Fundamentholfundamenthol

Anatomy of Dicotyledonous and Monocotyledonous Plants

BiologyAnatomy of Flowering PlantsFor NEET aspirants

The anatomy of dicotyledonous and monocotyledonous plants is studied in transverse sections of the mature zones of the root, stem and leaf. This page takes each section layer by layer: the dicot and monocot root, the dicot and monocot stem, and the dorsiventral and isobilateral leaf, as in the NCERT Class 11 chapter. The anatomy of dicotyledonous and monocotyledonous plants differs in the type, number and location of vascular bundles. NEET often asks layer sequences and identification of a section from its features.

On this page1Dicot root2Monocot root3Dicot stem4Monocot stem5Dorsiventral leaf6Isobilateral leaf7Identify a section8Exam essentials9Practice
Key Points at a Glance
  1. ★ Must learn Tissue organisation is studied in transverse sections of the mature zones of roots, stems and leaves.
  2. Dicot root (sunflower), outside to inside: epiblema, cortex, endodermis, pericycle, vascular bundles, pith.
  3. ★ Must learn Root endodermis: one layer of barrel-shaped cells, no intercellular spaces, suberin as casparian strips.
  4. Root pericycle: lateral roots and the vascular cambium arise here.
  5. ★ Must learn Stele = all tissues inside the endodermis: pericycle, vascular bundles and pith.
  6. Monocot root: usually more than six (polyarch) xylem bundles, a large pith and no secondary growth.
  7. ★ Must learn Dicot stem: collenchymatous hypodermis, starch sheath, and a ring of conjoint, open bundles with endarch protoxylem.
  8. Monocot stem: sclerenchymatous hypodermis; scattered conjoint, closed bundles; no phloem parenchyma.
  9. ★ Must learn Dorsiventral leaf: palisade and spongy mesophyll; more stomata on the abaxial (lower) epidermis.
  10. Isobilateral leaf: stomata on both surfaces; mesophyll not differentiated into palisade and spongy.
  11. Bulliform cells (grasses): when turgid, the leaf surface is exposed; when flaccid, the leaf curls inwards.

1. How Plant Organs Are Studied

  • To understand the tissue organisation of roots, stems and leaves, we study their transverse sections (T.S.).
  • The sections are cut through the mature zones of these organs.
  • ★ Exam imp Monocots and dicots show marked variation in internal structure.
  • They differ in the type, number and location of vascular bundles.
  • Secondary growth occurs in most dicotyledonous roots and stems.
Key idea
Compare dicots and monocots organ by organ, and always look first at the vascular bundles.

2. Dicotyledonous Root

  • The transverse section studied here is of the sunflower root.
  • The tissues, from the outside inwards, are:
  1. Epiblema: the outermost layer. Many of its cells protrude as unicellular root hairs.
  2. Cortex: several layers of thin-walled parenchyma cells with intercellular spaces.
  3. Endodermis: the innermost layer of the cortex; a single layer of barrel-shaped cells without intercellular spaces.
  4. Pericycle: a few layers of thick-walled parenchymatous cells next to the endodermis.
  5. Vascular bundles: usually two to four xylem patches and as many phloem patches.
  6. Pith: small or inconspicuous.

2.1 Key features of the dicot root

  • ★ Exam imp The tangential and radial walls of endodermal cells have a deposit of suberin in the form of casparian strips.
  • Suberin: a water-impermeable, waxy material.
  • ★ Exam imp Lateral roots and the vascular cambium (during secondary growth) are initiated in the pericycle.
  • Conjunctive tissue: the parenchymatous cells that lie between the xylem and the phloem.
  • Later, a cambium ring develops between the xylem and the phloem.

★ Very important Stele: all tissues on the inner side of the endodermis, that is, the pericycle, vascular bundles and pith.

