Notice that each euglena has a whiplike structure called a flagellum at one of its end. what fuction would a flagllum have a unicelluar orgaism? how would this a euglena survive in its environment?

Flagellum helps the cells to move.

Explanation:

The blunt, more rounded end is often the head part from which the whip-like tail (flagella) is attached because of the presence of a flagellum, Euglena are also known as flagellates.Although one flagellum is often seen, they have two flagella, one of which is often hidden in a part of the Euglena referred to as reservoir.  The longer, visible flagellum located at the anterior end of the organism twirls rapidly making it possible for these organisms to move across water surface

Membrane

Unlike most plant cells, this species do not have a cell wall. The organelles of the organism and its cytoplasm are therefore bound by a plasma membrane that allows for easier movement. Observation of Euglena under more powerful electron microscopes have revealed the presence of an ornamented pellicle under the plasma membrane. The presence of this thin protein layer protects the their cell membrane and also helps in maintaining their shape. Moreover, because of their flexible nature, they also facilitate movement.