Transcript Plant Structure

Plant Structure
Plant Tissues
• A tissue is a group of cells organized to
form a functional unit or a structural unit
• Plants have 3 tissue systems:
• Ground tissue (3 types)
• Vascular tissue (xylem and phloem)
• Dermal tissue (exterior)
Ground tissue
• Parenchyma - found throughout the plant,
these tissues perform important functions
like photosynthesis
• Colenchyma - structural support in
herbaceous plants
• Sclerenchyma- hard structural support
(trees)
Parenchyma
• Simple tissue found throughout the plant.
Functions include photosynthesis, food
storage, secretion
Collenchyma
• Provides structural support
• Found just under the stem epidermis and
along leaf veins
• Cells are alive at maturity and function only
when they are alive
Sclerenchyma
• Hard structural support
• may be alive or dead and still function
structurally
• one type of sclerenchyma is fiber (wood)
Xylem and Phloem
• Both add structural support
• Xylem - conducts water and minerals, long
tapering cells that act as pipes of a sort
• Phloem - conducts food
Dermal
• Epidermis - outermost layer composed of
single layer of ground parenchyma cells
• Periderm - many layers thick, found on
woody plants, replaces epidermis,
parenchyma cells
Growth
• Plant growth occurs at specialized areas
called meristems (meristematic tissue)
• primary growth - increase in length of plant,
occurs at apical meristems,
• secondary growth - increase in girth, occurs
at lateral meristems, vascular cambium (see
figure 26-16, pg 519)
Stems
Leaves
Leaves
• Arrangement on stem -pg 509
•
•
•
•
alternate
opposite
whorled
Large surface area to collect light and allow for
gas exchange but increases tendency for water loss
- cuticle reduces water loss
• Hairs on leaves are called trichomes
Leaves
• Cuticle is thicker on the top of a leaf than it
is on the bottom
• Stomata - opening controlled by guard cells.
More stomata on bottom of leaves
• Mesophyll- photosynthetic tissue of leaf
• Xylem and phloem pass through mesophyll
(xylem toward the top and phloem toward
the bottom)
Mesophyll
• Palisade layer - cells stacked more closely
together, toward the upper epidermis,
primary site of photosynthesis
• Spongy layer - cells more loosely
organized, toward lower epidermis, some
photosynthesis, but primarily engaged in
gas diffusion within the leaf
Monocots and Dicots
see page 529
Characteristic Monocot
Dicot
Leaf shape
Attach to stem Wrap around
Broad,
flattened
Petiole
Veins
Parallel
Netted
Mesophyll
Not
Contains both
differentiated spongy and
palisade layers
Narrow
Leaf function
• Photosynthesis - more later
• Transpiration - 99% of water absorbed by
plant is lost by transpiration
• Guttation- available water is high,
transpiration is low
• Abscission-allows plant to shed leaves