2. 9.1: Transport in the xylem of plants
http://131.229.88.77/microscopy/Portfolios/Arlene/Portf
olio4_files/Portfolio2.html
Orange xylem (magnified 2500x)
Essential Idea: Structure and function are correlated in the xylem of
plants
3. Understandings
Statement Guidance
9.2 U.1 Transpiration is the inevitable consequence of gas
exchange in the leaf
9.2 U.2 Plants transport water from the roots to the leaves to
replace losses from transpiration
9.2 U.3 The cohesive property of water and the structure of
the xylem vessels allow transport under tension
9.2 U.4 The adhesive property of water and evaporation
generate tension forces in leaf cell walls
9.2 U.5 Active uptake of mineral ions in the roots causes
absorption of water by osmosis.
4. Applications and Skills
Statement Guidance
9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation.
9.1 A.2 Models of water transport in xylem using simple
apparatus including blotting or filter paper, porous pots
and capillary tubing.
9.1 S.1 Drawing the structure of primary xylem vessels in
sections of stems based on microscope images
9.1 S.2 Measurement of transpiration rates using potometers.
(Practical 7)
9.1 S.3 Design of an experiment to test hypotheses about the
effect of temperature or humidity on transpiration
rates.
7. 9.1 U.1 Transpiration is the inevitable consequence of gas
exchange in the leaf
• Transpiration is the process where
plants absorb water through the
roots and then give off water vapor
through pores in their leaves. The
exchange of H2O and CO2 as gases
from the leaves must take place in
order to sustain photosynthesis.
Underside of the leaf contains:
• Stomata – pores
• Guard cells – found in pairs (1 in
either side stoma), control
stoma and can adjust from wide
open to fully closed
*Abscisic acid (hormone) stimulates
the stoma to close, stopping the
release of the two gases.
Click4biology.com
Water enters the
leaf as liquid
from the veins
Water leaves the
leaf as gas
through
Stomata
8. 9.1 U.1 Transpiration is the inevitable consequence of gas exchange in
the leaf
• Stomata are pores in the lower epidermis formed by two specialized Guard Cells.
• If the water loss is too severe the stoma will close. This triggers mesophyll cells to
release abscisic acid (hormone). Which stimulates the stoma to close by releasing
water from the Guard Cells.
• Decrease in water loss abscisic acid levels decrease, Guard Cells fill with water and
Stomata pore opens. The gases exchange of CO2, O2 and H2O can continue
http://pixgood.com/stomata-
open-and-close.html
Emptied
Of
water
Full
Of
water
10. 9.1 U.2 Plants transport water from the roots to the leaves to replace
losses from transpiration
• Water evaporates into the air, leaving
the leaf, pulling as it leaves.
• This pulling action draws new water
vapor into air space in the leaf.
• In turn the water molecules of
the air space draw water molecules
from the end of the xylem tube
(connecting all the way down the plant
roots).
*Water molecules are weakly attracted to
each other by hydrogen bonds
(Cohesion). Therefore this action
extends down the xylem creating a
'suction' effect.
11. 9.1 U.3 The cohesive property of water and the structure of the
xylem vessels allow transport under tension
Xylem Structure
•Structural adaptations which provides
support for the plant.
•Transpiration pull utilizing capillary action,
this is the primary mechanism of water
movement in plants. The intermolecular
attraction of water allows water flow upwards
(against the force of gravity) through the
xylem of plants.
Thickening of the
cellulose cell wall
and lignin rings
12. 9.1 U.3 The cohesive property of water and the structure of
the xylem vessels allow transport under tension
• In the diagram to the above
left the xylem shows a
cylinder of cellulose cell
wall. The xylem also rings of
lignin providing additional
strength
• The photograph to the left
show the thickening of the
cellulose walls of the xylem.
Click4biology.com
Click4biology.com
13.
14. 9.1 U.4 The adhesive property of water and evaporation generate
tension forces in leaf cell walls
15. 9.1 U.5 Active uptake of mineral ions in the roots causes absorption of
water by osmosis.
Loading water into the xylem:
Concentration of mineral
ions in the root 100 times
greater than water in soil.
ATP is used to pump ions
into the root hairs
•Diffusion of Ions Water
flows by osmosis from an area of
high concentration to an are of
low concentration. As minerals
are actively loaded into the
roots. A change in the
concentration of water in the
roots is created . Water diffuses
into the plant
Root
Hair
Clay Soil
16. 9.1 U.5 Active uptake of mineral ions in the roots causes absorption of
water by osmosis.
• Plant have a mutualistic
relationship with fungus.
There gains are a higher
absorptive capacity for water
and mineral nutrients due to
the funguses large surface.
http://www.sanniesshop.com/images/symbiosis-3.jpg
http://planthealthproducts.com/wp-content/uploads/2013/04/mycroot.gif
17. 9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation.
• Plants adapted to reduce water
loss in dry environments.
Examples of such water stress
habitats include:
• Desert (high temp, low
precipitation)
• High Altitude & High
Latitude (low
precipitation
• Tundra where water is
locked up as snow or ice.
