The vascular system of plants consists of xylem and phloem tissues that transport water, minerals, and sugars throughout the plant. Xylem contains specialized cells that transport water and dissolved minerals passively from the roots to the leaves through a process called transpiration. Phloem contains sieve tube elements and companion cells that actively transport sugars produced during photosynthesis from leaves to areas of the plant where they are used or stored through pressure differences in the phloem.

1. 21.2 The Vascular System
KEY CONCEPT
The vascular system allows for the transport of
water, minerals, and sugars.

2. 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
vessel
element
tracheid

3. 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.

4. 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

5. 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.

6. 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

7. 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.