Moderate

The rupture and fractionation do not usually occur in the water column in vessels/tracheids during the ascent of sap because of:

Correct answer: D. Cohesion and adhesion

  • A. Weak gravitational pull
  • B. Transpiration pull
  • C. Lignified thick walls
  • D. Cohesion and adhesion

Explanation

The transpiration process, pulls water upwards with the help of cohesion and adhesion properties of water molecules. According to transpiration pull theory, due to transpiration, the water column inside the plant comes under tension. This is called 'transpiration pull'. On account of this tension, the water column is pulled up passively from below to top of the plant (almost like a rope). Root pressure is the pressure that forces water, absorbed from the soil, to move through the roots and up (i.e., pushes it up) the stem of a plant. It may be due to both the osmosis of water from the soil into the root cells, and the active pumping of salts into xylem tissue which maintains a concent. So correct option is D.

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