• Areas with sandy soil
which causes water to
rapidly drain.
• Shorelines that contain
areas of high salt levels
18. Plants adapted to dry
Environments are called
Xerophytes. Xerophytes are
adaptations to reduce water loss
or indeed to conserve water.
They
occupy habitats in which there is
some kind of water stress.
Adaptations include:
1. Life Cycle Adaptations
2. Physical Adaptations
3. Metabolic Adaptations
9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation.
Example: Waxy Leaves:
The leaves of these plant have waxy
cuticle on both the upper and
lower epidermis
19. 1. Life Cycle Adaptations
I. Perennial plants bloom in the wet season
II. Seeds have the ability to stay dormant for many years
until conditions are ideal for growth
20. 9.1 A.1 Adaptations of plants in deserts and in saline soils for water
conservation.
Firs and Pines:
•Confers have their
distribution extended beyond
the northern forests. Plants in
effect experience water
availability more typical of
desert environments.
•Needles as leaves to reduce
surface area.
•Thick waxy cuticle
•Sunken stomata to limit
exposer.
•No lower epidermis.
http://fc08.deviantart.net/fs71/i/2014/127/1/c/pine_needles_by_neelfyn-d7hj7z4.jpg
21. 2. Physical Adaptations
I. Waxy Leaves: •The leaves of this plant
have waxy cuticle on both the upper
and lower epidermis
II. Rolled leaves The leaf rolls up, with the
stomata enclosed space not exposed to
the wind.
III. Hairs on the inner surface also allow
water vapor to be retained which
reduces water loss through the pores.
IV. Spikes Leaves reduced to spikes to
reduce water loss
V. Deep roots to reach water
23. 9.1 A.1 Adaptations of plants in deserts and in saline soils for water
conservation.
Succulent
•The leaves have been
reduced to needles to
reduce transpiration.
•The stem is fleshy in
which the water is
stored.
•The stem becomes the
main photosynthetic
tissue.
http://upload.wikimedia.org/wikipedia/commons/c/c9/Echinocactus_grusonii_kew.jpg
24. 3. Metabolic Adaptations
CAM: reduces water loss by opening pores at night but closing them
during the day.
At night CO2 is combined with (C3) to form Malic Acid (C4). This stores
the CO2 until required for photosynthesis during the day.
During the day the pore are closed and the Malic Acid degenerates to
PEP (C3) and CO2. The CO2 is then used in photosynthesis.
25. 9.1 A.1 Adaptations of plants in deserts and in saline soils for
water conservation
• Species of grass occupying sand
dunes habitat.
• Thick waxy upper epidermis
extends
• Leaf rolls up placing, containing
hairs. The stomata in an enclosed
space not exposed to the wind.
• The groove formed by the rolled
leaf also acts as a channel for rain
water to drain directly to the
specific root of the grass stem.
http://upload.wikimedia.org/wikipedia/commons/a/a2/
AmericanMarramGrassKohlerAndraeStateParkLake
Michigan.jpg
click4biology
26. 9.1 A.2 Models of water transport in xylem using simple apparatus
including blotting or filter paper, porous pots and capillary tubing.
27. 9.1 S.1 Drawing the structure of primary xylem vessels in sections of
stems based on microscope images
https://pw-biology-2012.wikispaces.com/file/view/Xylem.png/354386126/800x479/Xylem.png
https://classconnection.s3.amazonaws.com/263/flashcards/1226263/jpg/6959590336_b28341ed7a_z1354494841351.jpg
28. Transpiration
•Transpiration is the loss of water from
a plant by evaporation
•Water can only evaporate from the
plant if the water potential is lower in
the air surrounding the plant
•Most transpiration occurs via the
leaves
•Most of this transpiration is via the
stomata.
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)
In the plant: factors affecting the rate of
transpiration
1.Leaf surface area
2.Thickness of epidermis and cuticle
3.Stomatal frequency
4.Stomatal size
5.Stomatal position
29. 6 Environmental Factors Affecting Transpiration6 Environmental Factors Affecting Transpiration
1. Relative humidity:- air inside leaf is saturated
(RH=100%). The lower the relative humidity
outside the leaf the faster the rate of
transpiration as the Ψ gradient is steeper
2. Air Movement:- increase air movement
increases the rate of transpiration as it moves
the saturated air from around the leaf so the Ψ
gradient is steeper.
3. Temperature:- increase in temperature
increases the rate of transpiration as higher
temperature
• Provides the latent heat of vaporisation
• Increases the kinetic energy so faster
diffusion
• Warms the air so lowers the Ψ of the air, so
Ψ gradient is steeper
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)
4. Atmospheric pressure:- decrease in atmospheric
pressure increases the rate of transpiration.
5. Water supply:- transpiration rate is lower if there
is little water available as transpiration
depends on the mesophyll cell walls being wet
(dry cell walls have a lower Ψ). When cells
are flaccid the stomata close.
6. Light intensity :- greater light intensity increases
the rate of transpiration because it causes the
stomata to open, so increasing evaporation
through the stomata.
