Detailed notes on permanent tissues in plants for Class 9 from the NCERT Exploration textbook (Chapter 3: Tissues in Action). Topics covered: how permanent tissues form through differentiation, protective tissue (epidermis), simple permanent tissues (parenchyma, collenchyma, sclerenchyma), and complex permanent tissues (xylem and phloem). Aligned with CBSE syllabus 2026–27.
In the previous topic on meristematic tissue, you learnt that meristematic cells divide continuously to add new cells to the plant body. Not all of these newly produced cells remain meristematic — many of them undergo a fundamental change in their structure and function. This change is called differentiation.
Definition
Permanent tissues are plant tissues whose cells have lost the ability to divide and have become specialised to perform specific functions — such as protection, support, storage, or transport. They are formed from meristematic tissue through the process of differentiation.
Unlike meristematic cells (which are small, thin-walled, densely packed, and lack vacuoles), permanent tissue cells are mature — they have definite shapes, thickened walls (in many types), and often contain large central vacuoles. Once differentiated, these cells generally do not divide again under normal conditions.
Classification of permanent tissues:
Simple permanent tissues — composed of only one type of cell (e.g., parenchyma, collenchyma, sclerenchyma).
Complex permanent tissues — composed of more than one type of cell working together as a unit (e.g., xylem, phloem).
In addition, plants have a protective tissue — the epidermis — which forms the outermost covering of the plant body and is considered separately from simple and complex tissues.
Differentiation — The Bridge from Meristematic to Permanent
Q. What is the epidermis and what does it protect the plant from?
The epidermis forms the outermost layer of the entire plant body — covering the roots, stems, leaves, flowers, and fruits. It acts as the first line of defence for the plant.
2.1 Structure of Epidermis
Consists of a single layer of cells.
Cells are flat and rectangular in shape.
Cells are tightly packed with no intercellular spaces — this prevents easy entry of pathogens and limits water loss.
The outer surface of epidermal cells is covered with a waxy layer called the cuticle (composed of a substance called cutin).
2.2 Functions of Epidermis
Protection from mechanical injury — the tough outer layer guards the soft inner tissues from physical damage.
Prevention of water loss — the waxy cuticle reduces evaporation of water from the plant surface.
Protection from parasites and pathogens — the tightly packed layer prevents easy entry of harmful microorganisms.
Gaseous exchange — specialised pores called stomata (present in the epidermis of leaves and green stems) allow carbon dioxide to enter and oxygen and water vapour to exit.
Water absorption — epidermal cells in the root zone produce hair-like extensions called root hairs that greatly increase the surface area for absorption of water and minerals from the soil.
2.3 Special Features: Root Hairs and Stomata
Feature
Location
Structure
Function
Root Hairs
Epidermis of roots
Thin, hair-like outgrowths of epidermal cells
Increase surface area for absorption of water and minerals from soil
Stomata
Epidermis of leaves and green stems
Pores flanked by two guard cells that control opening and closing
Gaseous exchange (photosynthesis & respiration); transpiration (water vapour loss) — creates transpiration pull that drives water transport upward in xylem
2.4 Why do Desert Plants Have a Thick Cuticle?
In plants living in very dry (xeric) habitats such as deserts, the epidermis is covered by a thick layer of cuticle. Since water is scarce in such environments, a thick waxy cuticle minimises water loss through transpiration. This is an adaptation that helps the plant survive extreme conditions. Conversely, aquatic plants have very little or no cuticle, as they are surrounded by water and do not need to conserve it.
Ready to Go Beyond — Cork (Bark)
As plants grow older, the single-layered epidermis of the stem is replaced by a multi-layered cork. Some cells below the epidermis develop the ability to divide (cork cambium — a type of lateral meristem). Cork cells produced by this cambium are dead, compactly arranged, and contain a substance that makes them impermeable to water and gases. This forms the bark of a tree — a much tougher protective covering than the single-layered epidermis.
3. Simple Permanent Tissues
Simple permanent tissues are composed of only one type of cell. All cells in such a tissue are structurally similar and perform similar functions. These tissues provide support to the plant body. There are three types of simple permanent tissues:
3.1 Parenchyma
Q. What is parenchyma and what are its functions?
Cell type:Living cells with thin cellulosic walls.
Arrangement: Loosely packed with prominent intercellular spaces between cells.
Shape: Generally isodiametric (roughly equal in all dimensions) and somewhat oval or spherical.
Functions of Parenchyma:
Food storage — the primary function; stores starch, sugars, and other metabolites.
Photosynthesis — in the green parts of the plant (e.g., mesophyll of leaves), parenchyma cells contain chloroplasts and carry out photosynthesis. This green photosynthetic parenchyma is called chlorenchyma.
Buoyancy in aquatic plants — in plants like water hyacinth and lotus, parenchyma cells contain large air-filled intercellular spaces. This specialised form is called aerenchyma, which provides buoyancy and helps the plant float.
