8.1 Transport in Plants
• State the functions of xylem and phloem
• Identify the position of xylem and phloem as seen in sections of roots, stems and leaves, limited to nonwoody dicotyledonous plants
Water & Minerals = need to be transported from the ground, into the root cells and upwards to the
meristem (growing tip) of the shoot
Sucrose (food) = produced by photosynthesis, need to transported from the leaves to other parts of the plants
They are transported by VASCULAR BUNDLES which are made from:(a) XYLEM = that transports water and ions
(b) PHLOEM = that transports food (sugar) & amino acids
Xylem vessels = long hollow tubes made out of DEAD cells
containing no cytoplasm.
- Have small holes at their sides called pits in which
water can enter and move from one vessel to the other
- It also helps to provide mechanical support to the plant
Phloem tubes = living cells, contains cytoplasm but no nucleus
● Long narrow tubes with perforated sieve plates
● Activities controlled by companion cells
● transport sugar from the Source where they are taken
in or produced) to the Sink (where they are used/stored)
● In spring, sucrose (sugar) is transported from the store in the root to leaves
● In summer, it is transported from photosynthesizing leaves to roots to be stored
Vascular bundles are arranged differently in the stem and in the root:
- for most effective
transport of materials
and most effective
support
- In the stem, vascular
bundles are arranged
in a ring to help
support the stem
-
In the root, the
surrounding roots
hairs ensure larger
surface area for
absorption of water
8.2 Water Uptake
• Identify root hair cells, as seen under the light microscope, and state their functions
• Explain that the large surface area of root hairs increases the rate of the absorption of water by osmosis and
ions by active transport
• State the pathway taken by water through root, stem and leaf as root hair cell, root cortex cells, xylem and
mesophyll cells
• Investigate, using a suitable stain, the pathway of water through the above ground parts of a plant
The root hairs are long and thin, enabling it to penetrate the soil particles
and for easy diffusion. The root hair increases the surface area of the cell
to make it more efficient in absorbing materials
Functions of root hair cells
●
For absorption of water and mineral ions
●
Provide anchorage for the plant.
Water is important to support plants through turgidity, substrate for
photosynthesis, as a transport medium & as a reagent for biochemical reactions, cool leaves via evaporation
Mineral ions such a magnesium (
), nitate (
) enters into the plant from the soil through the roots.
● Affect the water potential of the plant tissues
They can enter via two ways:
1. Diffusion (down concentration gradient)
2. Active Transport (against concentration gradient)
- needs Energy, so depends on respiration
- lack of oxygen or low temperature, respiration reduce, rate of ion uptake also reduces
Water pathway:
Root hair � Root cortex cells � Xylem of Root � Xylem
of Stem � Xylem of Leaves � Mesophyll Cells
● Water is drawn up through the xylem to
replace water loss at leaves. This creates a
transpiration stream.
● Water enter into the root cell through
osmosis (water diffusion) down concentration
gradient as the soil water has higher water
potential compare to the root hair cell sap.
● Water crosses the living cells of cortex through:
a) Osmosis through the cells
b) “pulled” by transpiration through the freely permeable cell walls (in between cells)
● As it near the center of the root, a layer of cells with waxy cell wall prevents water moving through the
cell walls, forcing all water to go through the living cells to enter the xylem vessels.
● This allows the cell membrane to control substances that can enter into the xylem.
8.3 Transpiration
• State that water is transported from the roots to leaves through the xylem vessels
• Define transpiration as loss of water vapour from plant leaves by evaporation of water at the surfaces of the
mesophyll cells followed by diffusion of water vapour through the stomata
• Explain how water vapour loss is related to the large surface area of cell surfaces, interconnecting air spaces
and stomata
• Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that
draws up a column of water molecules, held together by cohesion
• Explain how and why wilting occurs
Transpiration is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the
mesophyll cells followed by diffusion of water vapour through the stomata
Function of stomata:
● Allow diffusion of gases (carbon dioxide and oxygen)
● Allow diffusion of water vapour
● Rate of diffusion are controlled by guard cells, which
control the closing and opening of stomata
● There are usually more stomata on the lower surface of
the leaves compared to the upper surface
● This is to prevent excess water loss due to evaporation as
the lower surface is less exposed to the Sun
Closing and Opening of the Stomata
● When lack of water, guard cells become flaccid.
● When plenty of water, guard cells become turgid.
● Because the inner layer is thicker and cannot
stretch as much as the outer surface, when the
guard cells swell with water, they curve away from
each other, opening the stomata.
