Transcript Chapter 9: Plant Organization

Chapter 9: Plant Organization
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Vascular Seed Plants
• Phyllum: Tracheophyta (Contain Xylem and Phloem)
• Both gymnosperms and angiosperms disperse
by seeds.
• A seed has a seed coat and contains an
embryonic sporophyte and stored food that
supports growth when the seed germinates.
• Gymnosperms have exposed or “naked” seeds.
• In angiosperms (flowering plants), seeds are
enclosed by a fruit.
Gymnosperm diversity
(naked-seed plants)
Angiosperms
(enclosed-seeds)
• Angiosperms are flowering plants and
include tropical and subtropical trees.
• All hardwood trees are angiosperms.
• Angiosperms are divided into monocots
(such as the grass family) and dicots (such
as the maple and rose families).
Monocot Versus Dicot Plants
• Flowering plants (angiosperms) are divided into
two groups depending on their number of
cotyledons (seed leaves).
• Monocots (monocotyledons) have one
cotyledon; dicots (dicotyledons) have two.
• Cotyledons provide nutrients for seedlings
before true leaves begin photosynthesizing.
Monocot Versus Dicot Plants
• Important monocots are rice, wheat and corn; oak trees
and dandelions are dicots.
Monocot and Dicot traits
• The vascular (transport)
tissue is organized
differently in monocots
and dicots.
• Monocot roots have
vascular tissue in a ring;
in stems, vascular
bundles are scattered.
• Dicot roots have vascular
tissue in a star shape with
phloem located between
arms of xylem. Stems
have vascular bundles in
a ring.
Monocot and Dicot traits
• Leaf veins are vascular
bundles within a leaf.
• Monocots usually have
parallel venation.
• Dicots exhibit netted
venation, which may be
either pinnate or palmate.
Monocot and Dicot traits
Dicot leaves
Plant Organization
• Vascular-seed plants have characteristic
organs and tissues. (Angiosperms…..)
• An organ is a structure that contains different
types of tissues and performs one or more
specific functions.
• The vegetative organs of a flowering plant –
the root, stem, and leaf – allow the plant to
live and grow.
• The body of a plant has a root system and a
shoot system.
Plant Organization
Plant Tissues
•
A plant grows throughout its lifespan because
of meristem (embryonic tissue) in stem and
root tips (apexes).
• Three specialized tissues are in plants:
1) Epidermal tissue – forms the outer protective
covering
2) Ground tissue – fills interior of a plant
3) Vascular tissue – transports water and
nutrients and provides support.
Epidermal Tissue
•
•
•
•
(epi = above, dermal = skin)
Epidermal tissue forms the outer protective
covering of a herbaceous plant and is modified
in roots, stems, and leaves.
Exposed epidermal cells are covered with waxy
cuticle to minimize water loss.
Epidermal cells in roots have root hairs.
Lower leaf epidermal cells have guard cells and
stomata.
Epidermal Tissue
(epi = above, dermal = skin)
• In older woody plants, the epidermis of the stem is replaced by
cork tissue.
• Cork, a component of bark, is made up of dead cells that may
be sloughed off.
• New cork cells are made by a meristem called cork cambium.
Vascular Tissue
• There are two types of vascular (transport) tissue
that extend from roots to leaves.
• Xylem transports water and minerals from roots
to leaves through two types of conducting cells.
• Phloem transports organic nutrients (phood) from
leaves to roots and has sieve-tube elements with
companion cells.
Vascular Tissue
Xylem structure
Phloem structure
Plant Organization
ROOTS!
• Roots have two main functions:
1. Anchorage
2. Absorption
• Roots are classified according to origin or form– Origin: The radicle is the root system of seedling,
from this, the primary root develops. Secondary
roots (branch roots) grow out from the primary.
ROOTS!
• Roots are classified according to origin or form– Origin: The radicle is the root system of seedling, from this,
the primary root develops. Secondary roots (branch roots)
grow out from the primary.
ROOTS!
• Roots have two main functions:
1. Anchorage
2. Absorption
• Roots are classified according to origin or form– Origin: The radicle is the root system of seedling,
from this, the primary root develops. Secondary
roots (branch roots) grow out from the primary.
– Form: There are two main forms,
Dicots typically have a large, singular tap-root and
Monocots have a diffuse, branched, fibrous system.
ROOTS!
• Roots are classified according to origin or form– Form: There are two main forms,
Dicots typically have a large, singular tap-root
Monocots have a diffuse, branched, fibrous system.
Root Diversity
• Roots have special adaptations
and associations to better
perform the functions of
anchorage, absorption of water
and minerals, and
carbohydrate storage.
• An example is the dicot plant,
CARROT, where its primary
root (taproot) is fleshy and
stores food (also, beets).
Root Diversity
• Roots may also develop from
from stem, above the first root,
these are called “adventitious
roots.”
• Because these roots tend to be
thicker and pass into the soil
below, they provide extra
support and are also known as:
PROP ROOTS.
ROOTS!
• The cylindrical
shape of the root
allows it to
penetrate the
soil.
• Root hairs greatly
increase the
absorptive
capacity of the
root.
ROOTS!
• Generally the root system is equivalent in size and
extent to the shoot system. (The iceberg principle)
• Some plants store the products of photosynthesis in
their roots. (Carrots or beets)
Organization of Roots
Dicot root tip:
Organization of Roots
• Within a root are zones
where cells are in various
stages of differentiation.
