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Chapter 12: Transport Processes (Water Potential (Measure of how freely…
Chapter 12: Transport Processes
Diffusion, Osmosis, and Active Transport
Osmosis
Instance in which particles move passed a semipermeable membrane
Particles does this to balance the concentrations of another substance
Diffusion through the membrane is called osmosis
Active Transport
Causes particles to move from an area of low concentration to an area of high concentration
Molecular Pump
Most membranes have membrane-bound molecular pumps that use the energy of ATP to force molecules across the membrane
The molecular pump, which is a protein, binds to both the molecule and ATP
ATP splits into ADP and phosphate
Energy is transferred to the pump, forcing it to change shape, carry the molecule across the membrane, and release it
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Direction of particles is that opposite of diffusion
Molecules are still forced across the membrane even if that type of molecule is extremely concentrated on the receiving side
Ex) Proton pumping in photosynthesis and respiration
Diffusion
Simplest method
Causes particles to move from an area of high concentration to an area of low concentration
In which the random movement of particles in solution
Direction of particles is that opposite of active transport
Three Membrane Types
Completely impermeable
Membranes do not allow anything to pass through and occur as isolation barriers
Differentially or selectively permeable membrane
Allow only certain substances to pass through
All lipid/protein cell membranes are differentially permeable
Freely permeable
Membranes allow all solutes through them and have little biological significance
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All membranes are important in transport processes
The plasma membrane governs movement of material into and out of the cell
Substances can across thevaculoar membrane by osmosis or active transport
Molecules
Many Polar, hydrophylic molecules
Can cross differentially permeable membranes only if the membranes have special protein channels through which the molecules can diffuse
Water molecules
Even though highly polar, pass through all membranes
But their movement is more rapid if the membrane has protein channels called aquaporins
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Hydrophobic molecules
Diffuse easily through any cell membrane
Parts of the Cell
Endoplasmic Reticulum and Dictyosome Membranes
Transports material that then accumulates in vesicles
Cuticle
Waterproof epidermal layer that acts as an isolation mechanism
Retains water within the plant
Keeps pathogens out
Vacuole
Acts as an accumulation space for sugars, pigments, crystals, and many other compounds
Intracellular Transport
Vesicles may be relatively permanent, remaining in the cell for long periods of time
During fusion - membranes merge and the vesicle contents are transferred into the organelle
Moving materials
From the endoplasmic reticulum to dictyosomes
Or from either of these organelles to the cell exterior by fusion with the plasma membrane
Vesicles migrate through the cytoplasm and fuse with another organelle
Water Potential
Pressure Potential
If water is under pressure
The pressure potential increases
And the water potential increases
If pressure decreases
So does the pressure potential
And the water potential
The effect that pressure has on water potential
Water potential has 3 components:
Equation:
Pressure can be positive
When something is compressed
Pressure can be negative
When something is stretched
Potential is measured in
units of pressure
Usually in megapascals (MPa) or bars
One megapascal is approximately equal to
Or 10 atmospheres of pressure
Pure water at one atmosphere of pressure
Is defined as having a water potential of zero
10 bars
Measure of how freely water molecules can move in a particular environment or system.
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Chemical potential is usually referred to as water potential
Water Potential Symbol
Water Potential can be increased in many ways
Put under pressure
Or elevated
Water can be heated
Water Potential can be decreased in many ways
Reducing pressure on it
Or lowering it
Cooling water
Water's capacity can be changed in other ways
When a sponge is added to a beaker of pure water
Water molecules adhere to the sponge material
Can no longer flow or easily dissolve things
When a large amount of sugar is added to a beaker of pure water
Water molecules adhere to the sugar molecules
Can no longer flow or easily dissolve things
When water adheres to a substance - forms hydrogen bonds
Capacity to do work has decreased
Osmotic Potential
In pure water, no solutes are present
Osmotic potential is given the value of 0.0 MPa
Is the effect that solutes have on water potential
Adding solutes can only decrease
Water's free energy because water molecules interact with solute molecules
And cannot diffuse easily
Related to the number of particles present in solution
Matric Potential
Adhesion can only decrease water's free energy
And thus, matric potential is always negative
Water's adhesion to nondisolved structures such as cell walls, membranes, and soil particles
Short-Distance Intercellular Transport
Motor Cells
They can either accumulate or expel potassium and thus adjust their water potential and turgidity
Leaves of sensitive plant (Mimosa pudica)
Prayer plant (Oxalis
Acts like a hinge and helps with movement
Transfer Cells
The rate at which material can be actively transported depends on the number of molecular pumps present
The walls are smooth on the outer surface
Has numerous finger-like and ridge-like outgrowths on the inner surface
Type of Parenchyma cell
Specialized cell
In glands that secrete salt
In areas that pass nutrients to embryos
Found in areas where rapid short-distance transport is expected to occur
Regions where sugar is loaded into or out of a phloem
Facilitate the transport of sugars
Increased surface area
Guard Cells
At night
When stomata is closed
Guard cells are somewhat shrunken and have little internal pressure
Except for CAM plants
Hydraulic equilibrium
Water enters and leaves guard cells at approximately the same rate
No net change occurs in the amount of water
Opening and closing of stomatal pores based on short-distance intercellular transport
Most plant cells communicate with their neighboring cells
Transferring
Sugars
Minerals
Water
Hormones
Symplast
All of the protoplasm of one plant can be considered one continuous mass
Osmosis
Molecular pumps in the plasma membrane,
Or fusion between transport vesicles and the plasma membrane
Apoplast
Most small molecules can move easily through both the wall and the intercellular spaces; the two together are called the apoplast
