plant organs roots

7/28/2019 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
http://www.hear.org/starr/hiplants/images/hires/html/starr_001228_0143_ficus_microcarpa.htm


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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.

plant organs roots

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