Anatomy of Flowering Plants
Explore the internal structure and organization of higher plants, understanding the differences between monocot and dicot plants at tissue and organ levels.
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Brief Introduction
Plant anatomy is the study of the internal structure and organization of plants. This chapter introduces you to the three main tissue systems in flowering plants - epidermal, ground, and vascular tissue systems - and compares the anatomical differences between monocotyledonous and dicotyledonous plants in their roots, stems, and leaves.
Learning Objectives
- Understand the three main tissue systems in plants
- Identify the components of epidermal, ground, and vascular tissues
- Compare monocot and dicot root anatomy
- Differentiate between monocot and dicot stem structure
- Analyze leaf anatomy differences between monocots and dicots
- Recognize adaptations in plant internal structures
Key Topics Covered
- Epidermal Tissue System
- Ground Tissue System
- Vascular Tissue System
- Dicotyledonous Root Anatomy
- Monocotyledonous Root Anatomy
- Dicotyledonous Stem Anatomy
- Monocotyledonous Stem Anatomy
- Dorsiventral (Dicot) Leaf Structure
- Isobilateral (Monocot) Leaf Structure
Interactive Chapter Index
The Tissue System
Explore the three fundamental tissue systems that make up plant anatomy and their specialized functions.
Epidermal Tissue System
Learn about the plant's protective outer layer and its specialized structures like stomata and trichomes.
Ground Tissue System
Understand the bulk of plant tissue responsible for photosynthesis, storage, and support.
Vascular Tissue System
Discover the plant's transport system consisting of xylem and phloem in different arrangements.
Dicot Root Anatomy
Examine the internal structure of dicot roots and their characteristic features.
Monocot Root Anatomy
Study the unique anatomical features that distinguish monocot roots from dicot roots.
Dicot Stem Anatomy
Analyze the structural organization of dicot stems and their growth patterns.
Monocot Stem Anatomy
Investigate the scattered vascular bundle arrangement characteristic of monocot stems.
Dicot Leaf Structure
Explore the dorsiventral organization of dicot leaves with differentiated mesophyll.
Monocot Leaf Structure
Understand the isobilateral structure of monocot leaves and specialized bulliform cells.
Full Chapter Notes
6.1 The Tissue System
Plants have cells as the basic unit, which are organized into tissues and then into organs. Different organs in a plant show differences in their internal structure. Within angiosperms, the monocots and dicots are anatomically different. Internal structures also show adaptations to diverse environments.
Three Types of Tissue Systems:
- Epidermal tissue system: Forms the outermost covering of the plant body
- Ground or fundamental tissue system: All tissues except epidermis and vascular bundles
- Vascular or conducting tissue system: Consists of complex tissues (phloem and xylem)
6.1.1 Epidermal Tissue System
The epidermal tissue system forms the outer-most covering of the whole plant body and comprises epidermal cells, stomata and the epidermal appendages - the trichomes and hairs.
Key Features:
- Epidermis: Outermost single layer of elongated, compactly arranged cells
- Cuticle: Waxy thick layer on the outside of epidermis (absent in roots)
- Stomata: Structures for transpiration and gaseous exchange, composed of guard cells
- Root hairs: Unicellular elongations of epidermal cells for absorption
- Trichomes: Multicellular hairs on stems that help prevent water loss
6.1.2 The Ground Tissue System
All tissues except epidermis and vascular bundles constitute the ground tissue. It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma.
Distribution in Plant Organs:
- Stems and roots: Present in cortex, pericycle, pith and medullary rays
- Leaves: Called mesophyll, consists of thin-walled chloroplast-containing cells
- Functions: Photosynthesis, storage, and mechanical support
6.1.3 The Vascular Tissue System
The vascular system consists of complex tissues, the phloem and the xylem. The xylem and phloem together constitute vascular bundles.
