Transport in Plants

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Transport in Plants

• By
• Danny Nemeth
• Michelle Drabish

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Water and Minerals Move Upward Through the Xylem

• Overview of Water and Mineral Movement Through
  Plants.

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Local Changes Result in the Long-Distance, Upward
Movement Through Plants.

• How can water move upward through trees and other
  plants when common sense tells us gravity should
  "pull" the water down?
• The answer is in the xylem of the plants.
• Water moves though the spaces between the
  protoplasts of cells, through plasmodesmata (the
  connection between cells), though the plasma
  membrane, and through the interconnected,
  water-conducting xylem elements that extend
  through the plant.
• Water enters roots, rises through xylem, and
  exits through stomata and leaves.

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What helps water move through xylem?

• Water moves the greatest distance through the
  xylem of the plant with the help these factors
• a small "pushing" pressure from water entering
  roots
• a larger "pulling" pressure cause by water
  evaporating called transpiration
• these are made possible by
• adhesion where water molecules stick to the
  walls of the tracheid or xylem vessel
• cohesion water molecules stick to each other
• aquaporins water channels that enhance osmosis

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Water Transport at the Cellular Level

• While this chapter focuses on the movement of
  water through xylem, the movement of water at the
  cellular level plays a large role in bulk water
  transport in the plant as well.

• Aquaporins are water-selective pores in the
  plasma membrane that increase the rate of
  osmosis. They do not alter the movement of water,
  however

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Water Potential

• Plant biologists often discuss the forces that
  act on water within a plant in terms of
  potentials.
• There are two components to water potential
• physical forces, such as plant cell wall or
  gravity, and
• the concentration of solute in each solution

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Water Potential the sum of its pressure
potential and solute potential it represents the
total potential energy of water in the
plant.   Water will move out of the cell because
the water potential is negative
Pressure Potential the turgor pressure, a
physical pressure that results as water enters
the cell vacuoles.   Cell walls exert pressure in
the opposite direction of turgor pressure.
Solute Potential the smallest amount of
pressure needed to stop osmosis of the
solution   Using the given solute potentials, you
can determine the direction of the water movement
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Transpiration

• Transpiration from leaves, which creates a pull
  on the water columns, indirectly plays a role in
  helping water enter the root cells.
• Water evaporating from the leaves through the
  stomata causes additional water to move upward in
  the xylem and also to enter the plant through the
  roots.

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Water and Mineral Absorption

• The Pathways of Mineral Transport in Roots
• Minerals are absorbed at the surface of the root,
  mainly by root hairs.
• In passing through the cortex, they must either
  follow the cell walls and the spaces between
  them, or go directly through the plasma membranes
  and the protoplasts of the cells, passing from
  one cell to the next by way of the plasmodesmata.
• When they reach the endodermis, their further
  passage through the cell walls is blocked by the
  Casparian strips,  and they must pass through the
  plasma membrane and protoplast of the cell before
  entering the xylem.

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More on Water/Mineral Absorption

• In terms of water potential, active transport
  increases the solute potential of the roots.
• The result is movement of water into the plant
  and up the xylem columns despite the absence of
  transpiration.
• This phenomenon is called root pressure

• Under certain circumstances, root pressure can be
  so strong that water will ooze out of a cut
  plant stem for hours or even days!
• When root pressure is high, it can force water up
  to the leaves, where it may be lost in a liquid
  form  in a process called guttation.

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Water and Mineral Movement

• The tensile strength of a water column varies
  inversely with the column diameter.
• More than 90 of water taken in  by the roots is
  lost to the atmosphere through transpiration.
• Plants have evolved to conserve water loss with
  dormancy, thick hard leaves, and trichromes.
•  Aerenchyma is a tissue that facilitates gas
  exchange in aquatic plants.This is mostly used in
  flooded areas where oxygen deprivation is common
  due to standing water.

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Stomata

• Stomata open and close due to changes in turgor
  pressure resulting from the active uptake of
  potassium.
• Other factors, such as CO2 concentration,light,
  and temperature,can also effect and control
  stomatal opening.

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•       Dissolved sugars and hormones are
  transported in the phloem
•  Translocation- carbohydrates manufactured in
  leaves  are distributed through the phloem to the
  rest of the plant. 
•   provides suitable carbohydrate building blocks
  for the roots and other actively growing regions
  of the plant.
• studies have shown, using radioactive carbon
  dioxide, that sucrose moves both up and down in
  the phloem.
•  Phloem also transports plant hormones and mRNA.

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Energy Requirements for Transport

• Mass-flow hypothesis- dissolved carbohydrates
  flow from a source and are releases at a sink.
• most widely accepted  model of how carbohydrates
  in solution move through the phloem. 
• Carbohydrates enter sieve tubes by osmosis, and
  the resultant increased turgor pressure drives
  the water throughout the sieve-tube system.
• At the sink, carbohydrates are actively removed.

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FIN!!!
Thank you for putting up with this! Hopefully you
didn't fall asleep! )