Transcript Leaves, Roots, Stems

Leaves, Roots, Stems
Plant organs and their functions
Leaves
Leaf Parts
• Two major parts to
the leaf:
• Blade
• Petiole
Leaf microanatomy
• Epidermis and
cuticle do what?
• Mesophyl does
what?
• Veins do what?
• Guard cells in the
lower epidermis do
what?
Photosythesis
• The purpose of photosynthesis is to
produce organic (carbon-based)
molecules (such as sugars).
• The plants use these molecules for two
purposes:
• As an energy source
• As building material
Roots
Types of root systems
• Taproot systems:
main root, lateral
branches.
• Fibrous root
systems: lose the
primary root,
replaced by many
smaller roots.
Root Anatomy
• Parts of a root:
• Root cap
• Root meristem
• Zone of
elongation
• Zone of
maturation
Roots: Epidermis
• Root epidermis
lacks a cuticle, and
is porous. Usually
has many root
hairs.
• Water enters
through membranes
of epidermal cells or
through spaces
between cells.
Roots: Cortex
• The cortex layer is
made up of
parenchyma cells.
What is the main
function of these
cells?
• Endodermis
separates the
cortex from the
vascular cylinder.
Roots: vascular cylinder
• Casparian strip
around endodermis
cells controls water
movement. Why?
• Pericycle: layer of
parenchyma cells,
inside of
endodermis, from
which branch roots
can arise.
Roots: vascular cylinder
• Vascular cylinder
contains:
• Phloem: what
does phloem do?
• Xylem: What
does xylem do?
Stems
Stems: Epidermis
• In herbaceous
plants and young
woody plants, the
stem is covered
with epidermis.
• Epidermis secretes
cuticle, has
stomata, and may
be photosynthetic.
Stems: Cortex and Pith
• Cortex layer
contains
parenchyma cells
and vascular
bundles.
• Pith makes up the
center of the stem,
and is absent in
hollow stems.
Stems: vascular tissue
• Vascular bundles
are in the cortex.
• Between the xylem
and phloem is the
vascular cambium,
a meristem layer.
What is it for?
Stems: Secondary growth
• Secondary growth
is seen in woody
plants.
• This kind of growth
produces stronger,
thicker stems from
the vascular
cambium and cork
cambium.
Stems: wood and bark
• What tissue makes
up the wood of a
tree trunk? (hint:
water flows there.)
• What tissue makes
up the “green
bark?” (hint: sap
flows there.)
• Dead cork cells
make up the bark.
Stems: Annual Rings
• Trees in temperate
zones grow at
different rates in
different seasons,
causing annual
rings to form.
• In some parts of the
tropics, if seasons
vary little, tree rings
are indistinct.