class 11 notes

Class 11 Biology Notes Chapter 6 (Chapter 6) – Examplar Problems (English) Book

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Philoid

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Examplar Problems (English)
Detailed Notes with MCQs of Chapter 6, 'Anatomy of Flowering Plants'. This is a crucial chapter for understanding the internal structure of plants, and questions frequently appear in various government exams. We'll break down the key concepts based on the NCERT Exemplar perspective.

Chapter 6: Anatomy of Flowering Plants - Detailed Notes

1. Introduction:

  • Anatomy deals with the study of the internal structure of organisms.
  • Plant anatomy helps understand structural adaptations of plants to diverse environments.

2. The Tissues:
A group of cells having a common origin and usually performing a common function. Plant tissues are broadly classified into Meristematic and Permanent tissues.

  • A. Meristematic Tissues:

    • Composed of actively dividing cells.
    • Cells are typically isodiametric, thin-walled (cellulose), with dense cytoplasm and prominent nuclei; vacuoles are small or absent.
    • Types based on Origin:
      • Promeristem: Earliest embryonic meristematic cells.
      • Primary Meristem: Derived from promeristem; forms primary plant body (e.g., Apical meristem, Intercalary meristem).
      • Secondary Meristem: Develops later from permanent tissues (dedifferentiation); responsible for secondary growth (e.g., Vascular Cambium, Cork Cambium/Phellogen).
    • Types based on Location:
      • Apical Meristem: Located at the tips of roots (Root Apical Meristem - RAM) and shoots (Shoot Apical Meristem - SAM). Responsible for primary growth (increase in length). RAM is sub-terminal (protected by root cap), SAM is terminal.
      • Intercalary Meristem: Located between mature tissues, typically at the base of internodes or leaf bases in grasses. Helps in regeneration of parts removed by grazing herbivores and contributes to length increase. It's a part of primary meristem separated from the apex.
      • Lateral Meristem: Located parallel to the longitudinal axis; responsible for secondary growth (increase in girth). Examples: Fascicular vascular cambium, Interfascicular cambium, Cork cambium. They are cylindrical meristems.

  • B. Permanent Tissues:

    • Composed of cells that have lost the ability to divide (temporarily or permanently) and have become structurally and functionally specialized (differentiation).
    • Types:

      • i. Simple Permanent Tissues: Composed of only one type of cell.

        • Parenchyma:
          • Most common, fundamental tissue.
          • Cells are generally isodiametric, thin-walled (cellulose), living, with intercellular spaces (can be absent).
          • Functions: Photosynthesis (chlorenchyma), storage (food, water, waste products), secretion, buoyancy (aerenchyma in hydrophytes).
        • Collenchyma:
          • Occurs in layers below the epidermis in dicot stems and petioles; absent in monocots and roots.
          • Cells are living, often elongated, with uneven thickening (cellulose, hemicellulose, pectin) primarily at the corners.
          • Provides mechanical support to growing parts like young stems and petioles; allows bending without breaking.
        • Sclerenchyma:
          • Composed of dead cells with thick, lignified secondary walls. Lumen is narrow or obliterated.
          • Provides mechanical strength and rigidity.
          • Types:
            • Fibres: Elongated cells with pointed ends, occur in groups. Found in pericycle, secondary xylem/phloem, hypodermis (monocot stem).
            • Sclereids (Stone cells): Variable shapes (spherical, oval, cylindrical, branched), highly thickened walls with narrow lumen and pits. Found in fruit walls (nuts), pulp of fruits (guava, pear), seed coats (legumes), leaves (tea), grit cells.

      • ii. Complex Permanent Tissues: Composed of more than one type of cell, working together as a unit. Involved in transport.

