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Chpt. 24: Structure of Flowering Plants. External Structure of a Flowering Plant Plants are divided into two portions. Over ground shoot system. Under ground root system. Roots Three types of roots

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External Structure of a Flowering Plant

Plants are divided into two portions

Over ground shoot system

Under ground root system



Three types of roots

Tap Roots (Primary Root): consist of one main root that develops from the initial root (radicle) that emerged from the seed e.g. carrot


Fibrous Roots:form when radicle dies away leaving a set of equal sized roots emerging from the base of the stem e.g. grasses.

Adventitious Roots:these are roots which do not develop from the radicle but develop from stem nodes e.g. roots at base of an onion, gripping roots of ivy.


Functions of Roots

  • To anchor the plant.
  • To absorb water and mineral salts from the soil.
  • To transport absorbed materials.
  • Some roots store food e.g. Carrots, turnips, radish

Four Root Zones

Differentiation Zone

Elongation Zone

Meristematic Zone

Protection Zone


Root Zones

  • Zone of Differentiation:here cells develop into three different types of tissue:
        • Dermal Tissue (epidermis): - protection
        • Ground Tissue: located between dermal and vascular tissues
        • Vascular Tissue (xylem and phloem): transport

Zone of Elongation: cells are stimulated to grow bigger by growth regulators such as auxins.

Meristematic Zone (Zone of cell Production): cells in the root meristem are constantly dividing by mitosis.

Apical meristem: - in root and shoot tip.

Other meristems: - edge of some plant stems, leaves and fruits.

Zone of Protection: root cap protects the root cells as they push through the soil.


Shoot System

  • The shoot system, of flowering plants, is the part above the ground which consists of three main parts:
          • Stems
          • Leaves
          • Flowers

The Stem:

  • The stem is the main part of the shoot on which all of the following parts can be found:
    • Node: the point of origin of a leaf on a stem.
    • Internode: is the part of the stem between two nodes.
    • Terminal (apical) bud: allows the stem to grow at the growing tip.
    • Axil: the angle between the upper side of a leaf and its stem.

The Stem:

    • Axillary (lateral buds): buds found at the axil which will develop into a side branch or a flower.
    • Lenticel: openings for gaseous exchange found in the stems of plants such as trees and shrubs.

Functions of the Stem:

  • Formation of buds, leaves and flowers.
  • Supports leaves in good light conditions to maximise
  • photosynthesis.
  • Transport food made in leaves to roots.
  • Transports water and minerals from roots to the leaves
  • and flowers
  • Food storage e.g. stem tuber of potato.
  • Vegetative reproduction e.g. stem tuber of potato
  • To carry out photosynthesis when they are green.

The Leaf:

  • Leaves are attached to stem at a node. The following parts can be found on a leaf:
    • Node: the point where the stem attaches to the leaf.
    • Petiole: stalk of the leaf.
    • *Sessile: leaves which do not have a petiole
    • Lamina: the leaf blade.
    • Midrib: the petiole continues through the lamina as the midrib.
    • Veins: emerge from the midrib and are clearly seen in the lamina.
    • The petiole, midrib and veins contain transport tissues called the xylem and the phloem

The Leaf:

  • Venation: the pattern of veins in a leaf. There are two types of venation:
    • Parallel Venation: the veins run alongside each other e.g. grasses, daffodils and tulips.
    • Net or Reticulate Venation: the veins form branching networks throughout the lamina e.g. horse chestnut, rose and buttercup.

The Leaf:



Functions of leaves:

  • Photosynthesis – make food.
  • Transpiration – loose water allowing fresh water and
  • minerals to be taken into plant.
  • Gas exchange; CO2 in - O2 and H2O out
  • Food storage e.g. thick fleshy leaves of onion bulb and
  • cabbage.


Flowers are the reproductive part of the plant that produces the seed; they will be discussed further in chapter 40.


