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Plant Science
Plant Structures
Instructional Materials Service
Texas A&M University
- 8384 -
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Plant Structures
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Parts of a Vascular Plant
Root Structure
Stem Structure (External)
Leaf Structure
Parts of a Complete Flower
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Parts of a Vascular Plant
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Plant Organ Functions
• Roots support the plant and supply it with water
and nutrients.
• Stems connect the root and leaves.
• Leaves capture energy from the sunlight and
use it to make food for the plant.
• Reproductive structures attract pollinators and
produce seeds and fruits.
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• All living organisms consist of cells.
Groups of cells with similar functions
form tissues. Tissues with similar
functions form organs.
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Plant Organs
Plant organs include their roots, stems,
leaves, and reproductive structures. Each
plant organ performs a specialized task in the
life of a plant.
• Roots, stems, and leaves are all vegetative
structures.
• Flowers, seeds, and fruits make up
reproductive structures.
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• The cell is the basic structural and
functional unit for all living organisms.
Organelles within a cell perform
specialized functions.
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Organelles with common functions in both
plant and animal cells include:
• Nucleus – synthesizes ribosomes and
RNA and stores DNA
• Endoplasmic Reticulum (ER) –
prepares protein for export;
synthesizes steroids; regulates calcium
levels; and breaks down toxins
• Mitochondrion – converts energy from
organic compounds to energy for
cellular activities
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• Ribosomes – organize protein production
• Microtubules – contribute to cell support
and division
• Golgi Complex – processes and packages
substances made by the cell
• Cell membrane – semi-permeable
structure that separates the cellular
contents from the outside
• Lysosomes – digest old organelles and
foreign substances
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• Three organelles that are found only in
plant cells are plastids, vacuoles, and
the cell wall. Plastids contain DNA,
store starches and fats, and contain
pigments involved in photosynthesis.
Vacuoles store metabolic wastes and
often occupy as much as 90% of a
cell’s volume. The cell wall is
composed of cellulose fiber and gives
plant cells a very defined shape.
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Root Structure
Zone of
Differentiation
Epidermis
Cortex
Root Hairs
Phloem Tubes
Zone of
Elongation
Xylem (water transport)
Root Cap
Meristem
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The Epidermis
Epidermis
The epidermis is the
outermost layer of cells
surrounding the root.
The cells of the epidermis
are responsible for
absorbing water and
minerals from the soil
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The Cortex
Cortex
The cortex is a layer
of tissue between the
epidermis and the
vascular tissue.
Cortex cells function in
the movement of
water and in food
storage.
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Root Hairs
Root hairs are found
along the main root and
perform much of the
actual work of water and
nutrient absorption.
Root Hairs
Most plants produce root
hairs that only live a few
days or a few weeks.
As a plant grows, new
root hairs form.
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Xylem
Xylem is the
supporting and water
conducting tissue of
vascular plants.
Xylem
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Phloem
Phloem
Phloem is the food
conducting tissue of
vascular plants, made up
of sieve tubes and other
cellular material.
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Meristem
The meristem is at the
tip of the root and is
responsible for
manufacturing new cells.
This is the area where
cell division and growth
occur.
Meristem
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PLANT TISSUE SYSTEMS
• A plant tissue is an organized mass made
up of similar types of cells. Three
classifications of tissues based on their
origin, structure, and physiology are:
dermal tissue, ground tissue, and vascular
tissue.
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• Dermal tissue forms the outer layer, or
epidermis, of the plant. This type of tissue
is responsible for a plant’s environmental
interactions including light passage and
gas exchange. In some types of plants,
this tissue often has environmental
adaptation features that regulate water
loss from the plant and the exchange of
carbon dioxide and oxygen from within the
plant.
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• Ground tissue consists of three types of
cells that function in storage, metabolism,
and support. Parenchyma cells have thin,
primary cell walls and highly functional
cytoplasm. These types of cells are the
most common and abundant type of cells
in plant tissues, making up the fleshy parts
of fruits, roots, and tubers.
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• Collenchyma cells are elongated cells with
thick cell walls. These types of cells
contain cellulose, which provides “flexible”
support for plant stems and leaves.
Sclerenchyma cells develop extensive
secondary cell walls that contain lignin,
suberin, and/or cutin. The longevity of
these types of cells is short because the
rigidity of their cell walls prevents them
from exchanging the necessary
components needed for active
metabolism.