T.S. of a dicot root (primary) Transverse section of a dicot root: root hairs on the epidermis, a wide cortex of rounded cells, a single-layered endodermis, the pericycle, and a central stele with four xylem arms, protoxylem towards the outside and metaxylem inside, alternating with phloem patches around a small pith Root hair Epidermis Cortex Pericycle Endodermis Protoxylem Metaxylem Pith Phloem
Figure 1: T.S. of a dicot root (primary). The stele (pericycle, vascular bundles and pith) lies inside the endodermis, and xylem and phloem lie on different radii.

Extra Depth: The figure labels protoxylem (the first-formed xylem, with narrow elements) and metaxylem (the later-formed xylem, with wider elements). In roots, the protoxylem lies towards the periphery and the metaxylem towards the centre. This is called exarch xylem.

Memory Trick

Layers of the dicot root, outside to inside: Every Cat Eats Plain Vanilla Pudding = Epiblema, Cortex, Endodermis, Pericycle, Vascular bundles, Pith.

Key idea
Dicot root: root hairs on the epiblema, casparian strips in the endodermis, lateral roots from the pericycle, 2 to 4 xylem patches and a small pith.

3. Monocotyledonous Root

  • The monocot root is similar to the dicot root in many respects.
  • It has an epidermis, cortex, endodermis, pericycle, vascular bundles and pith.
  • ★ Exam imp It usually has more than six xylem bundles; this condition is called polyarch.
  • The dicot root has fewer xylem bundles.
  • The pith is large and well developed.
  • Monocotyledonous roots do not undergo any secondary growth.
T.S. of a monocot root Transverse section of a monocot root: root hairs on the epidermis, a wide cortex, endodermis and pericycle, and a ring of many xylem bundles with protoxylem and metaxylem alternating with phloem around a large pith Pith Phloem Protoxylem Metaxylem Epidermis Endodermis Pericycle Root hair Cortex
Figure 2: T.S. of a monocot root. It has many xylem bundles (more than six) and a large, well-developed pith.
FeatureDicot rootMonocot root
Xylem bundlesUsually 2 to 4Usually more than 6 (polyarch)
PithSmall or inconspicuousLarge and well developed
Secondary growthOccurs in most dicot roots; a cambium ring develops later between xylem and phloemDoes not occur
Memory Trick

Poly means many: monocot roots are polyarch, with more than six xylem bundles. Dicot roots keep it small: 2 to 4 patches and a small pith.

Quick Recall: tap to check
Name the layer from which lateral roots arise.
The pericycle.
Which tissues together form the stele?
The pericycle, vascular bundles and pith, all inside the endodermis.
What are casparian strips made of?
Suberin, a water-impermeable, waxy material.
Which root has a large, well-developed pith?
The monocot root.
Key idea
Monocot root: the same layers, but polyarch xylem, a large pith and no secondary growth.

4. Dicotyledonous Stem

  • The transverse section is of a typical young dicotyledonous stem.
  • The tissues, from the outside inwards, are:
  1. Epidermis: the outermost protective layer, covered with a thin cuticle; it may bear trichomes and a few stomata.
  2. Hypodermis: a few layers of collenchyma just below the epidermis; it gives mechanical strength to the young stem.
  3. Cortical layers: rounded, thin-walled parenchyma cells with conspicuous intercellular spaces.
  4. Endodermis: the innermost layer of the cortex; its cells are rich in starch grains.
  5. Pericycle: on the inner side of the endodermis and above the phloem, as semi-lunar patches of sclerenchyma.
  6. Vascular bundles: a large number, arranged in a ring, with medullary rays between them.
  7. Pith: the central portion, made of many rounded parenchyma cells with large intercellular spaces.

