What is the main function of phloem in plants?

The main function of phloem in plants is food transport, specifically the movement of organic compounds, particularly sugars produced through photosynthesis, from the leaves (where they are made) to other parts of the plant, such as roots, stems, and fruits. This is essential for providing energy and building materials for growth and development throughout the plant. The process of transporting sugars through the phloem is termed translocation, and it is vital for the plant's metabolism and overall health.

The other processes mentioned in the choices relate to different plant systems or structures. For example, water transport is primarily the responsibility of xylem, which carries water and minerals from the roots to the rest of the plant. Calcium absorption is a function associated with roots and is not linked to phloem. Lastly, oxygen release is part of photosynthesis and primarily occurs in the leaves, where oxygen is produced as a byproduct, but does not involve the phloem's function. Therefore, the focus remains on the phloem's role in transporting food, which is crucial for the plant's energy distribution.