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Water Potential and Transport in Plants, Schemes and Mind Maps of Plant Morphology

An overview of water potential and its role in the transport of water and minerals in plants. It explains how water potential is composed of pressure potential and solute potential, and how these forces work together to move water from the soil to the leaves. The document also discusses the importance of osmosis and active transport in the movement of minerals. Finally, it touches upon the regulation of stomatal opening and its impact on water loss and CO2 uptake.

Typology: Schemes and Mind Maps

2021/2022

Uploaded on 09/27/2022

queenmary
queenmary 🇬🇧

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Summary
A plant is an integrated system
which:
1. Obtains water and nutrients
from the soil.
2. Transports them
3. Combines the H2O with CO2
to make sugar.
4. Exports sugar to where it’s
needed
Today, we’ll start to go over
how this occurs
Transport in Plants – Outline
I. Plant water needs
II. Transport of water and minerals
A. From Soil into Roots
B. From Roots to leaves
C. Stomata and transpiration
Why do plants need so much water?
The importance of water potential, pressure,
solutes and osmosis in moving water…
Transport in Plants
1. Animals have
circulatory
systems.
2. Vascular plants have
one way
systems.
Transport in Plants
One way systems: plants need
a lot more
water
than same sized animals.
A sunflower plant “drinks” and “perspires” 17
times as much as a human, per unit of mass.
Transport of water and minerals
in Plants
Water is good for plants:
1. Used with CO2 in photosynthesis to
make “food”.
2. The “blood” of plants – circulation
(used to move stuff around).
3. Evaporative cooling.
4. Used for turgor pressure to hold plant
erect.
Transport of water and minerals
in Plants
Water (with minerals) -
enters from the soil,
travels through xylem
exits the leaves (through stoma).
What makes it move?
pf3
pf4
pf5

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Summary

A plant is an integrated system which:

  1. Obtains water and nutrients from the soil.
  2. Transports them
  3. Combines the H 2 O with CO 2 to make sugar.
  4. Exports sugar to where it’s needed

Today, we’ll start to go over how this occurs

Transport in Plants – Outline

I. Plant water needs II. Transport of water and minerals A. From Soil into Roots B. From Roots to leaves C. Stomata and transpiration

Why do plants need so much water? The importance of water potential, pressure, solutes and osmosis in moving water…

Transport in Plants

  1. Animals havecirculatory systems.
  2. Vascular plants haveone way systems.

Transport in Plants

  • One way systems: plants need a lot more water than same sized animals.
  • A sunflower plant “drinks” and “perspires” 17 times as much as a human, per unit of mass.

Transport of water and minerals

in Plants

Water is good for plants:

1. Used with CO2 in photosynthesis to

make “food”.

2. The “blood” of plants – circulation

(used to move stuff around).

3. Evaporative cooling.

4. Used for turgor pressure to hold plant

erect.

Transport of water and minerals

in Plants

Water (with minerals) - enters from the soil, travels through xylem exits the leaves (through stoma).

What makes it move?

Transport of water and minerals

in Plants

What makes it move?

‹ Water potential = the tendency of water

to move from one place to another

 across a membrane.

‹ pure water (would have WP=0)

Transport of water and minerals

in Plants

Water potential = the tendency water

to move

Water is usually a solution

  • \ potential pulls water.
  • ⊕ potential pushes water.
  • Thus, water flows toward more \

water potential.

Transport in Plants

Water potential (Ψ Psi) =

Pressure potential + Solute Potential

Ψ=Ψp +Ψs

‹ Pressure potential, Ψp = hydraulic

pressure.

(like air pressure in tires).

Transport in Plants

Water potential (Ψ Psi)

has 2 parts, Ψ=Ψp +Ψs

‹ Pressure potential, Ψp = hydraulic

pressure.

(like in a car’s brake line, or like air pressure in tires).

Transport in Plants

  • Water potential (Ψ) has 2 parts,

Ψ=Ψp+Ψs

‹ Solute potential, Ψs = tendency of a

liquid to move across a membrane -

to the side with a higher concentration

of dissolved solutes.

 Water flows toward more \ solute

potential (unless resisted by ⊕

pressure potential).

Think of it like a tug of war –

The water is the ‘rope’

How water potential works

Ψ=Ψp+Ψs

In the tube: Ψs = -0. Ψp = 0 Ψ =?

Beaker has distilled water with Ψ = 0

Predictions?

Fig 36.

Transport of water and minerals in Plants

  • Osmosis has a major influence getting

water from the soil to the root xylem.

  • Pressure potential is responsible for

moving water through the xylem to the

leaves (and air).

Transport in Plants

  • Osmosis - water movement

between living cells.

  • Soil Æ root xylem, water

passes through living cells

Why?

From the soil to the root xylem

  • Water moves freely through cell walls and intercellular spaces, but,
  • Casparian strips preventing water and ions flow
  • Has to goes thru cytoplasm of the endodermis cells.

Fig 36.

Movement of minerals into the cells is through active transport

  • Mineral ions move across membrane transport proteins.
  • Active transport against a concentration gradient.

Fig 36.

Transport in Plants

Mineral ion concentrations affects

solute potential

Plants control:

  • the concentration of mineral

ions in living cells, hence

  • they control osmosis in roots.

2 Control Points with Transport Proteins

  • Cells near xylem

create an osmotic

gradient that moves

water into the xylem.

  • Endodermis – water from cortex Æ

endodermis

Fig 36.

Transport in Plants

Mineral ions move out of the cell (active

transport)

Water potential is more negative outside

So water moves out of the cell (osmosis)

SO:

Minerals – active/direct

Water follows passively

Transport in Plants

  • Xylem - movement is

controlled by pressure

potential (hydraulic

pressure).

  • Water and minerals are

pulled (\ pressure potential)

through the xylem without

expending energy. How?

  • Transpiration – evaporation of water from leaves
  • Tension – in the xylem sap from transpiration
  • Cohesion – in the xylem sap along the plant

How are water and minerals are pulled

through the xylem?

It’s like sucking on a straw……

Water diffuses out of leaf.

Water evaporates off leaf cells to replace it.

This pulls water from veins.

This tension pulls the water column up

Fig 36.

  • In the xylem - movement is controlled by pressure potential (hydraulic pressure).

Because: Dry air has very negative Ψ (Ψ = -95 MPa) Soil is between –0.01 to –3 MPa

It’s like sucking on a straw…… Transport of water and minerals in Plants

  • There is negative water

potential in stems.

  • What happens if you were to

cut the base of a stem?

  • Break the cohesion in the

water column

  • Light cues most plants to open stomata
  • Active transport of potassium ions into the guard cells.
  • What happens to the water potential of the guard cells?
  • What will happen to water?

Mechanism of stomatal opening

Fig

  • H2O moves into the guard cells to maintain osmotic balance.
  • Stretching and turgidity of the guard cells…..
  • Stomata open.
  • (Closing is the reverse started by passive diffusion of potassium out of guard cells.)

Mechanism of stomatal opening

Fig

  • Stomata typically open in the day (in response to light) and close at night. ‹ This provides CO2 for photosynthesis during the day, but saves water at night.

Regulation of stomatal opening

  • A low level of CO2 in the leaf constrains photosynthesis and favors stomatal opening.
  • If the plant is too dry: mesophyll cells release abscisic acid Æ stomata to close.

Signals for stomatal opening