Botany:(PartIII...
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Botany: Part III Plant Nutri0on
Transcript of Botany:(PartIII...
Botany: Part III Plant Nutri0on
Figure 36.2-1
H2O and minerals
H2O
Plant Nutri+on and Transport
Water and minerals in the soil are absorbed by the roots.
Transpira+on, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward.
Transpira0on
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GeDng Water Into The Xylem Of The Root
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Genera+on of Transpira+onal Pull
In addi+on to apoplas+c and symplas+c movement, there are newly discovered channels called aquaporins that allow only water to move across the membrane. Water movement through aquaporins is quicker since no lipids are involved.
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Movement of Minerals Into The Root
Plants need minerals to synthesize organic compounds such as amino acids, proteins and lipids.
Plants obtain these minerals from the soil and are transported by various transport proteins.
Macro-‐ and Micro-‐ Nutrients
Macronutrients are required by plants in rela+vely large amounts and compose much of the plant’s structure.
(C, N, O, P, S, H, K, Ca, Mg, Si, etc. )
Micronutrients are needed in very small quan++es. Typically func+on as cofactors.
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Roots
Fungus
Mycorrhizae: A Mutualis+c Rela+onship
Figure 36.2-2
H2O and minerals
O2
CO2
CO2 O2
H2O • Gas exchange occurs
through the stomata.
• CO2 is required for photosynthesis and O2 is released into the atmosphere.
• Roots exchange gases with the air spaces in the soil, taking in O2 and releasing CO2.
Figure 36.2-3
H2O and minerals
O2
CO2
CO2 O2
H2O
Light
Sugar • Sugars are produced by
photosynthesis in the leaves.
• Phloem sap(green arrows) can flow both ways.
• Xylem sap(blue arrows) transport water and minerals upward from roots to shoots.
• Root pressure is caused by ac+ve distribu+on of mineral nutrient ions into the root xylem.
• Without transpira+on to carry the ions up the stem, they accumulate in the root xylem and lower the water poten+al.
• At night in some plants, root pressure causes guZa+on or exuda+on of drops of xylem sap from the +ps or edges of leaves as pictured here.
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Water Is In The Root, So Now What?
• Water then diffuses from the soil into the root xylem due to osmosis.
• Root pressure is caused by this accumula+on of water in the xylem pushing on the rigid cells.
• Root pressure provides a force, which pushes water up the stem, but it is not enough to account for the movement of water to leaves at the top of the tallest trees.
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Water Is In The Root, So Now What?
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Let’s Apply Some TACT To The Situa+on!
A more likely scenario involves the Cohesion-‐Tension Theory (also known as Tension-‐Adhesion-‐Cohesion-‐Transpira1on or TACT Theory)
Tension: Water is a polar molecule. ! When two water molecules approach one
another they form an intermolecular aZrac+on called a hydrogen bond.
! This aZrac+ve force, along with other intermolecular forces, is one of the principal factors responsible for the occurrence of surface tension in liquid water.
! It also allows plants to draw water from the root through the xylem to the leaf.
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Let’s Apply Some TACT To The Situa+on!
• Adhesion occurs when water forms hydrogen bonds with xylem cell walls.
• Cohesion occurs when water molecules hydrogen bond with each other.
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Let’s Apply Some TACT To The Situa+on!
• Transpira0on: Water is constantly lost by transpira+on in the leaf.
• When one water molecule is lost another is pulled along by the processes of cohesion and adhesion.
• Transpira+on pull, u+lizing capillary ac+on and the inherent surface tension of water, is the primary mechanism of water movement in plants.
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Genera+on of Transpira+on Pull
Ode To The Hydrogen Bond
Water Poten0al
• Water poten+al quan1fies the tendency of free (not bound to solutes) water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects such as surface tension.
• Water poten+al has proved especially useful in understanding water movement within plants, animals, and soil.
• Water poten+al is typically expressed in poten1al energy per unit volume and very o`en is represented by the Greek leZer psi, ψ . (pronounced as “sigh” )
Water Poten0al
• The addi%on of solutes to water lowers the water's poten%al (makes it more nega+ve), just as the increase in pressure increases its poten+al (makes it more posi+ve).
