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parenchyma cells
- form much of the ground tissues
- living when mature
- variety of functions: metabolism (photosynthesis), storage (in cortex)
- makes up, for ex: phloem, epidermis, fruit and veggie edibles, sieve-tube members
- primary cell walls are generally thin and flexible
- some have chloroplasts, but usually don't
- divide when needed
- can elongate
- lack secondary cell walls
- some have colorless plastids that store starch
- mature, unspecialized cells do not generally undergo cell division, but can be induced to differentiation under special conditions, such as repair/replacement of organs after injury
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collenchyma cells
- provide flexible support for parts of still-growing plants, support the vascular tissues
- primary walls are unevenly thickened
- grouped into strands/cylinders
- living when mature
- do not have chloroplasts
- can elongate
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sclerenchyma cells
- thick secondary cell walls strengthened by lignin
- provide support in nongrowing regions
- cannot elongate
- dead at functional maturity
- ex: vessel elements and tracheids in xylem
- types:
- *fibers - specialized for support, long, slender, and tapered, usually occur in groups (ex hemp)
- *sclereids - specialized for support, shorter, irregular in shape, (ex hard shells of nuts and seed coats, gritty texture in pears)
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meristematic cells
- retain the capacity to undergo cell division (mitosis)
- small, six-sided cells with large nuclei
- produced cells that eventually become the other cells
- types include apical meristems, primary meristems, lateral meristems
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apical meristems
- tips of young shoots and roots
- produce all other cells of the plant, via primary and lateral meristems
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primary meristems
- produced by the apical meristem
- responsible for the primary growth (increase in length)
- protoderm - produces the outer epidermis to stems and roots
- procambium - produces the vascular tissues in stems and roots
- ground meristem - produces the ground tissues of stems and roots
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lateral meristems
- responsible for secondary growth
- increase the girth of individual stems and roots
- encompass vascular cambium and cork cambium
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vascular cambium
- produce secondary xylem and phloem
- layers of secondary xylem form over time and harden to produce wood
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cork cambium
- produce a thick covering for large stems and roots
- replace the epidermis
- made of parenchyma cells in mostly the cortex
- produces cork cells and secondary cortex cells
- periderm - the cork and cork cambium
- bark - periderm + secondary phloem
- old roots do not absorb water
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nonmeristematic tissues include...
dermal, vascular, ground tissues
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dermal tissues
- consist of the epidermis
- acts as the outer "skin"
- produces the waxy substance cutin to form the cuticle, which helps the shoot system to retain water
-
vascular tissues
- transport of materials throught the plant
- consists of xylem and phloem
-
ground tissues
- tissues other than the epidermis and vascular tissues
- parenchyma cells are the dominat cell type
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phloem
- phloem sap moves through tubes formed by chains of cells (sieve-tube members) lined up from end to end, forming sieve tubes
- sieve plates - porous end walls; allows for unimpeded movement from one cell to the next
- alive at functional maturity; lack nuclei, ribosomes, distinct vacuoles
- have companion cells
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companion cells
- nonconducting
- adjacent to and connected to sieve-tube members
- retain their nuclei and are living when mature
- assist sieve-tube members in maintaining cell metabolism and function
-
phloem sap
- aqueous solution; carbohydrates, sugar(is the dominant solute); minerals, amino acids, hormones
- translocation - sugars are moved by active transport into sieve tube members, and water follows by osmosis
- ATP needed
- increase in hydrostatic pressure then moves the sugar solution from one cell to the next, going from sources to sinks
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xylem
- conducts water and dissolved minerals upward from roots into the shoots
- consists of tracheids and vessel elements
- elongated cells, dead at functional maturity
- nonconducting sclerenchyma fibers may also be present
- secondary walls interupted by pits - thinner regions where only primary walls are present
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tracheids
- long, thin cells with tapered ends
- water/xylem sap moves from cell to cell mainly through pits
- generally moves upward through transpiration
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vessel elements
- generally wider, shorter, thinner walled, less tapered
- aligned end to end, forming long pipe-like structures called xylem vessels
- completed perforated
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The flow of water is enhanced by...
