Absorption, Transport And Water Loss In Plants

Zero

Step 1: Water potential (ψ) represents the tendency of water to move or do work. Step 2: Pure water has the highest possible water potential, which is taken as the reference point and assigned a value of zero (ψ = 0). Step 3: When solutes are dissolved in water, some water molecules are used up in dissolving, reducing the free energy of water. Step 4: Therefore, any solution (with dissolved solutes) has a water potential LESS than zero — a negative value. Step 5: The more concentrated the solution, the more negative its water potential. This is why water always moves from pure water (ψ = 0) in

Turgor pressure

Step 1: When water enters a plant cell by osmosis, the protoplasm expands and pushes against the cell wall. Step 2: The pressure exerted by the protoplasm (cell contents) against the cell wall is called turgor pressure (TP). Step 3: In response, the cell wall pushes back with an equal and opposite pressure called wall pressure (WP). Step 4: Osmotic pressure is the pressure needed to prevent osmotic entry of water. Root pressure is developed in roots due to osmotic absorption. Step 5: Turgor pressure is important for maintaining the shape of the plant and for stomatal opening.

Capillary water

Step 1: There are three main types of soil water — gravitational, hygroscopic, and capillary. Step 2: Gravitational water drains downward to the water table and is generally not available to plant roots. Step 3: Hygroscopic water is tightly held around soil particles by strong adhesive forces and is NOT available to plants — it remains in dry soils. Step 4: Capillary water is held in the fine pores between soil particles by capillary forces (surface tension) and is the most readily available water for plant roots. Step 5: The condition when soil holds good capillary water is called field capac

Symplast and apoplast

Step 1: Water absorbed by root hairs moves inward through two main pathways. Step 2: The symplast pathway uses the plasmodesmata — protoplasmic connections between cells — through which water moves by osmosis. Step 3: The apoplast pathway uses the cell walls and intercellular spaces — water moves through this pathway by capillarity and adsorption. Step 4: Phloem and xylem are vascular tissues — xylem conducts water upward but these are not the entry pathways. Step 5: Cortex and endodermis are layers that water passes through, but they are not the names of the pathways themselves.