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
AP Biology
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
AP Biology
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.
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
Mycorrhizae
AP Biology
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
AP Biology
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
AP Biology
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
AP Biology
What environmental conditions might impact transpiration of water?
3. Gas Exchange
AP Biology
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
AP Biology
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!
AP Biology
Homework Section 9.5 – pg. 326 #1-9 Read Transpiration Lab