stpm biology chapter 7
Post on 23-Feb-2018
332 Views
Preview:
TRANSCRIPT
-
7/24/2019 STPM Biology Chapter 7
1/23
THE STOMATA
-
7/24/2019 STPM Biology Chapter 7
2/23
Leaves
The exchange of oxygen and carbon dioxide in the leaf occurs
through pores called stomata(singular = stoma).
Normally stomata open when the light strikes the leaf in the
morning and close during the night.
The immediate cause is a change in the turgorof the guard cells.
The inner wall of each guard cell is thick and elastic. When turgordevelops within the two guard cells flanking each stoma the thin
outer walls bulge out and force the inner walls into a crescent
shape. This opens the stoma. When the guard cells lose turgor
the elastic inner walls regain their original shape and the stoma
closes.
The table shows the osmotic pressure measured at different times
of day in typical guard cells. The osmotic pressure within the other
cells of the lower epidermis remained constant at !"# lb$in%. When
the osmotic pressure of the guard cells became greater than thatof the surrounding cells the stomata opened. &n the evening when
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.html -
7/24/2019 STPM Biology Chapter 7
3/23
The immediate cause is a change in the turgorof the guard cells. The inner
wall of each guard cell is thick and elastic. When turgor develops within the
two guard cells flanking each stoma the thin outer walls bulge out and force
the inner walls into a crescent shape. This opens the stoma. When the guardcells lose turgor the elastic inner walls regain their original shape and the
stoma closes.
The table shows the osmotic pressure measured at different times of day in
typical guard cells. The osmotic pressure within the other cells of the lower
epidermis remained constant at !"# lb$in%. When the osmotic pressure of the
guard cells became greater than that of the surrounding cells the stomataopened. &n the evening when the osmotic pressure of the guard cells
dropped to nearly that of the surrounding cells the stomata closed.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.html -
7/24/2019 STPM Biology Chapter 7
4/23
STOMATA '
Is a pore on the epidermis of the leaves and
stems of plants which can open and close
FUNCTIONS
!" #na$le gases e%change $etween leave cells
and atmospheric
&" 'egulate and control water loss from plants
-
7/24/2019 STPM Biology Chapter 7
5/23
T(# ST'UCTU'# OF STOMATA
-
7/24/2019 STPM Biology Chapter 7
6/23
The stomata)
Is a tin* openings
in the epidermis of
a plant leaf)
are surrounded
$* a pairs of guard
cells"
The guard cellsopen and close the
stoma $* changing
shape
STOMATA
-
7/24/2019 STPM Biology Chapter 7
7/23
T(# ST'UCTU'# OF STOMATA
-
7/24/2019 STPM Biology Chapter 7
8/23
-
7/24/2019 STPM Biology Chapter 7
9/23
T *T+,-T,+ / 0 *T10 T02
( Stoma are found on epidermal layer of leaves, stems and part of flowers of floweringplant )
*tomata is bounded by a pair of guard cellswhich are
kidney shape in dicot and dumbell3shaped in monocot
leaves. 4uard cells (gc) is a specialised epidermal cellwhich
contain chloroplasts forphotosynthesis.
The cellulose cell walls of gc that surround the stoma
(inner cell wall) are thic+er and less elasticthan those in
contact with epidermis ( outer cell wall).
-
7/24/2019 STPM Biology Chapter 7
10/23
The different elasticity of the cellulose cell wall is
contributed by the microfibril cellulose that surround
the wall of the cell. The two guard cells are fused at their end allowing
the cell to bend as they expand.
The diff. causes the outer wall elongates morethan the inner wall when the cell is in turgor
pressure.
The presence of chloroplast enables the gc to
photosynthesise
-
7/24/2019 STPM Biology Chapter 7
11/23
/or gaseous exchange
35uring the day -%diffuse into the leaves for
photosinthesis and %produces fromphotusinthesis diffuses out.
35uring night %diffuse into the leaves for
respiration and -%diffuse out.
*tomata regulate the rate of photosynthesis based
on large number of internal and external signals.
-
7/24/2019 STPM Biology Chapter 7
12/23
0llow transpiration to cooling leaves
35uring transpiration water vapour diffuse out
through stomata due to water vapourconcentration gradient.(water vapour
concentration higher in spaces of leaves and
lower in atmosphere)
35iffusion of water vapour create a transpiration pull
in the xylem so that water in transported up to the
leaves for photosynthesis.
-
7/24/2019 STPM Biology Chapter 7
13/23
+educe exessive loss of water when pore close
35one physically as when water is lost from the
guard cells the cells become flaccid.The stomais automatically closed
-
7/24/2019 STPM Biology Chapter 7
14/23
There are two hypothesis
!. The starch3sugar hypothesis
%.The potassium ion accumulation hypothesis
-
7/24/2019 STPM Biology Chapter 7
15/23
STA'C( ,SU-A' (./OT(#SIS
0t a day time
the guard cell undergoes photosynthesis due to
the presence of chloroplast in the gc
sugarsare formed
the accumulation of sugar increase the
osmotic concentrationof gc water potential in gc
becomes lower than the water potential in
neighbouring epidemal cells
5ifference in water potential causes the
movement of water molecules from epidermal cells
into guard cells by osmosis"
-
7/24/2019 STPM Biology Chapter 7
16/23
The entrance of water causes the gc to
become swell and turgid
Turgor pressure increases the thinnerouter cellulose cell walls elongate more
than the inner thicker walls
The gc $end outwardand stoma opens"
-
7/24/2019 STPM Biology Chapter 7
17/23
At night)
4uard cells do not go through photosynthesis
There is no sugarproduced in guard cells sugar
converted to starch reduces osmotic
concentration in guard cells
Water potential in guard cells become higher
than the w.p in epidermis cells
-
7/24/2019 STPM Biology Chapter 7
18/23
Water potential in guard cells become higherthan
the w.p in epidermis cells
Water molecule diffuses outof gc into
neighbouring epidermis cells
4c becomesflaccid because of no turgor
pressure.
-losing the stoma
-
7/24/2019 STPM Biology Chapter 7
19/23
/OTASSIUM IONS 0 123 ACCUMULATION
(./OT(#SIS
( more recent hypothesis)
6otassium ions from neighbouring epidermis cells
actively transported to the guard cells
nergy needed is supplied by 0T6 generates
during phosphorylation of the light reaction of
photosynthesis
0T6 ( from photophosphorylation) is use to drive
theproton-pumpin the cell membrane of gc
activate by the light
-
7/24/2019 STPM Biology Chapter 7
20/23
44""/OTASSIUM IONS 0 123 ACCUMULATION (./OT(#SIS
( more recent hypothesis)
0s protons (7) are pumped outof the gc the inner
gc becomes more negatively charged. This activate
potassium channels to pumped inpotassium ions 87
into gc from epidermis cells. -l
9
ions then enter tobalance the charge
The accumulation of 87$ ( malate ions in some
plants ) causes the water potential of gc more negative
than that in epidermis cells.
-
7/24/2019 STPM Biology Chapter 7
21/23
The gc becomes turgid)
Turgor pressure increased thinner outer
cellulose cell walls expand morethan theinner wall
4uard cells bend outwardand the stoma
opens
Water from epidermis cells enters by osmosis into
the guard cells
-
7/24/2019 STPM Biology Chapter 7
22/23
6roton pump
6otassium channel
7 pumped out of the guard cells
lowest the electrochemical gradient
7ion
(2
1
Stoma opens
87channels activated 87
ions pumped in
-
7/24/2019 STPM Biology Chapter 7
23/23
top related