31. 1’’’’’’’’2’’’’’’’’3’’’’’’’’4’’’’’’’’5’’’’’’’’6’’’’’’’’7’’’’’’’’8’’’’’’’’9’’’’’’’’10’’’’’’’’11’’’’’’’’12’’’’’’’’13’’’’
The rate of water loss from
the shoot can be measured
under different
environmental conditions
volume of water taken upvolume of water taken up
in given timein given time
Limitations
•measures water uptake
•cutting plant shoot may damage plant
•plant has no roots so no resistance to water being pulled up
Water is pulled upWater is pulled up
through the plantthrough the plant
9.1 S.2 Measurement of transpiration rates using potometers. (Practical 7)
32. 9.1 S.3 Design of an experiment to test hypotheses about the effect of
temperature or humidity on transpiration rates.
33. 9.2 Transport in the phloem of plants
Essential idea: Structure and function are correlated in
the phloem of plants
http://commons.wikimedia.org/wiki/File:Taraxacum_offici
nale,_central_leaf_vein,_Etzold_green_2.JPG
34. Understandings
Statement Guidance
9.2 U.1 Plants transport organic compounds from sources to
sinks.
9.2 U.2 Incompressibility of water allows transport along
hydrostatic pressure gradients.
9.2 U.3 Active transport is used to load organic compounds
into phloem sieve tubes at the source
9.2 U.4 High concentrations of solutes in the phloem at the
source lead to water uptake by osmosis.
9.2 U.5 Raised hydrostatic pressure causes the contents of
the phloem to flow towards sinks.
35. Applications and Skills
Statement Guidance
9.2 A.1 Structure–function relationships of phloem sieve tubes
9.2 S.1 Identification of xylem and phloem in microscope
images of stem and root
9.2 S.2 Analysis of data from experiments measuring phloem
transport rates using aphid stylets and radioactively-
labelled carbon dioxide
37. Lumen of the
sieve tube with
no organelles
that would
obstruct the
flow of sap
Cell Wall resists
high pressures
inside the sieve
tube
Sieve Plate
cross walls
strengthens the sieve
tube with pores that
allow sap to pass
through in either
direction
https://classconnection.s3.amazonaws.c
om/558/flashcards/183558/png/picture91
335365188079.png
Cell Organelles
necessary for
carrying out
metabolic
activities
The cytoplasm of
Sieve-tube
Membrane and
Companion cells
Is connected by
plasmodesmata
Phloem sap
(mostly Sugar)
Passes vertically
Through pores in
The wall between
Sieve-tube members
9.2 A.1 Structure–function relationships of phloem sieve tubes
40. • The transport of materials in
plants is called translocation. The
organic compounds synthesized
during photosynthesis are carried
in the phloem tube.
• Plants will not transport glucose
as it is used directly it must be
converted into sucrose.
• Sucrose move through the plant:
With increased water pressure
The use of ATP (active transport)
Sink is any tissue
that is accepting
sugar
Source is any tissue
that makes sugar
available to the plant
9.2 U.1 Plants transport organic compounds from sources to sinks.
41. • During the growing season
plant leaves produce glucose.
• Glucose is used to produce ATP
for metabolic activities.
• Excess glucose is converted into
sucrose and stored in the roots
of the plant (called the sink).
• At the end of a growing season
plant tubers becoming the
source of glucose, as the leaves
glucose production ceases.
During non growing seasons
plants convert sucrose back into
glucose to carry out metabolic
activities (sink becomes the
source).
Potatoes
http://media-2.web.britannica.com/eb-
media/42/82542-004-4A7EA186.jpg
9.2 U.1 Plants transport organic compounds from sources to sinks.
43. Pressure-Flow Hypothesis
•Hydrostatic pressure is pressure in a liquid.
•The term water potential is used to
describe the tendency for water molecules
to move within and between cells.
•A net movement of water will occur from
one region to another as a result of a
difference in water potential.
•Water moves by osmosis from an area of
high water concentration to an area of low
water concentration.
•In the diagram water flow out of the xylem
and into the phloem due to this gradient.
•This change in water pressure in the
phloem helps push sucrose to the sink cell
(storage site) in the plant.
http://cnx.org/resources/cd8839949717d6b04f4f
ade2e6b0f7cf/Figure_30_05_07.jpg
9.2 U.2 Incompressibility of water allows transport along hydrostatic
pressure gradients.
45. • Phloem tissue is found in plants
(stems, roots & leaves).
• Phloem is composed of sieve tubes.
Sieve tubes along with companion
cells composes a column of
specialized cells making up most of
the phloem.
• The sieve tubes that make up
phloem tissue are composed of
living cells. These cells have
mitochondria which generate ATP
needed for active transport
• Sieve plates are found at either end
of a sieve tube. They contain by
perforated walls called sieve plate
pores
9.2 U.3 Active transport is used to load organic compounds into phloem
sieve tubes at the source.
47. 1. The source during the growing
season is the leaf which
produces organic molecules.
2. Photosynthesis produced
glucose in leaf cells.
3. Glucose is converted to sucrose
for transport.