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• Vascular tissues consist of xylem and
phloem. Xylem consists of trachids and
vessels, which function to conduct and
transport water and minerals from the soil
up through the plant. Phloem consists of
sieve elements and companion cells,
which function in the transport of sugars,
amino acids, and other small molecules
from the leaves to other parts of the plant.
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PLANT ORGANS
• Dermal, ground, and vascular tissues
within a plant associate to form the plant’s
organs, which include the roots, stems,
leaves, and flowers.
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Roots
• The root is the first plant structure to
emerge from a seed during germination.
• Roots are mostly found below the soil
surface and represent about 50% of a
plant’s weight.
• The primary functions of roots are to absorb
water and nutrients from the soil and to
support the plant in an upright position.
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Root Functions
• Roots distribute the food energy produced in the leaves to the
rapidly growing areas found at the root tips.
• Some plants use their roots as a specialized food storage
reserve.
• The first root to emerge from a seed is the primary root, or
radicle.
• Based on the relative sizes of primary and
secondary roots, classifications of root systems
include taproot, fibrous, and adventitious.
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Roots (taproot)
• Plant root systems are classified based on
the relative sizes of their primary and
secondary roots.
• Plants such as dandelions, carrots, turnips,
and most trees have a taproot.
• In taproot systems, the primary root thickens
and becomes the dominant root.
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Roots (fibrous)
• In fibrous root systems, the primary and
secondary roots are of similar diameter.
• They remain fairly close to the soil surface.
• Fibrous root systems help to prevent the
erosion of topsoil during heavy rains.
• Plants such as onions, grasses, and corn
have fibrous root systems.
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Root Types
Tap Root
Fibrous Roots
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Zones of root growth and
differentiation include the:
• Meristem – area of active cell division and
growth (root tip)
• Zone of elongation – nutrient and water
absorption occurs causing cells to
increase in size
• Zone of differentiation/maturation – cells
undergo changes to become specific
tissues (epidermis, cortex, and vascular
tissue)
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• Root hairs located along the main root
form as an outgrowth of the epidermal
cells. Their primary function is to absorb
water and nutrients from the soil. The root
cap, located at the outermost tip of a root,
covers and protects the root’s growing
region. It also directs root growth through
the soil.
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• A plant’s stems serve as supportive
structures for the plant’s leaves. They also
function in the transport of water and
nutrients from the roots to the leaves and
in the transport of food energy created in
the leaves to other plant parts.
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The internal anatomy of a woody
stem consists of:
• Xylem and phloem – to conduct water,
nutrients, and food reserves
• Cambium – the site of cell division and
active cell growth (meristematic tissue)
• Pith – the parenchyma layer at the center
of a stem
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Structures making up the external
anatomy of woody and herbaceous
stems include:
• Terminal buds – growing points located at
the tips of stems
• Axillary buds – growing points located in
the leaf axils
• Node – the point of leaf attachment to the
stem
• Internode – the area of the stem located
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between nodes
• Some plant stems have developed
modifications for protection and to store
additional food and water.
• Examples of above-ground stem
modifications include thorns, prickles,
stolons, spurs, pseudobulbs, and
cladophylls. Rhizomes, tubers, corms,
and bulbs are examples of below-ground
stem modifications.
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• The leaves on a plant function to capture
sunlight for the plant processes of
photosynthesis.
• Plant leaves contain stomata that allow for
gas exchange and transpiration.
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The internal anatomy of a leaf
consists of the:
• Cuticle – a thin film covering the outer layer of
the leaf to protect it from excessive temperatures
and water loss
• Epidermis – cell layer on the upper and lower
sides of a leaf that protects the inner cell layers
and contains the guard cells to regulate stomatal
opening and closing
• Mesophyll – innermost cell layers that contain
the palisade parenchyma cells for
photosynthesis and the spongy parenchyma
cells for gas exchange
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Leaf Structure
Vein
Midrib
Expanded
Portion of Blade
(Lamina)
Axillary
Bud
Node
Bladestalk
(Petiole)
Internode
Base of Leaf
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Midrib & Veins
Vein
Midrib
The midrib is the
most prominent,
central vein in a leaf.
Lateral veins are
secondary veins that
branch from the
midrib.
Both midribs and
lateral veins contain
vascular tissue.
