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PLANT STRUCTURES &
TAXONOMY
Plant Science
Unit 1
Introduction*
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Plants are a basic part of the food chain
Without plants the web of life cannot exists and
most animals and humans would die.
Plant Parts
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Stems
Branches
Leaves
Flowers
Fruit
Nuts
Basic necessities of Plant Life
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For a plant to survive these basic needs must be
met.
 Light
 Water
 Air
 Minerals
Roots
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The largest part of the plant
Adventitious Roots
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Seen above ground
Prop up plants
Tap Roots
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Main root of the plant
Grows straight down
Heavy and thick
Food storage organs so are often used for human and livestock
food
Able to survive periods of drought
Do not stabilize the soil well
Examples of plants with taproots
 Carrots
 Sugar beets
Fibrous Roots
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Generally thin
Somewhat hair like
Numerous
Normally very shallow
Hold the soil well
Dry out more easily & can not tolerate drought
conditions
Grasses & corn are good examples of fibrous root
systems.
Root Tissues
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A knowledge of the parts that make up the root is
helpful in diagnosing disease and other dysfunctions
of plants.
The Root
Root Cap
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Outermost part of the root
Protects the tender, outer growing tip as the root
penetrates the soil
A tough set of cells that are able to withstand the
course conditions that the root encounters as it pushes
its way through the soil
As the root cap wears away the cells are replaced by
more cells that develop at the root tip.
Area of Cell Division
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Provides new cells that allow the root to grow
longer
 Cells multiply in two directions
 tougher cells replace those on the root cap
 more tender cells are produced in the back
of the tougher ones and are used as the root
grows longer
 Thin—about the thickness of a strand of hair
Area of Cell Elongation
Become longer and specialized
 Begin to look like the older cells
 Start to do their specific job.
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Xylem & Phloem
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The most important cells in the root
Xylem
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Responsible for carrying the water and nutrients that are in
the soil to the upper parts of the plant
Phloem
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Functions as the pipeline that carries the manufactured food
from the down to the leaves & other plant parts, including
the roots, where it is used or stored.
Area of Cell Maturation
Cells become fully developed
 Root hairs emerge
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 Small,
microscopic roots
 Rise from existing cells located on the root surface
 Job is to take in water and nutrients
 Small, tender and break easily
 Once broken off they cannot re-grow or be replaced.
Stems
First thing seen by a casual observer
 Noticeable when leaves are gone
 Easily seen as plants grow
 Support the leaves, flowers, and fruit
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Types of Stems*
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Above ground Stems
 Woody
 Herbaceous
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Modified stems
 Bulbs
 Corms
 Rhizomes
 Tubers
Woody Stems
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Tough
Often have bark
Able to survive cold winter climates
Herbaceous Stems
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Succulent
Often green
Will not survive winter in cold climates
Bulbs
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Shortened stems surrounded by modified leaves
called scales.
Examples are:
 Easter
Lilies
 Onions
Corms
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Thickened
Compact
Fleshy
Ex. Gladiolas
Rhizomes
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Thick stems that run below the ground
Examples: Johnson grass & Iris
Tubers
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Thickened, underground stems that store
carbohydrates
We often eat this type of stem
I LOVE taters!
Parts of Stems
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Have the same internal parts as roots
The xylem and phloem run the length of the stem and
into the branches of the plant
In a subclass of plants called dicotyledons the xylem
and phloem occur together in tissues called vascular
bundles
In another subclass called monocotyledons the xylem
and phloem occur in separate areas
Parts of the Plant Stem
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External Parts
 The
node
 Internodes
 Axillary bud
 Lenticels
 Terminal bud
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Internal Parts
 Some
of the same
internal parts of the
roots.
 Xylem and phloem
continue to run the
length of the stem and
in to all branches
The Node
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Portion of the stem that is swollen or slightly
enlarged where buds and leaves originate
The Internodes
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The area between the nodes
Axil & Axillary Bud
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Axil Bud
 The
angle above a leaf stem or flower stem and the
stalk
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Axillary Bud
 Grows
out of the axil
 Function is to develop into a leaf or branch
Lenticels
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Pores in the stem that allow the passage of gases in
and out of the plant
Terminal Bud
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Located on the tip or top of the stem or it’s
branches
May be a vegetative or flowering bud
Vegetative Bud
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Produces the stem and leaf of the plant
Flowering Bud
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Produces flowers
Leaves
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Manufacture food for the plant by using light
energy
Leaves are capable of adjusting their angle of
exposure to the sun
Some plants leaves will turn to allow full sunlight
to shine on the leaf surface as the position of the
sun changes during the day.
 This process is known as phototropism
 Without phototropism plants would grow less
Leaf Margins
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Edge of leaf
Allow plants to be identified by the edge, shape,
and arrangement of the leaves
named or described according to the toothed
pattern on each leaf edge
Leaf Shape & Form
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Varies with species.
