| MadSci Network: Botany |
Yes, cellulose cell walls are present in all cells in leaves, fruits, roots and flowers. At maturity, some cells are dead and consist mainly of the cell wall. The dead cells lack a cell membrane and cytoplasm. Cells walls are considered completely permeable to mineral nutrients, unlike cell membranes which selectively absorb mineral nutrients. Mineral nutrients can flow into and through cell walls by diffusion but also often move by mass flow. For example, in roots, water moves across root cell membranes freely and carries dissolved mineral nutrients with it. As the water passes across a cell membrane, it may leave behind some of the mineral nutrients, and they can accumulate in the cell walls. The nonliving part of the plant, mainly the cell walls and intercellular spaces is termed the apoplast. That is in contrast to the symplast, which is the living part within the cell membranes. Diffusion and mass flow operate freely in the apoplast or apoplastic pathway. Water and mineral nutrients can move freely into the roots in the apoplast until the Casparian strip, at which point water and mineral nutrients must cross a membrane to continue further. Once across the Casparian strip, they can exit the symplast into the apoplast again. References Transport of Water and Minerals in Plants Diagram of root cross section and endodermis Diagram of apoplastic and symplastic pathways in the root
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