Environmental Engineering Reference
In-Depth Information
Cell wall
Cell membrane
Vacuole
Nucleus
Cytoplasm
Chloroplast
FIGURE 5.4
Plant cell.
V
ascular
p
lants
Va scu la r plants, also called
tracheophytes
, have special vascular tissue for the trans-
port of necessary liquids and minerals over long distances. Vascular tissues are
composed of specialized cells that create “tubes” through which materials can flow
throughout the plant body. These vessels are continuous throughout the plant, allow-
ing for the efficient and controlled distribution of water and nutrients. In addition
to this transport function, vascular tissues also support the plant. The two types of
vascular tissue are xylem and phloem:
•
Xylem
consists of a tube or a tunnel (pipeline) in which water and miner-
als are transported throughout the plant to leaves for photosynthesis. In
addition to distributing nutrients, xylem (wood) provides structural support.
After a time, the xylem at the center of older trees ceases to function in
transport and takes on a supportive role only.
•
Phloem
tissue consists of cells called
sieve tubes
and
companion cells.
Phloem tissue moves dissolved sugars (carbohydrates), amino acids, and
other products of photosynthesis from the leaves to other regions of the plant.
The two most important tracheophytes are gymnosperms (
gymno
, naked;
sperma
,
seed) and angiosperms (
angio
, vessel, receptacle, container).
•
Gymnosperms
—The plants we recognize as gymnosperms represent the
sporophyte generation (i.e., the spore-producing phase in the life cycle of a
plant that exhibits alternation of generation). Gymnosperms were the first
tracheophytes to use seeds for reproduction. The seeds develop in protec-
tive structures called
cones
. A gymnosperm contains some cones that are