- ... transpiration (provides the pull) and the cohesion of water (to each other) due to hydrogen bonding.
- no ATP needed
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stems
- main aerial stalk
- produce buds, flowers, leaves
- support the leaves and conduct water and inorganic minerals to them
- transport sugars and other photosynthetic products to the roots
- may be green (photosynthetic), store water/food (cacti), adaptions to thwart herbivores (spines)
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stem features:
- node, internode
- lenticels
- buds
-
node
- portion of the stem from which leaves and buds and branches arise
- contain meristematic tissues
-
internode
portion of the stem between 2 nodes
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lenticels
slightly raised circular or elongated slit-like structures on the bark of young woody twigs that function in gas exchange
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buds
- undeveloped shoots in which internodes are present but generally are not elongated
- may be protected (covered with specialized leaves called bud scales) or naked (lacking bud scales)
- terminal buds - found at the tips of stems
- axillary (lateral) buds - found in the axils of the leaves at the nodes
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dicot stem organization
out-->in
- >epidermis [single layer of parenchyma cells derived from the protoderm; cuticle; guard cells surrounding stomata may be present]
- >cortex [multi-layered; originates from the ground meristem, consists mainly of collenchyma/parenchyma]
- >vascular tissue [consists of primary xylem, primary phloem, and vascular cambium; typically form discrete, concentrically arranged in vascular bundles; vascular cambium is found between the xylem and phloem and called fascicular cambium]
- >pith [center of the stem, composed of parenchyma cells, large]
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monocot stem organization
- origin and development of the primary tissues are all the same as those of dicots
- >vascular bundles are scattered throughout the ground tissue
- >cortex and pith are indistinguishable, and all tissue tissue derived from the ground meristem is called ground tissue; vascular bundles are surrounded by a sheath of sclerenchyma
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secondary growth of stems
- a meristem (interfascicular cambium) develops between the vascular bundles from cortical parenchyma cells --> forms a complete ring called the vascular cambium
- secondary xylem to the inside
- secondary phloem to the oustide
- >these will form as complete rings or cylinders of conducting tissue
- cork cambium (phellogen) forms from parenchyma of the cortex
- monocots typically do not exhibit secondary growth
-
woody dicot stems and annual rings
- wood is made of secondary xylem
- if there is a yearly cessation of this growth, annual growth rings will be formed (like in temperate regions)
- yearly addition of phloem is not as conspicuous as that of xylem
- xylem is composed of spring wood and summer wood
- cells produced during the wetter parts of the growing season is less dense (larger cells and thinner cell walls; designed for transport)
- summer wood is composed of smaller cells and thicker walls (designed for support)
-
As the secondary xylem and phloem become differentiated (during secondary growth) ...
... a cork cambium arises in the outer cortex; forms boxy cork cells which become impregnanted with a fatty compound called suberin, which acts as a waterproofing agent. epidermis and outer cortical layers are sloughed off; periderm becomes the outermost tissues.
