Bulk transport Endocytosis – It is a form of active transport in which a cell transports molecules (such as proteins) into the cell by engulfing them in an energy-using process. Exocytosis – It is a form of active transport in which a cell transports molecules (such as proteins) out of the cell by expelling them Phagocytosis – the process a cell uses when engulfing solid particles into the cell membrane to form an internal phagosome, or "food vacuole." Tonicity – This is a measure of the effective osmotic pressure gradient (as defined by the water potential of the two solutions) of two solutions separated by a semipermeable membrane.