A Closer Look At Wood and Bark AP Biology Spring 2011.
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Transcript of A Closer Look At Wood and Bark AP Biology Spring 2011.
A Closer Look At Wood and Bark
AP BiologySpring 2011
Formation of BarkAs tree ages inner core of xylem continues its
outward expansion Resulting pressure is directed toward the
stem or root surface Will rupture the cortex and outer part of
secondary phloem When that occurs, parenchyma cells in this
region start dividing Give rise to cork cambium
Formation of BarkThe rupturing causes the cortex and
epidermis to split away Ongoing cell division at cork cambium gives
rise to periderm
Formation of BarkBark: the periderm and secondary phloem
Consist of living cells and dead tissues on the outside of vascular cambium
Formation of BarkCork: densley packed rows of cells
Each with a wall thickened by a fatty substance called suberin
Innermost cells are alive- have access to nourishment from xylem and phloem
Can protect, insulate, and waterproof the stem or root surface, forms over wounded tissues
When leaves are about to drop, cork forms at the place where petioles attach to stems
Formation of BarkLenticels: localized areas where the packing
of cork cells is loosened up a bitAllow passage of gases through bark
Heartwood and SapwoodHeartwood: lies at the center of older stems
and rootsIt is a depositary for resins, oils, gums, and
tannins It is clogged and no longer functions in
transportHelps tree defy gravity
Heartwood and SapwoodSapwood: secondary growth located
between heartwood and vascular cambiumIt is wet, pale in colour, and not as strong It is rich in a sugar-rich fluid transported from
the rootsUsed in the production of maple syrup
Early Wood, Late Wood, and Tree RingsIn regions with cool winters or dry spells, the
vascular cambium is inactive during part of the year
Early Wood, Late Wood, and Tree RingsEarly Wood: contains xylem with large
diameters and thin wallsStart of growing season
Early Wood, Late Wood, and Tree RingsLate Wood: contains xylem with small
diameters and thick walls
Early Wood, Late Wood, and Tree RingsGrowth Rings: appear as alternating light
bands of early wood and dark bands of late wood
Early Wood, Late Wood, and Tree RingsHardwoods:
Oak, hickory, other eudicot trees
Evolved in temperate and tropical zones
Has vessels, tracheids, and fibers in its xylem
Early Wood, Late Wood, and Tree RingsSoftwoods:
Pines, redwoods, other conifer species
No vessels or fibersTheir xylem has
tracheids and rays of parenchyma
Weaker and less dense than hardwoods