Download 21.2 The Vascular System - Bismarck Public Schools

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
tracheid
vessel
element
21.2 The Vascular System
• The cohesion-tension theory explains water movement.
– Plants passively transport water through the xylem.
– Cohesion is the tendency of water molecules to bond
with each other.
– Adhesion is the
tendency of water
molecules to bond
with other
substances.
21.2 The Vascular System
• Water travels from roots to the top of trees.
– absorption occurs at roots
– cohesion and adhesion in xylem
– transpiration at leaves
21.2 The Vascular System
• Transpiration is the loss of water
vapor through leaves.
– water vapor exits leaf stomata
– helps pull water to the top
branches
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
• The Pressure-flow model explains sugar movement.
– plants actively transport sugar from the source
– sugar flows to the sink due to pressure differences
phloem
xylem
sugars
1 Sugars move from their
source, such as
photosynthesizing
leaves, into the phloem.
3 The sugars move into
the sink, such as root
or fruit, where the are
stored.
water
2 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.