Ch. 35 Plant Structure, Growth, and Development & Ch. 36 Resource Acquisition and Transport in...
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Transcript of Ch. 35 Plant Structure, Growth, and Development & Ch. 36 Resource Acquisition and Transport in...
Ch. 35 Plant Structure, Growth, and Development
&Ch. 36 Resource Acquisition and
Transport in Vascular Plants
Objectives:
LO 4.17 The student is able to analyze data to identify how molecular interactions affect structure and function.LO 4.18 The student is able to use representations and models to analyze how cooperative interactions within organisms promote efficiency in the use of energy and matter.
Plant Structure
• Roots – anchors plants, absorbs minerals/water, and stores carbohydrates
• Stems – raises/separates leaves
• Leaves – main photosynthetic organ
Plant Structure
• Leaf anatomy:– Stomata: pores for gas
exchange– Guard cells: flank
stomata to open/close it– Mesophyll:
photosynthesizing area– Epidermis: protective
layer
Nonvascular vs Vascular Plants
• Nonvascular plants have no way to transport food or water (Ex: mosses, algae)
• Vascular plants have a transportation system– xylem (moves water and
dissolved minerals upward from roots into the shoots)
– phloem (transports organic nutrients from where they are made to where they are needed)
http://thomson.fosterscience.com/Biology/Unit-ProtistsFungiPlants/XylemPhloem.jpg
36.2 Different Mechanisms for Transport over short/long distances
• Transport in vascular plants occurs on three scales:– Transport of water and solutes by individual cells, such as
root hairs– Short-distance transport of substances from cell to cell at
the levels of tissues and organs– Long-distance transport within xylem
and phloem at the level of the whole plant
Minerals
H2O
H2O
CO2 O2
Sugar
Light
CO2
O2
Transport at Cellular Level
Relies on selective permeability of membranes• Transport proteins
– Facilitated diffusion– Selective channels (K+ channels)
• Aquaporins—water-specific protein channels that facilitate water diffusion across plasma membrane
Transport at Cellular Level• Proton pumps
– create a hydrogen ion gradient that is a form of potential energy
– contribute to a voltage known as a membrane potential
CYTOPLASM
ATP
EXTRACELLULAR FLUID
Proton pumpgenerates mem-brane potentialand gradient.
Transport at Cellular Level• Plant cells use energy stored in the proton
gradient and membrane potential to drive the transport of many different solutes
CYTOPLASM EXTRACELLULAR FLUID
Cations ( , forexample) aredriven into the cellby the membranepotential.
Transport protein
Membrane potential and cation uptake
Transport at Cellular Level• In the mechanism called cotransport, a transport
protein couples the passage of one solute to the passage of another
Cell accumulatesanions ( , for example) by coupling their transport to; theinward diffusionof through a cotransporter.
Cotransport of anions
Water Potential - Review• (Ψ) Direction water will move due to differing factors. (Ψ = Ψs + Ψp)
– Movement from high Ψ → low Ψ– Measured in megapascal (Mpa)
• Ψs = solute potential. Adding solutes decreases potential; always negative.
• Ψp = pressure potential. Can be positive or negativeSolutes have a negative effect on by bindingwater molecules.
Pure water at equilibrium
H2O
Adding solutes to theright arm makes lowerthere, resulting in netmovement of water tothe right arm:
H2O
Pure water
Membrane Solutes
Positive pressure has a positive effect on by pushing water.
Pure water at equilibrium
H2O
H2O
Positivepressure
Applying positivepressure to the right armmakes higher there,resulting in net movementof water to the left arm:
Solutes and positivepressure have opposingeffects on watermovement.
Pure water at equilibrium
H2O
H2O
Positivepressure
Solutes
In this example, the effectof adding solutes isoffset by positivepressure, resulting in nonet movement of water:
Negative pressure(tension) has a negativeeffect on by pullingwater.
Pure water at equilibrium
H2O
H2O
Negativepressure
Applying negativepressure to the right armmakes lower there,resulting in net movementof water to the right arm:
Differences in Water Potential
Drive Water Transport in Plant Cells
= P + S
36.3 Transpiration
• Root tips absorb water and minerals via diffusion and active transport.
• These diffuse into the xylem.– This creates pressure potential in the roots, but
this is not greater than gravity.• The rest gets pulled up due to transpiration;
loss of water vapor from leaves.
Transportation of Xylem Sap (Water): Transpiration-Cohesion Theory
• Water evaporates from leaves through stomata—creates a low pressure at top of water column
• Water replaced by water from xylem—water in areas of high pressure move to areas of low pressure
Strong cohesion of water with the pressure difference helps to pull the entire water column up from roots to rest of plant
Transpiration
• Water evaporates from leaves through stomata, leaving a pocket of air in cells.
• Due to cohesive and adhesive properties, nearby water molecules in xylem move in and take up the air space.
• Entire xylem column of water moves up due to hydrogen bonding of water molecules.
© 2011 Pearson Education, Inc.
Animation: Transport in Roots Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Animation: Water TransportRight-click slide / select “Play”
© 2011 Pearson Education, Inc.
Animation: TranspirationRight-click slide / select “Play”
36.4 The Rate of Transpiration is Regulated by Stomata
• Stomata allow the transport of CO2 in and O2 out for photosynthesis.– However, water is also lost due to transpiration
• Stomata are flanked with guard cells which can open/close the pore.
• During the day, K+ moves into guard cells causing water to move in by osmosis.– This builds turgor and opens
the stomata.
• At night, K+ moves out causing water to move out.– This makes the cells flaccid
and opens stomata.
Radially orientedcellulose microfibrils
Guard cells turgid/Stoma open
Guard cells flaccid/Stoma closed
Cellwall
VacuoleGuard cell
(a) Changes in guard cell shape and stomatal openingand closing (surface view)
(b) Role of potassium in stomatal opening and closing
K
H2OH2O
H2O
H2O H2O
H2O
H2O
H2O
H2O
H2O
Stimuli for Stomatal Opening and Closing
• Generally, stomata open during the day and close at night to minimize water loss
• Stomatal opening at dawn is triggered by– Light– CO2 depletion– An internal “clock” in guard cells
• All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles
• Drought, high temperature, and wind can cause stomata to close during the daytime
• The hormone abscisic acid is produced in response to water deficiency and causes the closure of stomata
Adaptations That Reduce Evaporative Water Loss
36.5 Sugars Are Transported From Sources to Sinks Via Phloem (Translocation)
• Phloem sap is an aqueous solution that is high in sucrose
• A sugar source is an organ that is a net producer of sugar, such as mature leaves
• A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb
Sugars are actively pumped via an H+ co-transporter into a sieve-tube
Source• Sugars are made in photosynthetic
cells and pumped by active transport into sieve tubes.
• Concentration of dissolved substances increases in the sieve tube and water flows in by osmosis
• Pressure builds up at the source end of the sieve tube
Sink • Sugars are pumped out • Water leaves the sieve tube by
osmosis• Pressure drops at the sink end of
the sieve tube
Difference in pressure causes sugars to move from source to sink
Loading of sugar
Uptake of water
Unloading of sugar
Water recycled
Source cell(leaf)Vessel
(xylem)
Sieve tube
(phloem)
SucroseH2O
H2O
H2OSucrose
Sink cell(storageroot)
Bu
lk f
low
by
neg
ativ
e p
ress
ure
Bu
lk f
low
by
po
siti
ve p
ress
ure
2
1
3
4
2
1
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