Transport in plants o levels notes

1. Transport in
Plants

2. Transport system of
flowering plants
• The vessels that transport materials in plants is
known as the vascular tissue
• There are two main transport tissues:
• Xylem
• Phloem

3. Xylem
• Functions
• Conduct water and mineral salts from roots to
stems and leaves
• Provide mechanical support
• Structure
• Xylem tissue consists mainly of xylem vessels
• A xylem vessel is a long hollow tube made of
many dead cells
• Inner walls are strengthened by lignin – rings or
spirals

4. Lignin Patterns
Rings
(annular)
Spiral Scalariform Reticulate Pitted

5. Adaptations of the Xylem
Feature Adaptation
Empty lumen without
protoplasm or cross walls
Reduces resistance to water
flow, allowing for rapid
transport of water
Walls thickened with lignin Lignin is hard and rigid. It
prevents collapse of the
vessel

6. Phloem
• Functions:
• Translocates sucrose and
amino acids from the leaves
to other parts of the plant.
• Structure
• Consists of two elements:
sieve tube and companion
cells

7. Phloem
a) Sieve tube
• Sieve tube cells or sieve
tube elements
• Elongated, thin walled
LIVING cells
• Cells separated by sieve
plates
• Cross walls that are
perforated with pores =
sieve
• Sucrose is loaded into
the sieve tube by active
transport.
Sieve
tube
cell
Xylem
Sieve
plate

8. Sieve tube cells
• Mature sieve-tubes has thin lining of cytoplasm.
• Nucleus, central vacuole as well as most organelles
are disintegrated.
• Degenerated protoplasm
• Sieve tube cells need help to sustain life
• Companion cells ‘accompany’ them and ‘feed’
them

9. Companion cells
• Each sieve tube cell has a companion cell beside it
• This carries out the metabolic processes to keep both
cells alive
• Structure:
• narrow, thin-walled, many mitochondria. Has cytoplasm
and a nucleus
• Function:
• Provides nutrients and helps sieve tube cells transport
food

10. Phloem
Feature Adaptation
Companion cells have
many mitochondria
Provides energy needed for
companion cell to load sugars
from mesophyll cells into sieve
tubes by active transport
Sieve plates have holes Allows rapid flow of manufactured
food substances through sieve
tubes

11. Differences between
Xylem and Phloem
Xylem Phloem
Consists of dead cells Consists of living cells
-Transports water and mineral
salts
-Provide mechanical support to
the plant
Transports sugar and amino
acids
Transport is unidirectional Transport –bi directional,
upwards and downwards
Substances are loaded by
passive transport - osmosis,
and transported by root
pressure, capillary action,
transpiration pull
Substances are loaded by
active transport, diffusion

12. Vascular tissues (Stems)
• The xylem and phloem are grouped together
to form a vascular bundle
• The phloem lies outside the xylem
• The two are separated by the CAMBIUM
- The cambium divides and differentiates to
form new xylem and phloem tissues

13. Vascular Bundle
2 pith
1 vascular bundles
3
4 cortex
5 epidermis
xylem
cambium
phloem
vascular
bundle

16. Vascular bundles (Stems)
• A stem will contain many vascular bundles arranged in
a ring
• This surrounds a central region called the pith
• The region outside the pith and between the vascular
bundles is called the cortex
• Both cortex and pith store up food substances e.g.
starch
• The stem is covered by a layer of cells called the
epidermis
• The epidermis is protected by the cuticle
• This is a waxy, waterproof layer
• Reduces loss of water by evaporation

17. Phloem
Cambium
Xylem
Vascular
Bundle
Pith
Cortex
Epidermis
Cuticle
Vascular bundles (Stems)

18. • The xylem and phloem alternate with each other
• Pericycle surrounds the vascular tissues
• Endodermis surrounds the pericycle
• Cortex acts as storage tissue
Pericycle
Endodermis
Cortex
Vascular tissues (Roots)
• Tubular outgrowth of an
epidermal cell
• Increases surface area to
volume ratio
• Increases efficiency of
water/mineral salt
absorption

19. • Piliferous layer: this is a epidermal layer that bears root hairs
• Cuticle is absent in the piliferous layer
1 xylem and phloem alternate with
each other.
2 cortex
endodermis 3 piliferous layer
4 root hair
Vascular tissues (Roots)