        • Xylem:
          • Conducts water and minerals from roots to stem and leaves (unidirectional). Provides mechanical strength.
          • Components:
            • Tracheids: Elongated, tube-like dead cells with lignified walls and tapering ends. Main water-conducting elements in pteridophytes and gymnosperms. Water moves through pits.
            • Vessels (Trachea): Long, cylindrical, tube-like structures made of vessel members connected end-to-end through perforations in their common walls. Dead cells with lignified walls and wide lumen. Characteristic feature of Angiosperms (absent in most gymnosperms and pteridophytes). More efficient water conduction than tracheids.
            • Xylem Parenchyma: Living cells with thin cellulosic walls. Store food (starch, fat) and tannins. Involved in radial conduction of water.
            • Xylem Fibres: Sclerenchymatous fibres associated with xylem. Dead cells with thick lignified walls and obliterated lumen. Provide mechanical support. Can be septate or aseptate.
          • Primary Xylem: Formed during primary growth from procambium.
            • Protoxylem: First formed primary xylem elements (narrower vessels/tracheids).
            • Metaxylem: Later formed primary xylem elements (wider vessels/tracheids).
          • Arrangement: Endarch (Protoxylem towards center, Metaxylem towards periphery - typical of stems). Exarch (Protoxylem towards periphery, Metaxylem towards center - typical of roots).
        • Phloem (Bast):
          • Conducts food materials (sucrose) usually from leaves to other parts (bidirectional).
          • Components (in Angiosperms):
            • Sieve Tube Elements: Long, tube-like structures arranged longitudinally. Associated with companion cells. End walls are perforated (sieve plates). Living cells, but lack nucleus, ribosomes, vacuole at maturity. Function controlled by companion cell nucleus.
            • Companion Cells: Specialized parenchymatous cells closely associated with sieve tube elements (originate from the same mother cell). Dense cytoplasm, prominent nucleus. Maintain pressure gradient in sieve tubes. Connected to sieve tubes by pit fields. Found only in Angiosperms.
            • Phloem Parenchyma: Elongated, tapering cylindrical cells with dense cytoplasm and nucleus. Cellulosic walls, connected by plasmodesmata. Store food, resins, latex, mucilage. Absent in most monocots.
            • Phloem Fibres (Bast Fibres): Sclerenchymatous cells. Generally absent in primary phloem, found in secondary phloem. Elongated, unbranched, pointed ends, thick walls. Dead at maturity. Provide mechanical support. (e.g., Jute, Flax, Hemp fibres).
          • Protophloem: First formed primary phloem (narrow sieve tubes).
          • Metaphloem: Later formed primary phloem (bigger sieve tubes).
          • Note: Gymnosperms and Pteridophytes have Albuminous cells and Sieve cells instead of companion cells and sieve tube elements.

3. The Tissue System:
Tissues are organized into systems based on their structure and location.

  • A. Epidermal Tissue System:

    • Forms the outermost covering of the whole plant body.
    • Components:
      • Epidermis: Outermost layer, usually single-layered (multi-layered in Nerium, Ficus roots - velamen). Cells are parenchymatous, compactly arranged, forming a continuous layer. Outer walls often thicker and cutinized (covered by Cuticle - prevents water loss; absent in roots).
      • Stomata: Structures present in the epidermis of leaves (and young stems). Regulate transpiration and gaseous exchange. Each stoma has two bean-shaped Guard Cells enclosing a Stomatal Pore. Guard cells have chloroplasts; their inner walls (towards pore) are thick, outer walls are thin. In grasses, guard cells are dumbbell-shaped. Guard cells are surrounded by Subsidiary Cells. Stomatal pore + Guard cells + Subsidiary cells = Stomatal Apparatus.
      • Epidermal Appendages:
        • Root Hairs: Unicellular elongations of epidermal cells in roots. Absorb water and minerals.
        • Trichomes: Epidermal hairs on the stem (and leaves). Usually multicellular, branched or unbranched, soft or stiff. Can be secretory. Help in preventing water loss (transpiration), protection, dispersal (seeds/fruits).

