Final answer:
The true statement about a protoplast at incipient plasmolysis is that it ceases to exert pressure against the cell wall because the cell membrane detaches and constricts the cytoplasm in a hypertonic solution.
Step-by-step explanation:
The correct answer to the question of what is true about a protoplast at incipient plasmolysis is 'B. It ceased to exert pressure against the cell wall.' During plasmolysis, the cell membrane detaches from the cell wall and constricts the cytoplasm, which is evident when a plant cell is in a hypertonic solution. The protoplast (the living part of the cell, which excludes the cell wall) shrinks and pulls away from the cell wall, which leads to the cessation of pressure against the cell wall. However, typically, the cell wall remains rigid and maintains the cell's shape. Conversely, in a hypotonic solution, the cell would become turgid as water enters, causing the protoplast to exert pressure against the cell wall, which provides the plant with structural support.