20. Regions of a root
Root cap
-Covers root tip
-Protects young cells from injury
Growing zone
- Small young cells that
actively divide
Zone of elongation
-Cells elongate
-Causes increase in
root length
Zone of maturation
-Bears numerous root hairs
-Where most of the water
and mineral salts are
absorbed

22. Translocation
• Translocation
• The movement of food substances e.g.
sugars and amino acids in a plant
• Translocation studies
• Aphid studies
• Ringing experiment
• Use of radioactive isotopes

23. Translocation Pathway
• Sugars form in leaf cells,
and are actively
transported by
companion cells (loaded)
into phloem.
• Bulk flow of water pushes
sap to sinks. Sink cells
actively remove sugars,
and convert them to
starches. Water is
recycled through xylem.

24. 1. Aphid studies
• Aphids are insects that feed on plant juices
• They have a long mouth piece called a proboscis
• The aphid uses its proboscis to penetrate a
leaf/stem and feed

25. 1. Aphid studies
• When the aphid is feeding, it is
anesthetized with CO2
• The body is cut off, leaving the
embedded proboscis
• Liquid that exudes from the
proboscis contains sucrose and
amino acids
• Sectioning the stem shows the
proboscis is in the phloem sieve
tube

33. 2. Ringing Experiment
• Cut off a ring of bark, including
the phloem, but leaving the
xylem
• Immerse in water and observe
• Swelling observed above the cut
• Due to accumulation of organic
solutes that came from higher
up the tree and could no longer
continue downward because of
the disruption of the phloem.
• Later, the bark below the girdle
died because it no longer
received sugars from the leaves.
• Eventually the roots, and then
the entire tree, died.

34. 3. Use of radioactive isotopes
• Carbon-14 (14C) is a radioactive isotope of
carbon
• If 14CO2 is supplied to the plant, it will be
fixed in the glucose upon photosynthesis:
• 14C6H12O6
• When the stem is cut and placed on a X-ray
film, only the phloem contains radioactivity

37. Absorption of water
1.Into the roots
• By osmosis
2. Up the stem
• Root pressure
• Capillary action
• Transpiration pull
3. Out of the leaves
• Transpiration

38. Entry of water into a plant
cytoplasm
vacuole
nucleus
cell wall
cell surface
membrane of
root hair cell
film of liquid
(dilute
solution of
mineral salts)
soil particles
Each root hair is a fine tubular outgrowth of
an epidermal cell. It grows between the soil
particles, coming into close contact with the
water surrounding them.
1
1
The thin film of liquid
surrounding each soil
particle is a dilute
solution of mineral salts.
2
2

39. Entry of water into a plant
The sap in the root hair
cell is a relatively
concentrated solution of
sugars and various salts.
Thus, the sap has a
lower water potential
than the soil solution.
These two solutions are
separated by the
partially permeable cell
surface membrane of
the root hair cell. Water
enters the root hair by
osmosis.
3
The entry of water dilutes the sap. The sap of the root
hair cell now has a higher water potential than that of
the next cell (cell B). Hence, water passes by osmosis
from the root hair cell into the inner cell.
4 Similarly, water passes from cell B into the
next cell (cell C) of the cortex. This process
continues until the water enters the xylem
vessels and moves up the plant.
5
A
B
C
xylem
phloem
cortex
root hair
piliferous layer
water entering
the root hair
3
4
5

40. 1. Into the roots
• Root hairs are fine tubular outgrowths
• Surrounded by soil particles
• Dilute solution of mineral salts surrounds soil
particles

41. Absorption in roots
Root hair cell sap is a concentrated solution of sugars and salts.
The more dilute soil solution has a higher water potential than the cell sap
Water enters the cell sap from the soil solution by osmosis, down the water
potential gradient
Water entry dilutes the sap and raises the water potential
Root hair cell has higher water potential than neighbouring cell
Water moves into neighbouring cell by osmosis, down the w.p.g
Process repeats and water moves from cell to cell, through the root cortex
until it enters the xylem

42. Ions and mineral salts
1. Diffusion –when the concentration of minerals
salts in the soil solution is higher than that in the
root hair cell.
2. Active transport –when the concentration of
ions in the soil solution is lower than that in the
root hair cell sap.
3. The energy comes from cellular respiration in
the root hair cells

43. Adaptations of the root
hair cell
Feature Adaptation
1 Long and
narrow
Increases SA:V, thus increasing rate of
absorption of water and mineral salts
2 Has cell
surface
membrane
Partially permeable
Maintains high conc. of sugars, amino acids
and salts in cell sap. Results in lower water
potential than soil solution so water can
enter by osmosis
3 Is living Able to provide energy for active transport
of ions into cell
4 Has protein
transporters
Able to transport specific mineral ions into
the cell.