  • B. Ground Tissue System:

    • All tissues except epidermis and vascular bundles.
    • Consists of simple tissues (parenchyma, collenchyma, sclerenchyma).
    • Components in Dicot Stem: Cortex (Hypodermis, General Cortex, Endodermis), Pericycle, Pith, Medullary rays.
    • Components in Dicot Root: Cortex, Endodermis, Pericycle, Pith (small/absent).
    • Components in Monocot Stem: Hypodermis, Undifferentiated Ground Tissue (vascular bundles scattered).
    • Components in Monocot Root: Cortex, Endodermis, Pericycle, Pith (large, well-developed).
    • In leaves, the ground tissue between upper and lower epidermis containing chloroplasts is called Mesophyll (Palisade parenchyma and Spongy parenchyma in dicots; undifferentiated in monocots).
    • Endodermis: Innermost layer of the cortex, typically single-layered, barrel-shaped cells, compactly arranged. Characterized by Casparian Strips (suberin deposition) on radial and tangential walls in roots, which block apoplast movement of water into vascular cylinder. Passage cells (thin-walled) may be present opposite protoxylem.

  • C. Vascular Tissue System:

    • Consists of complex tissues: Xylem and Phloem, which together form Vascular Bundles.
    • Types of Vascular Bundles:
      • Radial: Xylem and Phloem occur in different radii, alternating with each other (typical of roots).
      • Conjoint: Xylem and Phloem are situated at the same radius. Phloem located on the outer side of xylem (typical of stems and leaves).
        • Collateral: Phloem on the outer side only.
        • Bicollateral: Phloem on both outer and inner sides of xylem (e.g., Cucurbitaceae family).
      • Open: Cambium present between xylem and phloem. Capable of secondary growth (typical of dicot stems).
      • Closed: Cambium absent between xylem and phloem. No secondary growth (typical of monocot stems and leaves).

4. Anatomy of Dicotyledonous and Monocotyledonous Plants:

  • A. Dicotyledonous Root (e.g., Sunflower Root):

    • Epidermis (Epiblema/Rhizodermis): Outermost, unicellular root hairs. Cuticle absent.
    • Cortex: Multilayered parenchyma with intercellular spaces. Innermost layer is Endodermis with Casparian strips.
    • Stele (Vascular Cylinder): All tissues inside endodermis.
      • Pericycle: Few layers of thick-walled parenchymatous cells next to endodermis. Site of origin of lateral roots and vascular cambium/cork cambium during secondary growth.
      • Vascular Bundles: Radial. Xylem is exarch. Usually 2-6 (diarch to hexarch) xylem and phloem patches.
      • Pith: Small or inconspicuous, parenchymatous.
      • Conjunctivce Tissue: Parenchyma lying between xylem and phloem bundles.

  • B. Monocotyledonous Root (e.g., Maize Root):

    • Similar to dicot root in epidermis, cortex, endodermis, pericycle, radial vascular bundles, exarch xylem.
    • Differences from Dicot Root:
      • Usually more than 6 (polyarch) xylem bundles.
      • Pith is large and well-developed.
      • No secondary growth.

  • C. Dicotyledonous Stem (e.g., Sunflower Stem):

    • Epidermis: Outermost layer, cuticle present, may bear trichomes and stomata.
    • Cortex: Differentiated into:
      • Hypodermis: Few layers of collenchyma below epidermis (provides mechanical support).
      • General Cortex: Parenchymatous layers below hypodermis with intercellular spaces.
      • Endodermis (Starch Sheath): Innermost layer, rich in starch grains. Casparian strips generally absent.
    • Stele:
      • Pericycle: Present inside endodermis, above phloem as patches of sclerenchyma (bundle cap) and parenchyma.
      • Vascular Bundles: Conjoint, collateral, open. Arranged in a ring. Xylem is endarch.
      • Pith: Large, central, parenchymatous.
      • Medullary Rays: Radial strips of parenchyma between vascular bundles, connecting pith and cortex. Help in radial conduction.

  • D. Monocotyledonous Stem (e.g., Maize Stem):

    • Epidermis: Outermost, cuticularized.
    • Hypodermis: Sclerenchymatous (provides mechanical strength).
    • Ground Tissue: Large, parenchymatous. Not differentiated into cortex, endodermis, pericycle, pith.
    • Vascular Bundles: Numerous, scattered throughout the ground tissue. Conjoint, collateral, closed. Peripheral bundles are smaller and more numerous than central ones. Each bundle is surrounded by a sclerenchymatous Bundle Sheath. Xylem is endarch, often Y-shaped. Phloem parenchyma is absent. Water-containing cavities (lysigenous) often present in vascular bundles.
    • No secondary growth.