Useful in identification of plants.
Types of Leaves
Vary according to species
 Also used to ID species
 Single leaf arising from a stem is called a simple
leaf
 Two or more leaves arising from a
stem are called compound
leaves
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Leaf Parts
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Petiole
 The
petiole is the stem of the leaf; it may be almost
absent or very long
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Blade
 Wide
portion; it may be many shapes and sizes
Internal Structure
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Internal parts of the leaf:
Cuticle
Epidermis
Palisade cells
Spongy layer
Chloroplasts
Mesophyll
Stoma
Guard Cells
Cuticle
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Top most layer of the leaf
Waxy
Functions as a protective covering for the rest of the
leaf
Epidermis
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Surface layer on the lower & upper side
Protects the inner leaf
Palisade Cells & Spongy Layer
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Give the leaf strength
Manufacture food
Contain chloroplasts
Stoma
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Special cells located in the lower epidermis
Allow for the exchange of carbon dioxide &
oxygen as well as some water
Guard Cells
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Surround the stoma
They are responsible for opening and closing the
stoma
Flowers
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Primary function is to produce seeds
Not all flowers are really flowers
The poinsettia and flowering dogwood have
modified leaves called bracts
 Protect
the flower parts & attract insects for pollination
Flower Structure*
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Composed of many parts –see handout
Filament
 Anther
 Pollen
 Stigma
 Style
 Ovary
 Petals
 Sepals
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Male Flower Parts
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Stamen
 It
is made up of the filament, anther and pollen
 The
filament supports the anther
 The anther produces the pollen
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Pollen is the male sexual reproductive cell
Female Flower Parts
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The pistil
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Made up of the stigma, style and ovary
Stigma receives the pollen from the male
Pollen travels down the style and into the ovary
The ovary contains the ovules or eggs
Once fertilized by the pollen the eggs will ripen into
seeds.
http://www.youtube.com/watch?v=L4Ig8J2b2Ag&fe
ature=related
Perfect vs. Imperfect Flower
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Must have all the parts mentioned previously.
Imperfect flowers are missing one or more of the
parts
Flowering Plants in Horticulture
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In plant breeding the anther sac is removed from the
plant to prevent pollination
It may be destroyed or used to pollinate another
flower to create a new variety.
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Many hybrids are created this way.
Flowers in Pollination
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The colored petals of the flower attract insects or
other natural pollinators
Collectively the flower petals are called the corolla
The Sepals together function as a protective device
for the developing flower
Together the sepals are called the calyx
Fruits, Nuts & Vegetables
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After fertilization, the ripening seed develops in the
pistil.
The pistil then enlarges and becomes the fruit
true fruit is the seeds that carry the male and female
genetic characteristics
Did you know?*
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There are many kinds of fruits and vegetables.
However, the terms are often used incorrectly.
A vegetable can be ANY part of the plant that is
grown for it’s edible parts—root, leaf, or ripened
flower
Fruit however is a ripened or mature ovary, a specific
plant part, nuts are also a fruit
Plant Taxonomy*
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The science, laws, and principles of classification
provides the means to classify organisms into
established categories according to characteristics.
makes it easier to understand and remember plants &
animals by their differences and similarities
Latin is used to name living organisms because it is
regarded as the universal language of the biological
sciences.
Binomial System Used in Classifying Plants
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Identified by using the genus and the species
because those names are not used in combination
for any other plant or animal.
Similar to our own first and last name
Without it many different species would all carry
one common name
Genus
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A closely related and definable group of plants
comprising of one or more species
It is customarily capitalized when written with a
species name.
For example: Grain sorghums genus is sorghum
Species
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A group of plants or animals that all share similar
structure, common ancestors and maintain their
characteristics
The subgroup under genus
Generally not capitalized when written with its
genus.
italicized
Example
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Grain sorghum’s species is vulgare
Sorghum vulgare
Varieties
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Some species are broken down further into
varieties.
Subgroup of plants that were developed by
people, as opposed to the species that originated in
nature
Ranked within the a species.
Example
 Triumph
wheat.
Summary *
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Plants are made up of many parts- stems, branches,
leaves, flowers, fruit/nuts, roots
4 basic life needs-light, water, air, minerals
3 types of root systems- adventitious, tap & fibrous
Xylem-responsible for carrying water and nutrients
from the roots to the rest of the plant
Phloem- responsible for carrying manufactured
food from the leaves to the rest of the plant for use
or the roots for storage
Summary *
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Stems-Woody or Herbaceous, also modified stemsbulbs, corms, tubers and rhizomes
Dictoleydons- xylem and phloem occur together in
vasular bundles
Monocotyledons- xylem and phloem occur
seperately
Binomial system used to classify plants using a genus
and species
Varieties are subgroups of plants developed by
people rather than nature