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Order of Cell Differentiation
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4 Functions of the Root
- Anchorage
- Absorption
- Storage
- Conduction
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Types of Root System
Taproot system: Primary and lateral roots, found in eudicots, magnoliids, gymnosperms
Fibrous Root Systems: lateral roots only, found in monocots
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Longitudinal Regions of Roots
 - Area of Cell Maturation: differentiation of cells, root hairs form.
- Area of Elongation: increases root length
- Area of Cell Division: has apical meristem, actively dividing cells.
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Root Cap
- composed of parenchyma cells
- 3 functions: protect the apical meristem, aid in penetration of soil, and control the root's response to gravity.
- produces mucigel (slimy coating; helps with penetration)
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Monocots vs Eudicots (in roots)
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Epidermis
- root hairs (tubular extensions of epidermal cells) increase surface area
- may contain thin cuticle
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Cortex
- composed of parenchyma cells
- amyloplasts: store starch, lack chlorophyll
- large amount of intercellular space
- contains endodermis and exodermis
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Exodermis (found in cortex)
- the first cell layer in the epidermis
- prevents water loss
- a primary function is storage
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Endodermis (found in cortex)
- the endodermis is a sheath around the vascular region
- compact cells
- contains casparian strips, or hydrophobic bands of suberin in the cell wall which prevent the passage of water.
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Symplastic Movement
- movement through the cells
- symplast: interconnected cytoplasm of living cells
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Apoplastic Movement
- Movement through intercellular space
- most common type of movement
- useful in filtering
- apoplast: the interconnected cell-wall spaces
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Exodermis (found in cortex)
- outermnost layer of cortex cells
- contains casparian strips (see endodermis card for details)
- reduces water loss
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Vascular Cylinder
- contains vascular tissue and pericycle
- also known as the vascular stele
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Pericycle
- comprised of parenchyma cells
- non-vascular, but originates from procambium
- functions: it is the site of lateral root formation, and it contributes to cork cambium and vascular cambium.
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Secondary Growth in Roots
- secondary growth increases width
- two lateral meristems: vascular cambium and cork cambium
- vascular cambium --> secondary xylem and phloem
- Periderm originates freom pericycle
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Components of Periderm
- cork cambium
- cork
- cork parenchyma cells
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Cork Cambium
- lateral meristem
- produces cork
- phelloderm to inside
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Cork
- dead at maturity
- outer protective layer
- cells containing suberin, wax, and ligin
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Cork Parenchyma Cells
- inner layers of periderm
- alive at maturity
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Lateral Root Growth
- Forms from pericycle
- later joins with vascular cylinders of primary and lateral roots
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Food Storage Roots
- stored as a starch or sugar
- predominantly taproots
- some fibrous roots
- ex: carrots, beets
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Prop Roots
- above ground roots
- provides additional support
- produced from stem
- ex: mangroves
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Buttress Roots
- roots of tropical trees are often shallow
- provides support
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Air Roots (Pneumatophores)
- roots grow to the surface of water for oxygen
- ex: cypress trees
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Contractile Roots
- often in bulbs and corms
- Function: contracts and pulls plant further into soil
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Mycorrhizae
- most plants have it, to some extent
- fungi get sugar from plant, plant gets minerals
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Nodule
a small swelling on the root of a leguminous plants in which beneficial nitrogen-fixing bacteria (Rhizobium) live.
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