Include xylem and phloem — together called vascular tissues.
| Feature | Xylem | Phloem |
|---|---|---|
| Function | Transports water & minerals from roots to all parts | Transports food (sugars) from leaves to all parts |
| Direction | Upward (roots → leaves) | Both directions |
| Living/Dead | Mostly dead (except xylem parenchyma) | Mostly living |
| Components | Tracheids, Vessels, Xylem parenchyma, Xylem fibres | Sieve tubes, Companion cells, Phloem parenchyma, Phloem fibres |
| Extra function | Provides structural strength | Stores resin, tannins, latex (phloem parenchyma) |
Xylem — Components in Detail
- Tracheids — Tubular, thick-walled. Primarily sclerenchymatous (dead).
- Vessels — Tubular, thick-walled. Primarily sclerenchymatous (dead).
- Xylem parenchyma — The only living component of xylem.
- Xylem fibres — Primarily sclerenchymatous. Provide strength.
Phloem — Components in Detail
- Sieve tubes — Long, tubular cells joined end-to-end by perforated walls. Transport food from leaves to all parts.
- Companion cells — Specialised parenchyma. Regulate sieve tube functions. Monitor loading and unloading of sugars.
- Phloem parenchyma — Store food materials, resin, tannins and latex.
- Phloem fibres — Primarily sclerenchymatous. Support sieve tubes; provide strength.
🎯 Exam Point
Xylem parenchyma = only living component of xylem. Phloem is mostly living (unlike xylem). Companion cells regulate sieve tube cells because sieve tubes lose their nucleus at maturity.
✅ Check Your Understanding — Xylem and Phloem
Q7. Which tissue transports food from leaves to roots in plants?
AXylem
BPhloem
CEpidermis
DSclerenchyma
Q8. The only living component of xylem is:
ATracheid
BVessel
CXylem parenchyma
DXylem fibre
Q9. Companion cells in phloem are mainly responsible for:
AProviding structural strength
BMonitoring loading and unloading of sugars in sieve tubes
CTransporting water
DStoring food permanently
📋 Answer Key
Q7B — Phloem — Phloem’s sieve tubes transport food (sugars) in both directions. Xylem only transports water upward.
Q8C — Xylem parenchyma — Tracheids, vessels and xylem fibres are dead (sclerenchymatous). Only xylem parenchyma is living.
Q9B — Loading and unloading of sugars — Companion cells regulate sieve tube functions, including controlling sugar transport.
🌐 Three Tissue Systems in Plants
| Tissue System | Includes | Function |
|---|---|---|
| Dermal Tissue System | Epidermis | Outer covering of plant; protects inner parts; reduces water loss |
| Ground Tissue System | Parenchyma, Collenchyma, Sclerenchyma | Main body of plant between dermal and conducting tissues |
| Vascular Tissue System | Xylem and Phloem | Conduction of water, minerals, and food to all parts |
🧫
Sipra Guha Mukherjee & S. C. Maheshwari
Made a breakthrough discovery in plant tissue culture. Their research led to the development of a complete plant through anther culture using an artificial nutrient medium under controlled laboratory conditions. This pioneering work greatly contributed to crop improvement and modern agriculture.
📖 Important Definitions — Plant Tissues
TissueA group of cells similar in structure that work together to perform a specific function.
Meristematic TissueTissue made of actively dividing cells responsible for plant growth. Three types: apical (length), lateral (girth), intercalary (regrowth).
DifferentiationThe process by which meristematic cells lose the ability to divide and become specialised to perform specific functions, forming permanent tissues.
CuticleA waxy layer of cutin covering the epidermis of plants. Protects against mechanical injury, parasites, and reduces water loss.
TranspirationEvaporation of water vapours through stomata. Creates transpiration pull in xylem, helping water rise. Also helps in waste elimination.
ParenchymaLiving cells with thin walls and intercellular spaces. Mainly stores food; performs photosynthesis in green parts; forms air spaces in aquatic plants.
CollenchymaLiving cells with unevenly thickened corners due to pectin. Provides support and flexibility to stems and tendrils.
SclerenchymaDead cells with thick walls due to lignin deposition. Makes tissues hard and strong. Found in stems, leaf veins, coconut husk, walnut shell.
XylemComplex permanent tissue that transports water and minerals upward from roots to all parts. Also provides structural strength. Mostly dead cells.
PhloemComplex permanent tissue that transports food (sugars) from leaves to all parts of the plant in both directions. Mostly living cells.
🔑 Keywords — Plant Tissues
TissueDivision of LabourMeristematic TissueApical MeristemLateral MeristemIntercalary MeristemAnnual Growth RingsNodeInternodeDifferentiationPermanent TissueEpidermisCuticleStomataRoot HairTranspirationCork CambiumParenchymaCollenchymaSclerenchymaPectinLigninXylemPhloemTracheidsVesselsSieve TubesCompanion CellsDermal Tissue SystemGround Tissue SystemVascular Tissue System
❓ Frequently Asked Exam Concepts — Plant Tissues
Why does a fresh twig bend but a dry twig break? ▶
A fresh twig has collenchyma with pectin-thickened corners giving flexibility — bends without breaking. A dry twig loses water; sclerenchyma (dead, lignified) dominates making it rigid and brittle — breaks. Similarly, coriander leaf stalks (collenchyma) are soft; coconut husk fibres (sclerenchyma) are hard and brittle.
What is the difference between xylem and phloem? ▶
Xylem transports water and minerals from roots upward to all parts. It is mostly dead (except xylem parenchyma) and provides structural strength. Phloem transports food (sugars) from leaves to all parts in both directions. Phloem is mostly living. Xylem components: tracheids, vessels, xylem parenchyma, xylem fibres. Phloem components: sieve tubes, companion cells, phloem parenchyma, phloem fibres.
Why do meristematic cells lack vacuoles? ▶
Vacuoles are for storage of water, food, and waste. Meristematic cells are actively dividing — they use all space and energy for rapid cell division. Vacuoles would take up space needed for the nucleus and organelles involved in division. Having no vacuoles also keeps cells small and tightly packed, characteristic of meristematic tissue.
What are annual growth rings and what do they tell us? ▶
Annual growth rings are ring-like patterns on the cut surface of a tree trunk, formed by lateral meristem activity — one ring per year. Wide rings = favourable growth year (good rainfall/nutrients). Narrow rings = unfavourable year (drought/poor conditions). By counting rings, scientists can estimate the age of a tree and understand past climate conditions.
Why do plant tissues have more supporting tissues than animal tissues? ▶
Plants are fixed in one place and cannot move. They need rigid structural support to withstand environmental stresses (wind, rain, gravity) and to stay upright. They also need to support the weight of leaves, branches, and fruits. Animals have a skeletal system (bones) for support and can move to avoid stress, so they do not need as much structural supporting tissue within organs.
📌 Continue to Part 2 →
Animal Tissues (Epithelial, Connective, Muscular, Nervous) · Musculoskeletal System · Types of Joints · Skeletal System · Final Quiz