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Chapter 10 – Transport
in Plants
Transport in plants


Water and mineral
nutrients must be
absorbed by the roots
and transported
throughout the plant
Sugars must be
transported from site of
production, throughout
the plant, and stored
Cellular transport
mechanisms
Osmotic potential, solutes,
and water movement
Water potential influences
water movement

Water potential (Ψ) of a cell:
Ψcell = ΨΡ + ΨΟ
Ρ = pressure potential
Ο = osmotic (solute) potential
Ψp - Pressure potential (turgor)
Low Ψp
High Ψp
ΨΟ – Osmotic (Solute)
potential

Pure water ΨΟ = 0

All solutions, ΨΟ < 0

As solute concentration
increases, Ψcell …
Water movement in plants
Movement from high Ψcell to low
Ψcell
 Occurs in the xylem
 Involves adhesion, cohesion,
and pressure

Adhesion and cohesion
Water
transport
Tension-cohesion theory
explains xylem transport

Water is drawn up
the plant by
transpiration of
water from stomata
A water potential
gradient creates tension
higher ψ
higherψψ
lower
lower ψ
ψ
higher
Transpiration
creates tension
low ψ
cohesion
lower ψ
higher ψ
highest ψ
Water transport animation
Transpiration & water
transport
Importance of stomata

Regulate transpiration rate
– Controls rate of water uptake
 Water
required for photosynthesis
 Water required to maintain turgor
pressure
 Influences nutrient uptake

Regulate gas exchange
– CO2 required for photosynthesis
Turgid guard cells open
stomata
Guard cells & osmotic
potential
Transpiration & photosynthesis
Ψ and transpiration
rate

In terms of ψ, can you explain
how transpiration rate is
influenced by:
–
–
–
–
Atmospheric humidity?
Wind?
Air temperature?
Light intensity?
Which of the following
explains why water moves
into the root from the soil?
1.
2.
3.
4.
5.
The water potential of the root is lower
than the water potential of the soil
The roots exist in a hypertonic
environment
The pressure potential of the soil forces
water into the root
Water is actively transported into the
root
The soil has a higher solute
concentration than the roots, causing
water to diffuse into the roots
Stomata close when
1.
2.
3.
4.
5.
Photosynthesis lowers CO2
concentrations in the leaves
Potassium ions are pumped into
guard cells
Abscisic acid levels increase
Guard cells become turgid
All of these occur
A guard cell with a high
internal concentration of K+
1.
2.
3.
4.
5.
Is in a hypertonic condition
Has a low water potential
relative to outside of the cell
Has a higher water potential
than outside the cell
Both 1 and 2
Both 2 and 3
Water
transport
Sugar
transport
Source to sink
sugar transport
Pressure-flow hypothesis
explains sugar transport
Phloem loading
Sugar transport can be
explained by water potential
Transport in plants


Water and mineral
nutrients are absorbed by
the roots and transported
throughout the plant by
tension-cohesion
Sugars are transported
from site of production
(source), throughout the
plant, and stored (sinks)
by pressure-flow
Mineral
nutrition &
uptake
Soils and plant nutrition

14 essential mineral nutrients
– N,P,K,S,Ca,Mg,Fe,Cl,Mn,B,Zn,Cu,Mo,Ni

3 essential non-mineral nutrients
– C,H,O
– What makes these nutrients essential?
Magnesium and
photosynthesis
Nitrogen and amino acids
Nitrogen, phosphorus & DNA
Potassium and cell function
Macronutrients vs.
micronutrients
Fertilizers
Fertilizer analysis (N-P-K)
 Analysis varies depending
on growth objectives

How can essential
elements be determined?
Hydroponics
Recreational
hydroponics

Home hydroponics systems
A soil profile

Soil composition
–
–
–
–
Sand, silt, clay
Humus
Microorganisms
Animals
Mineral nutrients exist as ions
Cation exchange allows
mineral ions to be absorbed
by roots
Cation exchange and H+
Mineral nutrient
transport
How does cation exchange
affect soil pH?
Raising soil pH with lime
Ca(OH)2 + 2H+  Ca2+ + 2H2O

Soil pH and mineral
nutrition
Different types of plants have different soil pH
requirements (ex. truffles, filbert trees, and
alkaline soils)
Which of the following
statements concerning plant
nutrition is/are true?
1.
2.
3.
4.
5.
Macronutrients are large elements and
micronutrients are small elements
Macronutrients are essential to plant
growth and micronutrients are not
essential
Macronutrients are absorbed from the
atmosphere and micronutrients are
absorbed from the soil
All of these are true
None of these are true
Cation exchange
1.
2.
3.
4.
Occurs when plants release O2 and
absorb CO2 through their stomata
Involves plants releasing Ca2+ into the
soil in order to absorb H+ ions
Involves the release of H+ ions from
roots to displace mineral nutrient ions
from soil particles
Allows plant roots to absorb C, H, and
O through their roots by converting
these atoms to cations