2. LEARNING
OUTCOMES
• To state what translocation is.
• To explain the importance of
translocation in plants.
• To describe the process of transpiration.
• To explain the importance of
transpiration.
• To describe the pathway of water from
the soil to the leaves.
• To state external conditions affecting
transpiration
3. TR A N S L O C A TI
ON
• T h e t r a n s p o r t o f d is s o l v e d
o r g a n ic f o o d s u b s t a n c e s b y
t h e p h l o e m.
IM P O R T A N C E O F
T R A N S L O C A T IO N
• Ensures a plant’s survival
• Organic food molecules can be transported :
– To the growing regions in the plant for growth &
development
– To the plant cells for metabolism
– Downwards from the leaves to the storage organs such
4.
5.
6. T R A N S P IR A T
IO N
• The loss of water as water vapour from a living
plant to the atmosphere due to evaporation.
• M os t of th e wate r is los t th rou gh th e
stomata of le ave s .
• A s m all am ou nt is los t th rou gh th e cuticle
or th rou gh th e lenticels in wood y s te m
7. • T hree main sites of transpiration are :
– S T OM A T A – 90% of transpiration takes place
through minute pores on leaves called stomata
– C UT I C L E – 10% of transpiration takes place
through the cuticle. The amount of water loss
varies with the thickness of the waxy cuticle
– L E NT I C E L S – small pores in the stem which
allow gaseous exchange. Only small amounts of
water are lost through the lenticels.
8. • Transpiration occurs mainly during the day
when the stomata are opened.
• Heat from the sun causes the water to
evaporate from the walls of the spongy
mesophyll cells.
• The water vapour accumulates in the
substomatal air chambers before diffusing
from the plant through the open stomata
9. • Water move into the mesophyll
cells by osmosis from the
adjacent cell
• Water flows from the xylem
vessels along a chain of cells to
the outermost mesophyll cell.
• Water is pulled through the xylem
vessels from the root to the
10.
11.
12.
13.
14. T h e I mp o r t a n c e o f
T r a n s p ir a t io n
• Creates a transpirational pull that pulls
water & dissolved mineral ions from the
root to the leaves.
• Water supplied to the plant is used for
photosynthesis & cell metabolism. Mineral
ions is used for cell activities & growth &
development of the plant.
15. • Water keeps the cell turgid give support
to leaves & young stems (herbaceous
plants).
• To keep the plant cool, an important effect
particularly in hot condition.
• Water evaporates from the plants to the
atmosphere faster than it can be absorbed
from the soil, it is withdrawn from the plant
cells flaccid – leading to wilting
16.
17. P A TH WA Y O F WA TE R
F R O M T H E S O IL T O
TH E L E A VE S
• Water & mineral ions are absorbed by young
roots with thin epidermis. (osmotic forces +
active transport)
• The pressure of root hairs increases the
surface area for absorption.
• The cell sap in the root hair cell contains
sugars, amino acids, & minerals more
concentrated than the surrounding dilute soil
solution.
18. • Wate r d iffu s e s into th e root ce lls b y
os m os is .
• Th e e ntry of wate r into th e root ce lls
d ilu te s its ce ll s ap .
• Th e ce ll s ap of th e ad j nt corte x
ace
ce ll is now m ore conce ntrate d
wate r m ole cu le s d iffu s e into th e
ad j nt root ce ll.
ace
19. • The process continues & water is
transported from one root cell to
another by osmosis.
• In the cells of the endodermis,
mineral ions are actively pumped
from these cells into the solution in
the xylem vessels in the root.
• Solution in xylem more concentrated
water enters xylem by osmosis.
20. • This process creates an upward force called
ROOT PRESSURE.
• Helps to push water in the xylem up to a
certain height in the plant.
• Root pressure alone is insufficient to force the
water to the top part of a tall tree.
• Need CAPILLARITY ACTION &
TRANSPIRATIONAL PULL.
21. G U T T A T IO N
• In small plants, root pressure can push
water all the way up the stem & out of
special pores called hydathodes at the
edges of leaves Guttation
• Occurs on cool humid morning when the
air is too saturated for the water drops to
evaporate from the leaves.
22.
