Transcript Plant Cells and Tissues

Plant Cells and Tissues
Early embryonic plant tissues consist
of 3 primary cell types:
Collenchyma
Sclerenchyma
Parenchyma
- various combinations, percentages, of
these cells make up the different plant
tissues
Primary plant body:
- primary growth, first year
- forms long axis
- roots and shoots
- only growth in annuals
- made up of 4 primary tissues
Meristems
Ground Tissues
Dermal Tissues
Vascular Tissues
- found in all 3 plant organs
Meristems:
Localized regions of cellular division and
growth
 Only places plants grow
 At tips of roots and shoots, in rings
inside second growth plants
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Ground Tissue:
Arises from ground meristem
 Most of primary plant growth
 Throughout plant and in other tissues
 Ex. Pith and cortex
Functions: Basic metabolism
Storage
Support
Filler
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Basic Cells
There are three basic cells that make up
ground tissue and most other tissues
 Parenchyma
 Collenchyma
 Sclerenchyma
Parenchyma
Made by all plant’s meristems
 Throughout plant body
 Most abundant and simplest cell type
 Relatively unspecialized
 Any cell not recognized as another type
 Very diverse
 Gives rise to more specialized cells
Functions: storage, basic metabolism
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Differentiation, Dedifferentiation, and
Redifferentiation
Parenchyma cont.
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Thickened primary cell wall
Alive at maturity
Isodiametric shape
Many variations on shape and form
Collenchyma
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Elongated cells
Unevenly thickened primary cell walls
Support some parts (growing tissue)
Cell walls lack lignin
Can form into strands or cylinders (celery)
Alive at maturity
Sclerenchyma
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Rigid, thick, non-stretchable secondary cell walls
Support and strength for non-extending, nongrowing regions of plant
Found in mature stems and trunks
Dead at maturity
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! Cell wall “skeleton” of wood!
Found in all parts of plants
Classified into 2 types:
1) Sclereids
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Short, variable shape
Occur singly or in small groups forming
internal strands
Throughout plant, some support
Hard layers and surfaces
2) Fibers
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Long and slender
Normally in large strands
Single or bundles
Near vascular tissue
Between nodes on stems
Dermal Tissue:
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Covers plant body
Epidermis
Functions:
Water and nutrient absorption
Secretion of cuticle
Gas exchange
Prevents dehydration
Cuticle
 Fatty layer of material called cutin, waterproof
 May be covered by layer of epicuticular wax
Epidermal Cells and Stomata
Epidermal cells:
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Flat, tile-like, brick pattern
No intercellular spaces
Lack chloroplasts – clear
Only one cell layer thick
Store some water
Stomata:
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2 guard cells, subsidiary cells and gas exchange
Trichomes:
One or more cellular outgrowths of the epidermis
 One cell thick, many long
Functions: Protection, Nutrient absorption (root hairs)
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Cellular Recognition:
Loss of Epidermis: (with secondary growth)
Vascular Tissue:
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2 types
1)
2)
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Xylem
Phloem
Transport water and dissolved
materials
A composite tissue, many cell types
Xylem
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Transports water and nutrients
From roots to all parts of plant
Primary xylem and secondary xylem
Throughout plant
Secondary cell walls spiral, spring or hoop
shaped
Principle material of “wood”
Conducting cells in xylem: 2 types
Xylary Elements
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Elongated
Dead at maturity
Thick, lignified secondary cell walls
Water transport and support of plant
1. Tracheids
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Most primitive, long slender cells
Tapered ends, overlap
Bordered pits on cell wall
2. Vessel Elements
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Shorter than wide, fit end to end
Long hollow vessels
Transverse walls dissolved away
Phloem
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Transport food and organics
Throughout plant body
Transport both up and down directions
Primary and secondary phloem
Part of bark
Conducting cells in phloem: 2 types
Sieve Elements
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Alive at maturity
Cells lack nuclei
Typically live less than a year
Most delicate
Very thin primary cell walls only
Sieve areas and sieve pores
Stacked end to end
2 types:
1. Sieve Cells
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Found in non-flowering plants
Most primitive
Quite long, slender, with overlapping ends
Many sieve pores on ends and sides
2. Sieve Tube Members
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Shorter and wider
Found in flowering plants, more advanced
Sieve pores larger and found only on the ends
Lack nuclei but still alive
* Companion Cells *