NCERT Solutions for Class 9th Science Chapter 3 .2.4 Permanent tissues; protective and supporting tissues — In-text Questions

Book page 323 Updated on2026-09-08

Q1.

What do you observe? Are all the cells similar in shape and size? How many different types of tissues can you identify? What differences do you notice among them? What might be the reason for the presence of different types of cells and tissues?

Answer

No — in the T.S. of the sunflower stem (Fig. 3.7) the cells are clearly not all alike, and you can pick out several distinct tissues arranged in a definite order from outside inwards.

Moving inwards	What the cells look like	What it is doing
Cuticle + epidermis (with epidermal hair)	One layer of flat, rectangular, tightly packed cells under a waxy film	Protection; checks water loss
Collenchyma	Living cells, corners thickened	Flexible support just under the skin
Parenchyma / ground tissue	Large, thin-walled, loosely packed with air spaces	Storage, photosynthesis, packing
Sclerenchyma cap	Small cells with very thick, lignified walls; mostly dead	Hard mechanical strength
Vascular bundle — phloem outside, lateral meristem in the middle, xylem inside	Phloem: living sieve tubes. Xylem: wide, thick-walled dead tubes	Food transport, girth growth, water transport

The reason: one cell shape cannot do five jobs. A cell that conducts water must be hollow and dead; a cell that stores food must be alive and roomy; a cell that gives strength must be thick-walled. So the stem is built as a set of specialised tissues, each with the shape its job requires — division of labour once again.

Tip: permanent tissues are of two kinds — simple (one cell type: parenchyma, collenchyma, sclerenchyma) and complex (more than one cell type working together: xylem, phloem).

Q2.

What protects plants from mechanical injury, water loss, harmful microorganisms and extreme environmental conditions?

Answer

The epidermis — the single, outermost layer of flat, rectangular, tightly packed cells that covers every part of the plant body — together with the waxy cuticle of cutin laid over it.

Threat	How the epidermis deals with it
Mechanical injury	Cells are tightly packed with no gaps, and the cuticle forms a tough outer film
Water loss	Cutin is waxy and waterproof; in dry habitats the cuticle is laid down thicker still
Microbes and parasites	An unbroken layer with no intercellular spaces gives no entry route; the cuticle resists invasion
Extreme conditions	Epidermal hair traps a still layer of air and reduces heating and drying

The epidermis is not only a barrier — it is also modified for two jobs the plant cannot do without:

In the root, epidermal cells grow out as root hair, which greatly increase the surface area for absorbing water and minerals from the soil.
In the leaf, the epidermis carries pores called stomata, through which gases are exchanged and water vapour escapes as transpiration.

Why transpiration is useful, not just a leak: water evaporating from the leaf creates a transpiration pull in the xylem, and this pull is what lifts water all the way up a tall tree. Transpiration also helps the plant get rid of wastes.

Q3.

What keeps a plant upright? Why does a fresh twig bend but a dry twig break? Why are seed coats hard and how do aquatic plants float?

Answer

All four questions are answered by the three simple permanent tissues — parenchyma, collenchyma and sclerenchyma — and by which of them is present where.

Observation	Tissue responsible	The structural reason
A plant stands upright	Sclerenchyma (plus turgid parenchyma in soft herbs)	Lignin makes the walls rigid, so the stem resists bending under its own weight
A fresh twig bends	Collenchyma	Living cells with pectin-thickened corners — pectin behaves like rubber, so the wall gives and springs back
A dry twig snaps	Sclerenchyma	The cells are dead and lignified; with the water gone there is no give at all, so the wall cracks instead of bending
Seed coats are hard	Sclerenchyma	Layers of dead, thick-walled lignified cells — the same tissue as in coconut husk and walnut shell
Aquatic plants float	Specialised parenchyma	Large air-filled spaces between the loosely packed cells lower the average density of the plant below that of water

Why the difference between bending and breaking matters: a young stem in a storm must deform and recover — that is a job for collenchyma, which is strong but flexible. An old trunk must not deform at all — that is a job for sclerenchyma, which is strong but brittle. Plants use both, in different places and at different ages.

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