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NCERT Solutions · Class 11 Biology Anatomy of Flowering Plants

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Exercises 6.1–6.7

  1. Exercise 6.1

    Draw illustrations to bring out the anatomical difference between
    (a)
    Monocot root and Dicot root
    (b)
    Monocot stem and Dicot stem

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    Four transverse sections (T.S.) are needed — dicot root, monocot root, dicot stem, monocot stem. The features below are what the drawings must show and label.
    (a) Monocot root and Dicot root
    Dicot root (T.S. of sunflower root, Figure $\displaystyle 6.3$ a): draw concentric zones from outside inwards — epiblema (epidermis) with unicellular root hairs protruding from some of its cells; a wide cortex of several layers of thin-walled parenchyma with intercellular spaces; a single-layered, barrel-shaped endodermis whose tangential and radial walls carry casparian strips of suberin; a few layers of thick-walled pericycle; then the vascular region.
    Show only two to four xylem and phloem patches, placed alternately along different radii — a radial bundle — with conjunctive tissue (parenchyma) between xylem and phloem, and a cambium ring appearing later between them. The pith is small or inconspicuous.
    Monocot root (Figure $\displaystyle 6.3$ b): the same layers — epidermis, cortex, endodermis, pericycle, vascular bundles, pith — but draw more than six xylem bundles (polyarch) and a large, well-developed pith. Show no cambium: monocot roots do not undergo secondary growth.
    Labels for both: root hair, epidermis, cortex, endodermis, pericycle, protoxylem, metaxylem, phloem, pith.
    (b) Monocot stem and Dicot stem
    Dicot stem (Figure $\displaystyle 6.4$ a): outermost epidermis with a thin cuticle, some trichomes and a few stomata; a cortex in three sub-zones — collenchymatous hypodermis, rounded thin-walled cortical parenchyma with intercellular spaces, and an endodermis rich in starch grains (starch sheath); pericycle drawn as semi-lunar patches of sclerenchyma above the phloem; medullary rays of radially placed parenchyma between the bundles.
    The key point to draw: a large number of vascular bundles arranged in a ring — this ring arrangement is the characteristic of a dicot stem. Each bundle is conjoint, open (cambium between xylem and phloem) with endarch protoxylem. Show a large parenchymatous pith in the centre.
    Monocot stem (Figure $\displaystyle 6.4$ b): epidermis, then a sclerenchymatous hypodermis; a large number of vascular bundles scattered through a large, conspicuous parenchymatous ground tissue (no cortex–pith separation to draw).
    Each bundle is conjoint and closed (no cambium) and is enclosed in a sclerenchymatous bundle sheath. Draw the peripheral bundles smaller than the centrally placed ones, omit phloem parenchyma (it is absent), and show a water-containing cavity within each bundle.
    Labels for the dicot stem only: epidermis, hypodermis, cortex, endodermis (starch sheath), pericycle, medullary ray, cambium, protoxylem, metaxylem, phloem, pith.
    Labels for the monocot stem only: epidermis, sclerenchymatous hypodermis, ground tissue, bundle sheath, protoxylem, metaxylem, phloem, water cavity. Do not label an endodermis, pericycle, medullary ray or pith here — the monocot stem has undifferentiated ground tissue in place of cortex, endodermis and pith.

  2. Exercise 6.2

    Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons.

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    Look first at the arrangement of the vascular bundles: if they are scattered through the section it is a monocot stem; if they lie in a ring it is a dicot stem. The 'ring' arrangement is the characteristic of a dicot stem.
    Confirm with the other features visible in the same section.
    Reasons — it is a monocot stem if:
    The hypodermis is sclerenchymatous.
    The bundles are conjoint and closed — no cambium between xylem and phloem, so no secondary tissues are formed.
    Each bundle is surrounded by a sclerenchymatous bundle sheath, and water-containing cavities are present within the bundles.
    Phloem parenchyma is absent, and the peripheral bundles are smaller than the centrally located ones.
    The ground tissue is one large, conspicuous parenchymatous mass — cortex, endodermis, pericycle and pith are not marked off separately.
    Reasons — it is a dicot stem if:
    The hypodermis is collenchymatous, giving mechanical strength to the young stem.
    The bundles are conjoint and open — a cambium lies between xylem and phloem — and the protoxylem is endarch.
    The cortex is clearly zoned: hypodermis, thin-walled cortical parenchyma with intercellular spaces, and a starch-rich endodermis called the starch sheath.
    A pericycle is present above the phloem as semi-lunar patches of sclerenchyma, and medullary rays of parenchyma run between the bundles.
    A large parenchymatous pith occupies the centre.

