Suzette Tracy, age 15, of Lansing, Michigan,^for her question:
How does an amoeba move?
The single celled protozoa are miraculous midgets and one of the most amazing is the amoeba. He has no front or rear end and no left or right side. He has no permanent feet or legs, no wings or fins. Yet he manages to move around and keep going most of the time. True, he does not move very fast. But he can set forth, change course and proceed in any direction. The locomotion of the tiny amoeba rates high among the outstanding wonders of nature.
The microscope reveals that this shapeless blob of jelly is a single living cell. The cell is governed by a small nucleus, at some point within the mass of watery protoplasm. The entire blob is encased in a thin cell membrane, through which selected chemicals diffuse to and from the busy protoplasm.
We could compare the amoeba's shapless cell to a pliable polyethelene bag, partly filled with water. He makes good use of this pliable quality to move from place to place. In fact, the hungry little hunter rarely, if ever, pauses in his pursuit of food. He travels by stretching a piece of himself in his chosen direction and the rest of his single cell flows along from behind. The outstretched finger is called a pseudopod, meaning "false foot" perhaps because it is not permanent. Other pseudopods are extended to help him on his way. When this or that job is done, they merge back into his shapeless mass.
The first step begins when a portion of the membrane stretches forth, which can happen at any point around the cell. Jelly like protoplasm then flows into the extended membrane. A single pseudopod may stretch to hold all the cell's protoplasm. But as a rule, the amoeba puts forth two or more false feet and as they fill with protoplasm the entire cell is drawn toward a certain direction.
In mid stride, so to speak, the microscopic creature may take off on another track. Other pseudopods are extended toward a different direction. As they fill with protoplasm, the first ones shrink back and become part of the cell mass again. Since these false feet can be extended from any part of the cell wall, there is no limit to the routes he can take. As he goes, usually only the tips of his false feet touch the ground and the rest of his cell body is supported by the surrounding water.
The amoeba could not travel without his pseudopods and most likely he could not eat either. For they serve also as nets to capture scraps of food and as mouths to engulf them. When he senses a snack, several pseudopods flocs around and enclose it. The food is enfolded within the cell. When the nourishment is digested, the waste scraps are pushed out through the cell membrane. Meantime, the pseudopods have engulfed several. more small snacks.