4. Companion cell actively loads
the sucrose increasing the
concentration in the phloem.
5. Water flows from xylem by
osmosis into phloem (water
from the xylem helps transport
sucrose from the phloem). This
one reason why close proximity
is import between the two.
Combined Transpiration/ Translocation
9.2 U.4 High concentrations of solutes in the phloem at the source lead
to water uptake by osmosis
48. 6. SAP volume and pressure
increased leading to mass flow
(material moving together with
water).
7. Unload the organic molecules by
the companion cell occurs at the
sink (during the growing season
this is the roots).
8. Sucrose is converted and stored
as insoluble starch.
9. Water mixed with sucrose is
released and flows back into the
xylem by osmosis.
10. Water recycles as part of
transpiration to resupply sucrose
loading.
* Remember transpiration is the
movement of water from the
roots to the leaves of the plant.
Combined Transpiration/ Translocation
9.2 U.4 High concentrations of solutes in the phloem at the source lead
to water uptake by osmosis
49. 1.Translocation moves the
organic molecules (sugars,
amino acids) from their
source through the tube
system of the phloem to the
sink. Phloem vessels still
have cross walls called sieve
plates that contain pores.
2. Companion cells actively load
sucrose (soluble, not
metabolically active) into the
phloem.
3. Water follows the high solute
in the phloem by osmosis. A
pressure develops moving
the mass of phloem sap
forward.
Translocation theory
Click4biology.com
9.2 U.5 Raised hydrostatic pressure causes the contents of the phloem to flow towards sink.
50. 4. The sap must cross the
sieve plate.
5. The phloem still contains a
small amount of
cytoplasm along the walls
but the organelle content
is greatly reduced.
6. Companion cells actively
unload (ATP used) the
organic molecules
7. Organic molecules are
stored (sucrose as starch,
insoluble) at the sink.
Water is released and
recycled in xylem.Click4biology.com
Translocation theory
9.2 U.5 Raised hydrostatic pressure causes the contents of the phloem to flow towards sink.
51. • An understanding of sap flow rates through phloem has come from
the use of an insect called an aphid and its feeding technique
• Aphids have a long piercing mouthpart called a stylets, which they
insert into the plants sieve tube and draw out sap.
http://upload.wikimedia.org/wikipedia/commons/1/11/Aphid-giving-birth.jpg
9.2 S.2 Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-
labelled carbon dioxide
52. http://plantsinaction.science.uq.edu.au/book/export/html/23
9.2 S.2 Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-
labelled carbon dioxide
1. Plants grown in a lab with leaves
covered with a clear bag and then
exposed to CO2 containing the
radioactive isotope C14
.
2. The radioactive CO2 is taken and
incorporated into glucose by the
process of photosynthesis. The
glucose is then converted into
sucrose and move through the
phloem of the plant.
3. In the experiment colonies of
Aphids feed on the sucrose in the
phloem at different locations of
the plant stem.
4. When feeding sucrose drips down
into container below the colonies.
The distant between the colonies
is used to calculate sucrose flow
rates in the phloem.
53. Experiment numbers 1 2 3
Distance between
aphid colonies (mm)
650 340 630
Time for radioactivity
to travel between
colonies (hours)
2.00 1.25 2.50
Rate of movement
(mm hours -1
)
32.5 27.2 25.4
Example with two colonies
9.2 S.2 Analysis of data from experiments measuring phloem transport rates using aphid stylets and radioactively-
labelled carbon dioxide
54. Essential idea: Plants adapt their growth to
environmental conditions.
9.3: Plant Growth
55. Understandings
Statement Guidance
9.3.U1 Undifferentiated cells in the meristems of plants allow
indeterminate growth.
9.3.U2 Mitosis and cell division in the shoot apex provide cells
needed for extension of the stem and development of
leaves.
9.3.U3 Plant hormones control growth in the shoot apex
9.3.U4 Plant shoots respond to the environment by tropisms.
9.3.U5 Auxin efflux pumps can set up concentration gradients
of auxin in plant tissue.
9.3.U6 Auxin influences cell growth rates by changing the
pattern of gene expression.
56. Applications and Skills
Statement Guidance
9.3 A.1 Application: Micropropagation of plants using tissue
from the shoot apex, nutrient agar gels and growth
hormones.
9.3 A.2 Application: Use of micropropagation for rapid bulking
up of new varieties, production of virus-free strains of
existing varieties and propagation of orchids and other
rare species.
57. Dicotyledon Structure
1. Root system extracts minerals
(nitrates & phosphates) along
with water from the soil. The
main root has lateral divisions
that are either shallow or deep
depending on the water
availability of water.
2. Stem structure supports leaf and
contains the vascular tissue that
transports substances around
the plant.
3. Petioles divisions of the stem.
They support the leaf and
contains branches of the vascular
tissues.
www.click4biology.com
58. 4. Leaf large surface area to
absorb light energy for
photosynthesis. Concentrated
within the palisade tissue of
the leaf is chlorophyll to
absorb the photons of light.
