Download 9.2 Transport in angiospermophytes - IBDPBiology-Dnl

Assessment Statements
 9.2.1 Outline how the root system provides a large surface area for mineral ion and
water uptake by means of branching and root hairs.
 9.2.2 List ways in which mineral ions in the soil move to the root.
 9.2.3 Explain the process of mineral ion absorption from the soil into roots by active
transport.
 9.2.4 State that terrestrial plants support themselves by means of thickened
cellulose, cell turgor and lignified xylem.
 9.2.5 Define transpiration.
 9.2.6 Explain how water is carried by the transpiration stream, including the
structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation.
 9.2.7 State that guard cells can regulate transpiration by opening and closing
stomata.
 9.2.8 State that the plant hormone abscisic acid causes the closing of stomata.
 9.2.9 Explain how the abiotic factors light, temperature, wind and humidity, affect
the rate of transpiration in a typical terrestrial plant.
 9.2.10 Outline four adaptations of xerophytes that help to reduce transpiration.
 9.2.11 Outline the role of phloem in active translocation of sugars (sucrose) and
amino acids from source (photosynthetic tissue and storage organs) to sink (fruits,
seeds, roots).
Transport in angiospermophytes
 Transport in flowering plants
occurs on three levels:
 the uptake and loss of water
and solutes by individual
cells
 short-distance transport
of substances from cell to
cell at the level of tissues
or organs
 long-distance transport
of sap within xylem and
phloem at the level of
the whole plant
Variety of physical processes involved in the different
types of transport
Root system
 Functions of roots;
 absorb water
 absorb minerals
ions
 support and
anchor
 sometimes used
for food storage
Tap root
Fibrous roots
How the root system provides a large surface
area for mineral ion and water uptake
 the root system of a
plant must supply
sufficient water &
mineral ions
 for this reason, it has
developed a large
surface area due to;
 branching
 presence of root hairs
near the tip
Ways in which mineral ions in the
soil move to the root
 mineral ions are absorbed by




root hairs on the epidermis
root hairs increase the surface
area for absorption
mineral ions enter the root hairs
trough active transport which
uses energy in form of ATP
active transport uses of proteins
pumps to move ions across
membrane
against concentration gradient
i.e. from low concentration in
the soil into the root cells where
they are in high concentration
 the rate of absorption of mineral
ions is limited by the rate at which
the ions move through the soil to
the roots
 there are three ways in which the
ions move to the root:
 through facilitated diffusion
 through mass flow of water
containing dissolved ions
 through mutualistic fungal
hyphae growing around the
root
Adaptations of plant roots for absorption
of mineral ions from the soil
 mineral ions are absorbed by





active transport
large surface area is required
branching of the root &
presence of root hairs
increases surface area
root hair cells have carrier
protein (ion pumps) in their
plasma membrane
many mitochondria are
present in root hair cells to
provide ATP for active
transport
connections with fungi in the
soil (fungal hyphae)
How terrestrial plants support
themselves
 terrestrial plants support
their tissues through:
 thickening of the
cellulose cell wall
 lignified xylem vessels
 cell turgidity, turgor
pressure provide
mechanical support to
the plant tissue
Define transpiration
 transpiration is water
loss from plant by
evaporation
 excess water loss may
harm the plant
 transpiration is the
driving force that pulls
water up from the roots
to the leaves to supply
photosynthesizing tissue
 thus, transpiration is a
necessary evil
How water is carried by the
transpiration stream
 transpiration is water loss from plant
by evaporation
 cohesion of water to itself enhances
 flow of water through xylem from
roots to leaves is the transpiration
stream

 water enters roots through the root
hairs by osmosis
 root hairs provide an extended surface
area for active transport & osmosis
 active transport of ions from soil into
the roots enhances osmotic pressure



 osmotic pressure moves water into the
xylem
 water is carried in a transpiration
stream in the xylem
 adhesion of water to the inside of the
xylem helps move water up