Lateral conduction — parenchyma assists in the lateral (sideways) movement of water and nutrients within the plant.
Key Point: Parenchyma is the Most Common Plant Tissue
Parenchyma is the most abundant and widespread tissue in plants. It forms the bulk of soft plant parts — fruits, leaves, and the pith of stems. Its thin walls and living nature make it metabolically active and versatile. All other plant tissues are thought to have evolved from parenchyma.
3.2 Collenchyma
Q. What is collenchyma and why does a fresh twig bend rather than break?
Cell type:Living cells with unevenly thickened corners (at the angles where cells meet).
Thickening material: The extra thickness is due to deposition of pectin — a substance that gives flexibility similar to rubber. This is the key difference from sclerenchyma, where walls are thickened by lignin.
Arrangement: Cells are elongated and compactly arranged.
Functions of Collenchyma:
Mechanical support with flexibility — provides the plant with support while still allowing it to bend. This is why a fresh twig can be bent without breaking, while a dry twig (which has lost this tissue's flexibility) snaps easily.
Found in: Stems of herbaceous plants, stalks of leaves, tendrils of climbing plants — all parts that need to be both supportive and flexible.
Some collenchyma cells contain chloroplasts and can carry out photosynthesis.
Remember — Pectin gives Pliability
The pectin deposits at the corners of collenchyma cells are what give this tissue its characteristic flexibility. Pectin is also the substance used in jam-making as a gelling agent — this gives you a sense of its physical properties. Contrast this with lignin in sclerenchyma, which makes cells rigid and dead.
3.3 Sclerenchyma
Q. What is sclerenchyma and why are coconut husks so hard?
Cell type:Dead cells at maturity. The cells deposit thick layers of lignin in their walls during development, which eventually kills the cell by cutting off its supply of nutrients. What remains is a thick, hardened cell wall.
Wall thickness: Very thick, with the lumen (internal cavity) often almost obliterated.
Thickening material:Lignin — an extremely tough organic polymer that makes the walls hard, inflexible, and resistant to decay.
Functions of Sclerenchyma:
Mechanical strength and rigidity — gives the plant body hardness, stiffness, and resistance to mechanical stress.
Found in: Stems, around vascular bundles, leaf veins, and the hard outer coverings of seeds and nuts.
Everyday examples of sclerenchyma in action:
Coconut husk — the hard fibrous outer covering of a coconut is rich in sclerenchyma fibres. These fibres (coir) are used to make mats, ropes, and brushes.
Walnut shell, jute fibres, flax fibres — all owe their hardness or toughness to sclerenchyma.
Dry twig — breaks easily because the collenchyma has dried out and what remains is the rigid sclerenchyma.
Did You Know?
Fibres of coconut husk are hard and brittle, whereas the leaf stalks of coriander are soft and flexible. The reason lies in their tissue composition: coconut husk is predominantly sclerenchyma (lignified, dead cells), while coriander leaf stalks contain more collenchyma (pectin-thickened, living cells). This explains the fundamental difference in their mechanical properties.
4. Comparison Table — Parenchyma vs Collenchyma vs Sclerenchyma
How does water absorbed by the roots travel all the way to the leaves at the top of a tall tree? How does the food (glucose) manufactured in the leaves during photosynthesis reach the roots underground? These functions are carried out by complex permanent tissues.
Definition
Complex permanent tissues are conducting tissues made up of more than one type of cell, all working together as a single functional unit. They form the vascular system of the plant — responsible for long-distance transport of water, minerals, and food. There are two types: xylem and phloem, collectively called vascular tissue.
5.1 Xylem — The Water-Conducting Tissue
Q. What is xylem and how does it transport water?
Xylem is the vascular tissue responsible for transporting water and dissolved minerals from the roots upward to all parts of the plant. It also provides mechanical strength to the plant body. The word "xylem" comes from the Greek word xylon, meaning wood.
Components of Xylem:
Xylem is composed of four types of cells:
Tracheids — elongated, tubular, dead cells with thick, lignified walls. They have tapered ends and water passes from one tracheid to the next through pits (thin areas) in the wall. Found in all vascular plants.
Vessels (Vessel elements) — wider, shorter, cylindrical dead cells arranged end to end to form long continuous tubes (vessel members). The end walls between adjacent vessel elements are perforated or entirely dissolved, forming an unobstructed pipe. Water flows through these vessels much more efficiently than through tracheids. Mainly found in flowering plants (angiosperms).
Xylem Parenchyma — the only living component of xylem. These cells store food (starch and fats) and assist in the lateral (sideways) transport of water. They also participate in the loading and unloading of water from tracheids and vessels.
Xylem Fibres — elongated, dead cells with very thick lignified walls (sclerenchymatous). They provide additional mechanical support to the plant. They do not conduct water.
