Transpiration in plants. The release of water from plant leaves

Июль 22, 2022

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Transpiration in plants. The release of water from plant leaves

Содержание

2. TRANSPIRATION Transpiration is the loss of water from a plant by evaporation Water can only evaporate
3. HOW TRANSPIRATION IS MEASURED A Simple Potometer Air tight seals Plastic tubing Graduated scale Capillary tube
4. HOW TRANSPIRATION IS MEASURED 1’’’’’’’’2’’’’’’’’3’’’’’’’’4’’’’’’’’5’’’’’’’’6’’’’’’’’7’’’’’’’’8’’’’’’’’9’’’’’’’’10’’’’’’’’11’’’’’’’’12’’’’’’’’13’’’’ The rate of water loss from the shoot can be measured
5. ENVIRONMENTAL FACTORS AFFECTING TRANSPIRATION Relative humidity:- air inside leaf is saturated (RH=100%). The lower the relative
6. 4. Atmospheric pressure:- decrease in atmospheric pressure increases the rate of transpiration. 5. Water supply:- transpiration
7. THE EFFECT OF WIND SPEED ON THE RATE OF TRANSPIRATION Stomata diameter/µm 10 20 Stomatal transpiration
8. MOVING AIR REMOVES THE BOUNDARY LAYER OF WATER VAPOUR FROM THE LEAF Boundary layer Saturated air
9. MOVEMENT OF WATER THROUGH THE STOMATA H2O Diffusion shells Water moves from a higher (less negative)
10. INCREASE IN STOMATAL FREQUENCY INCREASES THE RATE OF TRANSPIRATION Boundary layer If the distance between the
11. WILTING If water lost by transpiration is greater than water uptake via the roots the plant
12. LEAF SECTION The upper epidermis has no stomata The lower epidermis has stomata. The guard cells
13. SURFACE VIEW OF LEAF EPIDERMIS SHOWING THE GUARD CELLS WHICH ARE FLACCID AND THE STOMA CLOSED.
14. THE GUARD CELLS CONTROL THE OPENING AND CLOSING OF THE STOMATA Thin outer wall Guard cells
15. REGULATING STOMATAL OPENING:-THE POTASSIUM ION PUMP HYPOTHESIS Guard cells flaccid Stoma closed K+ K+ K+ K+
16. REGULATING STOMATAL OPENING:-THE POTASSIUM ION PUMP HYPOTHESIS K+ K+ K+ K+ K+ K+ K+ K+ K+
17. Stoma open Guard cells turgid K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+
18. 24H CYCLE OF STOMATAL OPENING AND CLOSING 18.00 12.00 15.00 21.00 24.00 3.00 06.00 09.00 Why
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Слайд 2

TRANSPIRATION
Transpiration is the loss of water from a plant by evaporation
Water

can only evaporate from the plant if the water potential is lower in the air surrounding the plant
Most transpiration occurs via the leaves
Most of this transpiration is via the stomata.

Слайд 3

HOW TRANSPIRATION IS MEASURED
A Simple Potometer
Air tight seals
Plastic tubing
Graduated scale
Capillary tube
Leafy

shoot cut under water

Water evaporates from the plant

Movement of meniscus is measured over time

Слайд 4

HOW TRANSPIRATION IS MEASURED
1’’’’’’’’2’’’’’’’’3’’’’’’’’4’’’’’’’’5’’’’’’’’6’’’’’’’’7’’’’’’’’8’’’’’’’’9’’’’’’’’10’’’’’’’’11’’’’’’’’12’’’’’’’’13’’’’
The rate of water loss from the shoot

can be measured under different environmental conditions

volume of water taken up in given time

Limitations

measures water uptake

cutting plant shoot may damage plant

plant has no roots so no resistance to water being pulled up

Water is pulled up through the plant

Слайд 5

ENVIRONMENTAL FACTORS AFFECTING TRANSPIRATION
Relative humidity:- air inside leaf is saturated

(RH=100%). The lower the relative humidity outside the leaf the faster the rate of transpiration as the Ψ gradient is steeper
Air Movement:- increase air movement increases the rate of transpiration as it moves the saturated air from around the leaf so the Ψ gradient is steeper.
Temperature:- increase in temperature increases the rate of transpiration as higher temperature
Provides the latent heat of vaporisation
Increases the kinetic energy so faster diffusion
Warms the air so lowers the Ψ of the air, so Ψ gradient is steeper

Слайд 6

4. Atmospheric pressure:- decrease in atmospheric pressure increases the rate of

transpiration.
5. Water supply:- transpiration rate is lower if there is little water available as transpiration depends on the mesophyll cell walls being wet (dry cell walls have a lower Ψ). When cells are flaccid the stomata close.
6. Light intensity :- greater light intensity increases the rate of transpiration because it causes the stomata to open, so increasing evaporation through the stomata.

