AP Biology 2006-2007

Transport in Plants

AP Biology

Transport in plants1. H2O & minerals

transport in xylem transpiration

Water potential, adhesion & cohesion

2. Sugars transport in phloem bulk flow

Photosynthesis in leaves loads sucrose into phloem

3. Gas exchange photosynthesis

CO2 in; O2 out stomata

respiration O2 in; CO2 out roots exchange gases within air spaces in soil

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Overview Sugars travel from

leaves to roots through phloem

Water and dissolved minerals travel from root to shoot through xylem

It defiesgravity!

http://www.youtube.com/watch?v=w6f2BiFiXiM

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1. Transport of Water and Minerals Amount of water needed daily by plants

is small compared to the amount that is lost through transpiration

Transpiration: evaporation of water from plant surface

If water is not replaced, the plant will wilt and may die.

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Water Potential Water movement is governed by differences in

water potential The potential energy of water molecules

Solute concentration and pressure

Water moves from an area of higher water potential to lower water potential High solute concentration = low water potential Low solute concentration – high water potential

PE

PE

High Water Potential

Low Water Potential

Hydrostatic pressure causes water to travel

up tube

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The Process - Roots Minerals from the soil

Actively transported into the root hairs and start to accumulate

Increase solute concentration in root cells, decrease water potential

Water moves in through osmosis to xylem cells

High Water Potential

Low Water Potential

WATER

H2O

root hair

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As water enters the xylem, it forces fluid up the xylem due to hydrostatic root pressure positive pressure This pressure can only move

fluid a short distance.

The most significant force moving the water and dissolved minerals in the xylem The “pull” of water from transpiration

cohesion & adhesion

Hydrostatic pressure causes water to travel

up xylem

Pull =NegativePressure

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Adhesion and Cohesion

H2O

–

O

H H+ +

Water is a polar molecule unequal sharing of

electrons in the covalent bonds

oxygen atom has a stronger attraction for electrons then hydrogen O becomes slightly negatively

charged H becomes slightly positively

charged

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Cohesion and Adhesion Water molecules are attracted

to one another and other materials Cohesion

Due to: Hydrogen Bonds Force of attraction between

slightly “–” oxygen and slightly “+” hydrogen of adjacent water molecules

Adhesion Attraction between water

molecules and the side of xylem cells

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Transpirational Pull Starts in Leaves Evaporation of water through stomata

Lowers WP in the surrounding air spaces Water moves from spongy cells (higher WP) to air spaces

(lower WP) Water in spongy cells exerts a pull on column of water

molecules in the xylem all the way from the leaves to the roots (adhesion, cohesion)

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HIGH water

potential

LOW water

potential

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Mycorrhizae increase absorption Symbiotic relationship between fungi & plant

symbiotic fungi greatly increases surface area for absorption of water & minerals

increases volume of soil reached by plant increases transport of minerals to host plant

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Mycorrhizae

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2. Transport of Sugars Photosynthesis: CO2 + H2O CC66HH1212OO66 + O2

Storage form of sugar: Starch Cannot be transported, must be broken down

into smaller components

Transport form of sugar: Sucrose Very sweet sap

Usable form of sugar: Glucose

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Push and Pull Water and minerals are

mainly transported via transpiration negative pressure

or “pull”

Sucrose is mainly transported via: positive pressure

(hydrostatic pressure)

“push” force (+) pressure

due to accumulation of water

“pull” force (-) pressure

due to adhesion

& cohesion

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Companion cells Cells that

surround phloem Contain a lot of

mitochondria Why? A lot of active

transport!

ATP

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can flow 1m/hr

Transport of Sugars Mass flow hypothesis

“source to sink” flow Source = leaf, Sink = root

Phloem loading in leaf active transport of sucrose

into phloem increased sucrose concentration

decreases water potential Water flows in from xylem cells

increase in pressure due to increase in water causes flow

Hydrostatic pressure

ATP

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Phloem unloading into root cells active transport of

sucrose into root cells

Decreases pressure in bottom of plant

Sucrose will travel from high pressure near leaves to low pressure near roots

ATP

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What environmental conditions might impact transpiration of water?

3. Gas Exchange

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Chloroplasts

Epidermal cell

NucleusGuard cell

Thickened innercell wall (rigid)

Stoma open Stoma closed

H2O

water moves into guard cells

H2O H2O H2O

H2O H2O

H2O

H2O

H2O H2O H2O H2O

Gas Exchange Regulation

water moves out of guard cells

In dry conditions water leaves guard

cells by osmosis guard cells

become flaccid stomata close to

prevent water loss

In humid conditions water enters guard

cells by osmosis guard cells

become turgid stomata open to

facilitate water flow

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Control of transpiration Balancing stomate function

always a compromise between photosynthesis & transpiration leaf may transpire more than its weight in

water in a day…this loss must be balanced with plant’s need for CO2 for photosynthesis

AP Biology 2006-2007

Don’t get mad…

Get answers!!Ask Questions!

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Homework Section 9.5 – pg. 326 #1-9 Read Transpiration Lab