4.1 Key features of the dicot stem

  • Cortex: the multiple layers of cells between the epidermis and the pericycle.
  • The cortex has three sub-zones: hypodermis, cortical layers and endodermis.
  • ★ Exam imp The endodermis of the stem is also called the starch sheath.
  • Medullary rays: a few layers of radially placed parenchyma cells between the vascular bundles.
  • ★ Exam imp The ring arrangement of vascular bundles is characteristic of the dicot stem.
  • Each vascular bundle is conjoint, open and has endarch protoxylem.
  • Endarch: the protoxylem lies towards the centre (pith) and the metaxylem towards the periphery.
T.S. of a dicot stem with one vascular bundle enlarged Transverse section of a young dicot stem with epidermal hairs, epidermis, collenchymatous hypodermis, cortical parenchyma, endodermis, a ring of vascular bundles capped by pericycle, medullary rays and a large central pith, with one bundle enlarged to show pericycle, phloem, cambium, metaxylem and protoxylem Epidermal hair Epidermis Hypodermis Parenchyma Endodermis Vascular bundle Pericycle Medullary rays Pith Pericycle Phloem Cambium Metaxylem Protoxylem
Figure 3: T.S. of a dicot stem. Conjoint, open vascular bundles form a ring around the pith, with medullary rays between them. The enlarged bundle is drawn with its outer side (pericycle and phloem) at the top.
Pericycle of the dicot root
  • A few layers of thick-walled parenchyma.
  • Gives rise to lateral roots and the vascular cambium.
Pericycle of the dicot stem
  • Semi-lunar patches of sclerenchyma.
  • Lies above the phloem, inside the endodermis.
Memory Trick

Dicot stem cortex: a firm coat, a soft middle and a starchy lining = collenchymatous hypodermis, parenchymatous cortical layers, starch sheath (endodermis).

Tips and Tricks Endarch: the protoxylem points inwards, to the pith. This is the word for dicot stem bundles. If a statement calls dicot stem bundles exarch, it is false.
Key idea
Dicot stem: collenchyma hypodermis, starch sheath, sclerenchymatous pericycle patches, and a ring of conjoint, open, endarch bundles.

5. Monocotyledonous Stem

  • ★ Exam imp The monocot stem has a sclerenchymatous hypodermis.
  • It has a large number of scattered vascular bundles.
  • Each bundle is surrounded by a sclerenchymatous bundle sheath.
  • The ground tissue is large, conspicuous and parenchymatous.
  • The vascular bundles are conjoint and closed.
  • Peripheral vascular bundles are generally smaller than the centrally located ones.
  • ★ Exam imp Phloem parenchyma is absent.
  • Water-containing cavities are present within the vascular bundles.
T.S. of a monocot stem with one vascular bundle enlarged Transverse section of a monocot stem with an epidermis, a sclerenchymatous hypodermis and many vascular bundles scattered in a large ground tissue, with one bundle enlarged to show its bundle sheath, phloem and xylem Epidermis Hypodermis Vascular bundles Ground tissue Bundle sheath Phloem Xylem
Figure 4: T.S. of a monocot stem. Many vascular bundles lie scattered in a large ground tissue. The enlarged bundle is drawn with its outer side (phloem) at the top.
FeatureDicot stemMonocot stem
HypodermisCollenchymatousSclerenchymatous
Arrangement of bundlesIn a ringScattered
Type of bundleConjoint, open, endarchConjoint, closed, each with a sclerenchymatous bundle sheath
Inner tissuesCortex (3 sub-zones), pericycle, medullary rays, pithLarge parenchymatous ground tissue
Memory Trick

Monocot stem = SCAB: Scattered bundles, Closed bundles, Absent phloem parenchyma, Bundle sheath of sclerenchyma. Add the water-containing cavities.

NEET Focus
  • A section with conjoint, scattered bundles, each with a sclerenchymatous sheath, and no phloem parenchyma is a monocot stem.
  • Trap: "The monocot stem has a collenchymatous hypodermis." Correct: sclerenchymatous; collenchyma is the dicot stem hypodermis.
  • Trap: "Peripheral bundles of the monocot stem are larger." Correct: they are generally smaller than the central ones.
Key idea
Monocot stem: sclerenchymatous hypodermis, scattered closed bundles with sheaths, no phloem parenchyma, and water-containing cavities.

6. Dorsiventral (Dicotyledonous) Leaf

  • A vertical section through the lamina shows three main parts: epidermis, mesophyll and vascular system.

6.1 Epidermis

  • The epidermis covers both the upper surface (adaxial epidermis) and the lower surface (abaxial epidermis).
  • Both surfaces have a conspicuous cuticle.
  • ★ Exam imp The abaxial epidermis generally bears more stomata than the adaxial epidermis.
  • The adaxial epidermis may even lack stomata.

