Gases Exchange in Plants 1

8/2/2019 Gases Exchange in Plants 1

1/40

GASES

EXCHANGE IN

PLANTSPRESENTED BY :Siti Sarah binti Sekeri


2/40


3/40

Introduction

Gas exchange three major gases with the

environment

These are CO (for photosynthesis), O(for respiration) and water vapour

(transpiration)

These gases may be taken up or releaseby plants


4/40

During the day, most plants

produce oxygen through

photosynthesis and use up

carbon dioxide During the night, when there is

no photosynthesis, oxygen isconsumed for respiratory

processes


5/40

In aquatic plants, carbon dioxide

required for photosynthesis is

obtained from the surroundingwater in the form of hydrogen-

carbonate ions from the carbonicacid present


6/40

In terrestrial plants, the carbondioxide is obtained from the

atmosphere through the stomata

found on the surface of leaves,

stems and branches


7/40


8/40

Structure of Stoma

Stoma is a pore or aperture that

penetrates the epidermis of leaves,

branches and stems of green plants Normally, more stomata are found

on the lower epidermis compared to

the upper epidermis of leaves, and

much less on the epidermis of stems


9/40

Gaseous exchange in plants

occurs mainly through porescalled stomata

They are found on the epidermis

of leaves & stems of flowering

plants


10/40

Lenticels found in the bark ofstem & root hairs with thin walls

& large surface are also allowgaseous exchange to take place

Each stoma consist of a stomatapore surrounded by two guardcells


11/40

Each guard cell is kidney-shapes

& contains chloroplasts

It has a thinner outer wall & a

thicker, less elastic, inner wall


12/40

Changes in turgid pressure of

guard cells causes the opening or

closing of the stomatal pore


13/40

Besides, stoma is a formed by

two specialized epidermal cells,

bordering each other The guard cells play an important

role in the opening and closing ofthe stoma


14/40

Next, the guard cells are bean-

shaped, and are different fromother epidermal cells

These guard cells contain

chlorophyll, thus can

photosynthesise, whereas the

epidermal cells do not containchlorophyll and thus cannot

photosynthesise


15/40

Another unique characteristic ofthe guard cell is that the inner

cellulose wall bordering thestoma is thicker than the outercellulose wall bordering the

epidermal cells around the guardcells


16/40

Functions of Stoma

Stoma plays important role in the

gaseous exchange of respiratory

gases, in particular theabsorption of CO, and the

regulation of water in the plants


17/40


18/40

O produced during

photosynthesis diffuses outthrough the stomatal pores into

the atmosphere, while COdiffuses in from the atmosphere

into the leaves


19/40

Under water deficit conditions,

stoma closes automatically

This helps to prevent water loss

from the plants until the waterdeficit diminishes


20/40


21/40

STOMATAL

OPENING

STOMATALCLOSING

STOMATAL

OPENING

AND

CLOSING


22/40

STOMATAL OPENING

It has been observed that stomatal opening is

promoted by high light intensity and low

mesophyll CO levels.

Guard cells, which contain chloroplasts,

generate ATP by photophosphorylation during

photosynthesis.


23/40

Blue light (BL) is absorbed by

BL photoreceptors

Which activate a proto pump

(H-ATPase) in the cell

membrane of the guard cell.


24/40

ATPs generated by the light-

dependent reaction ofphotosynthesis are hydrolysed to

provide energy to drive the proton

pump. As proton (H) are pumped out of

the guard cells, the cells become

increasingly negatively charge.


25/40

Potassium channels are activated

and K ions diffuse fromsubsidiary cells through the

channels down this

electrochemical gradient into the

guard cells.

Chloride ions (Cl) then enter tobalance the charge.


26/40

In some plants, starch are

converted into malate (the oldhypothesis proposed that

starch was converted tosugar).

The older hypothesis is thestarch-sugar hypothesis.


27/40

During the daylight, starch is

converted into soluble sugars

to lower the water potential of

cell sap.

The reverse process occurs at

night.


28/40

The accumulation of K ions

(and malate ions) causes thewater potential in the guard

cells to become more

negative.

Water enters by osmosis from

neighbouring subsidiary cells

into the guard cells.


29/40

The guard cells become turgid.

The outer wall of guard cell is thinnerand more elastic than the thicker

inner wall.

There are cellulose microfibrils

radially arranged around the cell wall

and the ends of the two guard cellsare joined.


30/40

The increased turgor pressure

therefore causes the guard cells

to curve outward and the stomaopens.


31/40

Stomatal closure

Stomatal closure can be triggered by

water stress, high temperature,

increasing CO levels in the leaf

mesophyll and low light intensity (night-

time).

The hormone abscisic acid (ABA) issecreted by plant cell when transpiration

rate is high and soil water is low.


32/40

This often occurs around mid-day or

when a plant begins to wilt. The ABA binds the receptors at the

cell membrane of the guard cells.

This increases the permeability of

calcium channels in the cell

membrane.


33/40

Calcium ions (Ca ) enter into the

guard cell. The influx of Ca also triggers the

release of Ca from the cell vacuole

into the cytosol.

The accumulation of Ca inhibits

the proton pump.


34/40

Potassium ions (K) move out of

the guard cells into subsidiarycells.

In some plants, Cl and certainorganic ions e.g malate ions also

move out of the guard cells.


35/40

In the older hypothesis, at night

glucose is converted to insolublestarch.

The water potential in the guard cell

increases.

Water diffuses out to neighbouring

subsidiary cells by osmosis.


36/40

The turgor pressure in the guard cells

decreases, the cells become flaccidand the stoma closes.

At the night, the chloroplasts in the

guard cells do not photosynthesise.

Less ATP is produced.


37/40

There is no active uptake of K

ions.

Instead, the K ions diffuse out of

the guard cells.

The cells become flaccid and the

stoma closes.


38/40


39/40

Factors affecting the opening and

closing of stoma

Circadian rhythms

Some plants have biological clock whereby

stomata open during the day and close at

night

Plants were observed to continue opening

and closing their stoma even when exposed

to 24 hours of continuous light

However, some plants in hot dry conditions

(CAM plants) have an opposite rhythm


40/40

Water balance

When there is a shortage of water,

plants will wilt. Wilting closes stomata

Concentration of CO

A low concentration of CO in thesurrounding air causes stomata to open

Light

Light causes stomata to open wherebyplants are more sensitive to blue light

compared to red light

Gases Exchange in Plants 1

Documents

Transcript of Gases Exchange in Plants 1