5. Auxiliary bud provide the
tissues for the growth of
lateral branches in future
growing seasons.
6. Terminal bud contains the
structures for the growth and
elongation of the main stem.
www.click4biology.com
59. Dicotyledonous stem
Tissue types of the plant stem:
• Epidermis: surface of the stem
made of a number of layers
often with a waxy cuticle to
reduce water loss.
• Cortex Tissue: Forming a
cylinder of tissue around the
outer edge of the stem. Often
contains cells with secondary
thickening in the cell walls
which provides additional
support.
• Vascular bundle: contains
xylem, phloem and cambium
tissue.
www.click4biology.com
60. Dicotyledonous stem
• Xylem: a longitudinal set of tubes that
conduct water from the roots upward
through the stem to the leaves.
• Phloem (sieve elements) transports sap
through the plant tissue in a number of
possible directions.
• Vascular cambium is a type of lateral
meristem that forms a vertical cylinder in
the stem. The cambium produces the
secondary xylem and phloem through
cell division in the vertical plane.
• In the center of the stem can be found
the pith tissue composed of thin walled
cells called parenchyma. In some plants
this section can degenerate to leave a
hollow stem
www.click4biology.com
61. 9.3 U.1 Undifferentiated cells in the meristems of plants allow
indeterminate growth.
• Plants growth is restricted to
'embryonic' regions called
meristems. Having specific
regions for growth and
development (restricted to
just the meristematic
tissue).
• Meristems composed of
undifferentiated cells that
are undergoing active cell
division
Growth Occurs:
• Terminal & Axillary buds
• Tap and Lateral roots
• Cambium (stem thickness)
www.click4biology.com
62. 9.3.U.1 Undifferentiated cells in the meristems of plants allow
indeterminate growth.
• Apical Meristems – found at the tips of stems and roots
• Lateral Meristems – responsible for thickness of the stems
Apical meristem
www.click4biology.com
63. • Auxins (hormone) – initiating
the growth of roots,
influencing the development
of fruits and regulating leaf
development.
• Auxin influences cell division
growth rates and patterns.
• Auxins also influence cell
elongation.
(a) Shoot apical meristem
(b) Leaf primordial
(c) Auxiliary bud primordium
(d) leaf
(e) Stem tissue
http://www.geraniumsonline.com/apex1.jpg
Apical meristem at the top of the plant
9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth.
9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression
64. Root apical meristem:
(a) Root cap.
(b) Root apical meristem.
(c) Ground meristem.
(d) Protoderm.
(e) Epidermal tissue of the root.
(f) Vascular tissue (central stele).
Apical Meristem
www.click4biology.com
9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth.
9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression
Apical meristem at the root of the plant
65. Apical meristem : Axillary Bud Growth
• Stem differentiation at
the apical meristem
creates branching.
• The diagram illustrate
that the tissue added at
the apical meristem
differentiates into the
various primary plant
body structure (AB)
www.click4biology.com
9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth.
9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression
66. 1. Cambium that produces secondary xylem and
phloem
2. Cork cambium produces some of the bark layer of
a stem.
*secondary growth adding thickness usually in the
following years in a perennial plant.
www.click4biology.com
9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth.
9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression
Lateral meristem is secondary growth
67. • Cells in meristems are small, therefore they go through the cycle quicker to
produce more cells through mitosis and cytokinesis
• These new cell absorb nutrients and water which increase their volume &
mass http://www.navitar.com/images/bf2.jpg
9.3 U.2 Mitosis and cell division in the shoot apex provide cells needed
for extension of the stem and development of leaves.
68. PLANT GROWTH REGULATORS (aka PLANT HORMONES)PLANT GROWTH REGULATORS (aka PLANT HORMONES)
Plant hormones differ from animal hormones in that:
Unlike animal hormones, plant hormones are not made in tissues specialized for
hormone production. (e.g., sex hormones made in the gonads, human growth hormone
- pituitary gland)
Unlike animal hormones, plant hormones do not have definite target areas (e.g., auxins
can stimulate adventitious root development in a cut shoot, or shoot elongation or
apical dominance, or differentiation of vascular tissue, etc.).
There a several hormones found in plants. Auxins. Auxins (cell elongation), GibberellinsGibberellins (cell
elongation + cell division), CytokininsCytokinins (cell division), Abscisic acidAbscisic acid (Controls guard cells)
and EthyleneEthylene (promotes fruit ripening)
9.3 U.3 Plant hormones control growth in the shoot apex.
69. Cytokinins
•Hormones that stimulate cell
division, leaf aging (leaf
senescence) and leaf enlargement
•Cytokinins, in combination with
auxin, stimulate cell division and
differentiation.
•Produced in roots and travel
upward in xylem sap.
*The hormone has no direct effect
on the cell wall. For this reason it
work best with the plant hormone
Auxin
The plant, below left has been genetic
modification to increase levels of
cytokinin
Nicotiana (Solanaceae family)
71. Auxin
• Increases the flexibility of the cell wall. A more flexible wall will
stretch more as the cell is actively growing.
• Auxin accumulates in the apical meristem. Allows selective cell
elongation.
