Final answer:
The movement of water in the apoplastic pathway stops at the Casparian strip, a selective barrier requiring substances to enter the plant's cells for filtration before reaching the vascular system. Factors like high temperatures and water scarcity can also impact this movement.
Step-by-step explanation:
The movement of water in the apoplastic pathway stops at the Casparian strip, which is a waxy barrier that ensures that substances entering the plant's vascular system (the stele) have to pass through a cell membrane, where they can be selectively filtered. This pathway is essential for plants to effectively control their internal environment, especially with respect to the amount and type of minerals absorbed from the soil. When water and minerals reach the Casparian strip, they cannot continue in the apoplast and must enter the symplast to continue their pathway towards the xylem. The symplastic route involves the crossing of cell membranes and cytoplasm of cells to reach the vascular system. Other factors that may limit water movement include high external temperatures leading to reduced transpiration and closed stomata, low soil water potential, and overall water scarcity which initially causes the plant to cease photosynthesis due to a lack of required water for the process.