question: How do trees transport water from the roots to each of the leaves so many meters high?
comment: There is a good video on YouTube by Veritasium which will explain far better (and hopefully I’m remembering right) but the general idea is that water evaporates out of the leaves, this in turn sucks water along the branches from the trunk and roots. It uses the surface tension of the water to climb up the capillaries in the tree because even with a pure vacuum at the top it’s not enough to “suck” the water up that high.
passages: Section::::In plants and animals.
  
  Capillary action is seen in many plants. Water is brought high up in trees by branching; evaporation at the leaves creating depressurization; probably by osmotic pressure added at the roots; and possibly at other locations inside the plant, especially when gathering humidity with air roots.
  
  Capillary action for uptake of water has been described in some small animals, such as "Ligia exotica" and "Moloch horridus".
  
  Section::::Examples.
   Section::::Nutrient distribution.:Absorption.
  
  Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure. It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is usually due to high temperatures, high humidity, darkness or drought.
  
  Section::::Nutrient distribution.:Conduction.
   This mechanism is carried out without utilisation of metabolic energy. Here, only the roots act as an organ of absorption or passage. Hence, sometimes it is called water absorption 'through roots', rather 'by' roots. It occurs in rapidly transpiring plants during the daytime, because of the opening of stomata and the atmospheric conditions. The force for absorption of water is created at the leaf end i.e. the transpiration pull. The main cause behind this transpiration pull, water is lifted up in the plant axis like a bucket of water is lifted by a person from a well. Transpiration pull is responsible for dragging water at the leaf end, the pull or force is transmitted down to the root through column of water in the xylem elements. The continuity of the water column remains intact due to the cohesion between the molecules and it act as a rope. Roots simply act as a passive organ of absorption. As transpiration proceeds, water absorption occurs simultaneously to compensate the water loss from the leaf end. Most volume of water entering plants is by means of passive absorption. Passive transport is no different from diffusion, it requires no input of energy: there is free movement of molecules from their higher concentration to their lower concentration. The water will enter the plant via the root cells that can be found in the roots where mainly passive absorption occurs. Also, with the absorption of water, minerals and nutrients are also absorbed.
   The amount of water that trees and other plants move from the ground to the atmosphere with TEWL is of interest in botany and earth science, as transpiration by plants is a substantial component of the water cycle on Earth.
  
  Section::::Acronym variation.
   Recent studies have looked at the stomatal conductance of fast growing tree species to identify the water use of various species. Through their research it was concluded that the predawn water potential of the leaf remained consistent throughout the months while the midday water potential of the leaf showed a variation due to the seasons. For example, canopy stomatal conductance had a higher water potential in July than in October. The studies conducted for this experiment determined that the stomatal conductance allowed for a constant water use per unit leaf area. Other studies have explored the relationship between drought stress and stomatal conductance. Through these experiments, researchers have found that a drought resistant plant regulates it's transpiration rate via stomatal conductance. This minimizes water loss and allows the plant to survive under low water conditions.
   After this, the water moves up the xylem vessels to the leaves through diffusion: A pressure change between the top and bottom of the vessel. Diffusion takes place because there is a water potential gradient between water in the xylem vessel and the leaf (as water is transpiring out of the leaf). This means that water diffuses up the leaf. There is also a pressure change between the top and bottom of the xylem vessels, due to water loss from the leaves. This reduces the pressure of water at the top of the vessels. This means water moves up the vessels.
   Water is constantly lost through transpiration from the leaf. When one water molecule is lost another is pulled along by the processes of cohesion and tension. Transpiration pull, utilizing capillary action and the inherent surface tension of water, is the primary mechanism of water movement in plants. However, it is not the only mechanism involved. Any use of water in leaves forces water to move into them.
   BULLET::::- Transpirational pull: Similarly, the evaporation of water from the surfaces of mesophyll cells to the atmosphere also creates a negative pressure at the top of a plant. This causes millions of minute menisci to form in the mesophyll cell wall. The resulting surface tension causes a negative pressure or tension in the xylem that pulls the water from the roots and soil.
   Wood gives structural strength to the trunk of most types of tree; this supports the plant as it grows larger. The vascular system of trees allows water, nutrients and other chemicals to be distributed around the plant, and without it trees would not be able to grow as large as they do. Trees, as relatively tall plants, need to draw water up the stem through the xylem from the roots by the suction produced as water evaporates from the leaves. If insufficient water is available the leaves will die. The three main parts of trees include the root, stem, and leaves; they are integral parts of the vascular system which interconnects all the living cells. In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth. Because this growth ruptures the epidermis of the stem, woody plants also have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss. Both the production of wood and the production of cork are forms of secondary growth.
   Water is "consumed" in plants by the processes of photosynthesis (see above) and transpiration. The latter process (which is responsible for about 90% of water use) is driven by the evaporation of water from the leaves of plants. Transpiration allows plants to transport water and mineral nutrients from the soil to growth regions, and also cools the plant. Diffusion of water vapour out of a leaf, the force that drives transpiration, is regulated by structures known as stomata. These structure also regulate the diffusion of carbon dioxide from the atmosphere into the leaf, such that decreasing water loss (by partially closing stomata) also decreases carbon dioxide gain. Certain plants use alternative forms of photosynthesis, called Crassulacean acid metabolism (CAM) and C4. These employ physiological and anatomical adaptations to increase water-use efficiency and allow increased primary production to take place under conditions that would normally limit carbon fixation by C3 plants (the majority of plant species).
   The next stage in the transpiration stream is water passing into the xylem vessels. The water either goes through the cortex cells (between the root cells and the xylem vessels) or it bypasses them – going through their cell walls.
   Absorption of water
  
