Transcript Think of the plant as if its still an embryo, these are the

CHAPTER 35
PLANT FORM
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Meristems: They elaborate the plant
body after germination
- act as stem cells for plants- rapidly divide into
differentiated cells that make up the plant body
- two types:
- apical meristems= elongate the root and
stem of plant
- lateral meristems= produce and increase in
girth
- only present in vascular plants (shrubs
and trees)
Apical Meristems
- located at the tips of stems and roots
- after germination, meristems produce primary tissues
which becomes the primary plant body (soft shoots and
roots)
- develop into three types of embryonic tissue systems
- protoderm- forms the epidermis
- procambium- produces primary vascular tissue
- ground meristem- differentiates further into ground
tissue
(Think of the plant as if its still an embryo, these are the
developmental stages of plant life)
Lateral Meristems
- lateral meristems produce what is called secondary
growth= most of the trunk, branches, and older roots of
trees
- has the most dramatic effect in woody plants which have
two lateral meristems
- cork cambium- produces the cork cells of the outer
bark
- vascular cambium- produces secondary vascular
tissue and lies between the xylem (wood) and phleom
(cells close to woods surface)
- interesting fact: removing the bark of a tree damages the
phloem and may eventually kill the tree
Organization of the Plant Body
-- coordination of primary and secondary growth produces
an adult plant
- plants do not have a fixed size and vary between plants,
even of the same species
- number, size, structure, and location of leaves is
dependent on plant environment
- vascular plants have a root system ( grounds them and
provides the plant with ions) and a shoot system (the stem,
leaves, flowers, and fruit)
- nodes and internodes on the shoot develop axillary buds
that create new growth
-
Types of Plant Tissue: Dermal Tissue
-Epidermal cells cover all the primary plant body
- a number of specialized cells occur at the epidermis
- guard cells flank the stomta (epidermal openings)
- contain chloroplast
- stomata only occur on the epidermal tissue of leaves
- exchange of CO2 and O2 occur at stomata
- Trichomes- hair like outgrowths of the epidermis (the "fuzzy stuff" on
stems and leaves)
- keep leaf surfaces cool and reduce transpiration
- some secrete sticky or toxic substances
- Root hairs- occur at the tips of young roots
- keep the root in close contact with soil and increase absorption
efficiency
- in vascular plants, the cork cambium produces bark which replaces
the epidermis
Types of Tissue: Ground Cells
- Parenchyma cells: most common type of cell, less
specialized, mainly store food and water in large vacuoles
- Collenchyma cells: relatively flexible, provide support for
plant organs so they can bend without breaking (the strings
of celery)
- Scelrenchyma cells: two types
- fibers= long slender cells grouped in strands
- sclereids= form in branched bundles
- cell wall of scelrenchyma cells contain ligin- branched
polymer that causes the cell wall to become rigid
Types of Tissue: Vascular
- xylem cells: principle water conducting tissue of plants
- a combination of dead hollow cells that make vessels and
trachieds
- water and other ions travel from the roots through the
xylem to the leaves and diffuses as water vapor out of the
stomata
- Phloem cells: principal food conduction tissue of plants
- carried out by sieve cells and sieve-tube members
- sieve-tube memebers form sieve tubes and each cell is
pared with a parenchyma cell (called compaion cells)
-connected by plasmodesmata- which supplies the plant
cells with organic materialsr
Root Structure
-there are three types vegetative organs in plants;
- roots, stems, and leaves
-there are four parts recognized in developing roots;
-root cap, zone of cell division, the zone of
elongation,
and zone of maturation
-apical initials divide the cells that divide and end up on the tip
become root cap cells
-the other cells divide in opposite directions and pass through
the three zones then they are fully differentiated
The Root Cap
-the root cap consist of two types of cells; columella cells (the inner
cells) and root cap cells (the outer cells)
-the root cap cells are continuously replenished by the root apical
meristem
-there are golgi bodies in the root cap cells that secretes a slimy
substance, this helps the root through the soil. It also helps with the
growth of nitrogen-fixing bacteria
-the root cap also functions as the perception of gravity
-the inner (columella) cells are very specialized
-they have endoplasmic reticulum in the nucleus and the
periphery which is located in the middle or top of the cell
-contain no large vacuoles
-contain amyloplasts which form on the sides of the cells towards
the pull of gravitiy
The Zone of Cell Division
-apical meristem is located in the
center of the root tip , it is shaped like
a inverted concave dome
-cells divide every 12 to 36 hours at
the edge of the dome
-these new daughter cells go to one of
the three tissues; protoderm,
procambium, or ground meristem
-in this section genes have been
identified
-the inner cell layer regulates the flow
of water, the outer cell layer acts as
storage
-if a mistake occurs and a cell is not in
the correct place the cell will develop
according to the new postition
The Zone of Elongation
-the cells from the primary meristem become several times
longer than they are wide, this causes the root to lengthen
-the vacuoles inside these cells increasing until they occupy
90% of each cell
-cells do not grow anymore in size above the zone of
elongation
The Zone of Maturation
-the cells that elongated in the zone of elongation are
differentiated into specific cell types
-many epidermal cells develop roots hairs, increasing surface
area to absorb nutrients and water
-the ground meristem produces parenchyma cells, they are
found in the interior of the epidermis
-this layer called the cortex can by many cell layers thick
and it functions in storage
-the endodermis has walls filled with suberin, suberin is
produced in bands called Casparian strips
-the stele is everything inside of the endodermis
-the primary xylem conducts water
Modified Roots
-most plants either produce tap roots or fibrous roots, however
there are plants with roots specific to the function needed for
that plant
-a root that comes from something other than a root is called a
adventitious root
Stem Structure: External Form
-the shoot apical meristem produces stem tissue that creates
bulges (primordia) these bulges will form into leaves, shoots,
and flowers
-a node is the area where the leaf is attached
-the area between two nodes is called an internode
-the bud that is a product of the primary shoot apical meristem
is called the axillary bud
-a leaf scar is from the leaves falling off the trees in the fall, a
bundle scar is where the vascular connections were
Internal Form
-from the apical meristem three primary meristems develop;
the protoderm,the ground meristem, and the procambium
-cells of the vascular cambium divide indefinitely and create a
secondary tissue
Leaf External Structure
- two morphological groupsmicrophyll- one gapless vein, and
megaphylls- several veins
- leaves have evolved to have a
flattened blade and slender stalk
- mutant leaves have been found
to never flatten
Leaf Blades
- simple leaves= undivided
- compound leaves=
divided into leaflets
- pinnate= lined leaflets
- palmate= radial leaflets
- alternate leaves have
one bud per leaf
- compound leaves have
two leaves per bud
Leaf Internal Structure
- entire surface covered with
transparent epidermis and
cuticle, lower epidermis
contains stomata and guard
cells
- two layers of tissue ( the
palisade and spongy
mesophyll) rest between the
upper and lower epidermis
- veins, stomata, and
intercellular spaces function
together for gas exchange
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