Download - Plant Organs Roots
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Plant Anatomy
Plant Organs
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Types of Plant Organs
Vegetative organs: Roots
Leaves
Stems
Reproductive organs:
Flowers
Fruit
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Plant Body Systems
The plant body isorganized into a rootsystem and a shootsystem: Root system is
generally belowground.
Shoot system
consists of verticalstems, leaves,flowers, & fruit thatcontain seeds.
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Root SystemRoot System
A plants sponge and anchor
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The Root System
Although we do not see
much of roots, they are
equally important to plant
growth as stems and
leaves Leaves collect light and
CO2to produce sugar for
growth as long as the
plant can get enoughwater and nutrients from
its roots!
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Types of Root Systems
A true root system consists ofboth primary & secondaryroots (lateral roots)
Primary root system:
Taproot System* Fibrous Root System**Adventitious Roots**
*Found in most dicots (flowering plants with 2cotyledons in their seeds);
Example: Peas
**Found in most monocots (flowering plantswith 1 cotyledon in their seeds);
Example: Corn
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Primary Root System
The 1st root to emerge
from a seed is the
radicle (primary root),
which emerges to form
a taproot that persiststhroughout the life of
the plant.
Many progressively
smallerbranch roots(lateral roots) grow
from the taproot.
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Taproot System
Definition: the root systemconsisting of a thick, centralprimary root, which formsmany smallerlateral roots.
Common in dicots andconifers.
In some plants such ascarrots and beets, fleshytaproots are the plants food
pantry. In other plants such as
poison ivy the long taprootsare modified for reachingwater deep in the ground.
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Fibrous Root System
Definition: root system thatconsists of several to manyroots of the same size thatdevelop from the end of the
stem with smaller, lateralroots branching off of them.
Typically slender, smallroots Found in monocots like
onion, crabgrass, sweetpotatoes, etc
Form in plants in which theembryonic root is short-lived.
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Fibrous Root System
Most fibrous roots are
very extensive and
cling to soil particles,
which is why they are
often used forpreventing erosion.
Because fibrous roots
do not arise from
preexisting roots butrather from the stem,
they are said to be
adventitious
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Adventitious Roots
Definition: a mass of roots
that from on organs other
than roots
Usually begin growing
after the seed germinates
They form in all sorts of
places on plants including
leaves, petioles, and
stems.
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Adventitious Roots
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Why Different Root Types?
Help plants compete for water and
minerals
Example: Prairie plants Shallow, wide-spreading fibrous roots
(
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Root Functions
Primary & Specialized
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Primary Root Functions
Roots perform 4 main functions:
Absorption/Conduction of
water and dissolved minerals
Anchorage
Storage (carbohydrates) Production of hormones
(e.g., gibberellins) &
secondary plant compounds
(e.g., nicotine in tobacco
plants)
Some specialized roots are
modified for other functions .
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Specialized Roots
Prop roots
Aerial roots
Strangling roots
Contractile roots
Parasitic roots
(haustoria)
Storage roots
Buttress roots Pneumatophores
http://upload.wikimedia.org/wikipedia/commons/7/7d/MistletoeInSilverBirch.jpghttp://upload.wikimedia.org/wikipedia/commons/3/30/Air_roots_in_the_Amazon.jpg -
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Prop or Stilt Roots
Help to stabilize and
support the plant.
Examples:
Ficus Corn
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Aerial Roots
Absorb water fromthe air; may also bephotosyntheticExamples:
Orchids Poison ivy
Anchor plant to the
soil and support thetree
Example: Banyan tree
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Strangling Roots
Help the plants to
climb up another tree
to get to sunlight;
eventually will strangle
the host plant (parasitic)
Example: Fig
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Contractile Roots
Pull the plant shoot
closer to the ground or
deeper into the soil
where the soil is
relatively warm, helpingplants survive variable
early spring weather
Example: Dandelion
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Parasitic Roots (Haustoria)
Penetrate the stems &
roots of host plant to
obtain water, minerals,
and organic molecules
Examples: Mistletoe
Devils Dodder
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Storage Roots
Store water & food
Examples:
Carrot
Radish
Beet
Turnip
Parsnip Rutabaga
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Buttress Roots
Stabilize plants in
thin soil & prevent
uprooting
Common intropical plants
(e.g., ficus)
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Pneumatophores (air roots)
Supply oxygen to
plants growing in
swamps where
water may bedeoxygenated
Examples:
Cypress trees
Mangrove
trees
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Root Structure
Intimately related to root function
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Primary Structure of a Root
Relates to obtaining water
and dissolved minerals
Cross-section shows that
roots consist of cylinders:
Epidermis--protection Cortex--storage of
starch
Vascular tissue (stele)
transport of water &
food
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Monocot vs. Dicot Root
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External Root Structure
Branch roots
Root hairs
Root tip (root cap
and apical meristem)
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Branch Roots
Also known as lateral roots or
feeder roots when they are
young
Decrease in age from the soil
surface to the root tip
Youngest roots occur
closer to the root tip
Soil texture influences root
branching:
Plants that must growthrough hard, dry soil have
fewer branch roots than
those in moist, loose soil.
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Root hairs
Definition: short-lived,single-celled extensionsof epidermal cells nearthe growing root tip.
Form in the region ofmaturation Short, but numerous
Function: raiseabsorptive capacity of
the root by increasingsurface area of the rootthat is in contact withmoist soil.
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Root cap
Definition: a protective
thimble-like layer many
cells thick that covers
the delicate root apical
meristem As the root grows and
pushes its way through
the soil, parenchyma
cells of the root capslough off and are
replaced by new cells
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Columella cells
Elongate cells that
contain 15-30
amyloplasts that
sediment in response to
gravity to the lower sideof the cell. Many botanists think
this is how plant roots
perceive gravity.
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Peripheral cells
Columella cells differentiateinto peripheral cells within2-3 days, which surroundthe columella cells.
Thousands of these cellsare shed from the cap asthe plant pushes throughthe soil.
Peripheral cells secrete
large amounts ofmucigela slimy substance withmany functions
Peripheral cellsMucigel
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Mucigel
A hydrated polysaccharidecontaining sugars, organic acids,vitamins, enzymes, and aminoacids.
Functions: Protection from other
plants roots Lubrication lubricates roots
as they move through theground
Water absorption helpmaintain the connectionbetween roots and water fora continuous flow
Nutrient absorption helpstake in nutrients throughintake of water
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Root apical Meristem
Regions of growthand development
Located in the cone-shaped root tip
Divided into 3regions: Region of division
(grow & divide)
Zone of elongation
(enlarge & specialize) Zone of maturation
(differentiation)
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Roots Have Cooperative
Relationships with Others
Roots often form mutualistic(beneficial) relationships withother organisms: Mycorrhizae: mutualistic
associations between plantroots and soil fungi; Plants gain increased
absorption of minerals anddont need to produce asmany root hairs; also fungimay protect against disease-causing fungi & worms.(Fungus gets food.)
Occurs in 80% of plants.
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Roots Have Cooperative
Relationships with Others
Nitrogen-fixing Bacteria:
Bacteria can convert
nitrogen gas from the air
into ammonium, which is
incorporated into variousorganic molecules, which
plants can take up. Only way for plants to
get useable nitrogen.
Root nodules (seepictures to the right)
are the homes of
bacteria in the plants.