Transcript Plant Structures

MONOCOTS
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1 cotyledon (storage
tissue that provides
nutrition to the
developing seedling)
Parallel pattern of veins
in leaves
Flower parts in 3’s
Vascular bundles
scattered
Fibrous root system
DICOTS
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2 cotyledons
Branching pattern of
veins in leaves
Flower parts in 4’s, 5’s,
or multiples therof
Vascular bundles
organized in a circle
Taproot (a large single
root)
One
cotyledon →
Flower parts in 3’s
Scattered vascular bundles
Fibrous root
system
Parallel
venation
2 cotyledons
Branched venation
Taproot
Flower parts in 4’s, 5’s
Vascular bundles in rings
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Ground Tissues (3
types—differ mostly
in their cell walls)—
shown in light blue
Dermal tissues (cover
the plants surfaces)—
shown in pink
Vascular tissues
(transport
materials)—shown in
purple
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Parenchyma cells: most common component of
ground tissue, have thin walls and serve various
functions including storage, photosynthesis and
secretion
Collenchyma cells: have thick but flexible cell walls
Sclerenchyma cells: have thicker walls than
collenchyma, serve as mechanical support.
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Dermal tissue consists of epidermis cells that cover the
outside of plant parts, plus:
Guard cells that surround stomata
Specialized surface cells such as hair cells, stinging
cells, and glandular cells.
Epidermal cells secrete the cuticle (waxy coating)
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Two main kinds: Xylem and Phloem. The two
usually occur together in Vascular Bundles.
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Xylem function in the conduction of water and
minerals
It also provides mechanical support. (In addition to the
primary cell wall that all plant cells have, the xylem
cells have a secondary cell wall that gives them
additional strength).
Pits are locations where the secondary cell wall is
absent.
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Most xylem cells are dead at maturity. They are
essentially cell walls, completely lacking cellular
components & only contain the material being
transported.
There are 2 kinds:
Tracheids and Vessel elements
TRACHEIDS
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long and tapered; water
passes from one
tracheid to another
through pits
on the
overlapping
tapered ends
of the cells.
VESSEL MEMBERS
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shorter and wider with
no taper;
Water passes from one
vessel to the next
through areas devoid of
both primary and
secondary cell walls
(called perforations)
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Phloem functions in the
conduction of sugars.
It is made of cells called
sieve-tube members that
form fluid-conducting
columns called sieve
tubes.
Pores on the end walls of
sieve-tube members form
sieve plates where the
cytoplasm of both cells
combine.
Companion cells provide support to
the sieve-tube members.
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A seed consists of an
embryo, a seed coat,
and some kind of
storage material.
The major storage
material may be
endosperm or
cotyledons.
Cotyledons are formed
by digesting the storage
material in the
endosperm.
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Most of what you see when you look at the two
halves of a dicot seed are the two cotyledons.
In many monocots, such as corn, most of the
storage tissue is endosperm, with only one
cotyledon to transfer nutrients to the embryo.
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The embryo consists of: 
Epicotyl—becomes the
shoot tip
Young leaves called the
plumule
Hypocotyl-becomes the
shoot
Radicle –becomes the root
Coleoptile (in monocots)
surrounds and protects the
epicotyl.
Dicot
seed
Monocot
seed
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After a seed reaches maturity, it remains
dormant until specific environmental cues exist
Most important: water. Others include
temperature, light or seed coat damage (ex:
from fire or digestive enzymes from an animal)
Germination begins with absorption of water.
Water initiates the activity of certain enzymes,
which activate respiration. The seed swells, and
the coat cracks.
The radicle produces roots, then the shoot
grows.
Dicot Seed Germination
Monocot Seed Germination
For many plants, actively dividing cells occur
only at the apical meristems (the tips of roots
and shoots).This growth increases the length of
a shoot or root.
The tissues that develop from this growth are
primary tissues
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Some plants, like conifers and woody dicots
undergo secondary growth in addition to
primary growth.
Whereas primary growth
extends the length of plant
parts, secondary
growth increases their
girth and is the origin of
woody plant tissues.
Growth occurs at 2 places:
vascular cambium and cork
cambium.
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The functions of roots
are:
To anchor plants
To absorb water and
nutrients
May store
carbohydrates or
water
← A taproot system branches in
a way similar to human lungs—
the roots start as one thick root
on entrance into the grounds,
and then divide into smaller and
smaller branches called lateral
roots underneath the surface.
These serve to hold the plant in
place.
Dicots—Taproot
System
Fibrous Roots →
Provide plants with a
very strong anchor in
the ground without
going very deep into the
soil.
Monocots—Fibrous
Root System
Epidermis lines the outside surface of the root. In the zone of maturation,
epidermal cells produce root hairs, which increase the absorptive surface.
