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3.1.3 Plant Tissues (Xylem (Adaptations (bordered pits allow water…
3.1.3 Plant Tissues
Xylem
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lignin on walls of cells to strengthen and prevent collapsing; waterproof; cells die leaving hollow tube of dead cells;
when lignification is not complete, forms bordered pits on cells wall, so water can leave one vessel and go to the next; water can leave xylem to other parts of the plant sdeways
Adaptations
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lignin forms patterns: spiral, annular (rings), reticulate (network of broken rings) to allow flexibility and stop collapsing
Phloem
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sieve tube elements
make up tubes in phloem tissue that carry sap up and down plant, separated by sieve plate
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companion cells
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large nucleus, dense cytoplasm, many mitochondria to provide ATP for active processes
Arrangement
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Roots
meristem tissue: a layer of dividing cells, also called pericycle
vascular bundle found in centre of root; xylem in x shape and phloem triangles in between arms; strength to withstand pulling force of roots
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Stem
vascular bundle found near outer edges in triangle shapes; may form continuous rings in old woody plants; strength to withstand pulling force on phloem, and flexibility
xylem on inside of vascular bundle, then cambium in the middle, then phloem on outer side of bundle
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