  The absorption of water by plants is essential for various metabolic activities. Terrestrial plants get their water supply from soil which serves as the source of water and [minerals]. The way in which water from soil enters roots, particularly to the root xylem, is called "mechanism of water absorption". Both active and passive absorption have been proposed for mechanism of water absorption.This process is known as Conduction
  
  Section::::Active absorption.
   The ecological importance of hydraulically redistributed water is becoming better understood as this phenomenon is more carefully examined. Water redistribution by plant roots has been found influencing crop irrigation, where watering schemes leave a harsh heterogeneity in soil moisture. This influencing process also assist in seedling success. The plant roots have been shown to smooth or homogenize the soil moisture. This sort of smoothing out of soil moisture is important in maintaining plant root health. The redistribution of water from deep moist layers to shallow drier layers by large trees has shown to increase the moisture available in the daytime to meet the transpiration demand.
   The cohesion-tension theory explains how leaves pull water through the xylem. Water molecules stick together, or exhibit cohesion. As a water molecule evaporates from the surface of the leaf, it pulls on the adjacent water molecule, creating a continuous flow of water through the plant.
  
  Section::::Regulation.
   The movement of this water can be explained by a water transport theory throughout a plant. This well-established water transport theory is called the cohesion-tension theory. In brief, it explains the movement of water throughout the plant depends on having a continuous column of water, from the leaves to roots. Water is then pulled up from the roots to the leaves moving throughout the plant's vascular system, all facilitated by the differences in water potential in the boundary layers of the soil and the atmosphere. Therefore, the driving force for moving water through a plant is the cohesive strength of water molecules and a pressure gradient from the roots to the leaves. This theory is still applied when the boundary layer to the atmosphere is closed, e.g. when plant stomata are closed or in senesced plants. The pressure gradient is developed between soil layers with different water potentials causing water to move by the roots from wetter to drier soil layers in a similar manner as when a plant is transpiring.
   Stemflow
  
  In hydrology, stemflow is the flow of intercepted water down the trunk or stem of a plant. Stemflow, along with throughfall, is responsible for the transferral of precipitation and nutrients from the canopy to the soil. In tropical rainforests, where this kind of flow can be substantial, erosion gullies can form at the base of the trunk. However, in more temperate climates stemflow levels are low and have little erosional power.
  
  Section::::Measurement.
   BULLET::::- Researchers at University of California-Berkeley found that water loss from leaves in "Sequoia sempervirens" is ameliorated by heavy fog in the Western US. Their research suggests that fog may help the leaves retain water and enable the trees to fix more carbon during active growth periods.
   The ability of plants to access water depends on the structure of their roots and on the water potential of the root cells. When soil water content is low, plants can alter their water potential to maintain a flow of water into the roots and up to the leaves (Soil plant atmosphere continuum). This remarkable mechanism allows plants to lift water as high as 120 m by harnessing the gradient created by transpiration from the leaves.
   Trees, and plants in general, affect the water cycle significantly:
  
  BULLET::::- their canopies intercept a proportion of precipitation, which is then evaporated back to the atmosphere (canopy interception);
  
  BULLET::::- their litter, stems and trunks slow down surface runoff;
  
  BULLET::::- their roots create macropores – large conduits – in the soil that increase infiltration of water;
  
  BULLET::::- they contribute to terrestrial evaporation and reduce soil moisture via transpiration;
  
  BULLET::::- their litter and other organic residue change soil properties that affect the capacity of soil to store water.
   Plants recognize water in their environment in order to absorb it for metabolic purposes. The universally used molecules must be sensed and absorbed in order to be used by these organisms. In plants, water can be sensed and is mainly absorbed through the roots, chiefly through young fine roots as compared to mother roots or older fine roots as shown with maize in Varney and Canny’s research. The direction and rate of growth of these roots towards water are of interest because these affect the efficiency of water acquisition.
   Through evapotranspiration, forests reduce water yield, except in unique ecosystems called cloud forests. Trees in cloud forests collect the liquid water in fog or low clouds onto their surface, which drips down to the ground. These trees still contribute to evapotranspiration, but often collect more water than they evaporate or transpire.
   Active absorption refers to the absorption of water by roots with the help of ATP, generated by the root respiration: as the root cells actively take part in the process, it is called active absorption. According to Renner, active absorption takes place in low transpiring and well-watered plants, and 4% of total water absorption is carried out in this process. The active absorption is carried out by two theories; active osmotic water absorption and Active non-osmotic water absorption. In this process energy is required.
  
  Section::::Active absorption.:Active osmotic water absorption.
   This behavior is thought to have been developed millions of years ago when plants began their journey onto dry land. While this migration led to much easier consumption of CO, it greatly reduced the amount of water readily available to the plants. Thus, strong evolutionary pressure was put on the ability to find more water.
  
  Section::::Mechanism.
   The spile consists of a tube with one end sharpened and the other split. When pounded into a tree, a stream of fresh water flows from the tube. Most of the year, this is not consistent with the nature of trees, as water diffuses upward through very tiny capillary passages. When a tree is cut down, water does not flow out of the cut surface. The technique used in the movie would only work in early spring or late winter, when the watery sap runs high in the trees.
   Vacuolar pathway
  
  Vacuolar pathway:
  
  Movement of water molecules in plant cells via the vacuoles located in the cytoplasm of the cell. The water molecules encounter high resistance however and as a result little flow usually occurs making this pathway insignificant, the Apoplast pathway and Symplast pathway being the major pathways for movement of water in plants.
  
  Water moves by osmosis across the vacuoles of the cells of the root system. The water moves down a concentration gradient from the soil solution to the xylem.
  