Answer:
The correct answer is - cell membrane - regulates cell contents.
Step-by-step explanation:
Various cell structures have different cellular functions in the cells. The major function of the chloroplast is to produce sugar with the help of chlorophyll pigment by trapping the sunlight. The mitochondria perform cellular respiration and convert sugar to energy.
The vacuoles are the cell structure that helps in maintaining water balance and also store nutrients and sometimes help in waste disposal, however, it is not its major function. The cell membrane is the cellular structure and barrier that regulate what cell content will move outside the cell and what will enter.