AP BIOLOGY

Detailed explanation-1: -The mechanism by which sugars are transported through the phloem, from sources to sinks, is called pressure flow. At the sources (usually the leaves), sugar molecules are moved into the sieve elements (phloem cells) through active transport.

Detailed explanation-2: -The photosynthates from the source are usually translocated to the nearest sink through the phloem sieve tube elements. For example, the highest leaves will send sugars upward to the growing shoot tip, whereas lower leaves will direct sugars downward to the roots.

Detailed explanation-3: -The transport phloem has a dual function: it transports assimilates not only to terminal sinks (e.g. the roots and shoots) but also to lateral sinks along the path (e.g. the cambium) which are responsible for growth and tissue maintenance.

Detailed explanation-4: -Phloem transport is bidirectional because sucrose gets accumulated in the phloem tissue and absorbs water creating a high turgor pressure. Other areas have low turgor pressure due to loss of water.