The root apical meristem is
in the zone of cell
division; the root cap is
a protective covering for
the root tip.
Organization of Roots
• In the zone of
maturation, mature
cells are differentiated
and epidermal cells
have root hairs.
In the zone of
elongation, cells
become longer as
they specialize.
Tissues of a Dicot Root
• Epidermis – single layer of thin-walled,
rectangular cells; root hairs present in zone of
maturation
• Cortex – thin-walled, loosely-packed
parenchyma; starch granules store food
• Endodermis – between cortex and vascular
cylinder, single layer of endodermal cells
bordered by the Casparian strip; regulates
entrance of minerals into the vascular cylinder
Tissues of a Dicot Root
• Vascular Tissue – has star-shaped xylem in dicots
with phloem in separate regions between arms of
xylem; the pericycle gives rise to lateral roots
Organization of Monocot Roots
• In a monocot root’s centrally
located pith, ground tissue is
surrounded by a vascular
ring composed of alternating
xylem and phloem bundles.
• Monocot roots also have
pericycle, endodermis,
cortex, and epidermis.
Plant Organization
Stems
• The shoot system of a plant includes both
stems and leaves.
• A stem is the main axis of the plant along
with its lateral branches.
Shoot system
Shoot system
• At the tip of the stem is
tissue that allows the
stem to elongate and
produce leaves.
• A leaf attached to a stem
at a node; and internode
is the region beween
nodes.
Shoot system
• Stems also contain
vascular tissue that
transports water and
minerals from roots to
leaves, and also transports
the products of
photosynthesis in the
opposite direction.
Organization of Stems
• During primary growth, the shoot apical
meristem at the shoot tip produces new
cells that elongate and add length to the
stem.
• The shoot apical meristem is protected
within a terminal bud by bud scales. Bud
scales are actually modified leaves.
Organization of Stems
• Leaves are produced at nodes; the stem between two
nodes is called an internode.
• Internodes increase in length as the stem grows.
• Terminal buds form at the END of a branch.
• Lateral buds, are located on the SIDE of a branch.
Lateral buds which form at the axes of leaves are
called Axillary buds.
Organization of Stems
• Leaf scars appear if a twig is or has been dormant
and the leaves have been shed.
• The protective layer that forms before a leaf falls off is
the Abscision layer.
• Terminal bud scars appear as a flat, ring, around the
stem.
• Lenticles are small pores all over the stem used for
gas exchange.
Monocot vs. Dicot Stems
- In dicot stems, vascular bundles are in a
distinct ring; monocot vascular bundles are
scattered throughout.
Monocot
DICOT
Monocot stem
Herbaceous dicot stem
Woody Stems
• A woody plant has both primary and
secondary tissues.
• Primary tissues are new tissues formed
each year.
• Secondary tissues develop during the
second and subsequent years of growth
from lateral meristems (vascular cambium
and cork cambium).
• Primary growth, which occurs in all plants,
increases the length of the plant.
• Secondary growth, which occurs in conifers
and some dicots, increases the girth of a
plant.
• Trees undergo secondary growth because
of a change in vascular cambium.
• The secondary tissues produced by the
vascular cambium, called secondary xylem
and secondary phloem, add to the girth of
trunks, stems, branches, and roots.
Dicot stems
• As a result of secondary growth, a woody
dicot stem has an entirely different type of
organization.
• A woody stem now has three distinct areas:
the pith, the wood, and the bark.
• Pith rays are composed of living parenchyma
cells that allow materials to move laterally.
• The bark of a tree contains cork, cork
cambium, and phloem.
• Cork cambium replaces epidermis with cork
cells impregnated with suberin.
Secondary growth in a dicot stem
Annual Rings
• In trees that have a growing season,
vascular cambium is dormant during
winter.
• In spring, with plentiful moisture, xylem
contains wide vessels with thin walls in
spring wood; summer wood has a lower
proportion of vessels.
• Spring wood followed by summer wood
makes up one year’s growth or annual
ring.
Section of woody stem
Tree trunk
Stem Diversity
- Some stems have functions other than
transport; some are specialized for storage.
• Stems nay also function in reproduction, climbing (tendri
on a pea plant).
• Modified stems aid adaptation to different environments.
• Examples of stem modifications include:
-Stolons -Rhizomes -Tubers -Corms
Stem Diversity
Stolons and Bulbs
Onion or Garlic
Bulb
Bulb
Stem Diversity
Tubers and corms
Potato!
Gladiola
Leaves
• A leaf is a broad, thin organ that carries on
photosynthesis.
• This shape maximizes the surface area for
collection of solar energy and absorption
of carbon dioxide.
• The wide portion of a leaf is the blade, a
petiole is the stalk of the leaf, and axillary
buds are found at the leaf axil.
• Some leaves have other functions.
Leaves
Stoma of leaf
Dr. L Humphries
[email protected]
Spring 2005: Fundamentals of Biology
Section 1107
Biology 10
4-Units
EXERCISE 12:
Angiosperm Stem
Dr. L Humphries
[email protected]
Spring 2005: Fundamentals of Biology
Section 1107
Biology 10
4-Units
EXERCISE 13:
Angiosperm Root