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Transport In Plants – Chapter 36
• I – Surface Area Adaptations
• II – Cell to Cell Transport
• III – Radial (Lateral) Transport
• IV – Bulk Flow (Longitudinal) Transport
•…. we want SA (sah)
I - Root hairs, mycorrhizae, maximize
surface area of roots…..
• “Infected” roots form mycorrhizae, ????
• Why is this good?.
Fig. 36.8
Mycorrhizae…a good relationship
• Adaptation of Root Tip Epidermal Layer
• Recognize analogous structure to villi.
ROOT Hairs
• Transport in plants occurs on three levels:
(1) Cellular transport;the uptake and loss of water and solutes by individual cells
(2) Lateral transport
(3) long-distance, longitudinal transport.
Fig. 36.1
• The selective permeability of a plant cell’s plasma membrane controls the movement of solutes between the cell and the extracellular solution.
• When is it PASSIVE
• When is it ACTIVE.
• Transport proteins enhance selectivity, and active ability.
II - Cellular Transport
• The most important active transporter in the plasma membrane of plant cells is the proton pump.
• Pump hydrogen ions (H+) out of the cell.
• Why is this “good” for plant??
Proton pumps
• Both the concentration gradient and the membrane potential are forms of potential (stored) energy that can be harnessed to perform cellular work.
• Cotransport
• Cation exchange
Fig. 36.2a
• Water Potential=Pressure Potential+Solute Potential
• Explain this..
Water Potential ..Revisited
• Note;
• 1990s – realized osmosis TOO FAST
• FOUND Both plant and animal membranes have specific transport proteins, aquaporins,
• Aquaporins affect the rate at which water diffuses
• Manufacturing Aquaporins, cells might be able to regulate osmotic rate.
Aquaporins
• Vacuolated plant cells have three major compartments (WALL, CYTOPLASM,VACUOLE)
• The membrane is a barrier between two major compartments: the wall and the cytosol.
• Most mature plant have a third major compartment, the vacuole.
III - Radial (lateral) Transport
Fig. 36.6a
Three routes are available for lateral transport
• #1, substances move out of one cell, across the cell wall and membranes, and into the neighboring cell.
• This transmembrane route requires repeated crossings of plasma membranes. FAST
• #2, via the symplast, requires only one crossing of a plasma
membrane. FASTER• After entering one cell, solutes and water move from cell to cell via
plasmodesmata.
• #3 is along the apoplast, the extracellular pathway consisting of cell
wall and extracellular spaces. FASTEST• Rapid, non specific.
• In most plant tissues, two of the three cellular compartments are continuous from cell to cell.
• Plasmodesmata connect the cytosolic compartments of neighboring cells -
• This cytoplasmic continuum, = symplast route
• Between wall and membrane= apoplast.
Fig. 36.6b
WHAT IS THE FUNCTION OF THE CASPARIAN STRIP????
Fig. 36.7
This is a really important picture….
• Diffusion in a solution is fairly efficient for transport over distances of cellular dimensions (less than 100 microns).
• However, diffusion is much too slow for long-distance transport within a plant
• What cells make up phloem?
• What cells make up xylem?
IV Bulk flow functions in long-distance, longitudinal transport
• Water and solutes move through xylem vessels and sieve tubes by bulk flow; the movement of a fluid driven by pressure GRADIENTS.
• In phloem, for example, hydrostatic pressure drives flow.
• In xylem, it is positive pressure below (cation exchange)*, negative pressure above (transpiration)*
*Understand what drives these and what regulates them
• Flow rates depend on a pipe’s internal diameter.
• To maximize bulk flow;
• the sieve-tube members are almost entirely devoid of internal organelles.
• Vessel elements and tracheids are dead at maturity.
• The porous plates that connect contiguous sieve-tube members and the perforated end walls of xylem vessel elements also enhance bulk flow.
• QUESTIONs;
• How is bulk flow regulated???
• What drives/regulates cation exchange??
• What compromise issues do plants have to face as they transport materials?