chpt. 24: structure of flowering plants
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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 - PowerPoint PPT PresentationTRANSCRIPT
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Chpt. 24: Structure of Flowering Plants
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External Structure of a Flowering PlantPlants are divided into two portions
Over ground shoot system
Under ground root system
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RootsThree 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
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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.
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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
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Four Root Zones
Differentiation Zone
Elongation Zone
Meristematic Zone
Protection Zone
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Root ZonesZone 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
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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.
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Shoot System
The shoot system, of flowering plants, is the part above the ground which consists of three main parts:
1) Stems 2) Leaves3) Flowers
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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.
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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.
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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.
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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
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Structure of Leaf
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The Leaf:
Venation: the pattern of veins in a leaf. There are two types of venation:
1. Parallel Venation: the veins run alongside each other e.g. grasses, daffodils and tulips.
2. Net or Reticulate Venation: the veins form branching networks throughout the lamina e.g. horse chestnut, rose and buttercup.
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The Leaf: Venation
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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.
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Flowers:
Flowers are the reproductive part of the plant that produces the seed; they will be discussed further in chapter 40.
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Tissues in Flowering Plants
Plant tissue can be divided into four main types:
Meristematic Tissue
Dermal Tissue
Ground Tissue
Vascular Tissue
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1. 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.
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2. Dermal Tissue (Epidermis):
• Function: Protects plant from water loss and entry of disease.
• Location: The outer layer of stems, leaves and roots.
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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.
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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
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4. Vascular Tissue:Xylem
• made up of two main types of cells:
Xylem Tracheids Xylem VesselsOn maturity
both are dead, hollow and contain
no cytoplasm.
For this reason
xylem is a dead tissue
Found in coniferous
treesFound in
deciduous trees
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4. Vascular Tissue:
Xylem Tracheid Structure
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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
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4. Vascular Tissue:
Xylem Vessels Structure
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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
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4. Vascular Tissue:Phloem Structure
• made up of two main types of cells:- Companion cells- Sieve tube cells
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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
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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
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Tissue location in the root (transverse section)
Dermal Tissue
Xylem
PhloemVascular Tissue
Ground Tissue
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Tissue location in the root (Longitudinal section)
Dermal Tissue
Ground Tissue
Vascular Tissue
Ground Tissue
Dermal Tissue
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Tissue location in stem (Transverse section)
Dermal Tissue
Xylem
PhloemVascular Tissue
Ground Tissue
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Tissue location in stem( Longitudinal section)
Dermal
GroundVascular
Ground
Vascular
DermalGround
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Two categories of flowering plants
Monocotyledons Dicotyledons
Monocots – daffodils, grasses, cerealsDicots – beans, roses, trees; oak and ash
There are more dicots than monocots
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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
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Dicots• 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
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Identification of Monocots & Dicots