Types of Vascular Bundles:
- Open vascular bundles: Have cambium between phloem and xylem (dicot stems), can form secondary tissues
- Closed vascular bundles: No cambium (monocots), cannot form secondary tissues
- Radial arrangement: Xylem and phloem in alternate manner along different radii (roots)
- Conjoint arrangement: Xylem and phloem situated along same radius (stems and leaves)
6.2.1 Dicotyledonous Root
The transverse section of a typical dicot root (sunflower) shows distinct tissue organization from outside to inside.
Internal Structure:
- Epiblema (Epidermis): Outermost layer with root hairs
- Cortex: Several layers of thin-walled parenchyma cells with intercellular spaces
- Endodermis: Innermost cortical layer with Casparian strips (suberin deposits)
- Pericycle: Thick-walled parenchyma cells where lateral roots originate
- Vascular bundles: Radial arrangement with 2-4 xylem and phloem patches
- Pith: Small or inconspicuous in dicots
6.2.2 Monocotyledonous Root
The anatomy of the monocot root is similar to the dicot root in many respects but with some key differences.
Comparison with Dicot Root:
- Same basic tissues: epidermis, cortex, endodermis, pericycle
- More than six xylem bundles (polyarch) compared to 2-4 in dicots
- Pith is large and well developed (vs small/inconspicuous in dicots)
- No secondary growth occurs in monocot roots
| Feature | Dicot Root | Monocot Root |
|---|---|---|
| Xylem bundles | 2-4 (diarch to tetrarch) | More than 6 (polyarch) |
| Pith | Small or inconspicuous | Large and well developed |
| Secondary growth | Possible | Not possible |
| Pericycle | Gives rise to lateral roots | Same function |
6.2.3 Dicotyledonous Stem
The transverse section of a typical young dicotyledonous stem shows specific organization of tissues.
Tissue Organization:
- Epidermis: Outermost protective layer with cuticle, may bear trichomes and stomata
- Cortex:
- Hypodermis: Collenchymatous cells for mechanical strength
- Middle layers: Rounded parenchyma cells with intercellular spaces
- Endodermis (Starch sheath): Cells rich in starch grains
- Pericycle: Semi-lunar patches of sclerenchyma
- Vascular bundles: Arranged in a ring, conjoint, open, with endarch protoxylem
- Pith: Central portion with large, rounded parenchyma cells
6.2.4 Monocotyledonous Stem
The monocot stem differs from the dicot stem in several key anatomical features.
Distinctive Features:
- Hypodermis: Sclerenchymatous (vs collenchymatous in dicots)
- Vascular bundles: Scattered (not in a ring), each surrounded by sclerenchymatous bundle sheath
- Ground tissue: Large, conspicuous parenchyma between vascular bundles
- Vascular bundle structure: Conjoint and closed (no cambium)
- Phloem parenchyma: Absent in monocots
- Water cavities: Present within vascular bundles
6.2.5 Dorsiventral (Dicotyledonous) Leaf
The vertical section of a dorsiventral leaf through the lamina shows three main parts: epidermis, mesophyll and vascular system.
Structure and Organization:
- Epidermis:
- Adaxial (upper) epidermis with thick cuticle, fewer stomata
- Abaxial (lower) epidermis with more stomata
- Mesophyll: Differentiated into:
- Palisade parenchyma: Adaxially placed, elongated cells arranged vertically
- Spongy parenchyma: Below palisade, loosely arranged with air spaces
- Vascular system:
- Vascular bundles in veins and midrib
- Size varies with vein size (reticulate venation)
- Surrounded by bundle sheath cells
6.2.6 Isobilateral (Monocotyledonous) Leaf
The anatomy of isobilateral leaf is similar to the dorsiventral leaf in many ways but with characteristic differences.