water movement up the xylem
water vapour diffuses into air spaces in
spongy mesophyll of leaves
it passes out through the stomata by
evaporation i.e. transpiration
evaporation of water vapour sets up a
transpiration pull that keeps the water
moving
guard cells control the rate of
transpiration pull by controlling
evaporation
xylem vessels are tubes with helical
rings to enhance water movement by
resisting low pressure
How guard cells regulate transpiration
guard cells
gain water &
open
stoma is
large, rate of
transpiration
is high
guard cells
lose water &
close
stoma is
small, rate of
transpiration
is low
 stomata are pores usually in the
lower epidermis
 each stomata is formed by two
specialised guard Cells
 the epidermis & its waxy cuticle is
impermeable to carbon dioxide &
water
 during the day the pore opens to
allow carbon dioxide to enter for
photosynthesis
 however, the plant will experience
water loss, if the water loss is too
severe the stoma will close
 dehydration, low water potential, of
the mesophyll cell causes them to
release the hormone abscisic acid
 abscisic acid stimulates the stoma to
close
 during the night plants cannot
photosynthesis, so the plant closes
the pores thereby conserving water
Hormone abscisic acid causes the closing of
stomata
guard cells gain water
& open
stoma is large, rate of
transpiration is high
guard cells lose water
& close
stoma is small, rate of
transpiration is low
How the abiotic factors affect the rate of
transpiration in terrestrial plant
 transpiration is loss of water


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
vapour from the stomata of
leaves & stems of plants
temperature, humidity, light
intensity & wind all affect rate of
transpiration
humidity, less transpiration as
atmospheric humidity rises due
to smaller concentration
gradient of water vapour
relatively high temperatures,
more transpiration as
temperature rises due to faster
diffusion as a result of more
kinetic energy of water
molecules
faster evaporation due to more
latent heat available
 windy conditions, more
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
transpiration as wind speed
increases as water vapour blown
away from the leaf
increasing the concentration
gradient of water vapour
high light intensity, more
transpiration in the light due to
light causing stomata to open
wider opening of stomata with
brighter light hence more
transpiration
CAM plants opposite, narrower
stomata with high carbon
dioxide concentration hence less
transpiration
low air pressure, low levels of
carbon dioxide
Adaptations of xerophytes that help to reduce
transpiration
 xerophytes are plants that live in dry conditions

xerophytes are adapted in the following ways to
reduce water loss:
 reduced leaves (spines or needle like) to
reduce the surface area for transpiration
 rolled leaves with stomata on the inside to
prevent water loss by transpiration
 sunken stomata allows layer of humidity
to build up reducing water loss by
evaporation
 thick waxy cuticle on leaves epidermis to
prevent water loss by transpiration
 hairs allow water vapour to be retained
 reduced stomata / stomata on under side of
the leaf to prevent water loss by
transpiration
 special water storage tissue,
 wide-spreading network of shallow roots
obtain more water
 deep roots to absorb water from deep
sources
 vertical stems to avoid mid-day sun
 reversed stomata rhythm, take in carbon
dioxide at night to prevent water loss during
the day
Role of phloem in active translocation of
sugars (sucrose) & amino acids
 phloem is a living tissue

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composed of companion cells
& sieve tube membranes
companion cells involved in ATP
production
assimilate products of
photosynthesis, sucrose & amino
acids transported in phloem
translocation is a bi-directional
transport
from the source; leaves to the
sinks; fruits, roots, the storage
organs such as stem tubers, roots
pressure flow hypothesis;movement of water into phloem
causes transport
1. Loading of sugar (green
dots) into the sieve tube
at the source reduces
water potential inside the
sieve-tube members. This
causes the tube to take
up water by osmosis.
2. This uptake of water
generates a positive
pressure that forces
the sap to flow along
the tube.
3. The pressure is relieved
by the unloading of sugar
and the consequent loss
of water from the tube
at the sink.
4. In the case of leaf-to-root
translocation, xylem
recycles water from sink
to source.
How glucose is transported &
stored
 glucose transformed to
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sucrose
sucrose is translocation of
sugars by phloem
translocation is an active
process which requires
energy
it occurs from source to sink
the source is photosynthetic
tissue in the leaves
sink is fruits, seeds, roots &
other storage organs
sucrose is converted to starch
& stored in storage organs
such as roots, tubers, stem
etc.
Revision Questions
 Outline the adaptations of
 List four abiotic factors
plant roots for absorption
of mineral ions from the
soil.
[5]
 Describe the process of
mineral ion uptake into
roots.
[5]
 Describe how water is
carried by the
transpiration stream. [7 ]
 Explain how abiotic factors
affect the rate of
transpiration in a
terrestrial plant.
[8]
which affect the rate of
transpiration in a typical
mesophytic plant.
[4]
 Explain how wind affects
the rate of transpiration
from a leaf.
[5]
 Outline adaptations of
xerophytes that help to
reduce transpiration
[8]
 Outline the role of the
phloem in the active
translocation of
biochemicals.
[5]