Difference Between Capillary Action and Transpiration Pull

The key difference between capillary action and transpiration pull is that capillary action occurs due to the effect of adhesive and cohesive forces, whereas transpiration pull occurs due to evaporation.

Capillary action and transpiration pull are biological concepts we discuss under the movement of water through a plant. Both these terms explain the upward movement of water through the plant, opposite to the gravitational force. Therefore, these are very important phenomena to discuss.

CONTENTS

1. Overview and Key Difference
2. What is Capillary Action 
3. What is Transpiration Pull
4. Side by Side Comparison – Capillary Action vs Transpiration Pull in Tabular Form
5. Summary

What is Capillary Action?

Capillary action is the spontaneous movement of a liquid through a narrow tube such as a capillary. This movement is independent of gravity; thus, it can occur under gravity or in opposition to gravity. We can often observe this process in plants, especially as a process that occurs in opposition to gravitational force. Other synonyms for capillary action are capillarity, wicking and capillary motion. In addition to plant water transportation, we can observe capillary action taking place in the uptake of water in paper and plaster, movement of water through sand, capillarity of paint through paintbrush hairs, etc.

The capillary action takes place due to adhesive and cohesive forces. Adhesive forces are the attraction forces between the liquid and the wall of the capillary while cohesive forces occur between liquid molecules. As a result of both these forces, the liquid can move through the capillary spontaneously.

What is Transpiration Pull?

Transpiration pull is the movement of water through a plant in an upward direction due to the effect of transpiration. Transpiration is the process via which water moves through the plant from roots to leaves, finally evaporating into the atmosphere. Therefore, transpiration pull is the force which is caused by the evaporation of water from leaves, and it causes the movement of water through the plant.

Transpiration pull occurs in the xylem vessels of plants. It is very important in protecting the plant from embolism because it helps to keep a continuous flow of water through the plant.

What is the Difference Between Capillary Action and Transpiration Pull?

Both capillary action and transpiration pull are biological concepts we discuss under the movement of water through a plant. When considering each process, in capillary action, spontaneous movement of a liquid occurs through a narrow tube such as a capillary while in transpiration pull, the movement of water occurs through a plant from roots to leaves. The key difference between capillary action and transpiration pull is that capillary action occurs due to the effect of adhesive and cohesive forces, whereas transpiration pull occurs due to evaporation.

Furthermore, capillary action can occur in plants, uptake of water by paper or plasters, movement of water through sand, wicking of paint though hairs of a paintbrush, etc. while transpiration pull occurs in xylem vessels of plants.

Below infographic summarizes the difference between capillary action and transpiration pull.

Summary – Capillary Action vs Transpiration Pull

Capillary action is the spontaneous movement of a liquid through a narrow tube such as a capillary. Transpiration pull is the process of movement of water through a plant in an upward direction due to the effect of transpiration. The key difference between capillary action and transpiration pull is that capillary action occurs due to the effect of adhesive and cohesive forces, whereas transpiration pull occurs due to evaporation.

Reference:

1. Helmenstine, Anne Marie. “Capillary Action: Definition and Examples.” ThoughtCo, Jan. 13, 2019, Available here.

Image Courtesy:

1. “Capillary Action” By APN MJM – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Transpiration Overview” By Laurel Jules – Own work (CC BY-SA 3.0) via Commons Wikimedia