21.1 Plant Cells and Tissues KEY CONCEPT Plants have specialized cells and tissue systems.
Plants have specialized cells
Transcript of Plants have specialized cells
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Plants have specialized cells and tissue systems.
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Parenchyma cells are the most common plant cell type.
◦ store starch, oils and water
◦ help heal wounds to the plant
◦ have thin flexible walls
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◦ Collenchyma cells provide support to a growing plant.
they are strong and flexible.
celery strings are strands of collenchyma.
they have unevenly thick cell walls.
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Sclerenchyma cells are the strongest plant cell type. ◦ second cell wall hardened by lignin.
◦ die when they reach maturity.
◦ used by humans to make linen and rope.
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Dermal tissue covers the outside of a plant. ◦ protects the plant
◦ secretes cuticle of leaves
◦ forms outer bark of trees
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• Ground tissue is found inside a plant. ◦ provides support
◦ stores materials in roots and stems
◦most commonly made of parenchyma.
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Vascular tissue transports water, minerals and organic compounds.
◦ two networks of hollow tubes
◦ xylem transports water and minerals.
◦ phloem transports photosynthetic products (glucose, starch).
stem
leaf
root
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Xylem contains specialized cells. ◦ vessel elements are short and wide
◦ tracheid cells are long and narrow
◦ xylem cells die at maturity
vessel
element
tracheid
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◦ Plants passively transport water through the xylem.
◦ Cohesion is the tendency of water molecules to bond with each other.
• The cohesion-tension theory explains water movement.
– Adhesion is the tendency
of water molecules to
bond with other
substances.
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◦ absorption occurs at roots
• Water travels from roots to the top of trees.
– cohesion and adhesion in xylem
– transpiration at leaves
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◦ water vapor exits leaf stomata
◦ helps pull water to the top branches
• Transpiration is the loss of water vapor
through leaves.
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Phloem contains specialized cells. ◦ sieve tube elements have
holes at ends
◦ companion cells help sieve tube elements
◦ unlike xylem, phloem tissue is alive
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◦ plants actively transport sugar from the source
◦ sugar flows to the sink due to pressure differences
sugars
phloem xylem
water
Sugars move from their
source, such as
photosynthesizing
leaves, into the phloem.
1
The sugars move into
the sink, such as root
or fruit, where the are
stored.
3
Water moves from
the xylem into the
phloem by osmosis,
due to the higher
concentration of the
sugars in the phloem.
The water flow helps
move sugars through
the phloem.
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• The Pressure-flow model explains sugar movement.
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Meristematic – Constantly dividing, producing new cells. (Regions of growth.) ◦ Apical meristem – tips of
roots or stems. Increase plant length.
◦ Vascular cambium – between bark and wood. Increases diameter.