Transpiration. Transpiration: How do water molecules move upwards from the roots to the leaves against gravity? Transpiration is the process in which water molecules move upwards from the roots and eventually escape from the stoma of leaves in the form of vapor. The properties of water molecules which help in this upward movement against gravity are cohesion and adhesion. When a water molecule escapes out into the atmosphere through a stoma, it pulls the water molecule below it to take its place. That molecule then pulls the next water molecule below it. This process continues till the roots. This property of water molecules to attract and pull one another is called cohesion. Due to this cohesion, water molecules stick to each other forming a continuous chain. Whereas, adhesion is a property by which water molecules get attracted to other molecules. Due to this property, water molecules stick to the xylem while travelling upwards. Hence, with the help of adhesion and cohesion, water molecules move upwards from the roots to the leaves against gravity.