Roots, Stems, and Leaves
Specialized Tissues In Plants
A.Seed Plant Structure
1. Roots
2. Stems
3. Leaves
B. Plant Tissue Systems
C. Dermal Tissue
D.Vascular Tissue
1. Xylem
2. Phloem
E. Ground Tissue
F. Plant Growth and Meristematic Tissue
Seed Plant Structure
• The cells of seed plants are organized into
tissues and organs.
• The three main plant organs are roots,
stems, and leaves.
– Roots absorb water and dissolve
nutrients and anchor plants in the
ground.
– Stems support the plant body and
transport materials throughout the
plant.
– Leaves are the main organs of
photosynthesis. They also function in
gas exchange.
Root, Stem, and Leaf Tissues
Leaf
Stem
Root
Dermal tissue
Vascular tissue
Ground tissue
Plant Tissue Systems
• Within the roots, stems, and leaves are specialized tissue
systems. The three main tissue systems:
– Dermal tissue is like the skin of a plant. It protects the
plant and prevents water loss.
– Vascular tissue consists of xylem (move water
throughout the plant) and phloem (moves sugars and
other materials throughout the plant).
– Ground tissue is made up of all of the cells that lie
between dermal and vascular tissues. (made up of 3
kinds of cells)
• Parenchyma cells: function in photosynthesis and
storage
• Collenchyma cells: help support larger plants
• Sclerenchyma cells: make ground tissue tough and
strong
Plant Tissue Systems Cont.
• A fourth kind of tissue, meristematic tissue, is responsible for
plant growth.
– Meristematic tissue is the only plant tissue that produces
new cells by mitosis.
– The tips of stems and roots are made of meristematic
tissue.
Concept Map
Plant Tissues
include
Dermal
tissue
Meristematic
tissue
includes
Epidermal
cells
Ground
tissue
includes
Xylem
includes
Tracheids
Vascular
tissue
Vessel
elements
includes
Phloem
Parenchyma
cells
includes
Sieve tube
elements
Companion
cells
Collenchyma
cells
Schlerenchyma
cells
Roots
• The two main types of roots are taproots and fibrous roots.
• Taproots: the primary root grows long and thick, while the
secondary roots stay small.
• Fibrous roots: secondary roots that grow and branch out
• Roots have two main functions
– To anchor a plant in the ground
– To absorb water and dissolved nutrients form the soil
Taproots and Fibrous Roots
•
Taproots (Carrots)
Fibrous Roots (Grasses)
The Structure of a Root
Epidermis
Endodermis
Root hairs
Ground tissue
(cortex)
Phloem
Xylem
Vascular
Cylinder
Ground tissue (cortex)
Epidermis
Endodermis
Vascular cylinder
Zone of
maturation
Zone of
elongation
Apical meristem
Root cap
Cross Section of Plant Root
(magnification: 40x)
Stems
• Stems have three important functions
– To produce leaves, branches, and flowers
– To hold leaves up to the sunlight
– To carry water and nutrients between the roots and leaves
Plant stems grow in two ways
Comparing Primary and Secondary Growth of Stems
Characteristics
Primary Growth
Secondary Growth
Where It Occurs
At ends of plants
In stem
Effect on Plant
Increases plant length
Increases stem width
How It Is
Produced
By cell division in the apical By cell division in
meristem
meristems other than
the apical meristem
Leaves
• The structure of a leaf is optimized for absorbing light and
carrying out photosynthesis.
• To collect sunlight, most leaves have thin, flattened sections
called blades.
• Plants can lose water out of their leaves as they exchange
gases with the air (transpiration).
– To prevent major water loss plants allow air in and out of
their waterproof covering only through small openings
called stomata.
– Plants keep their stomata open just enough to allow
photosynthesis to take place but not so much that they
lose an excessive amount of water.
Transpiration
A
B
Evaporation of water
molecules out of leaves.
Pull of water molecules upward
from the roots.
Blades On Leaves
The Internal Structure of a Leaf
Cuticle
Veins
Epidermis
Palisade
mesophyll
Xylem
Phloem
Spongy
mesophyll
Epidermis
Stoma
Guard
cells
Vein
Transport in Plants
• Forces of Attraction
• Molecules of a similar substance are attracted to one
another by a force called cohesion.
• Molecules of different substances are attracted to one
another by a force called adhesion.
Transport In Plants
Phloem Xylem
Sugar
molecules
Source cell
Movement
of water
Movement
of sugar
Sink cell