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Tissues and the Primary Growth of Stems (Basic Types of Cells and TIssues,…
Tissues and the Primary Growth of Stems
Basic Types of Cells and TIssues
Parenchyma
Thin Primary walls
80-100 mm thick
5-10 layers of cellulose microfibrils
Most common type of cell and tissue
Subtypes
Chlorenchyma
Photosynthesis
Elevated [chloroplasts]
Glandular cells
Nectar
Fragrances
Mucilage
Elevated [Dictyosomes and ER]
Transformation of Sugars and Minerals
Low [Chloroplasts]
Transfer Cells
Mediation of short-distance transport
Large, extensive plasma membrane capable of holding numerous molecular pumps
Increase surface area by having knobs, ridges, and ingrowths on inner surface
Phloem
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Relatively inexpensive to build for plant
Collenchyma
Primary wall that is thin in some areas and thick in others
Plasticity
Vining plants
Vascular bundles
Provides support
Collenchyma and Parenchyma work together like Tire and Air Pressure
More expensive to build for plant
Usually produced in shoot tips or young petioles
Sclerenchyma
Primary wall and Thick secondary wall (lignified)
Develop from parenchyma cells in mature organs
Do not depend on another cell type to retain structure, unlike Collenchyma and Parenchyma
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2 types
Conducting Scherenchyma
Isodiametric (cuboidal)
Brittle and inflexible
Forms shells (walnuts, cherry pits, etc.)
Transports water (type of vascular cell)
Mechanical sclerenchyma
Long fibers
Strength and Flexibility
Abundant in the wood of most flowering plants
Allows for swaying in wind w/o breaking
Sclereids
Elastic secondary walls
Living sclerenchyma cells are involved in the storage of starch or calcium oxalate (crystallized)
External Organization of Stems
Stem Organization
Shoot= stem +leaves/flowers/buds
Nodes
Where leaves are attached
Internodes
Leaf axil
Axillary bud
Vegetative bud (grow into a branch)
Floral bud (grow into a flower or group of flowers)
Bud scales
Small, corky, and waxy
Modified leaves that protect delicate organs
Covers axillary buds
Terminal buds
Vines have elongated internodes
Allows plant to explore its surroundings
Stolons (runners)
Can form new plants in suitable habitats
Phyllotaxy
Arrangement of leaves on stem
Types of Phyllotaxy
Alternate (one per node)
Opposite (two per node)
Decussate (leaves located in four rows)
Whorled (3 or more leaves per node)
Spiral (leaves not aligned with their nearest neighbors)
Most common
Distichous (leaves located in two rows only)
https://www.youtube.com/watch?v=VHIvzlZlYUo
Important so that one leaf does not shade a neighboring leaf
Variations in Shoot Structure
Bulbs (short shoots w/ thick fleshy leaves
Examples
Onions
Daffodils
Garlic
Corms
Vertical thick stems
Thin papery leaves
Rhizomes
Fleshy horizontal stems
Allow a plant to spread underground
Examples
Bamboo
Irises
Canna lilies
Tubers
Horizontal Rhizomes
Storage of nutrients
Potatoes
Internal Organization of Stems: Arrangement of Primary Tissues
Epidermis
Outermost surface of an herbaceous stem
Regulates all interchange of materials with environment
Retention and release of water
Cutin encrusted outer tangential walls
Multiple layers of Cutin make up the Cuticle
If cuticle is insufficient, a layer of wax may be added
Also inhibit entry of CO2 needed for photosynthesis
Shield against bacteria, fungi, animals, etc.
Stoma
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2 guard cells
Special radial arrangement of cellulose materials
Swell by absorbing H20, back walls arch and form opening
1 stomatal pore
Opened during the daytime, permitting CO2 to enter the plant
Hairs (trichromes)
Make it difficult for an animal to land on or chew leaves
Shade underlying tissues, by blocking too intense light
Exist in multiple sizes and shapes
Most die shortly after formation, leaving cell wall for protection
May act as small secretory glands
Venus Fly Trap
Cortex
Inferior to the Epidermis
Simple and Homogenous in most species
Photosynthetic parenchyma and sometimes collenchyma
May sometimes have cortical air chambers that provide buoyancy
Vascular Tissues
Necessary in complex organisms with multiple different tissue types
Two types
Xylem
Conducts water and minerals from roots
Cells are dead usually
2 types of conducting cells
Tracheids
Water passed by Tracheids laying side by side and end overlapping
Pits of adjacent tracheids are aligned so that water can pass through (pit pair)
Pit membrane
Friction
Vessel elements
Moves water with less friction than Tracheids
Perforations aligned for adjacent cells for H2O transport
Vessel (stack of vessel elements) have only 1 perforation at either side
Absorb water from parenchymal cells or tracheids
Both are types of slerenchyma
Tracheary element refers to either type of cell
Formation of hollow tubular walls
Primary wall
Permeable to water
Secondary wall
Impermeable to water
Annular thickenings
Large surface area for water movement
small amount of secondary wall, organized as rings
Weak, but Large % of primary wall is available for water movement
Helical thickening
Scalariform Thickening
Reticulate thickening
Circular bordered pits
Strongest and most derived tracheary elements
Virtually all of primary wall is underlain by secondary wall
Weak points reduced by a border of extra wall material around the pit
Cannot conduct water well
Phloem
Distributes sugars and minerals
Living cells
Two types of Conducting cells
Sieve cells
Elongate and spindle shaped
Has sieve areas distributed over all its surface
Evolved first
Albuminous cells
Sieve tube members
Sieve areas on the two ends of the cell especially large
Nuclei degenerate but remain alive
Sieve element refers to either of the two cell types
Have only primary walls
Parenchyma cells
Must remain alive to conduct
Sieve pores (enlarged plasmodesmata
1 um
Sieve areas
Pores of adjacent cells must line up
Vascular Bundles
Xylem and Phloem together
Xylem=Primary system
Primary phloem
Just interior to the cortex
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Arranged in rings and surrounded by the Pith
Pith (region of parenchyma similar to the cortex
Collateral
Stem Growth and Differentiation
Stems grow longer by creating new cells at their tips
Apical meristems
Subapical meristem
Visible differentiation
Protoxylem
Extensible
Annular or secondary walls
Protoxylem cells dead at maturity
First cells to differentiate for vascular bundles
Metaxylem
Cell differentiate only after all surrounding stem tissues have stopped elongating
Any type of secondary wall is feasible
Metaphloem
Cells differentiate fully
Large sieve areas
Conspicuous companion cells
Protophloem
Cells are extremely short-lived
Never become well-differentiated
Primary tissues
Primary growth
Secondary tissues
Secondary Growth
Protoderm
Epidermal cells that are in the early stages of differentiation
Provascular tissues
Ground meristem
