Some plant species can take up toxic heavy metal ions that are dissolved in water in the soil. These ions accumulate in the aerial parts of the plant, which can be harvested and disposed of safely. An investigation was carried out into the ability of a plant species to remove a heavy metal ion from soil. This produced the following observations: • some heavy metal ions accumulated in the cells of the root cortex • within these cells, most of these ions were in the vacuole • in the roots and leaves, the ions were transported dissolved in water. Which suggestions about the transport and accumulation of heavy metals are valid? 1 After initial entry into the root, some of the ions can pass through the tonoplast. 2 In the roots and leaves, the ions pass through a symplastic or apoplastic pathway but at the endodermis they must take a symplastic pathway. 3 In xylem vessels, the ions pass through an apoplastic pathway only.