Transpiration Process
⮚ Transpiration is the loss of water vapour from the leaf;
⮚ Water in the mesophyll cells form a thin layer on their surfaces; (this helps with the diffusion of carbon
dioxide into the cells.
⮚ The water evaporates from the large surface area of spongy mesophyll cells and into airspaces;
⮚ This creates a high concentration of water molecules in the air spaces inside the leaf and low
concentration of water molecules outside the leaf.
⮚ Water vapour diffuses down concentration gradient out of the leaf into the surrounding air, through
the opened stomata
⮚ Water cannot diffuse into the leaves because the air spaces in the leaves are saturated with water
vapour. Thus it must be absorbed from the soil and drawn up the plant.
How water moves upwards in the xylem:
transpiration pull that draws up a column of water molecules, held together by cohesion
1) Transpiration: Water evaporates from leaves and lowers the water potential in the leaf tissues
2) Water moves from xylem to enter the leaves down water potential gradient
3) Water uptake occurs by osmosis from the soil solution (high water potential) into the root cells (lower
water potential)
4) Water moves up the stem in the xylem as a column of water due to the transpiration “pull” (tension
caused by water loss from the leaves) and the cohesion between the water molecules. (ensures
continuous, column of water won’t break).
5) The incoming water in roots also provides root pressure.
98% of water uptake in plants are lost through transpiration.
To measure water uptake, a Bubble Potometer is used:
Reservoir:
prevent air bubble entering the plant and to
move bubble back along capillary tube
Capillary tube: to be kept horizontal to avoid bubble moving
Air bubble: inserted by removal of tube from water.
�
Leafy shoot must be cut, apparatus filled and shoot
fixed all under water to prevent air locks in the system.
�
Rate of bubble movement = rate of water loss
How & Why Wilting occurs?
● Herbaceous plant stems and leaves rely on their cells being turgid to keep them rigid.
● If the amount of water lost from the leaves of a plant is more than the amount taken into the roots,
● The plant cells become flaccid (soft) and will no longer press against each other.
● Stems and leaves lose their rigidity, and wilt.
8.1 Transport in Plants
• State the functions of xylem and phloem
• Identify the position of xylem and phloem as seen in sections of roots, stems and leaves, limited to nonwoody dicotyledonous plants
__________& _________________ = need to be transported from the ______________, into the __________
and upwards to the __________________ (growing tip) of the shoot
____________= produced by photosynthesis, need to transported from the leaves to other parts of the plants
They are transported by VASCULAR BUNDLES which are made from:
(a) ____________ = that transports water and mineral ions
(b) ____________ = that transports food (sugar) & amino acids
Xylem vessels = long hollow tubes made out of _______________
containing _______________.
- Have small holes at their sides called __________ in which
water can enter and move from one vessel to the other
- It also helps to provide ___________________ to the plant
Phloem tubes = living cells, contains cytoplasm but ____________
● Long narrow tubes with ________________________
● Activities controlled by _________________________
● transport sugar from the Source where they are taken in or produced) to the Sink (where they are
used/stored)
● In spring, sucrose (sugar) is transported from the store in the root to leaves
● In summer, it is transported from photosynthesizing leaves to roots to be stored
Vascular bundles are arranged differently in the stem and in the root: for most effective transport of
materials and most effective support
- In the stem, vascular bundles are arranged in a ring to help __________________________
- In the root, the surrounding roots hairs ensure larger surface area for absorption of water
8.2 Water Uptake
• Identify root hair cells, as seen under the light microscope, and state their functions
• Explain that the large surface area of root hairs increases the rate of the absorption of water by osmosis and
ions by active transport
• State the pathway taken by water through root, stem and leaf as root hair cell, root cortex cells, xylem and
mesophyll cells
• Investigate, using a suitable stain, the pathway of water through the above ground parts of a plant
The root hairs are __________________, enabling it to _______________
particles and for ______________. The root hair ____________________
________ of the cell to make it more _____________________ materials.
Functions of root hair cells
●
For _______________________________
●
_____________________ for the plant.
Water is important to ________________ through turgidity, substrate for
______________, as a ______________ & as a reagent for biochemical reactions, cool leaves via evaporation.
Mineral ions such a ____________ ( ), __________ ( ) enters into the plant from the soil through the roots.
● Affect the water potential of the plant tissues
They can enter via two ways:
1. __________________ (down concentration gradient)
2. __________________ (against concentration gradient)
- needs _____________, so depends on __________________
- lack of oxygen or low temperature, respiration reduce, rate of ion uptake also reduces
Water pathway:
__________ � Root _____ cells � _____ of Root �
Xylem of Stem � Xylem of Leaves � _____________
● Water is drawn up through the xylem to
_______________________ at leaves. This
creates a _________________________.