Слайд 7

THE EFFECT OF WIND SPEED ON THE RATE OF TRANSPIRATION
Stomata diameter/µm
10
20
Stomatal

transpiration rate
/ gcm-2s-1

In still air closing the stomata is less effective in controlling the transpiration rate

moving air

still air

Слайд 8

MOVING AIR REMOVES THE BOUNDARY LAYER OF WATER VAPOUR FROM THE

LEAF

Boundary layer

Saturated air accumulates around leaf

Still air

Moving air

Lower Ψ

Water vapour is removed from the leaf surface

the Ψ gradient is increased, so faster rate of water evaporation via the stomata

cross section through a leaf

Слайд 9

MOVEMENT OF WATER THROUGH THE STOMATA
H2O
Diffusion shells
Water moves from a higher

(less negative) to a lower (more negative) water potential

Слайд 10

INCREASE IN STOMATAL FREQUENCY INCREASES THE RATE OF TRANSPIRATION
Boundary layer
If the

distance between the stomata is less than 10 X the pore diameter the diffusion shells overlap

So increasing the number of stomata per unit area will have no further effect on transpiration

stoma

Слайд 11

WILTING
If water lost by transpiration is greater than water uptake via

the roots the plant cells become flaccid and the plant wilts.

When the guard cells are flaccid the stomata close

Слайд 12

LEAF SECTION
The upper epidermis has no stomata
The lower epidermis has stomata.
The

guard cells control the opening and closing of the stomata

Слайд 13

SURFACE VIEW OF LEAF EPIDERMIS SHOWING THE GUARD CELLS WHICH ARE

FLACCID AND THE STOMA CLOSED.

Слайд 14

THE GUARD CELLS CONTROL THE OPENING AND CLOSING OF THE STOMATA

Thin outer wall

Guard cells flaccid

Stoma closed

Stoma open

Guard cells turgid

Thick inner wall

Слайд 15

REGULATING STOMATAL OPENING:-THE POTASSIUM ION PUMP HYPOTHESIS
Guard cells flaccid
Stoma closed
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+

ions have the same concentration in guard cells and epidermal cells

Light activates K+ pumps which actively transport K+ from the epidermal cells into the guard cells

Слайд 16

REGULATING STOMATAL OPENING:-THE POTASSIUM ION PUMP HYPOTHESIS
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Increased concentration of K+

in guard cells

Lowers the Ψ in the guard cells

Water moves in by osmosis, down Ψ gradient

Слайд 17

Stoma open
Guard cells turgid
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Increased concentration of K+ in guard cells
Lowers the

Ψ in the guard cells

Water moves in by osmosis, down Ψ gradient

H2O

Слайд 18

24H CYCLE OF STOMATAL OPENING AND CLOSING
18.00
12.00
15.00
21.00
24.00
3.00
06.00
09.00
Why is this cycle an

advantage to most plants?

Transpiration in plants. The release of water from plant leaves

Содержание

TRANSPIRATIONTranspiration is the loss of water from a plant by evaporationWater

HOW TRANSPIRATION IS MEASUREDA Simple PotometerAir tight sealsPlastic tubingGraduated scaleCapillary tubeLeafy

ENVIRONMENTAL FACTORS AFFECTING TRANSPIRATIONRelative humidity:- air inside leaf is saturated

4. Atmospheric pressure:- decrease in atmospheric pressure increases the rate of

THE EFFECT OF WIND SPEED ON THE RATE OF TRANSPIRATIONStomata diameter/µm1020Stomatal

MOVING AIR REMOVES THE BOUNDARY LAYER OF WATER VAPOUR FROM THE

MOVEMENT OF WATER THROUGH THE STOMATAH2ODiffusion shellsWater moves from a higher

INCREASE IN STOMATAL FREQUENCY INCREASES THE RATE OF TRANSPIRATIONBoundary layerIf the

WILTINGIf water lost by transpiration is greater than water uptake via

LEAF SECTIONThe upper epidermis has no stomataThe lower epidermis has stomata.The