6.2 Mesophyll

  • Mesophyll: the tissue between the upper and the lower epidermis.
  • It is made of parenchyma; it has chloroplasts and carries out photosynthesis.
  • It has two types of cells: palisade parenchyma and spongy parenchyma.
  • Palisade parenchyma: placed adaxially; elongated cells arranged vertically and parallel to each other.
  • Spongy parenchyma: oval or round, loosely arranged cells below the palisade, extending to the lower epidermis.
  • Spongy cells have numerous large spaces and air cavities between them.

6.3 Vascular system

  • The vascular bundles are seen in the veins and the midrib.
  • The size of the vascular bundles depends on the size of the veins.
  • The veins vary in thickness in the reticulate venation of dicot leaves.
  • Each vascular bundle is surrounded by a layer of thick-walled bundle sheath cells.
  • In Figure 5, find the xylem: it lies on the adaxial (upper) side of the bundle, with the phloem towards the abaxial side.
T.S. of a dorsiventral (dicot) leaf Transverse section of a dorsiventral leaf: adaxial epidermis on top, a layer of tall palisade mesophyll cells, loosely arranged spongy mesophyll with air cavities, a stoma with its sub-stomatal cavity in the abaxial epidermis, and a vascular bundle with xylem, phloem and a bundle sheath. Adaxialepidermis Palisademesophyll Bundle sheath Xylem Phloem Abaxialepidermis Spongymesophyll Air cavity Sub-stomatalcavity Stoma
Figure 5: T.S. of a dicot (dorsiventral) leaf. Palisade mesophyll lies below the adaxial epidermis, and spongy mesophyll with air cavities lies above the abaxial epidermis, which bears more stomata.
Palisade parenchyma
  • Adaxial, just below the upper epidermis.
  • Elongated cells.
  • Arranged vertically and parallel.
Spongy parenchyma
  • Below the palisade, up to the lower epidermis.
  • Oval or round cells.
  • Loose, with large spaces and air cavities.
Memory Trick

Palisade = posts; Spongy = spaces. Palisade cells stand upright like fence posts; spongy cells leave air spaces.

Memory Trick

Ad- is up, ab- is down. Adaxial = upper surface; abaxial = lower surface. In a dorsiventral leaf, most stomata are abaxial, and Figure 5 shows the xylem of a bundle on the adaxial side.

Key idea
Dorsiventral leaf: palisade above, spongy below, more stomata on the abaxial side, and bundles with a bundle sheath in the veins.

7. Isobilateral (Monocotyledonous) Leaf

  • Its anatomy is similar to the dorsiventral leaf in many ways.
  • It shows the following characteristic differences:
  • ★ Exam imp Stomata are present on both surfaces of the epidermis.
  • The mesophyll is not differentiated into palisade and spongy parenchyma.
T.S. of an isobilateral (monocot) leaf Transverse section of an isobilateral leaf: adaxial and abaxial epidermis, an even mesophyll of rounded cells, a stoma with its sub-stomatal cavity, and a vascular bundle with xylem and phloem. Adaxialepidermis Xylem Phloem Abaxialepidermis Mesophyll Sub-stomatalcavity Stoma
Figure 6: T.S. of a monocot (isobilateral) leaf. The mesophyll is not differentiated into palisade and spongy parenchyma.

7.1 Bulliform cells

  • In grasses, certain adaxial epidermal cells along the veins modify themselves.
  • They become large, empty, colourless cells called bulliform cells.
  • When bulliform cells absorb water and are turgid, the leaf surface is exposed.
  • When they are flaccid due to water stress, the leaves curl inwards.
  • Curling inwards minimises water loss.

★ Very important Bulliform cells: large, empty, colourless adaxial epidermal cells of grass leaves. Flaccid bulliform cells make the leaf curl inwards to reduce water loss.

