2. Ascent of sap
5. Root pressure
please define these
Answers
Answer : The ascent of sap in the xylem tissue of plants is the upward movement of water and minerals from the root to the crown. Xylem is a complex tissue consisting of living and non-living cells. The conducting cells in xylem are typically non-living and include, in various groups of plants, vessels members and tracheids. Both of these cell types have thick, lignified secondary cell walls and are dead at maturity. Although several mechanisms have been proposed to explain the phenomenon, the cohesion-tension mechanism[1] has the most evidence and support. Although cohesion-tension has received criticism, for example due to the apparent existence of large negative pressures in some living plants, experimental and observational data favor this mechanism.
'Root Pressure'. It is the transverse osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.[1]
Root pressure occurs in the xylem of some vascular plants when the soil moisture level is high either at night or when transpiration is low during the day. When transpiration is high, xylem sap is usually under tension, rather than under pressure, due to transpirational pull. At night in some plants, root pressure causes guttation or exudation of drops of xylem sap from the tips or edges of leaves. Root pressure is studied by removing the shoot of a plant near the soil level. Xylem sap will exude from the cut stem for hours or days due to root pressure. If a pressure gauge is attached to the cut stem, the root pressure can be measured.
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Root pressure
- The pressure developed in the root which helps in pushing the plant SAP upward is called root pressure.
Ascent of sap
- The upward movement of the water or SAP from Roots towards the top of the plant is called conduction or ascent of SAP.