Suppose a tree is 70 feet tall. How much pressure (in pascals) must be generated

Question

Suppose a tree is 70 feet tall. How much pressure (in pascals) must be generated just to get water to the top of the tree? (1 point) Refer to the information given in the handout under the heading "A primer on pressure". This is a numerical answer. You will need to convert from atmosphere to mega Pascals. Enter the final answer here in the form of "35 MPa". Note the space between letters and numbers, and the way the units are written. In case of the answer being less than 1, write it as 0.9 and not just !9 1 atm 0.1 MPa. Take a note of space between letters and numbers and the way the unit is written. Refer to the handout for units

Explanation / Answer

In plant, Xylem tubes are made by the cell wall remains of dead cells and the cellulose has a high affinity for water, so water is drawn up the xylem by capillary.

The average diameter of xylem tubes is about 25 µm and xylem tubes can support a column of water that is about 70 feet high. The comparetively larger negative pressures required is found in the leaves then other part. Because water is still attached to the column of water in the xylem surrounds the mesophyll cells of the leaf. So this extracellular space is in contact with the atmosphere through the stomata, water can evaporate. It creates air pockets in the leaves, and the water is reduced to a thin film that is strongly attracted to the cellulose fibers in the cell walls.

The water follows the irregular form of the fibers and curve surfaces with extremely small radii of curvature (perhaps 100 nm) are formed. It produces a considerable negative pressure in the water that may average 30 atmospheres (3 MPa), which is sufficient to supply the water need of the tallest tree.

This pressure must not only overcome gravity, it must also overcome the resistance to water flow of the delivery “pipes”, the xylem tubes. A 70 foot-tall tree requires about 2.33 atmospheree pressure (0.233 MPa) atmospheres of pressure just to overcome gravity, so there is adequate pressure. It

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