• By interacting with other hormones, Auxin also induces cell width
.
72. Acid Growth
hypothesis• Plant cell growth dependent on the growth hormone auxin.
• Auxin activates a plasma membrane proton pump, which acidifies the cell wall.
• The lower pH, in turn, activates growth-specific enzymes that hydrolyze the bonds holding
to cellulose. Breaking of these bonds results in the loosening of the cell wall. Causes
uptake of water – which leads to a passive increase in cell size.
Loosening of cell wallLoosening of cell wall
73. Enzymes break the bonds holding
xyloglucan to cellulose.
Enzymes break the xyloglucan
molecules.
Other enzymes break the pectin
Molecules (NOT SHOWN).
From: Biochemistry and Molecular Biology of plants
The cell is now free to expand
in a given direction.
74. When expansion has stopped:
From: Biochemistry and Molecular Biology of plants
Cell wall proteins lock the cells
new shape as these new wall
components are being made.
Enzymes form new xyloglucan
Molecules which re-attach to the
Cellulose microfibrils.
Also form New cross-links
with newly formed Cellulose
microfibrils.
75. For a plant to grow:
•new wall material has to be laid down as the cell expands
New cellulose microfibrils are
made as the cell expands. Plasma
membrane
These line up perpendicular
to the direction of growth.
As this happens the existing wall
has to be loosened.
From: Biochemistry and Molecular Biology of plants
76. • Darwin’s studied the of effects auxin on movement.
• Darwin studied phototropism using the germinating stem of the
canary grass.
• The cylindrical shoot is enclosed in a sheath of cells called the
coleoptile.
http://semoneapbiofinalexamreview.wikispaces.com/file/view/39_05bColeoptileDarwins-L.jpg/289955863/560x411/39_05bColeoptileDarwins-L.jpg
9.3 A.1: Micropropagation of plants using tissue from the shoot
apex, nutrient agar gels and growth hormones.
77. 9.3 A.1: Micropropagation of plants using tissue from the shoot
apex, nutrient agar gels and growth hormones.
Auxin was first isolated by F. W. Went
(m) Went isolated the growth medium auxin onto agar gel.
(n) The gel was cut up into block as a way of quantifying the dose of
auxin used.
(o) The agar block (containing auxin) are placed asymmetrically on the
stem.
(p) The angle of bending-growth was measured
http://plantphys.info/plant_physiology/images/paaltip.gif
78. 9.3 A.1: Micropropagation of plants using tissue from the shoot apex,
nutrient agar gels and growth hormones.
• Since Auxin (IAA3) was synthetically
produced more rigorous quantitative
bio-assay can be performed
• This graph measures the bending-
growth against the concentration of
IAA3.
Graph suggests:
• Increasing IAA3 increases the bending-
growth angle.
• Optimal angle of bending-growth is
achieved between 0.2- 0.25 mg
• Higher levels seem to have reduced-
bending growth
79. Tropisms: External Factors that Regulate Plant Development
• a change in the growth pattern or
movement of a plant in response to an
external stimulus that mainly come from
one direction.
• As tropisms effect the growth pattern of
plants, they greatly effect the plant cell
wall.
Best known:
Phototropism
Induces cells AWAY from light to elongate.
Cell wall expands in a specific direction.
9.3 U.4 Plant shoots respond to the environment by tropisms.
80. Phototropism
•Phototropism is the growth of stems of plants toward light - it is probably the best
known of the plant tropisms - phototropism is caused by elongation of the cells on the
shaded part of the plant - so that entire plant bends or curves toward the light
•This growth pattern is caused by the hormone auxin - auxin migrates to the shaded part
of the plant and stimulates increased cell growth and elongation on the shaded part of
the plant
IAA = Auxin
9.3 U.4 Plant shoots respond to the environment by tropisms.
83. Gravitropism:
Response of a plant to gravity. Causes roots to grow downwards
and stems to grow upwards. This response is governed by Auxin.
Auxin builds up in the cells of the upper surface of root
This induces localized cell
elongation and re-orientation
of the cell walls to allow the
root to grow downwards.
9.3 U.5: Auxin efflux pumps can set up concentration gradients of
auxin in plant tissue.
86. 9.3.A.2 Use of micropropagation for rapid bulking up of new varieties,
production of virus-free strains of existing varieties and propagation of
orchids and other rare species.
• Stock plant is identified for a
desirable feature.
• Micropropagation depends on
totipotent cells which retain the
ability to differentiate.
• Tissue from the stock plant are
sterilized and cut into pieces called
explant.
• The explant is placed into a growth
media along with plant hormones.
This undifferentiate mass is called a
callus.
• Once roots and shoots are
developed the cloned plant can be
transferred to soil.
• This technique is used to overcome
plant viruses or to produce large
numbers of rare plants.
http://www.toptenz.net/wp-content/uploads/2012/04/ghostorchid-570x427.jpg
87. 9.3 A.2 Use of micropropagation for rapid bulking up of new varieties,
production of virus-free strains of existing varieties and propagation of
orchids and other rare species.
