Transcript CB098-008.39_Plant_Structure_B

Three Tissue Systems Make Up the Plant Body
3) Dermal Tissue System
- Forms an outer protective covering of the plant.
- Covers and protects the plant surface from drying out, pathogens, & insects.
- Complex tissues make up this tissue system.
- Main Tissue Types: epidermis (primary) and periderm (secondary).
- The Dermal Tissue System also includes modified cells like guard cells, root
hairs and cells that produce a waxy cuticle.
- Dermal Tissue System is found in the epidermis of early growth and periderm
of later growth. It also found in the endodermis which is tightly packed
layer of cells that surrounds the vascular cylinder in the root of a plant.
Note: On the below cross sections, only dermal tissues are circled with red dots.
Leaf Cross Section
Stem Cross Section
Root Cross Section
The Complex Tissues of the Dermal Tissue System
A) Epidermis Tissue (Cells)
Epidermis is the outer
covering of the plant
made of complex
tissue.
The epidermis regulates
gas exchange in and
out of the plant.
The epidermis is
usually one cell layer
thick but 5-6 cells thick
in succulent (cacti)
plants.
Epidermal Cell Types:
Epidermal, Guard Cells,
Subsidiary Cell,
Trichomes (hairs).
Upper leaf surface of Sheppard's
purse (Magnified 350 times)
Epidermis Tissue (Cells) continued.
Epidermal Cells are living but lack chloroplasts. They posses thick cell walls.
The outer “facing outward” surface is coated with cutin, a waxy
substance forming an impermeable layer called the cuticle. Notice how a
drop of water beads on a leaf just like water beading on your freshly
waxed car. Only the shoot apex, root cap, and root hair surface lacks a
cuticle.
Guard Cells are found
in young stems,
leaves, flower parts
and rarely roots. They
contain chloroplasts.
Between each pair of
guard cells is a small
pore through which
gases enter or leave; a
pair of guard cells in
addition to the pore
constitute a stoma
(plural, stomata).
Guard cells are able to
open and close.
Subsidiary Cells
regulate the opening
of guard cells.
Epidermis Tissue (Cells) continued.
Trichome Cells are short filaments of one or more cells extending from the
epidermis. Trichomes are epidermal outgrowths (single or multicellular).
Root hairs are trichomes that are extensions of single epidermal cells that
increase root surface area in contact with soil water. In some leaves,
elaborate multicellular trichomes may form. Some trichomes can store
water, insulate heat or reflect sunlight.
Glandular
Hair in
Tobacco
The Complex Tissues of the Dermal Tissue System
B) Periderm Tissue (Cells)
Periderm is a protective
tissue that replaces the
epidermis after secondary
growth is initiated. In
similar words, the
periderm is a protective
layer that forms in older
stems and roots. The
periderm consists of cork
(phellem), cork cambium
(phellogen) and
phelloderm.
(Parenchyma Cells)
Cork is dead a maturity
and has suberin, a waxy
substance embedded in
its cell walls.
Now let’s look at
different plant parts
and understand the
cells and tissue
systems involved.
See next 4 Slides.
Clover Stem (Cross Section)
(Dermal Tissue System)
(Xylem and Phloem Cells:
Vascular Tissue System) (Made from Parenchyma Cells:
Ground Tissue System)
Corn Stem (Cross Section)
(Dermal Tissue System)
(Xylem and Phloem Cells:
Vascular Tissue System)
(Made from Parenchyma Cells:
Ground Tissue System)
Buttercup Root (Cross Section)
(Made from Parenchyma Cells:
Ground Tissue System)
(Dermal Tissue System)
(Xylem and Phloem Cells:
Vascular Tissue System)
Lilac Leaf (Side View)
Top of Leaf
(Dermal Tissue System)
(Made from Parenchyma Cells:
Ground Tissue System)
(Xylem and Phloem Cells:
Vascular Tissue System)
Meristems: Where Cells Divide
Meristems – sites in the plant body where cells divide and
where differentiation into specialized cells and tissues are
initiated.
Growth – Increasing the size and number of cells. This
includes cell division and cell enlargement.
Cell Differentiation – Cells become structurally and
biochemically different in order to do different functions.
Meristems are not necessarily tissues. They are “areas.”
Primary Growth
Primary growth allows for vertical growth to occur (For the shoots to grow up
and the roots to grow down). The Apical Meristems are the shoot apical
meristem (SAM) and root apical meristem (RAM). The apical meristems are
located at the tip of roots and shoots. The apical meristems are the Zone of Cell
Division. This cell division does not often occur forever. Plant growth is
determined by genetics, nutrients, and structural limitations.
Right behind the Zone of Cell Division (further from the apex) is the Zone of
Elongation. Here is where the cells elongate and are responsible for pushing
the root down and the shoot up.
Even further from the apex is the Zone of Differentiation (PRIMARY
MERISTEMS). This is where cells undergo specialization into the 3 Primary
Meristems. These 3 Primary Meristems give rise to the 3 tissue systems that we
covered.
PRIMARY MERISTEM
TISSUES
1) Protoderm . . . . . differentiates into . . . . . . . . . . . . . Epidermis.
2) Procambium . . . differentiate into . . . Primary Xylem & Primary Phloem.
3) Ground Meristem . . differentiate into . . . Pith and Cortex of Stems and
Mesophyll of
Leaves.
Primary Growth of Shoot Tip
Primary Growth of Root Tip
Secondary Growth
Secondary meristems produce secondary tissues which increases the girth of
a plant. In other words, secondary meristems allow for lateral or horizontal
growth. While growing, this allows for an increase in thickness and
circumference of stems and roots. Secondary growth is responsible for wood
in trees. In woody plants, secondary growth is responsible for the gradual
thickening of the roots and shoots formed from earlier primary growth.
Some plants lack secondary growth. In herbaceous (nonwoody) plants there
is only primary growth because they only grow during one year’s time.
SECONDARY MERISTEM
TISSUES
1) Cork Cambium . . . . . . differentiates into . . . . . . . . Periderm.
2) Vascular Cambium . . . differentiates into . . . . . Secondary Xylem &
Secondary Phloem.
Diagram of a tomato plant showing the relative positions of the root apical meristem
(RAM) and shoot apical meristem (SAM), the primary meristems (protoderm,
ground meristem, and procambium), and the secondary meristems (vascular
cambium and cork cambium in both the shoot and root system.
Summary of Meristems and the Tissues They Generate
^
*
*
^
*
#
#
* indicates Tissue from the Ground Tissue System.
^ indicates Tissue from the Dermal Tissue System.
# indicates Tissue from the Vascular Tissue System.
#
#
BIO 141 Botany with Laboratory
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