Pinching in of fluids by a unicellular organism is the process of pinocytosis or fluid endocytosis. The cell takes in surrounding fluids, including all of the substances available, without differentiating. It is a non-specific process. The membrane of the unicellular organism elongates, captures the fluid and small vesicles are pinched off intracellularly. These vesicles then are processed by the organelles of the cell.