Describe the cohesion-tension theory in simple terms

The cohesion-tension theory is the most widely accepted explanation for how water moves up the xylem of a plant, from the roots to the leaves, even against gravity.

It can be broken down into three simple parts:

1. Tension (The "Pull"): This is the driving force. Water evaporates from the leaves through tiny pores called stomata. This process is called transpiration. As each water molecule evaporates, it creates a "pull" or negative pressure (tension) on the water molecule behind it. This creates a "sucking" force, known as the transpiration pull, that pulls the entire water column up the plant.
2. Cohesion (The "Chain"): Water molecules are "sticky" and attract each other strongly due to hydrogen bonds. This property is called cohesion. This cohesion links all the water molecules together, forming an unbroken, continuous chain or column of water that extends from the leaves all the way down to the roots.
3. Adhesion (The "Grip"): Water molecules are also "sticky" to other surfaces. This property is called adhesion. The water molecules adhere to the walls of the xylem tubes. This grip helps to counteract the force of gravity and prevents the water column from breaking.

In simple terms: The evaporation from the leaves (tension) pulls up the entire "chain" of water (cohesion), which is "gripped" to the xylem walls (adhesion), moving water from the roots to the very top of the plant.