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Leaf Blade (Lamina)
Leaf Blade (Lamina)
The expanded flat
portion of a leaf is the
leaf blade, or lamina.
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Petiole (Bladestalk)
The petiole attaches
the lamina to the plant
stem.
Petiole
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Axillary Bud
Axillary Bud
An axillary bud
exists on the stem
just above the
point where the
leaf petiole
attaches to the
stem.
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• The flat portion of a leaf is the leaf blade
(or lamina). The petiole attaches it to the
plant stem. Stipules located in the leaf
axils function as food manufacturing
structures.
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Stem Structure (External)
Terminal Bud
Growing Point
Young Leaf
Axillary Bud
Nodes
Petiole
Internode
Abscission Layer
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Stems
Stems function as supportive
structures. They hold a plant’s
leaves up toward the sun so
the leaves can capture
energy from sunlight.
Stems transport water and
nutrients from the roots to the
leaves, and food energy from
the leaves to the roots.
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• Flowers are the plant organs that function
in plant reproduction. Flowers vary in size,
structure, and composition among plant
species.
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Parts of a complete flower include
the:
Calyx – leaf-like structures that form an outer ring around the
base of a flower and function to enclose and protect the
flower bud before it opens
Corolla – often colorful and/or scented to attract specific
pollinators to the flower
Pistil – the female reproductive organs (stigma, style, ovary)
Stamen – the male reproductive organs (anther, filament)
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Flower types based on the presence or
absence of the four floral parts include:
• Perfect complete – contains all four floral parts
• Perfect incomplete – lacks only petals and/or
sepals
• Incomplete – lacks one of the four floral parts
• Pistillate – has a pistil, but no stamens
(imperfect incomplete flower)
• Staminate – has stamens, but no pistil (imperfect
incomplete flower)
• Sterile – lacks both pistil and stamens
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• A monoecious plant is one in which
staminate and pistillate flowers exist on
the same plant.
• Dioecious plants are those in which the
male (staminate) and female (pistillate)
flowers exit on completely separate plants.
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Parts of a Flower
Pollen Grains
Stigma
Filament
Style
Anther
Petal
Pollen Tube
Ovule
Embryo Sac
Microphyle
Ovary
Sepal
Integuments
Receptacle
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Sepals
Sepals are leaf-like
structures that form an
outer ring around the
base of a flower.
Sepals enclose and
protect a flower bud
before it opens.
Sepals
The complete ring of
sepals is called the
calyx.
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Petals
Petals are often the
bright and colored
part of a flower.
Petal colors and
scents attract specific
pollinators.
Petals
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Stamens
Anther
Filament
The stamen contains
both the filament and
the anther.
The filament is a stalklike structure that
holds the anther.
Stamens are the male
reproductive parts of a
flower.
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Pistil
Stigma
The pistil includes
three parts:
1. Stigma
2. Style
3. Ovary
Style
Ovary
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Pistil 1. Stigma
Stigma
The stigma is a sticky,
flattened surface that
projects upwards
towards the pollinator.
Birds and insects collect
nectar from previously
visited plants and brush
against the sticky
surface of the stigma.
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Pistil 2. Style
The style is a
supportive structure
that holds the stigma in
a position to maximize
the chances of
pollination.
Style
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Pistil 3. Ovary
The ovary is an
enlarged structure
that contains the
female sex cells, or
ovules.
Pollen Tube
Ovule
Ovary
The pollen tube
grows through the
ovary and into an
ovule.
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Receptacle
The enlarged part of
the pedicel where it
joins the flower is the
receptacle.
Receptacle
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Pedicel
The pedicel (flower
stalk) supports the
flower.
Pedicel
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Acknowledgements
Kristi Falco, Graduate Assistant, Instructional Materials Service,
researched and developed the information used in this
PowerPoint Presentation.
Christine Stetter, Artist, Instructional Materials Service, developed
and illustrated this PowerPoint Presentation..
Keith Zamzow, Curriculum Specialist, Instructional Materials
Service, edited and reviewed this PowerPoint Presentation.
Vickie Marriott, Office Software Associate, Instructional Materials
Service, edited this PowerPoint Presentation.
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ALL RIGHTS RESERVED
Reproduction or redistribution of all, or
part, of this presentation without
written permission is prohibited.
Instructional Materials Service
Texas A&M University
2588 TAMUS
College Station, Texas 77843-2588
http://www-ims.tamu.edu
2006
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