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๐ฌ Think about it
Cut across a sunflower stem and look under a microscope. You will see many different kinds of cells, not just one. Each kind forms a tissue with a special job. Let us meet the permanent tissues of a plant.
What are permanent tissues?
- They are tissues made of cells that have stopped dividing.
- Each is specialised to do a specific job.
- They can be simple (one type of cell) or complex (more than one type).
Permanent Tissues
Permanent tissue
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Simple
One type of cell (parenchyma, collenchyma, sclerenchyma).
Complex
More than one type of cell (xylem, phloem).
What is the protective tissue of a plant?
- The epidermis is the outermost layer of the plant body.
- It is a single layer of flat, tightly packed cells.
- It is covered by a waxy layer called the cuticle.
- It protects against injury, water loss and microbes.
What extra features does the epidermis have?
- In roots, it forms root hairs that absorb water and minerals.
- In leaves, it has pores called stomata.
- Stomata help in gas exchange and transpiration.
- Transpiration helps pull water up and remove wastes.
Example:
Root hairs increase the surface area for soaking up water from the soil.
What are the simple permanent (supporting) tissues?
- They are the supporting tissues of a plant.
- There are three types: parenchyma, collenchyma and sclerenchyma.
- Each differs in structure and gives support in its own way.
Simple Permanent (Supporting) Tissues
Simple permanent tissue
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Parenchyma
Thin walls; stores food.
Collenchyma
Thick corners; flexible support.
Sclerenchyma
Thick lignified walls; hard strength.
What does parenchyma do?
- Parenchyma is made of living cells with thin walls.
- The cells are loosely packed with spaces between them.
- It mainly stores food and can do photosynthesis in green parts.
- In aquatic plants, special parenchyma forms air spaces that help floating.
Example:
The soft inner pulp of many fruits is parenchyma storing food.
What does collenchyma do?
- Collenchyma is made of living cells.
- Its corners are unevenly thickened with pectin.
- Pectin gives flexibility, like rubber.
- It lets stems and tendrils bend without breaking.
Example:
The soft, flexible leaf stalk of coriander is supported by collenchyma.
What does sclerenchyma do?
- Sclerenchyma cells have thick walls due to lignin.
- This makes them hard and strong, forming woody parts.
- Most of these cells are dead.
- It is found in stems, leaf veins and hard seed coverings.
Example:
The hard husk of a coconut and the shell of a walnut are sclerenchyma.
What are complex permanent (conducting) tissues?
- They are the conducting tissues, xylem and phloem.
- They are complex because they have different types of cells working together.
- Xylem carries water and minerals; phloem carries food.
What does xylem do?
- Xylem transports water and minerals from roots to other parts.
- It also gives strength to the plant.
- It has tracheids, vessels, xylem parenchyma and xylem fibres.
- Only xylem parenchyma is living; the rest are mostly sclerenchymatous.
Example:
Water from the soil reaches the top leaves of a tall tree through xylem.
How Xylem Moves Water
Roots absorb water
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Up the xylem
Water and minerals rise through hollow tubes.
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Reach the leaves
What does phloem do?
- Phloem is mostly made of living cells.
- It has sieve tubes, companion cells, phloem parenchyma and phloem fibres.
- Sieve tubes carry food from leaves to other parts.
- Companion cells control the sieve tubes and manage sugar loading.
Example:
Food made in leaves travels down to the roots through phloem.
How Phloem Moves Food
Food made in leaves
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Through sieve tubes
Companion cells help load the food.
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Reaches stem and roots
How are plant tissues organised into systems?
- Plant tissues are grouped into three tissue systems.
- Dermal tissue system forms the outer covering and reduces water loss.
- Ground tissue system forms the main body (parenchyma, collenchyma, sclerenchyma).
- Vascular tissue system is the conducting tissues, xylem and phloem.
Important Points
- Permanent tissues are simple (one cell type) or complex (many cell types).
- Epidermis protects; parenchyma, collenchyma and sclerenchyma support.
- Xylem carries water; phloem carries food.
- Plant tissues form dermal, ground and vascular tissue systems.
๐งฌ Pause and Ponder
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You may have noticed that fibres of coconut husk are hard and brittle, whereas the leaf stalks of coriander are soft and flexible. Find out the reason.
Coconut husk is made of thick, lignified, dead sclerenchyma, which is hard; coriander stalks have living collenchyma with flexible pectin-rich walls, so they bend.
๐งฌ Pause and Ponder
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Why do you think that a thick cuticle on the outer wall of epidermis is advantageous for a plant living in the desert but disadvantageous for a plant living underwater?
In the desert a thick cuticle cuts down water loss, which is vital; underwater there is no water shortage, so a thick cuticle would only block the easy exchange of gases and materials. -
Once water is absorbed by plant roots, it has to travel against gravity through xylem. How do the 'dead' cells of the xylem work together with the living cells of leaves at the top to keep the water moving?
The dead xylem cells form hollow tubes; when leaves lose water through stomata by transpiration, the pull created drags water up the xylem tubes from root to leaf. -
What do you think will happen if there were no stomata in the epidermis of the stem or leaves?
Gas exchange and transpiration would stop, so the plant could not take in carbon dioxide for photosynthesis or pull water up, and it would not cool or remove wastes.
๐ Ready to Go Beyond
- In young plants the outer layer is a single-layered epidermis.
- As plants grow older, some cells below the epidermis start to divide.
- These act as lateral meristematic cells and form the cork cambium.
- Cork cambium makes cork cells, which are dead and waterproof, forming the bark.
โ Test Yourself
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Which tissue is the protective tissue of a plant?
View Answer
The epidermis. -
Name the three simple permanent tissues.
View Answer
Parenchyma, collenchyma and sclerenchyma. -
Which tissue carries food, and which carries water?
View Answer
Phloem carries food; xylem carries water. -
Why are xylem and phloem called complex tissues?
View Answer
They are made of more than one type of cell working together. -
Name the three tissue systems of a plant.
View Answer
Dermal, ground and vascular tissue systems.
Important Definitions
- Permanent tissue — a tissue of specialised cells that have stopped dividing.
- Epidermis — the outermost protective layer of the plant body.
- Parenchyma — thin-walled living cells that store food and can do photosynthesis.
- Collenchyma — living cells with thickened corners that give flexible support.
- Sclerenchyma — thick, lignified, mostly dead cells that give hardness and strength.
- Xylem — complex tissue that carries water and minerals and gives strength.
- Phloem — complex tissue that carries food from leaves to other parts.
๐ NCERT Question 2 — If a plant is unable
If a plant is unable to transport food from leaves to roots, which tissue is malfunctioning?
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๐ NCERT Question 9 — Aamrapali observed that a
A mango sapling's stem bends without breaking — which tissue gives this flexibility?
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๐ NCERT Question 12 — Coconut husk fibres are
Coconut husk fibres are tough — which tissue gives this strength, and why not parenchyma?
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๐ NCERT Question 8 — In a forest, it
A tree was debarked by an elephant — which tissue is affected and which functions are hampered?
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๐ NCERT Question 15 — A textbook states, "Each
A textbook says each plant tissue does only one function — how would you examine this?
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๐ NCERT Question 11 — During the discussion in
Is a tissue always a group of similar cells? Explain for simple versus complex tissues.
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