  3. Exercise 6.3

    The transverse section of a plant material shows the following anatomical features -
    (a)
    the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths.
    (b)
    phloem parenchyma is absent. What will you identify it as?

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    NCERT publishes no answers for this textbook, so there is nothing in the book to check this working against. It has also not yet been read through by hand.

    The material is a monocotyledonous stem (T.S. of a monocot stem).
    Reasons
    (a) Vascular bundles that are conjoint, scattered through the ground tissue and each enclosed in a sclerenchymatous bundle sheath are found only in the monocot stem; in a dicot stem the bundles are arranged in a ring.
    (b) Absence of phloem parenchyma is a stated feature of the monocot stem.
    Supporting features you should also find: a sclerenchymatous hypodermis, bundles that are closed (no cambium, hence no secondary growth), water-containing cavities within the bundles, peripheral bundles smaller than the central ones, and a large, conspicuous parenchymatous ground tissue.

  4. Exercise 6.4

    What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.

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    Stomatal apparatus = the stomatal aperture (pore), the two guard cells and the surrounding subsidiary cells taken together.
    Structure of a stoma
    Stomata are structures present in the epidermis of leaves; they regulate transpiration and gaseous exchange.
    Each stoma is composed of two bean-shaped guard cells enclosing the stomatal pore. In grasses the guard cells are dumb-bell shaped.
    The outer walls of the guard cells (away from the pore) are thin, while the inner walls (towards the pore) are highly thickened. This unequal thickening is what makes the pore open and close.
    The guard cells possess chloroplasts and regulate the opening and closing of the stomata.
    A few epidermal cells near the guard cells become specialised in shape and size; these are the subsidiary cells.
    The labelled diagram to draw
    Draw a surface view of a small patch of epidermis. Show ordinary epidermal cells as irregular, wavy-walled cells filling the background.
    In the middle, place two curved, bean-shaped guard cells facing each other, their concave sides together, enclosing an elliptical stomatal pore between them. Draw the wall bordering the pore thick and the outer wall thin, and dot several chloroplasts inside each guard cell.
    Around the pair of guard cells, draw two or more distinctly shaped subsidiary cells.
    For the grass type, draw the same arrangement but with each guard cell dumb-bell shaped — narrow in the middle, swollen at both ends — with the pore as a narrow slit between the two narrow middle portions.
    Labels: epidermal cells, subsidiary cells, guard cells, stomatal pore, chloroplast.
    NCERT_Solution_Class11_Biology_Ch6_Q6-4

  5. Exercise 6.5

    Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.

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    NCERT publishes no answers for this textbook, so there is nothing in the book to check this working against. It has also not yet been read through by hand.

    The three basic tissue systems are the epidermal tissue system, the ground (fundamental) tissue system and the vascular (conducting) tissue system. They are recognised on the basis of the structure and location of the tissues in the plant body.
    1. Epidermal tissue system — the outermost covering of the whole plant body:
    Epidermal cells — elongated, compactly arranged, usually a single continuous layer; parenchymatous, with a large vacuole; often covered outside by a waxy cuticle (absent in roots).
    Stomata — guard cells and subsidiary cells.
    Epidermal appendages — root hairs (unicellular elongations of root epidermal cells) and trichomes (usually multicellular hairs of the shoot).
    2. Ground tissue system — all tissues except epidermis and vascular bundles:
    The simple tissues parenchyma, collenchyma and sclerenchyma.
    Parenchymatous cells occur in the cortex, pericycle, pith and medullary rays of primary stems and roots.
    In leaves the ground tissue is the thin-walled, chloroplast-containing mesophyll.
    3. Vascular tissue system — made of complex tissues:
    Xylem and phloem, which together constitute the vascular bundles.
    The bundles may be radial (xylem and phloem on different radii, as in roots) or conjoint (both on the same radius, as in stems and leaves), and conjoint bundles are open when cambium is present (dicots) or closed when it is absent (monocots).