Remember — Living vs Dead in Xylem
Only xylem parenchyma is living in xylem. Tracheids, vessels, and xylem fibres are all dead at maturity. Their death is actually essential — the living contents would block water flow. The empty, lignified cell walls form hollow tubes that act as efficient pipelines.
Direction of transport in xylem:
Water and minerals move unidirectionally — upward (from roots → stem → leaves).
The driving force is the transpiration pull — as water evaporates through stomata in leaves, it creates a tension that pulls water upward through the continuous xylem column.
Root pressure (osmotic pressure at the roots) also helps push water upward, especially at night when transpiration is low.
5.2 Phloem — The Food-Conducting Tissue
Q. What is phloem and how is it different from xylem?
Phloem is the vascular tissue responsible for transporting food (primarily sugars like sucrose) manufactured in the leaves during photosynthesis to all other parts of the plant — including roots, growing buds, fruits, and seeds. This process is called translocation. Unlike xylem, phloem is mostly composed of living cells.
Components of Phloem:
Phloem is composed of four types of cells:
Sieve Tubes — long, tubular living cells arranged end to end to form tubes. The end walls (sieve plates) are perforated with pores, allowing the movement of food materials from one sieve tube element to the next. Sieve tube cells lack a nucleus at maturity (it breaks down), but remain alive and metabolically active.
Companion Cells — specialised living parenchyma cells that lie alongside sieve tube elements. Each companion cell is closely associated with a sieve tube element and regulates its activity. Key functions: loading sugars into sieve tubes from the leaf mesophyll (source loading) and unloading sugars from sieve tubes at sink tissues (roots, fruits). They essentially act as the "control unit" for sieve tubes, since sieve tubes lack a nucleus.
Phloem Parenchyma — living cells that store food materials (sugars, starch) and also store resins, tannins, and latex in certain plants. They assist in the lateral movement of food within the phloem.
Phloem Fibres (Bast Fibres) — primarily dead cells with thick sclerenchymatous walls. They provide mechanical support and strength to the phloem. Commercially important bast fibres include jute and flax.
Direction of transport in phloem:
Food moves bidirectionally — from source to sink. The source is any organ that produces or releases sugars (mainly leaves); the sink is any organ that consumes or stores sugars (roots, growing tips, fruits, seeds).
Food can therefore move both upward and downward in the phloem, depending on the location of the source and sink at any given time.
This is a fundamental difference from xylem, in which transport is only upward.
Did You Know? — Aphids and Phloem
Aphids (small sap-sucking insects) insert their stylet (a needle-like mouthpart) directly into phloem sieve tubes to feed on the sugar-rich sap. Scientists sometimes allow aphids to feed on a plant stem, then anaesthetise the aphid and cut away its body, leaving the stylet in place. The phloem sap oozes out through the stylet and can be collected and analysed — this is one of the key techniques used to study phloem composition.
6. Comparison Table — Xylem vs Phloem
Feature
Xylem
Phloem
What it transports
Water and dissolved minerals
Food (sugars / sucrose) and organic compounds
Direction of transport
Unidirectional — upward only (roots → stem → leaves)
Bidirectional — from source to sink (can be up or down)
Permanent tissues form when meristematic cells lose the ability to divide and become specialised (differentiation). They are either simple (one cell type) or complex (multiple cell types).
The epidermis is the single-layered protective tissue covering all plant surfaces. Its waxy cuticle prevents water loss; stomata allow gaseous exchange; root hairs absorb water and minerals. Desert plants have a thick cuticle to minimise transpiration.
Parenchyma — living, thin-walled, loosely packed, with intercellular spaces. Functions: food storage, photosynthesis (chlorenchyma), and buoyancy (aerenchyma in aquatic plants).
Collenchyma — living, with pectin-thickened corners. Provides flexible mechanical support (fresh twig bends rather than breaks). Found in stems, leaf stalks, tendrils.
Sclerenchyma — dead at maturity, with thick lignified walls. Provides rigid support and hardness. Found in coconut husk, walnut shell, jute fibres, and around vascular bundles.
Related Concepts from Chapter 2 (Cell: The Building Block of Life)
Understanding permanent tissues builds on your knowledge of cell structure from Chapter 2. Review these related pages:
Cell: The Building Block of Life — Chapter 2 study material; revisit cell wall, cell membrane, and organelles before studying tissue structure
Cell Wall — parenchyma (thin wall), collenchyma (pectin-thickened) and sclerenchyma (lignin-thickened) are all variations of the cell wall structure you studied here
Cell Organelles — chloroplasts in chlorenchyma; vacuoles in mature permanent cells; xylem parenchyma and phloem cells are metabolically active
Osmosis and Diffusion — water entry into root hair cells by osmosis; stomata opening and closing involves osmotic changes in guard cells
Mitosis — the cell division in meristematic tissue that eventually gives rise to all permanent tissues
Cell Theory — foundational principles that explain why tissues are composed of cells
