Biology I / The Colonisation of Land
Practice question · Numerical answer

A tree moves water from its roots to leaves 30 m above ground. Atmospheric pressure can support a water column of about 10 m. How many times taller than that limit is the tree?

Hints
  1. Divide the tree height by the height atmospheric pressure alone could support.
  2. Compute 30 divided by 10.
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3 (answers within ±0.1 count)

Why

The tree is 3 times taller than a pressure-driven column could reach. That is precisely why the cohesion-tension mechanism is needed: water is pulled from above under tension, not pushed from below.

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