The soil solution is the source of mineral ions for the plant. These mineral ions are carried from the roots in the xylem. Mineral ions are also present in the phloem sap inside phloem sieve tubes. Suggest why mineral ions are found within phloem sieve tubes and state how they are transported within phloem sieve tubes.
Phloem tissue contains several cell types. Complete the passage using the most suitable terms to describe some of the features of phloem tissue. The end walls of sieve tube elements are altered to permit efficient phloem sap flow by the formation of ................................................ . These structures also prevent the cells from bursting under pressure. The cytoplasm of sieve tube elements is greatly reduced and is located at the ................................................ of the cells. Most of the organelles in the cell are absent. Next to sieve tube elements are ................................................ cells that perform the metabolic roles of the missing organelles, enabling the sieve tube elements to function.