The phenomenon that causes water to move against gravity in plants is known as capillary action, which is driven by cohesion and adhesion. Cohesion refers to the attraction between water molecules, while adhesion describes the attraction between water molecules and the polar surfaces of plant tissues, like xylem cells. This combined effect allows for the upward movement of water from the roots to the leaves, crucial for photosynthesis and nutrient transport. Capillary action contributes significantly to a plant's ability to maintain hydration and perform vital biological functions.