A gardener removes a complete ring of bark from a tree trunk, all the way round, and cuts through…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A gardener removes a complete ring of bark from a tree trunk, all the way round, and cuts through the phloem but not the xylem. What will happen to the roots, and later to the whole tree? Why does the part above the ring not wilt at once?
Need a reminder? The key ideaShow
Xylem carries water and minerals up, and is mostly dead cells. Phloem carries food up and down, in living sieve tubes with companion cells.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. What was cut. The phloem, which carries food from the leaves down to the roots.
Step 2. The roots. No food reaches them, so after some weeks they starve and die.
Step 3. The whole tree. Dead roots take in no water, so in the end the whole tree dies.
Step 4. Why no wilting at first. The xylem, deeper inside, is not cut, so water still rises to the leaves for a while.
Answer: the roots starve, then the tree dies; the leaves do not wilt at once because the xylem still works.
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