● Water enter into the root cell through
______________ down concentration
gradient as the __________ has higher water
potential compare to the
_______________________.
● Water ______________________________________ through:
a) Osmosis through the cells
b) “pulled” by transpiration through the freely permeable cell walls (in between cells)
● As it near the center of the root, a layer of cells with __________ cell wall _______________________
_________________, forcing all water to ____________________________ to enter the xylem vessels.
● This allows the cell membrane _________________________that can ___________ into the xylem.
8.3 Transpiration
• State that water is transported from the roots to leaves through the xylem vessels
• Define transpiration as loss of water vapour from plant leaves by evaporation of water at the surfaces of the
mesophyll cells followed by diffusion of water vapour through the stomata
• Explain how water vapour loss is related to the large surface area of cell surfaces, interconnecting air spaces
and stomata
• Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that
draws up a column of water molecules, held together by cohesion
• Explain how and why wilting occurs
Transpiration is the ___________________________ from plant leaves by _______________________ at the
_________________________ followed by ______________________________ through the ______________
Function of stomata:
● Allow ___________________ (carbon dioxide and oxygen)
● Allow _________________________
● Rate of diffusion are controlled by ______________, which
control the closing and opening of stomata
● There are usually more stomata on the _________ surface
of the leaves compared to the ___________ surface
● This is to _________________________________ as the
lower surface is _____________________________
Closing and Opening of the Stomata
● When lack of water, guard cells become flaccid.
● When plenty of water, guard cells become turgid.
● Because the ______________________ and cannot
stretch as much as the outer surface, when the
guard cells swell with water, they ______________ from each other, opening the _________________.
Transpiration Process
⮚ Transpiration is the __________________________ from the leaf;
⮚ ________________ in the mesophyll cells form a ___________________________; (this helps with the
_________________________________________.
⮚ The water _______________________________ of spongy mesophyll cells and into _______________
⮚ This creates a _____________________________ in the air spaces inside the leaf and
________________________________ outside the leaf.
⮚ Water vapour _________________ down concentration gradient ______________________ into the
surrounding air, through the opened _____________.
⮚ Water cannot diffuse into the leaves because the air spaces in the leaves are _____________________
_____________________. Thus it must be absorbed from the soil and drawn up the plant.
How water moves upwards in the xylem:
transpiration pull that draws up a column of water molecules, held together by cohesion
1) Transpiration: Water evaporates from leaves and _____________________________ in the leaf tissues
2) Water moves from xylem to enter the leaves down water potential gradient
3) Water uptake occurs by _________________ from the ________________ (high water potential) into
the __________________ (lower water potential)
4) Water moves up the stem in the xylem as _________________________________________ due to the
______________________________ (tension caused by water loss from the leaves) and the
______________________________________. (ensures continuous, column of water won’t break)
5) The incoming water in roots also provides root pressure.
*98% of water uptake in plants are lost through transpiration.
To measure water uptake, a _____________________ is used:
Reservoir:
_______________________________________
_______________________________________
Capillary tube: to be kept horizontal to avoid bubble moving
Air bubble: inserted by removal of tube from water.
�
Leafy shoot must be cut, apparatus filled and shoot
fixed all ___________ to prevent air locks in the system.
�
Rate of bubble movement = _______________________
How & Why Wilting occurs?
● Herbaceous plant stems and leaves rely on their cells being ________________ to keep them rigid.
● If the _________________________________ from the leaves of a plant is ____________ than the
________________________________________,
● The plant cells become _________________ (soft) and will no longer press against each other.
● Stems and leaves will no longer be ________________, and _____________.
Effects of temperature & humidity on transpiration rate
● Investigate and describe the effects of variation of temperature and humidity on transpiration rate
● Explain the effects of variation of temperature and humidity on transpiration rate
Transpiration can be increased by:
1. _______________________:
a. by increasing ___________________ of water molecules (movement), so water diffuse faster.
