Euglena excrete waste in the same way as other protozoans, through a vacuole sack that can take in and push out water loaded with nutrients or metabolic products. The vacuole sack enlarges as the waste products accumulate. These vacuoles are discharged as frequently as every half minute.
The cytosol of the plasma membrane of euglena makes them always hypertonic to their surrounding aquatic environment. This enables water to flow freely across the plasma membrane, facilitating the expulsion of waste from the vacuole. Contractile vacuoles consist of two sub-compartments, each of which is encircled by a different membrane. One membrane is divided into minute tubules and vesicles containing proton-translocating enzymes that enable active transport of components in and out of the protozoa. This active transport involves the generation of an electrochemical gradient though the membrane enzymes, which pumps out unwanted waste components and pumps desirable nutrients into the protozoan.
The other membrane serves as an enclosure for a reservoir, lacking the enzymes of the first. This second membrane is elastic, enabling its expansion for the storage of excess fluid. The elastic membrane may fuse with the outer plasma membrane surrounding the two sub-compartments to eject unwanted waste products. In addition to waste product expulsion, the vacuole sack is responsible for the osmoregulation of the interior of the euglena with its surrounding environment.