Transport in plants

• Dicotyledonous plant - plants with two seed leaves and a branching pattern of veins in the leaf
• Endodermis - sheath of cells that surrounds the vascular bundle
• Pericycle - a layer of meristem cells just inside the endodermis
• In woody plants, vascular bundles become continuous rings which provide strength and flexibility
• Between the xylem and phloem is a layer of cambium tissue made up of meristem cells
• Xylem vessel walls are impregnated with lignin to make them waterproof and prevent them from collapsing
• Xylem vessels are narrow so they do not break easily and to create effective capillary action
• Lignin is deposited in patterns that allow the xylem to stretch as the plant grows and allows the stem to bend
• Bordered pits - incomplete lignification to allow the movement of water between adjacent vessels and into the living parts of the plant
• Xylem are empty
• Assimilates - sucrose and amino acids
• Phloem is made up of sieve tube elements, companion cells and sieve plates
• The sieve tube elements contain no nucleus and very little cytoplasm to allow mass movement of sap
• Sieve plate - a perforated cross wall that supports the phloem and deposition of callose blocks pores when the plant is infected
• Companion cells have a large nucleus, dense cytoplasm and many mitochondria for active processes
• Vascular tissue - cells specialised for transporting fluids by mass flow
• Plasmodesmata - junction at which the cytoplasm of one cell is connected to that of another cell through gaps in the cell walls
• Apoplast pathway - water moves through spaces in cell walls and between cells by mass flow
• Symplast pathway - water moves through the plasma membrane and enters the cytoplasm, passing through the plasmodesmata
• Vacuolar pathway - similar to the symplast pathway but water is able to pass through the vacuoles
• Water potential is always -ve in plants
• Pressure potential - water inside a cell starts to exert pressure on the cell wall and reduces the influx of water
• Plasmolysis - plant cell loses water and membrane loses contact with the cell wall, causing a flaccid tissue
• Transpiration - The loss of water vapour from the stomata of a plant
• Transpiration stream - the movement of water from the roots to the leaves through the xylem
• In high light intensity, stomata open
• The apoplast pathway is blocked by the Casparian strip
• Water in the apoplast pathway must enter the symplast pathway to be transported to the rest of the plant
• The casparian strip is located in the cell wall of the endodermis of vascular bundles
• Mineral ions are actively transported from the soil to make water potential more negative so that water follows by osmosis
• Root pressure pushes water up the stem
• Transpiration pull - cohesion between water molecules causes the stream to be pulled up as one column when water evaporates from the leaf. This causes tension in the xylem
• The cohesion tension theory relies on a plant maintaining an unbroken column of water all the way up the xylem
• Adhesion - hydrogen bonds attract the water to the walls of the xylem, which pulls the water up the sides of the vessel
• Source - a part of a plant that loads materials into the transport system
• Sink - a part of a plant that removes materials from the transport sysytem
• Sucrose is loaded in the sieve tube by an active process
• Cotransporter proteins - only allow the movement of H+ ions if accompanied by a sucrose molecule
• The flow of sap is caused by a difference in hydrostatic pressure
• Sap flows from the source to the sink