7.2 Venation and vascular bundles

  • Monocot leaves have parallel venation.
  • So, in vertical sections, the vascular bundles are of near similar sizes, except in the main veins.
FeatureDorsiventral (dicot) leafIsobilateral (monocot) leaf
StomataMore on the abaxial surface; adaxial may lack themOn both surfaces
MesophyllPalisade and spongy parenchymaNot differentiated
VenationReticulate; veins vary in thicknessParallel
Size of bundlesDepends on the size of the veinsNear similar, except in main veins
Memory Trick

Bulliform cells bulge when turgid and buckle when flaccid. Turgid: the leaf opens out. Flaccid: the leaf curls inwards and saves water.

Quick Recall: tap to check
Which surface of a dorsiventral leaf bears more stomata?
The abaxial (lower) epidermis.
Name the two types of mesophyll cells in a dorsiventral leaf.
Palisade parenchyma and spongy parenchyma.
What happens to a grass leaf when its bulliform cells become flaccid?
The leaf curls inwards, which minimises water loss.
Why are the vascular bundles of a monocot leaf of near similar size?
Because of parallel venation; only the main veins have larger bundles.
Key idea
Isobilateral leaf: stomata on both surfaces, undifferentiated mesophyll, bulliform cells in grasses, and near-equal bundles.

8. Identifying a Section

  • Use these features to tell what a transverse section shows:
Features seen in the sectionIt is a
Radial bundles; 2 to 4 xylem patches; small or inconspicuous pithDicot root
Radial bundles; more than six xylem bundles (polyarch); large pithMonocot root
Ring of conjoint, open bundles; collenchymatous hypodermis; starch sheathDicot stem
Scattered conjoint, closed bundles with sclerenchymatous sheaths; no phloem parenchymaMonocot stem
Palisade and spongy mesophyll; more stomata on the lower surfaceDorsiventral (dicot) leaf
Undifferentiated mesophyll; stomata on both surfaces; bulliform cells (in grasses)Isobilateral (monocot) leaf
Tips and Tricks
  1. Look at the bundles first. Radial means a root; conjoint means a stem or a leaf.
  2. For a root, count the xylem bundles and look at the pith.
  3. For a stem, check whether the bundles form a ring or are scattered.
  4. For a leaf, check whether the mesophyll has palisade and spongy layers.
Key idea
Bundles decide the organ, and their number, arrangement and type decide dicot or monocot.

9. Exam Essentials

Pairs to Match

List IList II
EpiblemaUnicellular root hairs
Endodermis of the rootCasparian strips of suberin
Pericycle of the rootOrigin of lateral roots and vascular cambium
Conjunctive tissueParenchyma between xylem and phloem of the root
StelePericycle, vascular bundles and pith
Monocot rootPolyarch: more than six xylem bundles
Hypodermis of the dicot stemCollenchyma; mechanical strength
Endodermis of the dicot stemStarch sheath
Pericycle of the dicot stemSemi-lunar patches of sclerenchyma
Medullary raysRadially placed parenchyma between bundles
Hypodermis of the monocot stemSclerenchyma
Monocot stem bundlesSclerenchymatous sheath; water-containing cavities
Palisade parenchymaAdaxial; elongated, vertical, parallel cells
Spongy parenchymaLoose cells with large air cavities
Bulliform cellsInward curling of grass leaves under water stress
Exceptions
  • Monocot roots do not undergo secondary growth.
  • Root endodermal cells have no intercellular spaces, unlike the cortical cells outside them.
  • The pith is small in the dicot root but large in the monocot root.
  • Phloem parenchyma is absent in the monocot stem.
  • Peripheral bundles of the monocot stem are generally smaller than the central ones.
  • The adaxial epidermis of a dorsiventral leaf may lack stomata.
  • In an isobilateral leaf, the mesophyll is not differentiated into palisade and spongy parenchyma.
  • Monocot leaf bundles are of near similar size, except in the main veins.

Numbers to Remember

  • 2 to 4: xylem and phloem patches in a dicot root.
  • More than 6: xylem bundles in a monocot root (polyarch).
  • 1: the endodermis is a single layer of barrel-shaped cells.
  • 3: sub-zones of the dicot stem cortex (hypodermis, cortical layers, endodermis).
  • 3: main parts of a leaf section (epidermis, mesophyll, vascular system).
  • 2: types of mesophyll cells in a dorsiventral leaf (palisade, spongy).