• Pure water is usually defined as having an osmo+c poten+al (ψ) of zero, and in this case, solute poten+al can never be posi+ve.
• Free water moves from regions of higher water poten0al to regions of lower water poten0al if there is no barrier to its flow.
Water Poten0al • The word “poten+al” refers to water’s poten1al energy which is water’s capacity to perform work when it moves from a region of higher water poten0al to a region of lower water poten0al.
• The water poten+al equa+on is ψ = ψS + ψP where ψ is the water poten+al, ψS is the solute poten+al (directly propor+onal to its molarity and some+mes called the osmo+c poten+al and the ψS of pure water is zero) and ψP is the pressure poten+al.
Water Poten0al
• ψP is the physical pressure exerted on a solu+on. • It can be either posi+ve or nega+ve rela+ve to the atmospheric pressure.
• Water in a nonliving hollow xylem cells is under a nega+ve poten+al (tension) of less than −2 MPa.
• BUT the water in a living cell is usually under posi+ve pressure due to the osmo+c uptake of water.
Solutes have a negative effect on ψ by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
H2O
Pure water
Membrane Solutes
Positive pressure has a positive effect on ψ by pushing water.
Pure water at equilibrium
H2O
H2O
Positive pressure
Applying positive pressure to the right arm makes ψ higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
Pure water at equilibrium
H2O
H2O
Positive pressure
Solutes
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on ψ by pulling water.
Pure water at equilibrium
H2O
H2O
Negative pressure
Applying negative pressure to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
"
Solutes have a negative effect on ψ by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
H2O
Pure water
Membrane Solutes
Positive pressure has a positive effect on ψ by pushing water.
Pure water at equilibrium
H2O
H2O
Positive pressure
Applying positive pressure to the right arm makes ψ higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
Pure water at equilibrium
H2O
H2O
Positive pressure
Solutes
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on ψ by pulling water.
Pure water at equilibrium
H2O
H2O
Negative pressure
Applying negative pressure to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
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Solutes have a negative effect on ψ by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
H2O
Pure water
Membrane Solutes
Positive pressure has a positive effect on ψ by pushing water.
Pure water at equilibrium
H2O
H2O
Positive pressure
Applying positive pressure to the right arm makes ψ higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
Pure water at equilibrium
H2O
H2O
Positive pressure
Solutes
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on ψ by pulling water.
Pure water at equilibrium
H2O
H2O
Negative pressure
Applying negative pressure to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
$
Solutes have a negative effect on ψ by binding water molecules.
Pure water at equilibrium
H2O
Adding solutes to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
H2O
Pure water
Membrane Solutes
Positive pressure has a positive effect on ψ by pushing water.
Pure water at equilibrium
H2O
H2O
Positive pressure
Applying positive pressure to the right arm makes ψ higher there, resulting in net movement of water to the left arm:
Solutes and positive pressure have opposing effects on water movement.
Pure water at equilibrium
H2O
H2O
Positive pressure
Solutes
In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water:
Negative pressure (tension) has a negative effect on ψ by pulling water.
Pure water at equilibrium
H2O
H2O
Negative pressure
Applying negative pressure to the right arm makes ψ lower there, resulting in net movement of water to the right arm:
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Water Poten+al vs. Tonicity
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Water Poten+al and Plant Vocabulary
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Once More With Feeling! Ini+al condi+ons: cellular ψ greater than environmental ψ
0.4 M sucrose solution:
Initial flaccid cell:
Plasmolyzed cell at osmotic equilibrium with its surroundings
ψP = 0
ψ S = −0.7
ψ P = 0 ψ S = − 0.9
ψ P = 0 ψ S = − 0.9
ψ = − 0.9 MPa
ψ = − 0.7 MPa
ψ = − 0.9 MPa
Ini+al condi+ons: cellular ψ less than environmental ψ
Distilled water:
Initial flaccid cell:
Turgid cell at osmotic equilibrium with its surroundings
ψ P = 0 ψ S = − 0.7
ψ P = 0 ψ S = 0
ψ P = 0.7 ψ S = − 0.7
ψ = − 0.7 MPa
ψ = 0 MPa
ψ = − 0 MPa
Last Time, I Promise!