  • E. Dicotyledonous Leaf (Dorsiventral Leaf - e.g., Mango):

    • Epidermis: Upper (adaxial) and lower (abaxial) epidermis, covered with cuticle. Stomata generally more numerous on the lower epidermis (hypostomatic).
    • Mesophyll: Ground tissue between epidermises, differentiated into:
      • Palisade Parenchyma: Elongated cells arranged vertically and parallel, below adaxial epidermis. Rich in chloroplasts, main site of photosynthesis. Can be 1 or more layers.
      • Spongy Parenchyma: Oval or rounded, loosely arranged cells below palisade layer, extending to lower epidermis. Large intercellular spaces and air cavities. Facilitates gaseous exchange. Fewer chloroplasts than palisade.
    • Vascular System: Vascular bundles seen in veins and midrib. Size depends on vein size. Surrounded by a Bundle Sheath (parenchymatous). Vascular bundles are conjoint, collateral, closed. Xylem towards adaxial side, phloem towards abaxial side.

  • F. Monocotyledonous Leaf (Isobilateral Leaf - e.g., Grass/Maize):

    • Epidermis: Stomata present on both surfaces (amphistomatic), roughly equal in number. Cuticle present. Some adaxial epidermal cells along veins modify into large, empty, colourless Bulliform Cells. When turgid, they keep leaf surface exposed; when flaccid (water stress), they make leaves curl inwards to minimize water loss.
    • Mesophyll: Not differentiated into palisade and spongy parenchyma. Cells are somewhat isodiametric with chloroplasts and intercellular spaces.
    • Vascular System: Similar size bundles (except main veins) arranged in parallel venation. Conjoint, collateral, closed. Surrounded by bundle sheath (can be parenchymatous or sclerenchymatous, often conspicuous in C4 grasses like maize - Kranz anatomy). Xylem towards adaxial, phloem towards abaxial side.

5. Secondary Growth:
Increase in girth of dicot stems and roots due to the activity of lateral meristems (Vascular Cambium and Cork Cambium). Absent in monocots.

  • A. Vascular Cambium:

    • Meristematic layer responsible for cutting off vascular tissues (secondary xylem and phloem).
    • Formation in Dicot Stem: Develops from intrafascicular cambium (within vascular bundle) and interfascicular cambium (formed by dedifferentiation of medullary ray cells between bundles). These join to form a continuous Cambial Ring.
    • Activity: Cells divide periclinally. Cells cut off towards pith mature into secondary xylem; cells cut off towards periphery mature into secondary phloem. Cambium is generally more active on the inner side, producing more secondary xylem than secondary phloem. Primary xylem/phloem get crushed.
    • Cambial Cells: Fusiform initials (produce xylem/phloem elements) and Ray initials (produce vascular rays/medullary rays for radial conduction).
    • Spring Wood (Early Wood): Formed during spring (favourable conditions). Cambium is more active, produces wider vessels/tracheids. Lighter in colour, lower density.
    • Autumn Wood (Late Wood): Formed during winter/autumn (unfavourable conditions). Cambium less active, produces narrower vessels/tracheids, more fibres. Darker in colour, higher density.
    • Annual Ring: One ring of spring wood + one ring of autumn wood = represents one year's growth. Can be used to estimate tree age (Dendrochronology). Distinct in temperate regions.
    • Heartwood (Duramen): Central, dark brown, non-functional part of secondary xylem. Cells are dead, lignified, filled with tannins, resins, oils, gums etc. Makes it hard, durable, resistant to microbes. Provides mechanical support.
    • Sapwood (Alburnum): Peripheral, lighter coloured, functional part of secondary xylem. Involved in water and mineral conduction. Living cells (parenchyma) present.