Sugar Cain
http://www.sciencephoto.com/image/212210/350wm/G28002
82Cereal_plants_being_grown_from_tissue_culture-SPL.jpg http://php.med.unsw.edu.au/cellbiology/images/6/6e/Plant_Tis
sue_Culture_Lab.jpg
88. 9.3 A.2 Use of micropropagation for rapid bulking up of new varieties,
production of virus-free strains of existing varieties and propagation of
orchids and other rare species.
Sugar Cain
http://vsisugar.com/gallery/tissueculture-gallery/img/photo15.jpghttp://3.imimg.com/data3/IQ/AA/WSITE-5570267/files-resized-
199442-470-353-aebeec90aa3a60f977156f626701cf17c8bb5439-
250x250.jpg
89. 9.4 Reproduction in plants
Essential idea: Reproduction in flowering plants is influenced by the biotic and abiotic
http://www.people.fas.harvard.edu/~ccdavis/weblinks/El_Pais_fil
es/Imagen_Rafflesiaceae_alcanza_metro_diametro_kilos_peso.jp
g
Rafflesia keithii Meijer
90. Understandings
Statement Guidance
9.4 U.1 Flowering involves a change in gene expression
in the shoot apex
9.4 U.2 The switch to flowering is a response to the
length of light and dark periods in many plants.
9.4 U.3 Success in plant reproduction depends on
pollination, fertilization and seed dispersal.
9.4 U.4 Most flowering plants use mutualistic
relationships with pollinators in sexual
reproduction.
91. Applications and Skills
Statement Guidance
9.4.A.1 Methods used to induce short-day plants to
flower out of season.
9.4 S.1 Draw internal structure of seeds.
9.4.S.2 Drawing of half-views of animal-pollinated
flowers.
9.4 S.3 Design of experiments to test hypothesis about
factors affecting germination.
92. 9.4 U.1 Flowering involves a change in gene expression in the shoot
apex
• Production of plant hormones
which when exposed to the
proper amount of photo-
inductive daylight convert
vegetative structure in
reproductive structure.
• The hormone is then transport
from the leaf to the shoot apex
cause genes to switch on
causing transcription of
proteins to begin.
• An increase in morphological
and molecular changes at the
shoot apex, especially involving
floral organ identity genes.
93. The mechanism of flowering
• mRNA moves from leaf to
flower meristem.
• This mRNA provides a link
between the phytochrome
system (the receptor), its
activation of genes in the
leaf (mRNA synthesis)
• Differentiation of the
meristem into the flower
structure comes about due
to the construction of
protein from protein
synthesis.
http://eatbetea.com/wpcontent/uploa
ds/2014/04/IMG_1211.jpg
9.4 U.1 Flowering involves a change in gene expression in the shoot
apex
94. 9.4 U.2 The switch to flowering is a response to the length of light and
dark periods in many plants.
Phytochrome and the control of
flowering
Flowering Cues:
• Plant have to coordinate the production of
flowers to coincide with the best reproductive
opportunities. There are many environmental
cues that affect flowering however the
photoperiod is the most reliable indicator on
'time' of year.
• The photoperiod the period of day light in
relation to dark (night). In northerly and
southern regions this photoperiod is a reliable
indication of the time of year and therefore
one of the most reliable indicators of the
seasonal changes.
Short and Long day Plants:
• Short day plants (SDP) typically flower in the
spring or autumn when the length of day is
short.
• Long day plants (LDP) typically flower during
the summer months of longer photoperiod
95. 9.4 U.2 The switch to flowering is a response to the length of light and
dark periods in many plants.
Critical Night Length
•Experiments have shown that
the important factor determining
flowering is the length of night
rather than the length of day.
•SDP have a critical long night.
That the length of night has to
exceed a particular length before
there will be flowering.
•LDP have a critical short night.
That the length of night must be
shorter than a critical length
before there will be flowering.
96. 9.4 U.2 The switch to flowering is a response to the length of light and
dark periods in many plants.
Phytochrome System:
•The receptor of photoperiod is located within the leaf.
•The cellular location of the receptor is unclear.
•The chemical nature of the receptor is a the molecule PHYTOCHROME.
•Phytochrome can be converted from one form to another by different
types of light.
http://www.putso.com.ne.kr/lecture/img/pfr.gif
97.
98.
99. 9.4 U.2 The switch to flowering is a response to the length of light and
dark periods in many plants.
www.click4biology.com
100. 9.4 U.2 The switch to flowering is a response to the length of light and
dark periods in many plants.
Flowering in Short day plant (SDP)
•Short day plants flower when the night
period is long.
*Night length is critical
Steps
In day light or red light, Phytochrome
Red (Pr) is converted to Phytochrome
Far Red (Pfr). The conversion actually
only requires a brief exposure to
white or red light
In the dark, Pfr is slowly converted
back to Pr. A long night means that
there is a long time for the
conversion.
Under short day conditions (long
night) at the end of the night period
the concentration of Pfr is low.
