Download 9.2 : Transport in Angiospermophytes ROOTS Main function is

9.2 : Transport in Angiospermophytes
ROOTS
Main function is mineral ion and water uptake for the plant.
Root hairs increase the surface area over which water and mineral ions may be absorbed.
The Root cap is important in protecting the apical meristemduring primary growth of the root
through the soil.
How do mineral ions and water move into the root?
WATER- must pass through the epidermis and cortex to get to the vascular tissue.
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Water moves into the root hairs via osmosis. There is a higher solute concentration
and a lower water concentration than the surrounding soil.
IONS (ie nitrates, ammonium, potassium, phosphates, calcium)
DIFFUSION –when the concentration of minerals is higher in the soil than in the root.
They dissolve in water and then move into the root. May also come in with water
during MASS FLOW in which the plant takes in large volumes of water.
FUNGAL HYPHAE – some plant species have developed a symbiotic relationship
(mutalism) with fungus to help absorb minerals. They can grow into the plant roots
and transport minerals to the roots that the plant cannot absorb without it. Also
creates a larger surface area for absorption
ACTIVE TRANSPORT
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Used when the concentration of minerals is higher inside the root than outside.
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Requires energy and transport proteins, specific to certain ions.
1. Proton pump uses energy from ATP to pump H+ out of the cell.
2. Higher [ H+] outside the cell than inside  creating a negative charge inside the cell and
an ELECTROCHEMICAL GRADIENT.
3. Now the positive ions can move into the cell via diffusion.
Support in terrestrial plants
Support provided by….
1. thickened cellulose
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in the cell walls of the supporting regions of the plant
2. cell turgor pressure
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the pressure inside the cell that is exerted on the cell wall by the plasma membrane
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created by water entering the cell via osmosis
3. and lignified xylem
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lignin- highly branched polymer that increases support in trees and plants that have
woody stems.
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Can provide +25% of the mass of dry wood.
Transpiration
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The loss of water vapour from leaves through the stomata. Often leaves are exposed
to direct sunlight. They have a large surface area to capture light for photosynthesis
but also creates a large surface for water to be evaporated out. (A medium sized tree
can evaporate +1000L on a hot, dry day.)
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The water that is lost by transpiration is replaced by the intake of water in the roots.
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TRANSPIRATION PULL is a continuous stream of water from the roots to the upper
parts of the plant, aided by cohesion and adhesion.
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COHESION: H bonds between water molecules
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ADHESION: H bonds between water molecules and the sides of the vessels – it
counter acts gravity.
Factors that affect transpiration
Light – warm leaf and open stomata
Humidity- decrease in humidity increases transpiration
Wind – increases rate – because humid air near the stomata is carried away
Temperature – increases – because more evaporation
Soil water – if intake of water by the roots does not keep up with transpiration, cells lose turgor
pressure and stomata close.
Carbon Dioxide – high levels around the plant cause guard cells to lose tugor and the stomata
close.
Xylem Vessels
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Large vessels, made of dead cells, responsible for transporting water.
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Created from cells from the cambium; when they die, they become hollow allowing
them to transport water.
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Reinforced by lignin.
STOMATA
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Hormone absicis acid (ABA) causes the stomata to close.
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Changes the particles in the guard cells of the stomata, causing the guard cells to
lose water, become flaccid and close.
XEROPHYTES
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Plants that can tolerate dry conditions
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Less competition in these environments
Adaptations:
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Reduced leaves – smaller surface area reduces transpiration
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Rolled Leaves – reduces stoma exposure to air and sun thus reduces transpiration
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Spines – decrease in surface area
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Thickened waxy cuticle – less water can escape
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Low growth form – closer to the ground and thus less wind exposure
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Reduced number of Stomata
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Stomata in pits surrounded by hairs – the water vapour stays in the pit reducing the
concentration gradient.
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Hair like cell on leaf surface – trap a layer of water vapour maintaining a higher
humidity
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Shedding leaves in driest months
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Fleshy stems – with water stored from rainy seasons
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CAM photosynthesis
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C4 photosynthesis
PHLOEM – vessel transporting food (sucrose, amino acids) via TRANSLOCATION
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Sugars are made in photosynthetic organs (the leaves) and stored in the root.
“source” – where food is made or stored
“sink” – where food in used
Pressure Flow Hypothesis
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Sugar is brought into the phloem by active transport
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Water follows in (from the adjacent xylem) via osmosis
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High pressure created
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Sap will be pushed to a low pressure area, a sink
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Phloem cells move sugar out
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Water follows by osmosis
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Low pressure recreated in the sink, resulting in more sap flowing to the area.
Animations
http://glencoe.mcgrawhill.com/sites/0003292010/student_view0/chapter38/animations_and_videos.html#