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rays
- streaks of parenchyma cells
- radiating outward from the center of the trunk
- function is the lateral conduction of water and nutrients across the stem
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heartwood
- older annual rings near the center become discolored by the deposition of various organic compounds
- prevent further conduction of water
- darkened
- functions only in mechanical support
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sapwood
- outer, lighter region
- functions in both support and transport
-
specialized stems:
- stolons - below ground, horizontal (runners of strawberry plants)
- rhizomes - underground horizontal stems (ginger)
- tubers - modified stems for storing food (white potatoes)
- bulbs - a shoot made of modified leaves surrounding a short stem (onion)
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leaf features:
- principle organs of photosynthesis
- no secondary growth
- come about by primary meristems
- blade - thin, flattened, photosynthetic part
- petiole - stem-like stalk of a leaf that attaches the blade to the stem node
-
leaf venation:
- netted (reticulate) venation - one of more large veins from which smaller veins diverge; dicots
- parallel venation - several veins that are more or less of equal size, which run parallel; monocots
-
internal anatomy of angio leaves:
- epidermis - single layer of modified parenchyma cells with a waxy cuticle, covering both upper and lower blade surfaces; guard cells, stomata (lower surface on dicots, evenly distributed on monocots)
- mesophyll - photosynthetic parenchyma between the upper/lower epidermis
- >differentiated into 2 layers in dicots
- >palisade mesophyll - layers of elongated cells, adjacent to upper epidermis
- >spongy mesophyll - loosely organized, adjacent to lower epidermis
- bundle sheath surrounds the xylem and acts in a fashion that is analogous to the endodermis of the roots; prevents exposure of vascular tissue to the air
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abscission zone
- the process of leaf shedding; preceded by the active resorption of nutrients from the leaves
- a zone develops at the base of the petiole with the formation of a protective cell layer and an adjacent separation layer of cells
- leaf scar - protected area on the stem, left after abscission
- deciduous plants - plants whose leaves drop periodically with the change in seasons
- evergreen plants - do not periodically drop their leaves
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roots
- anchor the plant in the soil, absorb minerals and water, store food
- primary root is first organ to emerge from the germinating seed
- system of roots composed mainly of lateral roots become established
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fibrous root system
- monocots
- shallow, dense
- increases the plant's exposure to soil water and minerals
- high surface area
- no secondary growth
- no lateral meristems
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taproot system
- dicots
- one large vertical root that produces many small lateral roots
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Development of a root...
... may involve both primary growth and secondary growth (esp dicots).
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root cap
- thimble-like structure composed of rather loosely arranged parenchyma cells that covers the root apex
- protection of root apical meristem
- produce a slimy polysaccharide lubricant that facilitates the movement of the root through the soil
- may perceive gravity
-
zone of division
compact tissue immediately behind the root cap composed of small, densely cytoplasmic cells
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zone of cell elongation
- adjacent to the apical meristem
- consists of cells that are increasing in size longitudinally
- some differentiation has begun
- have 3 primary meristems:
- >protoderm - single layer of cells on the outside that will differentiate into the epidermis
- >ground meristem - several cell layers thick between protoderm and center (procambium); produces the cortex and the endodermis
- >procambium - give rise to the tissues of the stele (vascular cylinder)
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zone of differentiation
- aka root hair zone
- root hairs form and other cells differentiate
- comprise primary tissues
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epidermis (primary tissue in roots)
- derived from the protoderm
- consists of a single layer of parenchyma cells
- normally lack a cuticle
-
cortex (primary tissue in roots)
- broad area of parenchyma cells
- derived from the ground meristem
- store starches
-
endodermis (primary tissue in roots)
- innermost layer of cortex cells
- characterized by Casparian strip
- surrounds the stele and regulates which minerals pass from cortex to vascular tissue
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casparian strip
- an area of cell wall that has been secondarily thickened with lignin and waterproofed with suberin
- ensures that no minerals can reach the vascular tissue of the root without crossing at least one selectively permeable plasma membrane of a living cell
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pericycle (primary tissue in roots)
- outermost layer of the stele
- unspecialized parenchyma cells that retain a potential to undergo cell division
- lateral roots are created
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primary phloem (primary tissue in roots)
- derived from the procambium
- occurs in strands between the radiating arms of the primary xylem
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vascular cambium (primary tissue in roots)
- undifferentiated procambial cells between the primary xylem and primary phloem
- appear roughly rectangular in cross section
-
primary xylem (primary tissue in roots)
- derived form the procambium
- occupies center of the root
- 3+ radiating arms
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pith (primary tissue in roots)
- central region
- parenchyma cells
- characteristic of monocot roots
-
stele (primary tissue in roots)
- central part of the root
- includes all tissues interior to the cortex (pericycle, vascular tissues)
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hypodermis/exodermis (primary tissue in roots)
- outermost layer of cortex cells, just underneath the epidermis
- may have Casparian strips and suberin
- important in preventing absorbed water and nutrients from escaping
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