In SDP, low Pfr concentration is the
trigger for flowering.
http://cnx.org/resources/da0cef9ea401465d69b8142665006a50/Figure_30_06_01.jpg
101. 9.4 U.2 The switch to flowering is a response to the length of light and
dark periods in many plants.
Flowering in Long day Plants
(LDP):
*Night length is critical
•Long day plants flower when the
night period is short.
Steps
In day light (white or red) the
Pr is converted to Pfr.
During periods when the day
light period is long but
critically the dark period is
short, Pfr does not have long
to breakdown in the dark.
Consequently there remains
a higher concentration of
Pfr.
In LDP, high Pfr
concentration is the trigger
to flowering. http://jordantimes.com/uploads/repository/a98b
24c425cded558dc267e1366e05003088e2d4.jpg
102. 9.4 A.1 Methods used to induce short-day plants to flower out of season
http://www.silversurfers.com/wp-
content/uploads/2012/09/red-white-parrot-tulip.jpg
103. 9.4 U.3 Success in plant reproduction depends on pollination,
fertilization and seed dispersal.
Pollination
•The process in which pollen is
transferred from the anther to
the stigma.
•Requires a vector e.g. insects
mammals, winds, birds, water.
•Cross fertilization involves pollen
from one plant landing on the
stigma of a different plant
•Self pollination involves the
transfer of the plants own pollen
to its own stigma
http://www.pollinator.ca/bestpractices/ima
ges/conifer%20pollen%20release.jpg
105. 9.4 U.3 Success in plant reproduction depends on pollination,
fertilization and seed dispersal.
Fertilization
• Fusion of the gamete nuclei
(in the pollen grain) with the
female gamete (in the ovule)
to form a zygote.
• Pollen grains often contain an
additional nuclei used in the
‘fertilization’ of the food
store cells.
Seed dispersal
• Fertilized ovules form seeds.
The seeds are moved away
from the parental plant
before germination to reduce
competition for limited
resources with parental
plant. There are variety of
seed dispersal mechanism
including fruits, winds, water
and animals
http://leavingbio.net/The%20Structure%20and
%20Functions%20of%20Flowers_files/image018.jpg
Fertilization
107. 9.4 U.4 Most flowering plants use mutualistic relationships with
pollinators in sexual reproduction.
• Sexual reproduction in
flowering plants depends on
the movement of pollen from
stamen to a stigma
• Pollen is transferred by wind,
water (less common) and
animals known was
pollinators (more common)
• Pollinators: birds, bats &
insects (bees & butterflies)
• Mutualism – close association
between 2 organisms that
both benefit from the
relationship. Pollinators gain
food by nectar and plants
gains a means to transfer
pollen to another plan
http://upload.wikimedia.org/wikipedia/commons/d/db/Colibri-thalassinus-001-edit.jpg
108. 9.4 U.4 Most flowering plants use mutualistic relationships with
pollinators in sexual reproduction.
• Sexual reproduction in flowering plants depends on the movement of pollen from stamen to a stigma
• Pollinators: birds, bats & insects (bees & butterflies)
109. 9.4 S.1 Draw internal structure of seeds
Dicotyledonous seeds
• Testa protects the plant embryo and the cotyledon food stores
• Cotyledons contain food store for the seed
• Plumule is the embryonic stem
• Radicle is the embryonic root
• Micropyle is a hole in the testa ( from pollen tube fertilization)
through which water can enter the seed prior to germination
• Scar is where the ovule was attached to the carpel wall
111. 9.4 A.2 Drawing of half-views of animal-pollinated flowers.
• Sepals cover the flower structure while the
flower is developing. In some species these are
modified to ' petals'.
• Petals surround the male and female flower
parts. Function is to attract animal pollinators.
• Pistil (female reproductive part)
Stigma is the surface on which pollen lands
and the pollen tube grows down to the
ovary.
Style connects the stigma to the ovary.
Ovary contains the ovules (contain single
egg nuclei).
• Stamen (male reproductive part)
Filaments support the anthers
Anther that contain the pollen. Together
they are called the stamen.
112.
113.
114. 9.4 A.3 Design of experiments to test hypothesis about factors affecting
germination.
The metabolic events of
seed germination:
a) Water absorbed and the activation of
cotyledon cells
b) Synthesis of gibberellin which is a plant
growth substance. (Hormone is no longer a
term used to describe such compounds).
c) The gibberellin brings about the synthesis of
the carbohydrase enzyme amylase
d) Starch is hydrolyzed to maltose before
being absorbed by the embryonic plant
e) The maltose can be further hydrolyzed to
glucose for respiration on polymerized to
cellulose for cell wall formation causing
growth.
117. 9.4 A.3 Design of experiments to test hypothesis about factors affecting
germination.
Conditions for Germination
Seeds require a combination of:
Oxygen for aerobic respiration
Water to metabolically activate the cells
Temperature for optimal function of enzymes
All are need for successful germination. Each seed has its own particular
combination of the three factors.
http://www.emperorswithoutclothes.com/images/seed_growth.jpg
118. 9.4 A.3 Design of experiments to test hypothesis about factors affecting
germination.