  6. Exercise 6.6

    How is the study of plant anatomy useful to us?

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    The study of plant anatomy tells us how a plant is built and organised on the inside, and that internal structure explains how the plant works.
    It shows that a plant is organised in levels — cells are the basic unit, cells are organised into tissues, and tissues into organs.
    It reveals similarities and differences that the external morphology does not show, just as external form shows similarities and variations between organisms.
    It shows that different organs of the same plant differ internally — root, stem and leaf each have their own tissue organisation.
    It lets us distinguish monocots from dicots, which are anatomically different in the type, number and location of their vascular bundles even within the angiosperms.
    It shows how internal structure is adapted to diverse environments — for example the bulliform cells of grass leaves, which curl the leaf inwards under water stress to minimise water loss.
    It explains function from position: a tissue's structure and function depend on where it lies in the plant body, so anatomy accounts for the conduction of water and minerals by xylem, the translocation of food by phloem, storage, and mechanical support by collenchyma and sclerenchyma.

  7. Exercise 6.7

    Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.

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    A vertical section of a dorsiventral (dicotyledonous) leaf through the lamina shows three main parts — epidermis, mesophyll and vascular system.
    1. Epidermis
    Covers both the upper surface (adaxial epidermis) and the lower surface (abaxial epidermis), and has a conspicuous cuticle.
    The abaxial epidermis generally bears more stomata than the adaxial epidermis; the adaxial may even lack stomata altogether.
    2. Mesophyll
    The tissue lying between the upper and the lower epidermis. It is made of parenchyma, possesses chloroplasts and carries out photosynthesis.
    It is differentiated into two types of cells.
    Palisade parenchyma — placed adaxially, made of elongated cells arranged vertically and parallel to each other.
    Spongy parenchyma — oval or round, loosely arranged cells lying below the palisade cells and extending to the lower epidermis, with numerous large spaces and air cavities between them.
    3. Vascular system
    Vascular bundles are seen in the veins and the midrib; the size of a bundle depends on the size of the vein, and the veins vary in thickness because dicot leaves have reticulate venation.
    Each bundle is surrounded by a layer of thick-walled bundle sheath cells.
    The bundles are conjoint, with the xylem towards the upper (adaxial) side and the phloem towards the lower (abaxial) side.
    The labelled diagram to draw
    Draw a rectangular vertical strip of the lamina. Along the top edge, a single row of squarish upper (adaxial) epidermis cells capped by a thin dark line for the cuticle; along the bottom edge, the same for the lower (abaxial) epidermis, and place a stoma (two guard cells enclosing a pore, with an air chamber above it) in the lower epidermis.
    Immediately below the upper epidermis, draw one or two rows of tall, narrow, closely packed cells standing vertically side by side — the palisade parenchyma — dotted with chloroplasts.
    Below them, fill the rest of the space with rounded, loosely packed cells separated by large air spaces — the spongy parenchyma — reaching down to the lower epidermis.
    Somewhere in the middle of the mesophyll, draw one vascular bundle cut across: a ring of thick-walled bundle sheath cells enclosing xylem on the upper side and phloem on the lower side.
    Labels: cuticle, upper (adaxial) epidermis, palisade parenchyma, spongy parenchyma, air space/cavity, bundle sheath, xylem, phloem, lower (abaxial) epidermis, stoma, guard cell.
    NCERT_Solution_Class11_Biology_Ch6_Q6-7