21.2 The Vascular System KEY CONCEPT The vascular system allows for the transport of water,...
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Transcript of 21.2 The Vascular System KEY CONCEPT The vascular system allows for the transport of water,...
21.2 The Vascular System
KEY CONCEPT The vascular system allows for the transport of water, minerals, and sugars.
21.2 The Vascular System
Water and dissolved minerals move through xylem.
• Xylem contains specialized cells. – vessel elements are short and wide– tracheid cells are long and narrow – xylem cells die at maturity
vesselelement
tracheid
21.2 The Vascular System
– 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.
21.2 The Vascular System
– absorption occurs at roots
• Water travels from roots to the top of trees.
– cohesion and adhesion in xylem– transpiration at leaves
21.2 The Vascular System
– water vapor exits leaf stomata– helps pull water to the top
branches
• Transpiration is the loss of water vapor through leaves.
21.2 The Vascular System
Phloem carries sugars from photosynthesis throughout the plant.
• Phloem contains specialized cells. – sieve tube elements have
holes at ends– companion cells help sieve
tube elements – unlike xylem, phloem tissue is
alive
21.2 The Vascular System
– 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.
2
• The Pressure-flow model explains sugar movement.