How does water get to the top of a tree?

What do xylem vessels transport?

Leaves have [blank_start]stomata[blank_end], which open to let [blank_start]carbon dioxide[blank_end] in for photosynthesis. This, unavoidably, lets water diffuse out of the leaf due to the surrounding air usually having a [blank_start]lower[blank_end] [blank_start]water potential[blank_end] than inside the leaf. This process is called [blank_start]transpiration[blank_end] which defines as the evaporation of water vapour, mainly through the stomata in the surface of a leaf. It is a [blank_start]passive[blank_end] process, using energy from the sun, which evaporates water from the [blank_start]mesophyll[blank_end] cells. As water vapour diffuses from the air spaces in the mesophyll and through the stomata, it is replaced by water from the [blank_start]mesophyll[blank_end] cells. This in turn is replaced by water from the [blank_start]xylem[blank_end] in the veins of the leaf.

Water cannot be pulled up more than [blank_start]10[blank_end]m, which is a problem tall trees must be overcome. Xylem vessels are very narrow, and water molecules tend to stick together because of the [blank_start]hydrogen[blank_end] bonds between them - this property of water is called [blank_start]cohesion[blank_end]. As water moves out of the [blank_start]xylem[blank_end] in a leaf, it drags other molecules of water behind it. Because the vessels are so [blank_start]narrow[blank_end], the column of water behind does not break, and water is pulled up all the way from the roots. The pulling force is so great that the column of water is actually being [blank_start]stretched[blank_end] - it is under [blank_start]tension[blank_end]. The tension in the column of water tends to pull the walls of the vessels [blank_start]inwards[blank_end] slightly. However, the [blank_start]lignin[blank_end] in the walls is strong enough to stop the vessels [blank_start]collapsing[blank_end].

Water enters the roots by [blank_start]osmosis[blank_end] and passes up the stem to the leaves, where it evaporates into the [blank_start]air spaces[blank_end] inside the leaf and then passes out to the atmosphere through the [blank_start]stomata[blank_end]. The air has a low [blank_start]water potential[blank_end] because it normally has a low percentage of [blank_start]water vapour[blank_end].

Which of these are advantages of transpiration

The two ideas, of cohesion and tension, used to explain how water is pulled up in a plant, are brought together by what theory?