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The cortex makes up
the bulk of the root.
Its main function is
the storage of starch.
The cortex often
contains numerous
intercellular spaces,
providing air for
cellular respiration.
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The endodermis is a ring of tightly packed cells
at the innermost portion of the cortex.
A band of fatty material, called suberin,
impregnates the endodermal cell walls where
they make contact with
adjacent endodermal cell
walls. This encircling
band around each cell is
called the Casparian Strip.
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The Casparian Strip creates a waterimpenetrable barrier between the cells.
As a result of the Casparian Strips, all water
passing through the
endodermis must pass
through the endodermal
cells and not between
them
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Inside the endodermis is the Stele (vascular
cylinder). The outer part of the stele consists of
one to several layers of cells called the
pericycle (from which lateral roots arise).
Inside the pericycle
is the vascular tissue.
The structures of the
xylem and phloem
differ between
monocots and dicots.
MONOCOT ROOT
Note that in monocots the xylem and
phloem occur in bundles in a circle
around the pith.
DICOT ROOT
Note that in dicots, the xylem forms a
cross in the center with phloem in
clusters between the “arms” of the
cross.
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In most plants stems are located above the soil
surface but some plants have underground
stems. A stem develops buds and shoots and
usually grows above the ground. Inside the
stem, materials move up and down the tissues
of the transport system.
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The stem’s epidermis contains epidermal cells covered
with a waxy substance called cutin. The cutin forms a
protective layer called the cuticle.
The cortex consists of the various ground tissue types
that lie between the epidermis and the vascular
cylinder.
The vascular cylinder consists of xylem, phloem, and
pith.
A single layer of cells between the xylem and phloem
may remain undifferentiated and later become the
vascular cambium.
Close-up view of vascular bundle in a
monocot stem
Monocot Stem Cross-Section—
notice how the vascular bundles
are scattered throughout the pith
and cortex.
Below: Dicot Stem Cross
Section—Note that the vascular
bundles are arranged in a ring
surrounding the pith.
Above: vascular bundle in a dicot stem
cross-section
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The vascular cambium originates between the
xylem and phloem and becomes a cylinder of
tissue that extends the length of the stem and
roots.
The cambium layer is meristematic, producing
new cells on both the inside and outside of the
cambium cylinder.
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Cells on the inside of the cambium cylinder
differentiate into secondary xylem cells; those
on the outside differentiate into secondary
phloem cells.
Over the years, secondary xylem accumulates
and increases the girth of the stem and root.
Similarly, new secondary phloem
is added yearly to the outside of
the cambium layer. As a result,
tissues beyond the secondary
phloem are pushed outward as
the xylem increases in girth.
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Tissues outside the secondary phloem get
pushed outward and are eventually shed.
In order to replace the shed epidermis with a
new protective covering, new cells are
produced by the cork
cambium. The cork
cambium produces
new cells primarily
on the outside.
Each year, new layers of
secondary xylem are produced
by the vascular cambium.
Recall that xylem tissue, which is
the actual wood of the plant, is
dead at maturity. Xylem
produced during the most recent
years remains active in the
transport of water.
This xylem is referred to as
sapwood. Older xylem, located
toward the center of the stem is
called heartwood and functions
only as support.
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In many environments, conditions vary during
the year, creating seasons during which plants
alternate growth with dormancy.
During periods of growth, the vascular
cambium is actively dividing, then stops at the
end of the season.
The alternation of growth and dormancy
produces annual rings in the secondary
xylem tissue. These rings can be used
to determine the age of a tree. Since
the size of the rings is related to the
amount of water available during the
year, rings can provide a record of
rainfall.
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Leaves are the
primary
photosynthetic organs
of the plant.
Their structures
provide optimal
conditions for
photosynthesis to
occur.
Leaves are
protected by the
waxy cuticle of the
epidermis, which
functions to
decrease the
transpiration rate
(and loss of water).
Inside the
epidermis lies the
ground tissue of
the leaf, the
mesophyll, which
is involved in
photosynthesis.
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Most of the
photosynthesis occurs
in the palisade
mesophyll, where
there are many
chloroplasts
The spongy
mesophyll cells
provide CO2 to the
cells performing
photosynthesis.
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Stomata are controlled by
guard cells that line the walls
of the epidermis (especially
on the underside).
When open, mesophyll cells
have access to CO2 and water
and photosynthesis can
continue.
However, they could dry out
due to excess transpiration.
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The process of
opening and closing
the stomates must be
carefully controlled.
When water flows
into guard cells (↑
turgor pressure), the
stomates open.
When water flows out
of the guard cells, the
stomates close.