Wil0ng
• Turgor loss in plants causes wil+ng – Which can be reversed when the plant is watered
Ascent of Xylem Sap
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Stomata Regulate Transpira+on Rate
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• When water moves into guard cells from neighboring cells by osmosis, they become more turgid.
• The structure of the guard cells’ wall causes them to bow outward in response to the incoming water.
• This bowing increases the size of the pore (stomata) between the guard cells allowing for an increase in gas exchange.
Homeostasis and Water Regula+on
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• By contrast, when the guard cells lose water and become flaccid, they become less bowed , and the pore (stomata) closes.
• This limits gas exchange.
Role Of Potassium Ion In Stomatal Opening And Closing
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H2O
H2O
H2O H2O
H2O
K+
H2O H2O
H2O
H2O H2O
The transport of K+ (potassium ions, symbolized here as red dots) across the plasma membrane and vacuolar membrane causes the turgor changes of guard cells.
Homeostasis and Water Balance
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• Trees that experience a prolonged drought may compensate by losing part of their crown as a consequence of leaves dying and being shed.
• Resources may be reallocated so that more energy is expended for root growth in the “search” for addi+onal water.
Natural Selec+on and Arid Environments
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Natural Selec+on and Arid Environments
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Plants that have adapted to arid environments have the following leaf adapta+ons:
1. Leaves that are thick and hard with few stomata placed only on the underside of the leaf
2. Leaves covered with trichomes (hairs) which reflect more light thus reducing the rate of transpira+on
3. Leaves with stomata located in surface pits which increases water tension and reduces the rate of transpira+on
4. Leaves that are spine-‐like with stems that carry out photosynthesis (cac+) and store water.
Natural Selec+on and Flooding
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• Plants that experience prolonged flooding will have problems.
• Roots underwater cannot obtain the oxygen needed for cell respira+on and ATP synthesis.
• As a result, leaves may dry out causing the plant to die.
• Addi+onally, produc+on of hormones that promote root synthesis are suppressed.
Adapta+ons to Water Environments
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Adapta+ons to Water Environments
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Plants that have adapted to wet environments have the following adapta+ons:
1. Forma+on of large len+cels (pores) on the stem. 2. Forma+on of adven++ous roots above the water
that increase gas exchange. 3. Forma+on of stomata only on the surface of the
leaf (water lilies). 4. Forma+on of a layer of air-‐filled channels called
aerenchyma for gas exchange which moves gases between the plant above the water and the submerged +ssues.
Bulk Flow of Photosynthe+c Products
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Vessel (xylem)
H2O
H2O
Sieve tube (phloem)
Source cell (leaf)
Sucrose
H2O
Sink cell (storage root)
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Sucrose
Loading of sugar (green dots) into the sieve tube at the source reduces water potential inside the sieve-tube members. This causes the tube to take up water by osmosis.
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4 3
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2 This uptake of water generates a positive pressure that forces the sap to flow along the tube.
The pressure is relieved by the unloading of sugar and the consequent loss of water from the tube at the sink.
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4 In the case of leaf-to-root translocation, xylem recycles water from sink to source.
Tran
spir
atio
n st
ream
Pres
sure
flow
Nutri+onal Adapta+ons in Plants
• Epiphytes-‐ grow on other plants, but do not harm their host
• Parasi0c Plants-‐absorb water, minerals, and sugars from their host
• Carnivorous Plants-‐photosynthe+c but supplement their mineral diet with insects and small animals; found in nitrogen poor soils
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Halophytes
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Adapta0ons of Plants: Saline Environments
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• Soil salinity around the world is increasing. • Many plants are killed by too much salt in the soil. • Some plants are adapted to growing in saline
condi+ons (halophytes) • Have spongy leaves with water stored that
dilutes salt in the roots • Ac+vely transport the salt out of the roots or
block the salt so that it cannot enter the roots • Produce high concentra+ons of organic
molecules in the roots to alter the water poten+al gradient of the roots
Created by:
Jackie Snow AP Biology Teacher and Instruc+onal Facilitator, Belton ISD Belton, TX
