Which component occupies up to 90% of the volume in mature plant cells?

The component that occupies up to 90% of the volume in mature plant cells is the vacuole. Vacuoles are large, membrane-bound organelles that store various substances, including water, ions, sugars, and waste products. In mature plant cells, especially in plant tissues that are not actively dividing, vacuoles tend to be very large and contain a significant amount of cell sap, which is a solution of water and solutes. This large size of the vacuole contributes to the turgor pressure within the cells, helping to maintain structural integrity and support for the plant.

While plastids, cell walls, and cytoplasm are all essential components of plant cells, they do not occupy the same substantial volume as vacuoles. Plastids are involved in photosynthesis and storage but are typically much smaller. Cell walls provide structural support and protection but do not fill the cell's volume as vacuoles do. The cytoplasm, which includes the fluid matrix and organelles, also does not occupy the same volume percentage as the vacuole. Thus, vacuoles play a crucial role in the physiology of mature plant cells, which is why they account for such a significant proportion of cellular volume.