23. TH E E XTE R N A L
C O N D IT IO N S
A F F E C T IN G T H E R A T E
O F T R A N S P IR A T IO N
• The external factors that affect the rate of
evaporation.
– Air movement
– Temperature
– Light intensity
– Relative humidity
24. A IR MOVE ME NT
• Movement of air carries away water
molecules that have diffused from the
leaves.
• The faster the air movement (wind speed)
the greater the rate of transpiration.
• When there is little air movement/ in still
air, water vapour diffusing out of the leaf
accumulates around the stomata.
• Decreases the concentration gradient of
water, the transpiration rate reduces.
25. TE M P E R A TU R E
• A rise in temperature increases the kinetic
energy of water molecules & increase the
rate of evaporation (transpiration).
• Lowers the relative humidity of the air
increase the rate of transpiration.
• Temperature low, kinetic energy of water
molecules is decreased.
• Relative humidity of the air is higher
decrease the rate of transpiration
26. L IG H T IN T E N S IT Y
• The light intensity increased, the
rate of evaporation increases.
• Light not effects evaporation but
causes the stomata to open
increasing water loss from the
plant.
• At night @ dark, stomata close
27. ð ^
• The rate of evaporation depends on the
difference in concentration of water molecules in
the sub-stomatal spaces & in the surrounding
atmosphere.
• The lower the relative humidity of the
surrounding atmosphere, the faster will the water
vapour escape from the stomata.
• High relative humidity reduces water loss.
28. ROOT
PRESSURE
• If a stem is cut just above ground level,
a considerable amount of sap will exude
from the cut stump, showing that there is
a force pushing water up the stem from
the roots.
• Its ROOT PRESSURE The result of an
active process in which energy from ATP is
used.
29. ROOT
PRESSURE
• Root pressure alone is not strong enough to
drive water to the tops of tall trees at the
speeds achieved during a normal growing
season.
30. COHESION &
ADHESION OF
WATER
• COHESION = the force of attraction
between the same molecules
• The cohesive forces between water
molecules hold the continuous columns of
water together & when water transpires
from the leaf, the whole of the water
column moves up the xylem vessels.
31. • ADHESION = the force of attraction
between different molecules
• Water molecules tend to adhere to the
walls of the xylem vessels.
• The adhesive forces can support a
considerable mass of water.
• Cohesion + adhesion = capillarity (the rise
of water in a capillary tube).
32. O P E N IN G &
C L O S IN G O F
• Dicotyledonous O Mon the lower surface
S T leaves = A T A
• Monocotyledonous leaves = both the upper &
lower surfaces.
• Each stoma consists of a pair of kidney-shaped
guard cells surrounding a stomatal pore.
33. • A guard cell has a thinner elastic
outer cell wall & a thicker, less elastic
inner cell wall. It has a nucleus,
cytoplasm & chloroplasts.
• The opening & closing of the stomata
in the leaf controls the diffusion of
CO2 & O2 into & out of a leaf as well
as the rate of transpiration.
34. S TOMA TA L OPE NING
• DAY : photosynthesis occurs & CO2 level is low
in the leaf.
• Potassium ions (K+) diffuse from surrounding
epidermal subsidiary cells into the guard cells.
• In many plant species, starch stored in the guard
cell is converted into malate.
• The accumulation of K+ & malate ions increase
the osmotic pressure in the guard cell.
35. • Water enters by osmosis from surrounding
epidermal cells into the guard cells
• Two guard cells become turgid & curve
outward & the stoma opens.
36. S TO M A TA L
• NIGHT : no photosynthesis &G level
C L O S I N CO2
is high. Potassium ions move out of the
guard cells into the epidermal cells.
• Malate ions are converted to starch. The
osmotic pressure in the guard cells
decreases.
• Water diffuses out to the surrounding
epidermal cells by osmosis.
37. • Guard cells become flaccid & stoma
closes.
• The stomata also close, when there is
insufficient water supply & the
transpiration rate is high.
38. Rasulullah bersabda:
Yang menjadikan orang mukmin itu
pemurah adalah agamanya,yang
menjadikan orang mukmin itu
mempunyai kehormatan adalah
akalnya dan yang menjadikan
orang mukmin itu mulia adalah
budi pekertinya
