Final answer:
The end cell walls of sieve-tube members contain sieve plates, which are porous regions enabling cytoplasm connectivity and essential for the transport of substances in phloem tissue.
Step-by-step explanation:
The porous regions at the end cell walls of sieve-tube members through which the cytoplasms of adjacent cells connect are called sieve plates. These sieve plates are essential for the function of the phloem, which is the tissue responsible for the transport of organic substances such as sugars and amino acids. Phloem tissue is composed of various cell types including sieve-tube cells, companion cells, phloem parenchyma, and phloem fibers. The sieve-tube cells lack a nucleus at maturity and rely on adjacent companion cells for metabolic support. These companion cells have an abundance of ribosomes and mitochondria and are closely associated with the sieve-tube cells for the efficient transport of phloem sap via a process known as bulk flow.