b. Warmer air can also ______________________ (increased water-holding capacity of air)
2. ____________________
a. Increases the steepness of _____________________ between inside of leaf and atmospheric air
3. __________________
a. Moves humid air away from leaf surface and increase diffusion and water potential gradient
4. ________________________
a. Causes stomata to open (to allow ________________) which allows transpiration to occur
Some plants have adapted to survive at dry conditions
by reducing transpiration:
● ___________________________ to reduce
evaporation from epidermis
● Leaves are _____________ shape to_________
____________________ for water loss
● Stomata may be ______________ in pits with
hairs to __________ a pocket of humid air
● Leaves may be ____________ with stomata on
inner surface, near trapped layer of humid air
● Cactus: swollen stem to store water,
● Shallow widespread roots to _________________________________ & deep roots to tap groundwater
● Leaf fall and wilting: decrease water loss and plants can remove chlorophyll from leaves to be stored
before leaves fall
8.4 Translocation
Translocation is the ___________________________________ such as sucrose and amino acids in _________:
– from regions of production (s___________)
– to regions of s_____________ OR to regions where they are used in respiration or growth (s_______)
Carbohydrates are transported through a plant in the form of sucrose, glucose, and proteins as amino acids.
Substances can be transported in any direction in phloem:
● from photosynthesising leaves down to roots for storage.
● upwards to ________________________________________________ for respiration and growth.
● from storage organs such as the ___________________ to all parts of the plant.
Sucrose and amino acids are transported to every tissue of the plant; each cell use it in a different way.
● Root cells convert sucrose into glucose for respiration and store it.
● Growing cells make cellulose for cell walls from sucrose and use the amino acids to make proteins for
growth.
● And fruits use the sucrose to make the attractive scent and tasty nectar to attract insects.
Explain that some parts of a plant may act as a source and a sink at different times during the life of a plant.
Example: potato plants – in winter, leaves and plants die
Ringing Experiment
The phloem vessels are situated nearer to the bark in comparison with xylem à they can be selectively
removed by cutting a ring in a stem just deep enough to cut the phloem but not the xylem.
After a week there is:
● a swelling above the ring
● reduced growth below the ring
● the leaves are unaffected.
This was early evidence that sugars were transported downwards in
the phloem.
Sourced from: http://biology-igcse.weebly.com/translocation-oforganic-foods-in-plants.html
Effects of temperature & humidity on transpiration rate
● Investigate and describe the effects of variation of temperature and humidity on transpiration rate
● Explain the effects of variation of temperature and humidity on transpiration rate
Transpiration can be increased by:
5. High temperature:
a. by increasing kinetic energy of water molecules (movement), so water diffuse faster.
b. Warmer air can also hold more water (increased water-holding capacity of air)
6. High Humidity
a. Increases the steepness of water potential gradient between inside of leaf and atmospheric air
7. Wind
a. Moves humid air away from leaf surface and increase diffusion and water potential gradient
8. High light intensity
a. Causes stomata to open (to allow photosynthesis) which allows transpiration to occur
Some plants have adapted to survive at dry conditions
by reducing transpiration:
● Thick, waxy cuticle to reduce evaporation from
epidermis
● Leaves are needle shape to reduce surface area
for water loss
● Stomata may be sunken in pits with hairs to
trap a pocket of humid air
● Leaves may be rolled with stomata on inner
surface, near trapped layer of humid air
● Cactus: swollen stem to store water,
● shallow widespread roots to absorb water from lightest rainfall & deep roots to tap groundwater
● Leaf fall and wilting: decrease water loss and plants can remove chlorophyll from leaves to be stored
before leaves fall
8.4 Translocation
Translocation is the movement of organic substances such as sucrose and amino acids in phloem:
– from regions of production (source)
– to regions of storage OR to regions where they are used in respiration or growth (sink)
Carbohydrates are transported through a plant in the form of sucrose, glucose, and proteins as amino acids.
Substances can be transported in any direction in phloem:
● from photosynthesising leaves down to roots for storage.
● upwards to growing buds, flowers, leaves and fruits for respiration and growth.
● from storage organs such as the root tubers to all parts of the plant.
Sucrose and amino acids are transported to every tissue of the plant; each cell use it in a different way.
● Root cells convert sucrose into glucose for respiration and store it.
● Growing cells make cellulose for cell walls from sucrose and use the amino acids to make proteins for
growth.
● And fruits use the sucrose to make the attractive scent and tasty nectar to attract insects.
Explain that some parts of a plant may act as a source and a sink at different times during the life of a plant.
Example: potato plants – in winter, leaves and plants die
Ringing Experiment
The phloem vessels are situated nearer to the bark in comparison with xylem à they can be selectively
removed by cutting a ring in a stem just deep enough to cut the phloem but not the xylem.
After a week there is:
● a swelling above the ring
● reduced growth below the ring
● the leaves are unaffected.
This was early evidence that sugars were transported downwards in
the phloem.
Sourced from: http://biology-igcse.weebly.com/translocation-oforganic-foods-in-plants.html