Soil Plant Water Relationships - Transport Processes

• Short-distance transport involves distances of a few cell diameters or less.
• Long-distance transport is between cells that are not close neighbors.
• Short-distance transport involves the transfer of basic nutrients from cells with access to the nutrients to cells that need them but are not in direct contact with them
• Short-distance transport became necessary to the survival of internal cells.
• Long-distance transport is not absolutely essential in the construction of a large plant.
• Diffusion is the random movement of particles in solution which causes them to move from areas where they are in relatively high concentration to areas where they are in relatively low concentration.
• Diffusion through a membrane is technically known as osmosis.
• Freely permeable membranes allow all solutes to diffuse through them and have little biological significance.
• Completely impermeable membranes do not allow anything to pass through and occur as isolation barriers.
• Differentially or selectively permeable membranes allow only certain substances to pass through.
• All lipid/protein cell membranes are differentially permeable.
• Hydrophobic molecules diffuse easily through any cell membrane.
• Polar, hydrophilic 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.
• The movement of water molecules is more rapid if the membrane has protein channels called aquaporins.
• In active transport, membrane-bound molecular pumps use the energy of ATP to force molecules across the membrane.
• Water potential is the free energy of water.
• Water potential can be increased by heat, pressure, and altitude
• Pressure potential is the effect that pressure has on water potential.
• Osmotic potential is the effect that solutes have on water potential.
• Matric potential is water’s adhesion to non-dissolved structures such as cell walls, membranes, and soil particles.
• Water moves whenever there is a difference in water potential within the mass of water.
• Water moves from regions where water potential is relatively positive to regions where water potential is relatively more negative.
• If the water potentials of two regions are equal, the regions are in equilibrium, and there is no net movement of water.
• Water potentials must always be considered in pairs or groups.
• The sites from which water and nutrients are transported are sources.
• Sinks are sites that receive transported phloem sap, and they are extremely diverse.
• Pressure flow hypothesis is the hypothesis that flow in phloem is due to active loading in sources and active unloading in sinks.
• Liquid water is said to be cohesive, and any force acting on one molecule acts on all neighboring ones as well.
• Liquid water is said to be adhesive - almost all substances in plants, except lipids, interact with water: Cellulose, enzymes, DNA, sugars, and so forth have a shell of water molecules rather firmly attached to them.
• Cohesion-tension hypothesis is the hypothesis that as water is pulled upward by transpiration, its molecules cohere sufficiently to withstand the tension
• Transstomatal transpiration is water loss through stomata.
• Transcuticular transpiration is water loss through the cuticle
• Water is the principal medium for the chemical and biochemical processes that support plant metabolism.
• Water transports minerals through the soil to the roots where they are absorbed by the plant.
• Under pressure within plant cells, water provides physical support for plants.
• Water acts as a solvent for dissolved sugars and minerals transported throughout the plant.
• Evaporation within intercellular spaces provides the cooling mechanism that allows plants to maintain the favorable temperatures necessary for metabolic processes.
• Concentration gradient is the difference in concentration of side A and side B
• Transport of substances to short distances starts with one cell then onto the next.