Final answer:
The process that occurred when the wilted plant was watered and regained its upright position is known as the restoration of turgor pressure, which is a result of water entering the plant's cells through osmosis.
Step-by-step explanation:
When the wilted plant was watered and later stood up straight, the process that occurred is known as turgor pressure. When water moves into the plant cells by osmosis, it increases the internal pressure, which helps the plant maintain its structure and resist the force of gravity. This restored turgor pressure is due to the expansion of water inside the plant cells' vacuoles, pushing the cell membranes against the rigid cell walls, leading to the stiffness and erect posture of the plant. Turgor pressure is crucial for maintaining the plant's rigidity and is a direct consequence of osmotic water movement into the plant's cells.