44. 2. Up the stem
a. Root pressure
• Root cells actively pump inorganic ions into the xylem
and the root endodermis holds the ions there.
• As ions accumulate in the xylem, water enters by
osmosis, pushing the xylem sap upward ahead of it.
• This force, called root pressure, can push xylem sap
up to a few metres.
• Root pressure is not enough to bring water up all trees.

45. 2. Up the stem
b. Capillary action
- If water is present in a narrow (capillary) tube, forces
of attraction exist between:
- Water molecules
- Water molecules and surface of the tube
- Causes water to move up the tubes
- Effect is called capillary action
- Cannot account for water rising up a tall tree

46. Up the stem
c. Transpiration pull
- Transpiration: Loss of water vapours from aerial parts
of plant, especially through stomata of leaves
- Transpiration pull: Suction force caused by
transpiration
- Main factor that causes water to move up the xylem
- Transpiration stream: Stream of water moving up

53. Why is transpiration
important?
• Draws water and mineral salts from the
roots to the stems and the leaves.
• Evaporation of water from the cells in the
leaves removes latent heat of vaporisation,
so the plant is cooled.
• Water transported to the leaves is used for
photosynthesis and maintaining the turgidity
of the leaf cells.

54. ENVIRONMENTAL FACTORS
THAT AFFECT TRANSPIRATION
1. Temperature of air
2. Air humidity
3. Light intensity
4. Wind/air movement
5. Carbon dioxide concentration

55. 1. Temperature of air
• Higher temperatures increases the rate of
evaporation
• The higher the temperature, the greater the rate
of transpiration
30
T
degrees
Stomata
closed

56. 2. Air Humidity
• Air inside leaf is saturated with
water vapour
• Increasing the humidity of the
air will decrease the water
vapour concentration gradient
between the leaf and the
atmosphere, therefore
decreasing the rate of
transpiration
• The lower the humidity, the
faster the rate of transpiration
T
Humidity

57. 3. Light Intensity
• When light intensity is increases, guard cells become
turgid.
• The stomata opens, increasing the rate of transpiration.
• When light intensity is reduced, the stomata closes.
• In greater the light intensity, the greater the rate of
transpiration
Stomata closed
T

58. 4. Wind/air movement
• Blows water vapour away at the
surface of leaves
• Increases concentration gradient
between water vapour in the leaf
and outside the leaf
• This would increase transpiration
• When the air is still, transpiration
reduces or stops
• The stronger the wind, the faster
the rate of transpiration
T
Wind

59. 5. Carbon dioxide
concentration
• When carbon dioxide concentration in the intercellular
spaces of the leaf falls below a critical concentration, the
stomata opens. This increases transpiration.
• An increase in carbon dioxide concentration decreases
the rate of transpiration.
T
Co2 concentration

60. Wilting
• Turgor pressure of mesophyll cells supports the leaf and keep it firm
and spread out widely to absorb sunlight for photosynthesis.
• In strong sunlight, when the rate of transpiration exceeds the rate of
absorption of water by the roots, the cells lose their turgor, become
flaccid and the plant wilts.
• Wilting also occurs in the soft stems of certain plants in which the
stem mesophyll cells lose water.
• If rate of transpiration > rate of water absorption, cells become flaccid
and plant wilts
• Advantages: Reduces rate of transpiration and thus, reduces water
loss
• Disadvantage: Stomata are closed, reducing entry of CO2. Rate of
photosynthesis decreases

61. Plant adaptations
• Xerophytes -- Plants that live in dry
conditions
• Adapted to preventing water loss and storing
water
• Hydrophytes – Water plants
• Fully submerged plants adapted to receiving
more sunlight
• Partially submerged plants adapted to float
• Floating plants adapted to float and compete
for sunlight

