Please enable JavaScript.
Coggle requires JavaScript to display documents.
Plant transport, plant defences - Coggle Diagram
Plant transport
-
movment across roots
symplast pathway
Water moves through the symplast – the continuous cytoplasm of the living plant cells that is connected through the plasmodesmata. The root hair cell has a higher water potential than the next cell along, so water diffuses into it via osmosis. This ren repeats itself for the next cell along until it reaches a xylem stem.
apoplast pathway
-
-
• As water molecules move into the xylem, more water molecules are pulled through the apoplast due to water’s cohesive forces.
• The pull from water moving into the xylem and up the plant creates tension resulting in a continuous flow of water through the open structure of the cellulose wall – that offers little or no resistance.
-
-
transpiration
rate of transpiration
• Light – required for photosynthesis. At night most stomata close, increasing light intensity increases the number of open stomata, increasing the rate of water loss via transpiration.
• Relative humidity – the more humid the air is, the lower the rate of water loss as the air is already so saturated. Dry air has the opposite effect.
-
o An increase in temperature increases kinetic energy of the water molecules and therefore increases rate of evaporation form the spongy mesophyll cells
o An increase in temperature increases the concentration of water vapour so that external air can hold before it becomes saturated.
• Air movement – each leaf has a layer of still air around it trapped by the shape of the leaf. The more air that’s trapped around the leaf the lower the rate of water loss.
mass flow
- sucrose moved from source cells into the cell adjacent to the phloem
- sucrose is then moved into the sieve tube elements at the top of the phloem
- this increases hydrostatic pressure at the top of the phloem due to osmosis
- this causes the water with the dissolved sugars to move down the phloem to the roots whereby the sucrose is taken in and pumped into the source cell tissues to be used
- once complete water moves back up through the transpiration steam of the xylem
stomata
-
-
• When conditions are more favourable guard cells pump in solutes via active transport, increasing their turgor.
• Cellulose hoops prevent the cells from swelling in width, so they extend lengthways
• Because the inner wall of the guard cell is less flexible than the outer wall, the cell becomes bean-shaped and open the pore
• However when water is more scarce, hormonal signals from the roots can trigger turgor loss from the guard cell, which close the stomatal pore and so conserve water.
-