Ascent of Sap in Botany

Ascent of Sap

• Ascent of sap is the upward movement of water from the roots to the aerial parts of plants.
• This essential process transports water and dissolved minerals throughout the plant.

Introduction

• The upward movement of water from the root xylem to aerial parts of the plant is called Ascent of sap.

Theories of Ascent of Sap

• There are various theories explaining the mechanism of ascent of sap, including vital force theory, root pressure theory, physical force theory, and transpiration pull and cohesion-tension theory.

Vital Force Theory

• This theory proposed by J.C. Bose (1923) suggests that the innermost cortical cells in the roots absorb water and pump it into the xylem channels.

Root Pressure Theory

• Proposed by Priestley (1916), this theory suggests root pressure helps in upward water movement.
• Root pressure is highest during the rainy season.
• However, the theory is not universally accepted as root pressure is absent in all plants, especially tall trees where water needs to be transported to great heights.

Physical Force Theory

• This theory includes atmospheric pressure theory, imbibitions force theory, and capillary force theory.
• Atmospheric pressure theory suggests atmospheric pressure raises water up to 3.3 ft.
• Imbibition force theory states that ascent of sap occurs due to imbibition of thick walls of xylem vessels.
• Capillary force theory proposes that xylem vessels act as minute capillaries, lifting water due to capillary action.

Transpiration Pull and Cohesion-Tension Theory

• This comprehensive theory offers a detailed explanation of water movement in plants.
• Cohesion and adhesion between water molecules are crucial for pulling water upwards due to transpiration.
• Transpiration creates a negative pressure (tension) pulling water column upwards.
• The cohesion-tension forces in the xylem play a major role in transporting water against gravity.
• This theory emphasizes the crucial role of transpiration in generating the pull.
• Water moves through the xylem vessels to replace the water lost through transpiration at the leaves. Through xylem vessels, this process is supported by cohesion (water molecules attracting each other) and adhesion (attraction between water molecules and the walls of the xylem vessels).
• Transpiration stream refers to the flow of water from the root to the leaves. It relies on the cohesive and adhesive properties of water alongside the transpiration pull.

Explore the concept of Ascent of Sap, which describes the upward movement of water from the roots to the aerial parts of plants. This quiz covers different theories explaining this vital process, including vital force theory and root pressure theory. Test your understanding of how plants transport water and minerals throughout their structure.