Examples to Remember

ExampleWhat it shows
SunflowerT.S. of a dicot root (primary)
GrassesIsobilateral leaves with bulliform cells
Quick Recall: tap to check
Which layer of the dicot stem is called the starch sheath?
The endodermis, whose cells are rich in starch grains.
Name the tissue in the dicot stem that gives mechanical strength to the young stem.
The collenchymatous hypodermis.
Which tissue is absent from the vascular bundles of a monocot stem, and what is present within them?
Phloem parenchyma is absent; water-containing cavities are present within the bundles.
Key idea
Pair each layer with its organ: the endodermis and pericycle differ between root and stem, and the hypodermis differs between dicot and monocot stems.

10. Quick Revision

  • Organs are studied in transverse sections of their mature zones.
  • Dicot root (sunflower): epiblema, cortex, endodermis, pericycle, vascular bundles, small pith.
  • Root endodermis: barrel-shaped cells, no intercellular spaces, casparian strips of suberin.
  • Root pericycle: origin of lateral roots and vascular cambium.
  • Conjunctive tissue: parenchyma between xylem and phloem.
  • Stele: pericycle, vascular bundles and pith.
  • Monocot root: polyarch (more than six xylem bundles), large pith, no secondary growth.
  • Dicot stem cortex: collenchymatous hypodermis, parenchyma, starch sheath.
  • Dicot stem pericycle: semi-lunar patches of sclerenchyma above the phloem.
  • Dicot stem bundles: ring; conjoint, open, endarch; medullary rays between them.
  • Monocot stem: sclerenchymatous hypodermis; scattered, closed bundles with sheaths.
  • Monocot stem bundles: no phloem parenchyma; water-containing cavities.
  • Dorsiventral leaf: palisade (adaxial) and spongy mesophyll; more abaxial stomata.
  • Isobilateral leaf: stomata on both surfaces; undifferentiated mesophyll.
  • Bulliform cells: flaccid cells make grass leaves curl inwards.

11. Solved Examples

Solved Example 1
Arrange the tissues of a dicot root from the outside inwards.
A. Pericycle; B. Cortex; C. Epiblema; D. Endodermis; E. Pith
Choose the correct order.
(A) C, B, A, D, E
(B) C, B, D, A, E
(C) C, D, B, A, E
(D) B, C, D, A, E
Solution:

Answer: (B). The epiblema is outermost, then the cortex. The endodermis is the innermost cortical layer, and the pericycle lies next to it. The vascular bundles and the small pith lie at the centre.

Solved Example 2
Match List I with List II.
List I: A. Dicot root; B. Monocot root; C. Dicot stem; D. Monocot stem
List II: I. Scattered closed bundles with bundle sheaths; II. More than six xylem bundles and a large pith; III. Ring of conjoint, open bundles; IV. Two to four xylem patches and a small pith
Choose the correct answer.
(A) A-IV, B-II, C-III, D-I
(B) A-II, B-IV, C-III, D-I
(C) A-IV, B-II, C-I, D-III
(D) A-III, B-II, C-IV, D-I
Solution:

Answer: (A). Dicot roots have 2 to 4 xylem patches and a small pith; monocot roots are polyarch with a large pith. Dicot stems have a ring of open bundles; monocot stems have scattered closed bundles.

Solved Example 3
Read the statements about the monocot stem.
A. The hypodermis is collenchymatous.
B. The vascular bundles are conjoint and closed.
C. Phloem parenchyma is present.
D. Peripheral bundles are generally smaller than the central ones.
E. Water-containing cavities are present within the vascular bundles.
Choose the correct answer.
(A) A, B and D only
(B) B, C and E only
(C) B, D and E only
(D) C, D and E only
Solution:

Answer: (C). A is false: the hypodermis is sclerenchymatous. C is false: phloem parenchyma is absent. B, D and E are true.

