Differentiation of Cells

The changes occurring in the cells of a multicellular orgnism so that each different type of cell becomes specialised to perform a specific function.Erythrocytes and neutrophils both originate as undifferentiated stem cells in bone marrow. The cells destined to become erythrocytes lose their nucleus, golgi apparatus and rough endoplasmic reticulum. They are filled with haemoglobin, the shape of the cell changes to become a biconcave disc so that it is capable of transporting oxygen from the lungs to tissues.The cells destined to become neutrophils keep their nucleus; a huge number of lysosomes are produced, so their cytoplasm appears granular. The lysosomes contain enzymes so that the neutrophil can ingest invading microorganisms.The xylem and phloem both come from meristem cells.In the xylem, the meristem cells elongate and the walls become elongated and waterproofed by deposits of lignin, which kills the cells contents. The ends of the cell break down so they become long tubes with wide lumen. They are suited to transporting water and minerals up the plant, and also support the plant. In the phloem, the cells also elongate, but their ends do not break down completely, but form sieve plates between the cells. Next to each sieve plate is a companion cell with is very metabolically active and used in moving the products of photosynthesis up and down the plant.