Transpiration - PowerPoint Presentation

Slide1

Transpiration

Mr. West

AP Biology Slide2

1. Definition

Transpiration

is the evaporation of water from the aerial parts of plants.

Of all the water plant absorbs, over 95-99% is transpired to the air as water vapor.

Slide3

4. From where water is transpired?

Aerial parts of whole young plant

Lenticels (lenticular transpiration)

0.1%

Cutin (cuticular transpiration) 3%~10% Stomatum (stomatal transpiration) ~ 90%Slide4

What is most likely leaving through the stomata of the leaf picture here?

Water (H

2

O)

What is this process called?

Stomatal TranspirationSlide5

Cuticle

Cuticle

Mesophyll

Stomata

Guard cells

Prevents water loss

Site of photosynthesis

Openings allow gases and water to move in and out of leaf

Open and close the stomata

Stomatal transpirationSlide6

Transport in plants

H

2

O & minerals

transport in

xylem

transpiration

evaporation, adhesion & cohesion

negative pressure

Sugars

transport in

phloem

bulk flow

Calvin cycle in leaves loads sucrose into phloem

positive pressure

Gas exchange

photosynthesis

CO

2

in; O

2

out

stomatesrespirationO2 in; CO2 out

roots exchange gases within air spaces in soil

Why does

over-watering

kill a plant? Slide7

Water & mineral absorption

Water absorption from soil

osmosis

aquaporins

Mineral absorptionactive transportproton pumpsactive transport of H+

H

2

O

root hair

aquaporin

proton pumpsSlide8

Control of transpiration

Balancing stomate function

always a compromise between photosynthesis & transpiration

leaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO

2 for photosynthesisSlide9

Stoma Open

Stoma Closed

Guard Cells

Stoma

Importance of transpiration

Guard Cells

CO

2

O

2

H

2

O

What goes in?

What goes out?

What process involves using CO

2

and

H

2

O releasing O

2

as a waste product?

Photosynthesis

What is the plant using this process to make?

Carbohydrates-glucose

If the plant needs

water

for photosynthesis, why is

water

coming out of the stoma?Slide10

Stoma Open

Stoma Closed

Function of Stomata

Guard Cells

These stomata (leaf openings) naturally allow water to evaporate out.

Why would the plant close stomata with guard cells?

Prevent

excess

water loss through

transpiration

. (conserve water)

So what is the point of having stomata?

Allows gas exchange for photosynthesisSlide11

How do the guard cells react to the availability of water?

Dry – guard cells

CLOSE

lots of H

2O – guard cells OPEN

http://www.ualr.edu/~botany/images.html

Function of Guard CellsSlide12

Guard Cells

Guard cells

:

cells that open and close the stoma

Stomata

:

openings in leaf’s surface; when open:

GAS EXCHANGE

:

Allows CO

2

in & O

2

out of leaf

TRANSPIRATION:

StomataSlide13
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5. Characteristics of guard cellsSlide15

Guard cell properties and their relationship with stomatal control

Thickness of CW varies in the ventral and dorsal part of the guard cells.

Contains chloroplast and can perform light reaction. (not dark reaction for the lack of key enzymes)

Structurally isolated from epidermal cells for the lack of plasmodesmata (water and ions transmit only through cellular pathway, thus helps to build up water gradient)

Little volume, little amount of water absorption or loss controls stomtal aperture.Slide16

6. Factors influencing stomatal aperture

Light

Temp.

CO2

Water contentPlant hormoneSlide17

(1). Light

Stomata of most plant open in the day and close at night, while CAM plants are just the opposite.

Stomata opening are sensitive to red light and blue light, and blue light is more effective, it stimulates opening by a blue-light receptor: zeaxanthin.Slide18
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(2) Temperature

Stomatal aperture increase with Temp, within 20- 30℃ (the optimal).Slide20

(3). CO

2

Low CO

2

conc. promotes stomatal opening, while high CO2 conc. inhibits stomatal opening through its acidification of the guard cell thus inhibits PM hyperpolarization.Slide21

(4) Water content

Stomta open when the leaf contain enough water. When there is a water shortage, they close.Slide22

(6) Plant hormones

CTK promotes opening

ABA inhibitsSlide23

Factors that influence transpiration

Transpiration from the leaf depends on two major factors:

Difference in water vapor gradient

Diffusional resistanceSlide24

The driving force of transpiration is the “

vapor pressure gradient

.” This is the difference in vapor pressure between the internal spaces in the leaf and the atmosphere around the leaf

Diffusional resistance comprises

stomatal resistance

and

boundary layer resistanceSlide25

Transpiration rate=Driving force/resistance

water vapor inside the leaf - water vapor of the air

=

stomatal resistance + boundary layer resistanceSlide26

Environmental factors that affect the rate of transpiration

Light

Plants transpire more rapidly in the light than in the dark. This is largely because light stimulates the opening of the stomata , Light also speeds up transpiration by warming the leaf . Slide27

2. Temperature

Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises.

3. Humidity

When the surrounding air is dry, diffusion of water out of the leaf goes on more rapidly.Slide28

4. Wind

When a breeze is present, the humid air is carried away and replaced by drier air.

5. Soil water

A plant cannot continue to transpire rapidly if its water loss is not made up by replacement from the soil. When absorption of water by the roots fails to keep up with the rate of transpiration, loss of

turgor occurs, and the stomata close. This immediately reduces the rate of transpiration. If the loss of turgor extends to the rest of the leaf and stem, the plant

wilts. Slide29

If you were an aquatic plant where would your stomata be?

Fringed Water-lily

Stomata are found only on the upper epidermis because the lower epidermis is submerged in water. If the stomata were to be on the underside, they wouldn't be able to perform their function (i.e to allow water to evaporate and thus contribute to transpiration). Slide30

Reviewing Concepts:Slide31
Slide32

Water Transport

Movement of water and minerals in a plant involves entry into

roots

,

xylem, and leaves

.3 processes:

Osmosis

Capillary Action (Adhesion)

Cohesion-Tension TheorySlide33

Water Transport

Osmosis

- Water entering root cells creates a positive pressure called

root pressure

.

Root pressure

(primarily at night) tends to push xylem sap upward in plant.

Guttation

is appearance of drops of water along the edge of leaves, it is result of root pressure.

Root pressure is not a sufficient mechanism for water to rise to the tops of trees

Slide34
Slide35

Water Transport

Capillary Action

– is the rise of liquids in narrow tubes.

Adhesion

– Molecular attraction between UNLIKE substances.

Capillary Action is also not a sufficient mechanism for water to rise to the tops of treesSlide36

Water Transport

Cohesion-Tension Theory

Transpiration

– evaporation of water from plants

Cohesion – water molecules attracted to other water molecules. (polarity & hydrogen bonds)

Bulk Flow – water movement from roots to leaves as water molecules evaporate from the leaf surface.Slide37
Slide38

Opening and Closing of

Stomates

Each

stomate

has two

guard cells with a pore between them.

Stomates OPEN - when guard cells

take up

water =

increase

in

turgor

pressure

Stomates

CLOSE

- when guard cells

lose

water =

decreases

in

turgor

pressure .

Guard cells are attached to each other at their ends; inner walls are thicker than outer walls.As they take up water, they buckle out, thereby creating an opening between cells. Slide39
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