  • B. Cork Cambium (Phellogen):

    • Another lateral meristem, usually develops in the cortex region (can also originate from pericycle or epidermis). Arises due to dedifferentiation.
    • Activity: Divides periclinally. Cuts off cells on both sides.
      • Cells towards outside differentiate into Cork (Phellem). Impervious to water due to suberin deposition in cell walls. Dead cells.
      • Cells towards inside differentiate into Secondary Cortex (Phelloderm). Parenchymatous, living cells.
    • Periderm: Collective term for Phellogen + Phellem + Phelloderm. Protective in function, replaces epidermis.
    • Bark: Non-technical term referring to all tissues exterior to the vascular cambium (includes secondary phloem). Technically, includes Periderm + Secondary Phloem. Bark formed early in season is 'early/soft bark'; late in season is 'late/hard bark'.
    • Lenticels: Lens-shaped openings in the periderm. Phellogen cuts off loosely arranged parenchymatous cells (complementary cells) instead of cork cells here. Permit gaseous exchange between living stem tissues and the atmosphere. Occur on most woody stems.

  • C. Secondary Growth in Dicot Root:

    • Vascular cambium originates secondarily from conjunctive tissue just below phloem bundles and parts of pericycle tissue above protoxylem. Forms a complete, initially wavy ring, which later becomes circular.
    • Activity is same as in stem: produces secondary xylem inwards and secondary phloem outwards.
    • Cork cambium originates from the pericycle. Produces cork outwards and secondary cortex inwards (periderm).

Multiple Choice Questions (MCQs):

  1. Which of the following tissues provides mechanical support to the growing parts of a plant such as young stem and petiole of a leaf?
    a) Parenchyma
    b) Collenchyma
    c) Sclerenchyma
    d) Xylem

  2. In a dicot stem, vascular bundles are:
    a) Conjoint, collateral, and closed
    b) Conjoint, collateral, and open
    c) Radial, exarch, and open
    d) Scattered, conjoint, and closed

  3. Casparian strips are characteristic features found in the:
    a) Epidermis of root
    b) Endodermis of root
    c) Pericycle of stem
    d) Cortex of stem

  4. Identify the correct pair of components of Phloem tissue:
    a) Tracheids and Vessels
    b) Sieve cells and Albuminous cells
    c) Sieve tube elements and Companion cells
    d) Xylem parenchyma and Xylem fibres

  5. Heartwood differs from sapwood in:
    a) Being susceptible to pests and pathogens
    b) Containing living cells
    c) Conducting water and minerals efficiently
    d) Having deposition of tannins, resins and being non-functional in conduction

  6. Bulliform cells are found in the epidermis of:
    a) Dicot roots
    b) Dicot leaves
    c) Monocot stems
    d) Monocot leaves

  7. Lateral roots originate from:
    a) Endodermis
    b) Pericycle
    c) Cortex
    d) Epidermis

  8. Which of the following is formed during secondary growth by the activity of Cork Cambium (Phellogen)?
    a) Secondary Xylem
    b) Secondary Phloem
    c) Phellem and Phelloderm
    d) Vascular Rays

  9. In roots, the arrangement of xylem where protoxylem lies towards the periphery and metaxylem towards the center is called:
    a) Endarch
    b) Exarch
    c) Mesarch
    d) Polyarch

  10. The ground tissue system in a monocot stem is:
    a) Differentiated into cortex, endodermis, pericycle and pith
    b) Composed mainly of collenchyma below the epidermis
    c) Undifferentiated mass of parenchyma in which vascular bundles are scattered
    d) Absent, as vascular bundles occupy the entire space

Answer Key for MCQs:

  1. b) Collenchyma
  2. b) Conjoint, collateral, and open
  3. b) Endodermis of root
  4. c) Sieve tube elements and Companion cells (Albuminous cells and Sieve cells are in Gymnosperms/Pteridophytes)
  5. d) Having deposition of tannins, resins and being non-functional in conduction
  6. d) Monocot leaves
  7. b) Pericycle
  8. c) Phellem and Phelloderm
  9. b) Exarch
  10. c) Undifferentiated mass of parenchyma in which vascular bundles are scattered

Study these notes thoroughly. Pay close attention to the differences between monocots and dicots in root, stem, and leaf anatomy, the components and functions of complex tissues, and the process of secondary growth. Understanding the 'why' behind structural features (like Casparian strips, bulliform cells, heartwood formation) is key for competitive exams. Good luck!

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