62. Xerophytes
Mechanism Adaptation
Limit water loss Waxy stomata – Reduces water loss by transpiration
Few stomata – Reduces transpiration rate
Sunken stomata – hairs of grooves trap water vapour that
diffuses out. Increases humidity around stomata, therefore
reducing transpiration
Reduced leaf size – Reduces exposed surface area
Curled leaves – Reduces exposed surface area
Water storage Succulent leaves
Succulent stems
Fleshy tubers

63. Hydrophytes
Mechanism Adaptation
- Thin/no cuticle.
-Since cuticle is to prevent water loss, there is
less need for cuticle
Large intercellular air spaces – aids buoyancy
Abundant stomata
- No need to reduce water loss
- Maximise gaseous exchange

64. Using a potometer
1. Insert plant into
cork with hole
2. Smear opening
with petroleum jelly
– makes the
apparatus airtight
3. Open tap to fill
tube with water
4. As plant transpires,
water moves to replace
water lost in the plant.
Bubble moves along
capillary tube

65. The basic design of a
potometer
It consists of:
*'''A length of capillary tube''‘
An air bubble is introduced to the capillary. As water is taken up by the plant, the
bubble moves and its length of movement is measured by the scale attached
with capillary tube . The distance the bubble travels in a given time is determined
by the rate of transpiration by the plant.
*''' A reservoir'''.
By turning the tap on the reservoir, the position of the bubble can be set at the
start of the experiment. Some designs of potometer use a syringe instead of a
funnel with a tap.
• '''A tube for holding the shoot'''.
• In the diagram the shoot is held in place by inserting a rubber bung in the
tube. The hole in the bung through which the shoot passes must be thoroughly
greased with petroleum jelly to keep it airtight.

66. Setting up:
# Cut a ''leafy'' shoot from a plant (e.g. Pelargonium) and plunge its base into water
(try not to get any water on the leaves). This prevents the xylem from taking up any
air.
#Back in the laboratory, put the stem into a large sink full of water and carefully trim
the shoot again, by cutting off the bottom '''under water''' with a sharp razor blade.
Keep the leaves out of the water.
#Immerse the whole of the potometer into the sink. Move it about until all the air
bubbles come out.
#Put the shoot stem into the bung, grease the joint with plenty of petroleum jelly,
then put the bung into the potometer.
#Make sure the tap is closed, then lift the whole ensemble out of the water.
#Leave the end of the capillary tube out of the water until an air bubble forms then
put the end into a beaker of water.

67. Using a potometer=
Allow the bubble time to go around the corner and start at the
beginning of the millimeter scale. Then measure how far the bubble
moves in a given period of time. Repeat under different conditions and
compare. The usual conditions to try are placing the plant in a bright
light, placing it by a fan, and placing it in a humid atmosphere. If the
surface area (both sides) of the leaves are measured then it is possible
to compare the transpiration rates of different species of plant.

68. 'Limitations of a
potometer'
# Introducing the air bubble is not easy.
# The leafy shoot may not remain fully alive for as long as
wanted.
# Any changes in the outside air temperature may affect the
position of the air bubble in the capillary tube.

76. Experiment to demonstrate Transpiration
by Four-Leaf Experiment:
Requirements:
Four leaves, Vaseline and a string.
Experiment:
To demonstrate the transpiration from the leaf surface, four banyan leaves
are taken. Both the surfaces of the A leaf, lower surface (with stomata) of B
leaf, upper surface (without stomata) of C leaf are vaselined. The Vaseline is
not applied on the D leaf. Now, as shown in the figure the leaves are hanged
so that they may transpire freely.

77. Observation and Explanation:
When the observations are taken after a day or two, they are as
follows — the A leaf, which is vaselined on its both the surfaces, looks
fresh and green, as no surface transpires. The B leaf is vaselined on
its lower surface (with stomata), and transpiration takes place only
from the upper surface which is negligible. This leaf also remains
turgid and green like the A leaf.
If few stomata are present on the upper surface of the leaf, then it
shrivels to some extent. The C leaf is vaselined on its upper surface,
which contains less number of stomata or no stomata. The
transpiration takes place from the lower stomatal surface, and the leaf
shrivels to a large extent.
The D leaf is not vaselined and both the surfaces transpire freely
releasing much water. The leaf wilts completely in this case. This
experiment proves that the rate of stomatal transpiration is fairly
higher than the cuticular transpiration.