Solved Example 4
The layer of a dicot stem whose cells are rich in starch grains is the
(A) hypodermis
(B) pericycle
(C) endodermis
(D) pith
Solution:

Answer: (C). The endodermis, the innermost layer of the cortex, is rich in starch grains and is called the starch sheath.

Solved Example 5
Which of the following is NOT a feature of an isobilateral leaf?
(A) Stomata on both surfaces of the epidermis
(B) Mesophyll differentiated into palisade and spongy parenchyma
(C) Bulliform cells in the adaxial epidermis of grasses
(D) Vascular bundles of near similar sizes, except in main veins
Solution:

Answer: (B). In an isobilateral leaf, the mesophyll is not differentiated. Palisade and spongy parenchyma are features of the dorsiventral leaf.

Solved Example 6
Statement I: When bulliform cells are flaccid due to water stress, grass leaves curl inwards.
Statement II: Inward curling of the leaves minimises water loss.
Choose the correct answer.
(A) Both Statement I and Statement II are correct
(B) Both Statement I and Statement II are incorrect
(C) Statement I is correct but Statement II is incorrect
(D) Statement I is incorrect but Statement II is correct
Solution:

Answer: (A). Both are correct. Turgid bulliform cells keep the leaf surface exposed; flaccid ones make the leaf curl inwards, which reduces water loss.

12. Practice Questions

Practice Questions
  1. Draw illustrations to bring out the anatomical differences between (a) a monocot root and a dicot root, and (b) a monocot stem and a dicot stem.Answer: (a) Show 2 to 4 xylem patches and a small pith in the dicot root, and more than six xylem bundles with a large pith in the monocot root. (b) Show a collenchymatous hypodermis and a ring of conjoint, open bundles around a pith in the dicot stem; show a sclerenchymatous hypodermis and scattered bundles with bundle sheaths in a large ground tissue in the monocot stem. Use Figures 1 to 4 as a guide.
  2. You cut a transverse section of a young stem from your school garden. How would you decide whether it is a monocot stem or a dicot stem? Give reasons.Answer: Look at the vascular bundles. A ring of conjoint, open bundles with cambium, medullary rays and a collenchymatous hypodermis means a dicot stem. Many scattered, closed bundles with sclerenchymatous sheaths in a large ground tissue, with a sclerenchymatous hypodermis, means a monocot stem.
  3. A transverse section shows: (a) conjoint, scattered vascular bundles surrounded by sclerenchymatous bundle sheaths; (b) no phloem parenchyma. What will you identify it as?Answer: A monocot stem. Scattered conjoint bundles with sclerenchymatous sheaths and the absence of phloem parenchyma are its features.
  4. Describe the internal structure of a dorsiventral leaf with the help of a labelled diagram.Answer: It has an adaxial and an abaxial epidermis with a conspicuous cuticle; the abaxial side bears more stomata. The mesophyll has adaxial palisade parenchyma (elongated, vertical, parallel cells) and spongy parenchyma (loose, with air cavities). Vascular bundles in the veins and midrib are surrounded by a bundle sheath. Label as in Figure 5.
  5. Match List I with List II. List I: A. Casparian strips; B. Starch sheath; C. Bulliform cells; D. Conjunctive tissue. List II: I. Grass leaf epidermis; II. Root endodermis; III. Parenchyma between xylem and phloem; IV. Dicot stem endodermis.
    (1) A-II, B-IV, C-I, D-III
    (2) A-IV, B-II, C-I, D-III
    (3) A-II, B-IV, C-III, D-I
    (4) A-II, B-I, C-IV, D-IIIAnswer: (1). Casparian strips are in the root endodermis; the starch sheath is the dicot stem endodermis; bulliform cells are in grass leaves; conjunctive tissue lies between the xylem and phloem of the root.
  6. Arrange the layers of a young dicot stem from the outside inwards. A. Endodermis; B. Hypodermis; C. Pericycle; D. Epidermis; E. Cortical parenchyma.
    (1) D, B, E, A, C
    (2) D, E, B, A, C
    (3) D, B, A, E, C
    (4) B, D, E, C, AAnswer: (1). Epidermis, collenchymatous hypodermis, cortical parenchyma, endodermis (starch sheath), then the pericycle.
  7. Read the statements about roots. A. The dicot root usually has more than six xylem bundles. B. Lateral roots are initiated in the pericycle. C. The pith of the monocot root is large and well developed. D. Monocot roots undergo secondary growth. Choose the statements that are NOT correct.
    (1) A and B only
    (2) A and D only
    (3) B and C only
    (4) C and D onlyAnswer: (2). A is incorrect: the dicot root has 2 to 4 xylem patches; more than six is the monocot root. D is incorrect: monocot roots do not undergo secondary growth.

