When the bark of a tree is removed in a circular fashion all around near its base, it gradually dries up and dies because

The correct answer is B. Circular removal of bark, called girdling or ringing, cuts through the phloem, the living tissue that carries sugars made in the leaves down to the roots. The xylem, which carries water and minerals upward, lies deeper in the wood and usually stays intact, so the crown keeps getting water for a while. The roots, however, stop receiving food and gradually run out of energy for growth and maintenance. The tree then dies slowly, usually from the base upward.

• A is wrong because water moves through xylem, which ringing of the bark alone does not remove.
• C is wrong because microbial infection is at most a secondary effect, not the cause of drying.
• D is wrong because roots in aerated soil are not suffocated by bark removal; the failure is of food supply, not oxygen.

Core concept: translocation of food through phloem versus water transport through xylem. This links to plant physiology in the Science syllabus and to the practice of girdling in forestry and silviculture.

Trap: candidates pick A because removing bark sounds like cutting the water supply. Remember that the inner layer of bark is phloem, and xylem lies deeper.