Key Differences from Dicot Leaves:
- Stomata: Present on both surfaces (vs mainly abaxial in dicots)
- Mesophyll: Not differentiated into palisade and spongy parenchyma
- Bulliform cells: Large, empty, colorless cells in adaxial epidermis (in grasses)
- Venation: Parallel venation reflected in similar sizes of vascular bundles
Chapter Summary
Key Takeaways:
- Plants have three tissue systems: epidermal, ground, and vascular
- Epidermal system includes epidermis, stomata, and appendages
- Ground tissue forms the bulk of plant body with various functions
- Vascular bundles can be open (dicots) or closed (monocots)
- Dicot and monocot roots differ in xylem pattern and pith size
- Dicot stems have vascular bundles in a ring; monocots have scattered bundles
- Dicot leaves are dorsiventral; monocot leaves are isobilateral
- Secondary growth occurs in dicots but not monocots
NCERT Solutions
Question 1: Draw illustrations to bring out the anatomical difference between
(a) Monocot root and Dicot root
Key differences to illustrate:
- Number of xylem bundles: Dicot (2-4), Monocot (more than 6)
- Pith size: Small/inconspicuous in dicot, large in monocot
- Vascular bundle arrangement: Similar radial pattern but different in number
(b) Monocot stem and Dicot stem
Key differences to illustrate:
- Vascular bundle arrangement: Ring in dicot, scattered in monocot
- Hypodermis: Collenchyma in dicot, sclerenchyma in monocot
- Bundle sheath: Present around each bundle in monocot
- Cambium: Present in dicot (open bundles), absent in monocot
Question 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.
To determine whether the stem is monocot or dicot:
- Examine vascular bundle arrangement:
- If in a ring → Dicot
- If scattered → Monocot
- Check hypodermis:
- Collenchymatous → Dicot
- Sclerenchymatous → Monocot
- Look for cambium:
- Present between xylem and phloem → Dicot (open bundle)
- Absent → Monocot (closed bundle)
- Check pith:
- Well-defined → Dicot
- Not clearly demarcated in monocots
Question 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?
The plant material is a monocot stem because:
- Vascular bundles are conjoint and scattered - characteristic of monocot stems (dicots have bundles arranged in a ring)
- Sclerenchymatous bundle sheaths surround each vascular bundle - typical of monocots
- Absence of phloem parenchyma - monocots lack phloem parenchyma which is present in dicots
- These features match the anatomical structure of monocotyledonous stems
Question 4: What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.
Stomatal Apparatus: The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.
Structure of Stomata:
- Guard cells:
- Two bean-shaped cells (dumb-bell shaped in grasses)
- Enclose the stomatal pore
- Outer walls thin, inner walls (towards pore) thickened
- Contain chloroplasts
- Regulate opening/closing of stomata
- Stomatal pore: Opening between guard cells for gas exchange
- Subsidiary cells: Specialized epidermal cells surrounding guard cells
Question 5: Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
The three basic tissue systems in flowering plants are:
- Epidermal Tissue System:
- Epidermal cells
- Stomata
- Trichomes and root hairs
- Ground Tissue System:
- Parenchyma
- Collenchyma
- Sclerenchyma
- Vascular Tissue System:
- Xylem
- Phloem
- Cambium (in dicots)
Question 6: How is the study of plant anatomy useful to us?
The study of plant anatomy is useful because:
- Helps in understanding the structural organization of plants
- Reveals adaptations to different environmental conditions
- Provides basis for plant classification and identification
- Helps distinguish between monocots and dicots
- Important for agriculture (crop improvement, grafting techniques)
- Useful in forestry and horticulture
- Helps understand physiological processes (water transport, photosynthesis)
- Provides insights into evolutionary relationships
- Essential for pharmacognosy (study of medicinal plants)
- Important in wood technology and paper industry
Question 7: Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.
