Sugar and water transport in Plants Lecture 9a Flashcards
Explain why plants loose water
Transpiration: loss of water via evaporation from the aerial parts of the plant.
• Transpiration occurs when 2 conditions are met:
1. Stomata are open.
2. Air surrounding the leaves is drier than the air inside the leaves.
–> If water that is lost is not replaced, cells will die.
Define transpiration.
loss of water via evaporation from the aerial
parts of the plant.
Define osmosis
Diffusion of water across a selectively permeable membrane from region of high water concentration (low solute concentration) to a region of low water concentration (high solute concentration)
Define water potential and state the direction in which water flows relative to water potential.
Water potential = the potential energy that water has in a particular environment, compared to the potential energy of pure water at room temperature under atmospheric pressure.
• Under these conditions, water potential = 0
Water always flows from areas of high water potential to areas of
low water potential.
Describe the two factors that affect water potential and how they do so.
- Solute concentration
• Defined by the solution’s solute concentration relative to pure water.
• The solute potential of pure water is 0.
• Since solutes bind water molecules they lower the capacity of water to move and do work. - Pressure
is any kind of physical pressure on a solution.
• Can be positive (push) or negative (tension) relative to atmospheric pressure. ex. turger pressure
State which way water will flow given the solute potential and pressure potential of two solutions.
Si = Si S + Si P
Explain how the physical properties of plant cells are changed when the plant is placed into solutions that have higher, lower, or the same solute concentration.
If the solution has higher solute concentration the water will move out of the cell (flacid)
if the solution has lower solute concentration water will move into the cell (turger pressure)
and if it is the same there will be no net movement
Define the terms flaccid, turgor pressure, and turgid
Flaccid- limp, droppy and soft
turgor pressure: The pressure exerted by water inside the cell against the cell wall.
Turgid: means distended or swollen, especially due to high fluid content. A plant cell is said to be turgid when its vacuoles have maximum amount of water.
Describe the role of turgor pressure in plant cells.
the cell turgor is the pressure of water on the walls of the cell, this pressure gives rigidity to the cell and thus to the plant and for that non woody plant can stand even though they have no wood and can resist bad environmental conditions.
Define bulk flow.
Movement of water due to a pressure gradient,
always occurs from higher to lower pressure and is independent of solute concentration
occurs in the trachieds and vessel elements of xylem and the seive- tube members of phloem
Differentiate between diffusion and bulk flow.
Diffusion is slow, Diffusion: Net movement down a
concentration gradient due to the random
motion of individual molecules. (Note:solutes may move independently of water.)
Bulk flow: Movement of water and solutes
together due to a pressure gradient
Relate the structure of sieve-tube members, vessel elements, and tracheids to their roles in bulk flow.
Sieve-tube members are cells that Must maintain sugar concentration so they are simplified for lower resistance
Vessel elements and tracheids are dead and empty for lower resistance
Explain the routes that soil solution can take from the soil to the vascular cylinder of the root.
transmembrane route: via water channels ( in and out of cells)
apoplastic route: within porus of cell walls (never moves into cells just goes through cell walls)
symplastic route: via plasmodemata (stays in cells)
Explain how the endodermis functions as a selective barrier between the root cortex and
vascular cylinder and why this function is important.
Endodermis = innermost layer of the cortex.
• Cylinder one cell thick.
• Forms a selective barrier between the cortex and the vascular cylinder.
• Within the walls of each cell is the Caspian strip.
• Waxy belt
• Forces the water and minerals passively moving through the apoplast to cross the plasma membrane of an endodermal cell before they can enter the vascular tissue!
important gate keeper to make sure bad things do not enter the plant
Explain the cohesion-tension hypothesis of how transpirational pull moves xylem sap up
from the roots to the leaves. Make sure to describe the importance of the cohesive and
adhesive properties of water and surface tension in your explanation.
The leading hypothesis to explain water movement in vascular plants is the cohesion-tension hypothesis.
• Water is pulled to the tops of trees via forces generated by transpiration at the leaf surface
The movement of fluid from root to shoot is driven by a water potential difference at opposite ends of xylem tissue.
• The water potential difference is created at the leaf end of the xylem by evaporation of water from leaf cells (i.e. transpiration).
• This evaporation lowers the water potential at the air-water interface, generating the negative pressure (i.e. tension).
• The negative pressure or pull is transmitted to the water in nearby cells
water inside the xylem water in the vascular tissue of roots water in the soil.
• This continuous transmission of pulling forces is possible because the water molecules hydrogen bond to one another in a continuous fashion
(i.e., cohesion), makes it possible to pull xylem sap from above without water molecules separating.
adhesion!
• Cellulose is a polar molecule strong attraction between water and the cellulose molecules in the xylem cell walls.
• This adhesion is believed to help offset the downward force of gravity.