Tissues in Flowering Plants

  • Plant tissue can be divided into four main types:
      • Meristematic Tissue
      • Dermal Tissue
      • Ground Tissue
      • Vascular Tissue

Meristematic Tissue:

      • A meristem is a plant tissue capable of mitosis.
      • They are found in the root tips and the shoot tips.
      • When meristematic tissue divides it produces new cells which initially are unspeciallesed but eventually they form three categories of plant tissue: dermal, ground, vascular.

2. Dermal Tissue (Epidermis):

    • Function: Protects plant from water loss and entry
    • of disease.
    • Location: The outer layer of stems, leaves and
    • roots.

3. Ground Tissue (Cortex):

    • Function: carries out a range of functions –
    • photosynthesis, storage of food and wastes, and
    • gives strength and support to plant.
    • Location: between the dermal and vascular
    • tissues in the stem, root and leaves.

4. Vascular Tissue:

      • In vascular bundles
      • Consists of Xylem and the Phloem
      • Function:
      • xylem transports water and mineral salts and
      • provides support, especially in woody plants e.g.
      • trees.
      • phloem transports food.

Inner layer of vascular bundle

Outer layer of vascular bundle


4. Vascular Tissue:

  • Xylem
  • made up of two main types of cells:

Xylem Tracheids

Xylem Vessels

On maturity both are dead, hollow and contain no cytoplasm. For this reason xylem is a dead tissue

Found in coniferous trees

Found in deciduous trees


4. Vascular Tissue:

Xylem Tracheid Structure


4. Vascular Tissue:

Xylem Tracheid Structure

  • Long cells tapered at both ends.
  • Pits in the walls – allow water and minerals to move sideways from cell to cell.
  • Walls thickened with lignin for support

4. Vascular Tissue:

Xylem Vessels Structure


4. Vascular Tissue:

  • Xylem Vessels Structure
    • Elongated cells
    • Spiral lignin for strength
    • No end walls - form a continuous tube
    • Pits to allow sideways movement of water
    • Location of Xylem
    • Found in: roots, stems, leaves and flowers

4. Vascular Tissue:

  • Phloem Structure
  • made up of two main types of cells:
  • - Companion cells
  • - Sieve tube cells

4. Vascular Tissue:

  • Phloem Structure
    • Sieve tubes:
    • - long tubular structures
    • - mature cells have no nucleus
    • - end walls called sieve plates as they contain numerous pores which allow the passage of
    • materials.
    • - cytoplasm extends from cell to cell through the
    • sieve plate.
    • - transport food from leaves to rest of plant

4. Vascular Tissue:

  • Phloem Structure
    • Companion Cell:
    • - nucleus controls activities of both companion and sieve tube cell.
    • - phloem forms a living tissue because of the companion cells.
    • - control the activities of the sieve tubes
    • Phloem Location
    • Found in: roots, stems, leaves and flowers

Tissue location in the root

(transverse section)

Dermal Tissue


Vascular Tissue


Ground Tissue


Tissue location in the root

(Longitudinal section)

Dermal Tissue

Ground Tissue

Vascular Tissue

Ground Tissue

Dermal Tissue


Tissue location in stem (Transverse section)

Dermal Tissue


Vascular Tissue


Ground Tissue


Tissue location in stem( Longitudinal section)






  • Ground



Two categories of flowering plants

Monocotyledons Dicotyledons

Monocots – daffodils, grasses, cereals

Dicots – beans, roses, trees; oak and ash

There are more dicots than monocots



  • Have one cotyledon in the seed (A cotyledon is a food
  • storage leaf in the seed)
  • Monocots are mostly herbaceous – soft, no woody parts
  • Long narrow leaves with parallel venation
  • Scattered vascular bundles
  • Flowers are arranged in multiples of three


  • 2 cotyledons in the seed e.g. peanuts
  • Dicots may be herbaceous (peas, sunflowers) or woody
  • (roses, oak trees)
  • Broad leaves with net venation
  • Vascular bundles are arranged in a ring inside the stem
  • Flowers arranged in multiplies of 4 or 5