Common Mistakes to Avoid

Watch out
  • Writing that lateral roots arise from the endodermis. Correct: they are initiated in the pericycle.
  • Leaving the pericycle out of the stele. The stele includes the pericycle, vascular bundles and pith.
  • Writing that monocot roots have 2 to 4 xylem bundles. Correct: they are polyarch; the dicot root has 2 to 4.
  • Saying the pith is large in the dicot root. Correct: it is small; the monocot root has a large pith.
  • Calling the pericycle the starch sheath. Correct: the endodermis of the stem is the starch sheath.
  • Giving the monocot stem a collenchymatous hypodermis. Correct: it is sclerenchymatous.
  • Placing more stomata on the adaxial surface of a dorsiventral leaf. Correct: the abaxial surface has more.
  • Calling dicot stem bundles exarch. Correct: they are endarch, with the protoxylem towards the pith.

Frequently Asked Questions

What are the main differences between a dicot root and a monocot root?

A dicot root usually has two to four xylem and phloem patches and a small or inconspicuous pith, and a cambium ring develops later. A monocot root usually has more than six (polyarch) xylem bundles and a large, well-developed pith. Monocot roots do not undergo secondary growth.

What is the stele in a root?

The stele is made of all the tissues on the inner side of the endodermis. In a root, these are the pericycle, the vascular bundles and the pith. The parenchyma between the xylem and phloem, called conjunctive tissue, also lies within the stele.

What are casparian strips?

Casparian strips are deposits of suberin in the walls of root endodermal cells. Suberin is a water-impermeable, waxy material. The endodermis is a single layer of barrel-shaped cells without intercellular spaces, and the strips are laid on their tangential and radial walls.

Why is the endodermis of a dicot stem called the starch sheath?

The endodermis is the innermost layer of the cortex of the dicot stem. Its cells are rich in starch grains, so the layer is also called the starch sheath. The pericycle lies on its inner side, as semi-lunar patches of sclerenchyma above the phloem.

How can you tell a monocot stem from a dicot stem in a transverse section?

A dicot stem has a collenchymatous hypodermis and a ring of conjoint, open, endarch bundles with medullary rays and a pith. A monocot stem has a sclerenchymatous hypodermis and many scattered, closed bundles, each with a sclerenchymatous sheath, in a large ground tissue, with no phloem parenchyma.

What is the difference between a dorsiventral and an isobilateral leaf?

A dorsiventral (dicot) leaf has palisade and spongy mesophyll and more stomata on its abaxial surface. An isobilateral (monocot) leaf has stomata on both surfaces and a mesophyll that is not differentiated into palisade and spongy parenchyma. Its vascular bundles are of near similar size, except in the main veins.

What are bulliform cells and what do they do?

Bulliform cells are large, empty, colourless cells formed from certain adaxial epidermal cells along the veins of grass leaves. When they are turgid, the leaf surface is exposed. When they become flaccid under water stress, the leaf curls inwards and water loss is reduced.

Which parts of plant anatomy are most important for NEET?

NEET mainly asks the NCERT points on the layers of the dicot root and stem in order, the root endodermis and pericycle, polyarch monocot roots, the monocot stem's closed scattered bundles, and dorsiventral versus isobilateral leaves, including bulliform cells. Practise identifying sections from their features.

Previous year questions on Anatomy of Dicotyledonous and Monocotyledonous Plants

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