The internal structure of a dorsiventral (dicot) leaf shows three main parts:
- Epidermis:
- Upper (adaxial) epidermis: Single layer with thick cuticle, fewer stomata
- Lower (abaxial) epidermis: More stomata, may have trichomes
- Cuticle present on both surfaces to prevent water loss
- Mesophyll: Differentiated into two regions:
- Palisade parenchyma:
- Adaxially placed
- Elongated cells arranged vertically
- Tightly packed with many chloroplasts
- Main site of photosynthesis
- Spongy parenchyma:
- Below palisade layer
- Irregular, loosely arranged cells
- Numerous air spaces for gas exchange
- Fewer chloroplasts than palisade cells
- Palisade parenchyma:
- Vascular System:
- Vascular bundles in veins and midrib
- Size varies with vein size (reticulate venation)
- Xylem towards upper side, phloem towards lower side
- Surrounded by bundle sheath cells (may be parenchymatous or sclerenchymatous)
Practice Questions
Correct Answer: d) Pericycle
Explanation: The pericycle is part of the vascular tissue system located inside the endodermis, not the epidermal system. The epidermal tissue system includes epidermis, stomata, trichomes, and root hairs.
Correct Answer: b) Scattered
Explanation: Monocot stems have vascular bundles scattered throughout the ground tissue, unlike dicot stems where they are arranged in a ring.
Correct Answer: b) Endodermis
Explanation: Casparian strips are bands of suberin found in the radial and transverse walls of endodermal cells, forming a water-impermeable barrier.
Answer:
Bulliform cells are large, empty, colorless cells found in the adaxial epidermis of grass leaves (monocots).
Functions:
- When turgid, they help expose the leaf surface to sunlight
- When flaccid (during water stress), they cause the leaf to curl inwards, reducing surface area and minimizing water loss through transpiration
- Play a role in leaf rolling/unrolling in response to water availability
Answer:
| Feature | Open Vascular Bundle | Closed Vascular Bundle |
|---|---|---|
| Cambium | Present between xylem and phloem | Absent |
| Secondary growth | Possible | Not possible |
| Occurrence | Dicot stems | Monocot stems and all leaves |
| Phloem parenchyma | Present | Absent in monocots |
Answer:
Internal structure of dicot root:
- Epiblema (Epidermis): Outermost single layer with root hairs for absorption
- Cortex: Multiple layers of thin-walled parenchyma cells with intercellular spaces
- Endodermis: Innermost cortical layer with Casparian strips (suberin deposits) on radial and tangential walls
- Pericycle: Single layer of thick-walled cells inside endodermis; gives rise to lateral roots
- Vascular bundles: Radial arrangement with 2-4 xylem and phloem patches
- Conjunctive tissue: Parenchyma between xylem and phloem
- Pith: Small or inconspicuous in dicots
Differences from monocot root:
| Feature | Dicot Root | Monocot Root |
|---|---|---|
| Xylem bundles | 2-4 (diarch to tetrarch) | More than 6 (polyarch) |
| Pith | Small or inconspicuous | Large and well developed |
| Secondary growth | Possible | Not possible |
Answer:
Types of vascular bundles:
- Based on presence of cambium:
- Open: Have cambium between xylem and phloem (dicot stems), can undergo secondary growth
- Closed: No cambium (monocots, leaves), no secondary growth
- Based on arrangement of xylem and phloem:
- Radial: Xylem and phloem in alternate radii (roots)
- Conjoint: Xylem and phloem on same radius (stems and leaves)
- Collateral: Phloem on outer side, xylem on inner side (most common)
- Bicollateral: Phloem on both sides of xylem (some cucurbits)
Arrangement in different organs:
- Roots: Radial arrangement (xylem and phloem in alternate radii)
- Dicot stems: Conjoint, collateral, open bundles arranged in a ring
- Monocot stems: Conjoint, collateral, closed bundles scattered in ground tissue
- Leaves: Conjoint, collateral, closed bundles in veins (size varies with vein size)
Special features:
- In stems, protoxylem is endarch (towards center)
- In roots, protoxylem is exarch (towards periphery)
- Monocot vascular bundles have sclerenchymatous bundle sheaths
Interactive Flashcards
What are the three tissue systems in plants?
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The three tissue systems are:
- Epidermal tissue system: Forms the outer protective layer
- Ground tissue system: Makes up the bulk of plant body (parenchyma, collenchyma, sclerenchyma)
- Vascular tissue system: Conducting tissues (xylem and phloem)
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