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Lecture 3: Plant cells and tissues 2 (Complex tissue (Types (Xylem (wood),…
Lecture 3: Plant cells and tissues 2
Complex tissue
Are made up of more than one type of cells which works together.
Function: transport water, minerals and food to various parts of the plant body
Types
Xylem (wood)
Is basically a sclerenchyma tissue and is dead
conducts water and dissolved minerals from the root to other parts of the plants
Provides of the plants
Phloem (Bast)
Usually found close by to xylem
Is basically a parenchyma tissue and thus living
Carries organic nutrients (sugar) from the leaves, where they are produces, to all other parts of the plant.
Xylem and Phloem are also called vascular tissues and together, they constitute the vascular bundle
Xylem
Tracheids
Long and tapering or elongated cells, closed at both ends
Thick- walled and have no cytoplasm
Conduct from cell to cell perforation plates through pits in the side walls
Matured tracheids have annular, spiral, or reticulate wall thickenings
Vessel elements
Cylindrical tube-like structures formed by a row of cells placed end to end. Connected by means of plates with pores and are known as perforation plates through which water moves upwards
Are thick-walled, dead, hollow cells
Lack end walls and wall thickenings are pitted
Large diameter cells of the xylem that are extremely specialized and efficient at conduction. (An evolutionary advance over tracheids)
Xylem sclerenchyma (fibers)
Sclerenchyma cells
Provides strength
Xylem Parenchyma
Living
Thin- walled
Food storage
Phloem
Sieve- tube elements
Living cells with typical thin walls
Long cells joined end to end, forming sieve tubes
End walls are perforated, known as sieve plates
Specialized for conducting carbohydrates, amino acids, etc.
Cytoplasm extends from one sieve-tube member into the next
Companion cells
Assist sieve tubes
living cell (have typical nucleus and dense cytoplasm)
connected to sieve-tube members by numerous openings in the cell wall
Phloem Parenchyma
Alive, thin walled
Food storage
Phloem sclerenchyma (Fibres)
Sclerenchyma cells for mechanical strength
Plant tissue system
Dermal tissue
Epidermis: the outermost layer of cells that covers the plant surface
Made of tightly packed parenchyma cells
Can be specialized according to the plant part it covers
Shoot epidermis can be covered by cuticle (thick covering on the outer surface of the epidermis)
Cuticle
Cuticle main constituent is cutin, which is secreted by the epidermal cells into their outer and radial cell walls.
Thickness dependent on humidity of envt.
Multilayered. Lower layers intermingle with cell wall constituents, whereas, upper layer consists of cuticle only
Covered with hydrophobic layer of epicuticular waxes
Stomata
Pores that are surrounded by guard cells (Specialized epidermal cells)
Permits gas exchange (water loss, CO2 uptake and O2 release or uptake)
Trichomes
Epidermal cell extensions or outgrowths
Can be unicellular or multi-cellular, glandular or non-grandular
reflect light, protects the more delicate tissues underneath in hot, dry and open habitats
Protective function against pests and helps reduce water loss
Root surface
Root epidermis adapted from absorption of water and minerals
Outer surface of root epidermis do not have waxy cuticle
Have root hair extensions from the root epidermal cells: help increase absorption by increasing surface area
Periderm
Outer bark of older stem and roots
Secondary tissue produced by the Cork Cambium
Cells are known as Cork or Phellem (Mentioned in future lectures)
Dead at maturity, walls impregnated with suberin (waterproof and resists microbial degradation)
Functions
Restricts water loss in shoot and leaf (Cuticle and Trichomes)
Provides resistance to microbial attacks (Periderm)
In woody plants, protects underlying tissues (Periderm)
Acts as insulator against extreme temperatures
Ground tissue
Shoot and root ground tissue: cortex
Leaves ground tissue: Mesophyll
Various functions: food storage, photosynthesis and support
Vascular tissue
Extends throughout the plant to conduct water, dissolved minerals and dissolved food
Support