The cohesion-tension theory explains the movement of water from roots to leaves in xylem vessels in plants.

It suggests that water is pulled up through the plant under tension, due to the transpiration pull and the cohesive and adhesive properties of water.

1. Apoplast pathway - water moves through the spaces in cell walls and between cells, due to the cohesive and adhesive properties of water
2. Symplast pathway - water moves from cell to cell through the cytoplasm and plasmodesmata, due to the water potential gradients 

Adhesion is the attraction of polar water molecules to the non-polar cellulose in xylem vessel cell walls.

This helps water to rise through the plant against gravity.

Cohesion is the attraction between polar water molecules due to hydrogen bonding.

This helps water molecules stick together and move up the plant as a continuous column in the xylem vessels.

The transpiration pull is the upward movement of water from the roots to the aerial parts of a plant, driven by the evaporation of water from the leaves.

The Casparian strip is a band of a waterproof substance called suberin around plant endodermis cells.

The Casparian strip blocks the apoplast pathway, forcing water into the symplast pathway.

1. Water enters a plant's root hair cells via osmosis 
2. It moves through cell cytoplasm or cell walls towards the xylem
3. The xylem transports water from the roots up to the leaves