78. Observation and Explanation:
When the observations are taken after a day or two, they are as
follows — the A leaf, which is vaselined on its both the surfaces, looks
fresh and green, as no surface transpires. The B leaf is vaselined on
its lower surface (with stomata), and transpiration takes place only
from the upper surface which is negligible. This leaf also remains
turgid and green like the A leaf.
If few stomata are present on the upper surface of the leaf, then it
shrivels to some extent. The C leaf is vaselined on its upper surface,
which contains less number of stomata or no stomata. The
transpiration takes place from the lower stomatal surface, and the leaf
shrivels to a large extent.

79. Experiment to demonstrate that there is a loss in the
total weight of plant due to transpiration:
Requirements:
1. Spring balance (2), two leaves of almost equal size, test tube (2), water,
vaseline and stand.
Method:
1. Take two test tubes filled with water and close their mouth with a cork having
a hole.
2. Insert the petiole of both the leaves, one in each test tube, and note that it is
dipped in water.
3. Apply vaseline on both the surfaces of leaf ‘B’.
4. Connect both the spring balances with the stand and hang both the tubes on
the hook of spring balances (Fig. 27).

80. 5. Make both the corks air-tight by applying vaseline.
6. Note the weight of both the tubes.
7. Put the whole apparatus in light and wait for a few hours. Note
the weight of both the tubes again.

81. It is observed that there is a clear loss in weight of test tube having leaf
‘A’ and there is no change in weight in leaf ‘B’.
Results:
Loss in the weight of leaf ‘A’ indicates that this is due to the process of
transpiration because the leaf is continuously transpiring the water vapours.
But on both the surfaces of leaf ‘B’ vaseline has been applied and so the leaf is
not transpiring and so there is no change in its weight. These results clearly
indicate that during the transpiration there is a loss in the total weight of the
plant.Rate of transpiration can be calculated as shown below
Rate of transpiration= loss in mass/time taken g/h

82. Experiment to demonstrate the water-
lifting power of transpiration process:
Requirements:
Beaker, water, mercury, stand, capillary tube, vaseline, cork, plant twig, oil cloth.
Method:
1. Take some amount of mercury in the beaker and invert a wide-mouthed
capillary tube over it.
2. Fill the capillary tube with water.
3. Insert the plant twig into the hole of the cork in such a way so that its cut end
is dipped in the water.
4. Apply the vaseline on the cork and hole to make it air-tight (To make the cork
region air-tight oil cloth may also be used instead of vaseline).
5. Keep the whole apparatus in sun.
6. Note the mercury level in the capillary tube and wait for some time.

83. Observations:
Mercury level rises in the capillary tube(Fig.16).

84. Results:
Mercury level rises in the capillary tube because of the pull
or suction exerted by the transpiration process. Aerial parts
of the plants are continuously evaporating water because of
transpiration process. To compensate this loss the water is
absorbed by the plant and lifted. So, the space in the
capillary tube, which was first occupied by this absorbed
water, is now occupied by the mercury. This demonstrates
the water-lifting power of the transpiration process.

85. WILTING

86. WILTING
Wilting is the loss of rigidity of non-woody parts of plants. This occurs
when the turgor pressure in non-lignified plant cells falls towards zero, as a
result of diminished water in the cells.The cells become flaccid.
The rate of loss of water from the plant is greater than the absorption of
water in the plant.
Lower water availability may result from:
• drought conditions, where the soil moisture drops below conditions most
favorable for plant functioning;
• the temperature falls to the point where the plant's vascular system
cannot function;
• high salinity, which causes water to diffuse from the plant cells and
induce shrinkage;
• saturated soil conditions, where roots are unable to obtain
sufficient oxygen for cellular respiration, and so are unable to transport
water into the plant; or
• bacteria or fungi that clog the plant's vascular system.

87. Advantages and Disadvantages of
wilting
Advantage: with the guard cells not turgid, the stomata close and the rate of
water loss is reduced. Rate of transpiration is reduced because the leaf folds
up that is reducing the surface that is exposed to sunlight.
Disadvantage: Rate of photosynthesis reduced because water becomes the
limiting factor .Also as the stomata are closed,gas exchange in the leaves
slows, and therefore so does photosynthesis.