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Transport processes (Diffusion, osmosis, and active transport (Membrane…
Transport processes
Diffusion, osmosis, and active transport
Diffusion
Random movement of particles causes transport
High concentration to low concentration
Osmosis
Diffusion through a membrane
Membrane types
Freely permeable
Completely impermeable
Differentially/selectively impermeable
Aquaporins
Promote diffusion of water
Molecular pumps
Use ATP to pump molecules across a membrane
This is called active transport
Intracellular transport
Vesicles migrate through cytoplasm and fuse with other organelles
Short-distance intercellular transport
Guard cells
Control opening and closing of stomatal pores
K+ ions transported into the guard cells causes them to open
Motor cells
Cells at "joints," or location of flexure on a plant
Transfer cells
Walls are smooth on outer surface
Numerous finger-like and ridge-like outgrowths on inner surface
Symplast
Mass of protoplasm in the cell
Apoplast
Cell wall + intercellular spaces
Long-distance transport: phloem
Sources
Sites from which water and nutrients are transported
Mass transfer
Actual amount of sugars and other nutrients transported by phloem per hour
Sinks
Sites that receive transported phloem sap
Roots, seeds, flowers, fruits
Long-distance transport: xylem
Properties of water
Cohesive
Water molecules interact strongly with each other
Adhesive
Water molecules interact with many other substances
Water transport through xylem
Cohesion-tension theory
Transstomatal transpiration
Cells around stomata begin to lose water, all the way back to xylem
Tension on xylem + cohesion of water molecules pulls water from root
Embollism
Air bubble in xylem
Prevented by Casparian strip of endodermis
Control of water transport by guard cells
Leaf has adequate moisture content
Light and CO2 are controlling factors
Stress hormone
Closes guard cells when stomata is losing too much water
CAM plants
Stomata are open at night to prevent water loss
Water potential
Cells and water movement
Water flows from a more negative water potential to a less negative water potential
Free energy of water
