Chapter 23: Roots, Stems, and Leaves
The three principle organs of seed plants
Roots
• absorb water and dissolved nutrients
• anchor plants in the ground
• hold plants upright through wind and rain
Stems
• support the plant
• transports nutrients to the rest of the plant
• compete for sunlight by holding leaves higher
Leaves
• are the principle organ for photosynthesis
• have broad, flat surfaces, inc S.A. for sunlight
• pores conserve water and allow gas exchange
Meristem Tissue
Stem
The only plant tissue
that produces new
cells by mitosis
Apical meristem is
found at the tips
of stems and roots.
Root
Tissue Systems
Plants consist of 3 tissue systems:
• Dermal tissue – outermost layer; forms the “skin” of the plant
• Vascular tissue – transports water & nutrients; “bloodstream”
• Ground tissue – tissue between the dermal and vascular tissues
Dermal tissue – generally consists of a single layer of
epidermal cells.
The outer layer is often covered with a thick, waxy layer
called the cuticle, which protects against water loss and
injury.
Vascular tissue – contains
several different cell types;
transporting water and nutrients
around the plant.
Ground tissue – cells that lie
between the dermal and vascular
tissues.
Roots
Roots absorb water and dissolved nutrients from
the soil. Plants have a one-way system to generate
enough pressure to move water out of the soil and
into the body of the plant.
The water has no where else to go, but
UP!
Root hairs increase surface area!
Fibrous roots
Tap roots
Stems
Stems have 3 important functions:
•
Produce leaves, branches and flowers
•
hold leaves up in the sunlight
•
transport substances between roots and leaves
Leaves are attached to a
stem at structures called
nodes.
Some stems can also
carry out photosynthesis
Formation of Wood
The most important “stem” is the stem of the tree.
Wood is actually layers of xylem!
Read p.
592
Leaves
Transpiration –
The loss of water from a
plant through its leaves
Maple tree leaves
Black Walnut tree leaves